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MAPG 1st International Convention Marrakech 2007
Field trip B4 Guidebook
WESTERN ANTI-ATLAS WESTERN HIGH ATLAS TRAVERSE: Evolution of a Paleozoic Basin at the NW border of the West African Craton
(Nov. 1-6, 2007)
Abderrahmane SOULAIMANI Université Cadi Ayyad Faculty of Sciences Departement of Geology Marrakech - Morocco
Hassan OUANAIMI Université Cadi Ayyad Ecole Normale Supérieur Departement of Geology Marrakech - Morocco
[email protected]
[email protected]
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Dedication to the memory of
Martin Burkhard We dedicate the present guidebook to the memory of Martin Burkhard. Martin was a professor of structural geology at the University of Neuchâtel (Switzerland) for over 30 years and was well known for his work on the geology of the Alps. Martin’s passion for field geology was unmatched. He was a great lover of the wide southern Morocco areas where he was interested with several of his students to the tectonic evolution of the Paleozoic series of the Anti-Atlas. He would have participated as a co-leader to the present excursion - alas! the destiny decided another way. His wealth of ideas, large knowledge of structural geology made Martin a perfect colleague and mentor. Many of the ideas in this guidebook originated during conversations with him. It is only justice to dedicate this book to his memory.
A superb field geologist Accidentally deceased in the Alps, summer 2006
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Contents USEFUL REFERENCES (Books and review papers, geological maps) GENERAL Introduction An overview of the geodynamical evolution of the south-western Moroccan domains Paleoproterozoic and Eburnian orogeny Neoproterozoic and Pan-African orogeny Paleozoic and Variscan orogeny Mesozoic and the central Atlantic opening The Cenozoic and Atlasic deformation ITINERARY AND STOPS Day 1 (J1): Marrakech-Agadir par by the Argana corridor Stop J1.1: The north Atlasic border at Imi n’Tanoute Stop J1.2: The Imi n’Tanoute fault Stop J1.3: Lower Cretaceous Sauropod tracks (?) Stop J1.4: Triassic series in the Argana corridor Stop J1.5: Triassic extensional tectonics Stop J1.6: The southern border of High Atlas: Ameskroud Fault Geological evolution of the Souss basin Day 2 (J2) : Agadir-Tafraoute via Aït Baha The Proterozoic basement of the Western Anti-Atlas: The Kerdous inlier and its edges Paleoproterozoic basement Neoproterozoic rocks Proterozoic deformations in the Kerdous inlier: Stop J2.1: Cambrian of the southern edge of the Kerdous inlier at Imi M’qorn Stop J2.2: Precambrian-Cambrian transition east of the Kerdous inlier Stop J2.3: Petrographic and structural markers of the Late Precambrian extension at Ida Ougnidif Stop J2.4: Variscan inversion of the eastern edge of Kerdous inlier Stop J2.5: Evidences of the Lower Cambrian extension Stop J2.6: Upper Neoproterozoic unconformity on the Proterozoic basement at Aferni pass Stop J2.7: The Kerdous slates Stop J2.8: Adrar Ouiharen augen-orthogneiss Stop J2.9: Tafraout Granite Day 3 (J3) : Tafraout-Tiznit-Goulmine Kerdous inlier (continuation) Stop J3.1: The Tafraout pink granite at Aday Stop J3.2: Tahala Paleoproterozoic basement and the Upper Neoproterozoic Anezi unconformity Stop J3.3: Tifermit pass panorama (Kerdous Hotel) on the western border of the Kerdous inlier Stop J3.4: The western border of Kerdous inlier Variscan deformation in the Cambrian Lakhssas Plateau Stop J3.5: Variscan deformation at the base of Jebel Inter Stop J3.6: Variscan deformation along the Jebel Inter shear zones Stop J3.7: The southern border of the Lakhssas Plateau
Day 4 (J4) : Goulmine-Assa-Tata The folded Paleozoic cover in the Western Bani and the WAC boundary Stop J4-1: The Fask fault Stop J4-2: Deformation of Schistes à Paradoxidès Stop J4-3: Amazloug collar Stop J4-4: Jebel Tazout : Upper Devonian -Tournaisian Stop J4-5: The Carboniferous of Jebel Ouarkziz
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Lower Devonian Rich Group and Variscan folds beyond Jebel Bani Stop J4.6: The Lower Devonian Rich: Rich 1 and Rich 2 Stop J4.7: The tilted Ordovician anticine of Icht Stop J4.8: Optional - the Tissenral folded Rich 1 and 2 Stop J4.9: Optional: the Sellanarcestes calcareous level of Oued Maskaou Day 5 (J5) : Tata-Taroudant via Tagmoute-Irherm : Folds, fracturation and detachments Stop J5-1: Folding interferences and fracturation: the El Bouir Anticline Stop J5-2: The Tata-Akka bar at Oufrane: Folding interferences and fracturation Stop J5-3: The Tata-Akka bar virgation at Jbaïr Stop J5-4: South Tata: lithological control on jointing at Jbaïr Stop J5-5: Variscan thrusts of Jebel Bani: section view Stop J5-6: Variscan thrusts of Jebel Bani: front view Stop J5-7: Detachment folds in the Adoudounian limestones (NW of Tagragra de Tata) Stop J5-8: Detachment between the “Serie de base” and the Cambrian limestones in Wadi Tagmoute
Day 6 (J6) : Taroudant-Marrakech via the Tizi n’Test pass Permanent dynamics of the northern edge of the Western Anti-Atlas: the Tizi n’Test Fault Zone (ZFTT) Stop J6-1: The meridional Atlasic zone of the NE of Taroudant and the southern flank of the High Atlas Stop J6-2: "Belle Vue" Inn: The main segments of the ZFTT and the tectonics of the South Atlas flank Stop J6-3: The Tizi n’Test pass Stop J6-4: Idni Inn: The Atlasic ZFTT lineament and the Tadafelt horst Stop J6-5: The Triassic basin of Talat n’Ya’qoub at Tinemal Stop J6-6: A NNE-SSW segment of the ZFTTh in Nfis Stop J6-7: The northern subatlasic zone: The Upper Triassic–Cretaceous of the Kik plateau Stop J6-8: Rerhaia bridge: The Visean of Souktana Stop J6-9: Panorama of Douar Sour: Northern Subatlasic zone and Haouz plain Acknowledgements References cited
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USEFUL REFERENCES Books and review papers: (NMSGM = Notes Mém. Serv. Géol. Maroc, Rabat) - A. Michard, Eléments de Géologie marocaine, NMSGM, N°252, 1976, 420 pp. - A. Piqué, A. Soulaimani et al., Géologie du Maroc, Edit. Géode, Marrakech, 2007, 288 pp. - D. Frizon de Lamotte et al., Transmed transect I (Betics, Alboran Sea, Rif, Moroccan Meseta, High Atlas, Jebel Saghro, Tindouf basin). In: Cavazza et al. (Eds.), The Transmed Atlas – the Mediterranean region from crust to mantle. Springer, Berlin, 2004. - D. Frizon de Lamotte, O. Saddiqi, A. Michard (Eds.), Some recent developments on the Maghreb geodynamics. C. R. Geoscience 338 (2006) - A. Michard, O. Saddiqi, A. Chalouan (Eds.), Geology of Morocco, Springer Verl., in press.
Regional geological maps: (NMSGM = Notes Mém. Serv. Géol. Maroc, Rabat) - Carte géologique du Maroc au 1/1 000 000, NMSGM, N°260, 1985. - Carte géologique du Maroc au 1/500 000, feuille Marrakech, NMSGM, N°70, 1957. Detailed geological maps: Day 1 (J1): - Carte géologique d’Imi n'Tanoute au 1/100 000, NMSGM, N°203, 1981 - Carte géologique d’Argana au 1/100 000, Tixeront, NMSGM, N°205, 1974 Day 2 (J2): -
Carte géologique de Tafraoute au 1/100 000, NMSGM, N°307, 1983 Carte géologique de Tiznit au 1/100 000 Carte géologique de Bou Izakarne au 1/100 000, NMSGM, 1992 Carte géologique de Tanalt 1/50 000, NMSGM, N°401 , 2001
Day 3 (J3): - Carte géologique d’Akka-Tafagount-Tata au 1/200 000 NMSGM, N°163, 1970. - Carte géologique de Fask au 1/100 000 NMSGM, 1997. - Carte géologique de Foum el Hassan - Assa au 1/200 000, NMSGM, n°159, 1963 Day 4 (J4): - Carte géologique de Akka-Tafagount-Tata au 1/200 000, NMSGM N°163, 1970. - Carte géologique de la terminaison occidentale de l'Anti-Atlas. Région de Goulmine et Dra inférieur, au 1/200 000, NMSGM. - Carte géologique du flanc sud de l'Anti-Atlas occidental et des plaines du Dra: feuille de Foum-el-Hassane et Assa, NMSGM n°159, 1969. - Carte géologique de Goulmine au 1/100 000, NMSGM °. 437, 2004. Day 5 (J5): - Carte géologique de Akka-Tafagount-Tata au 1/200 000. NMSGM, N°163, 1970. - Carte géologique de Taroudant au 1/100 000, NMSGM, 1983 - Carte géologique d’Irherm au 1/ 100 000, NMSGM, 1983 Day 6 (J6): - Carte géologique d'Amizmiz au 1/100 000, NMSGM, N°372, 1996. - Carte géologique de Tahannawt au 1/50 000, NMSGM, N°445, 2002.
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GENERAL Introduction The southwest part of Morocco is one of the most attractive touristic areas. It shows diversified landscapes, from snowy mountains to desert plains, under an arid climate moderated by oceanic influences. These regions are occupied by berberespeaking populations, and include toward the Atlantic Ocean the specific niche of the famous argan tree. Its contrasted scenery vary from karstic plateaus (Atlantic AntiAtlas), swimming resorts (Agadir), crystalline escarpments (Kerdous window) and granitic chaos (Tafraoute), green oases and palm plantations (Tata) and the famous Tizi n’Test Pass which crosses the High Atlas chain at 2100 m a.s.l. This six-day field trip is designed to give participants, not only the opportunity to visit these attractive areas, but also to have a geological overview of the south-western domains of Morocco, namely the western High Atlas and south-western Anti-Atlas mountains, through carefully selected, outstanding stops. The itinerary will make possible to illustrate the complex geological history of these areas from 2 Ga to presentday. Our purpose is to present and discuss various regional and thematic (sedimentological, structural, magmatic and metamorphic) features which record the main geodynamical events during this long geological history. The tour contains 48 stops distributed along approximately 1600 km (Fig. 1). On Day (D) 1 and D6, we will explore representative exposures of the Western High Atlas Paleozoic and Mesozoic rocks, and and discuss the structures along two transects, the Triassic Argana Corridor in
the west and the Tizi n’Test pass further east, respectively. D2 and D3 will concentrate on the Late Proterozoic-Early Paleozoic deposits around the Kerdous massif. Proterozoic rocks and related polycyclic Eburnian - PanAfrican structures will be observed and analysed when crossing the Kerdous, one of the largest Proterozoic inlier (“boutonnière”) of the Anti-Atlas. The well exposed Paleozoic cover of the Western Anti-Atlas, with a total thickness of over 10km, and the intriguing Variscan folds will be examined crossing the Ordovician series of the Jebel Bani and that of the Devonian along the Jebel Rich on D4, whereas the impressive fold interferences in the Lower Cambrian limestones north of Tata constitute the main topic of D5. The exceptional exposures of the Devonian folds along the Rich ridge will allow us to observe the various geometrical and genetic relationships between folds and fractures. Detailed roadlog for the trip are provided with instructions and distances from one stop to another, along with GPS (Global Positioning Satellite) locations at each stop to aid those wanting to use the guidebook on future field trips. Note that all the stops are on public roads, and that the use of hammers and the collection of rocks are permitted. Transport will be ensured by four-wheel vehicles or minibuses on asphalt roads, seldom on tracks. Only short hikes are required during the trip. Lodging will be in comfortable hotels, and visits of the stopover cities are considered. We wish everyone a safe and enjoyable 2007 Southwestern Morocco field trip.
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Fig. 1: Simplified geological map of the Western High Atlas and Anti-Atlas, redrawn from the geological map of Morocco, scale 1/1000 000. Black line with arrows indicates the itinerary and direction of the trip. Stops are indicated in the white circles.
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Geodynamic evolution of the south-western Morocco domains: An overview
Paleoproterozoic orogeny
rocks
and
Eburnian
The oldest rocks of Morocco, Archean in age, crop out in the Reguibat shield, being part of the West African Craton (WAC). Further north, in the Anti-Atlas chain, the basement units are Paleoproterozoic in age (Kerdous and Taznakht Group, former” PI”), and crop south of the Anti-Atlas Major Fault (AAMF) only. They are metamorphic rocks (greenschist to amphibolite facies) intruded by peraluminous and calc-alkaline granitoids dated around 2Ga. The corresponding tectono-magmatic and metamorphic events are assigned to the Eburnian/Birrimian orogeny. Neoproterozoic orogeny
rocks
and
Pan-African
As everywhere in the WAC, Mesoproterozoic rocks are lacking in the Anti-Atlas. Neoproterozoic formations overlie directly the Paleoproterozoic basement. The Neoproterozoic/Paleoproterozoic boundary is often a tectonic contact (thrust, strike-slip or detachment faults) and seldom a stratigraphic contact (Tizi n’Taghatine). Globally, the Neoproterozoic deposits relate three main stages of the Pan-African cycle: i) The early Neoproterozoic platform development is marked by the accumulation of thousands of meters of quartzites and stromatolitic limestones (Taghdoute Group, former “PII”), intruded by doleritic dykes and gabbroic intrusions. These rocks are associated with the rifting of the WAC margin, broadly contemporaneous with the oceanic accretion further north (760 Ma), witnessed along the AAMF by the Bou Azzer-El Graara and Siroua ophiolitic sequences (Bou Azzer Group); ii) Oceanic closure and subsequent PanAfrican collision are associated with oceanic subduction along the northern margin of the WAC and accretion of oceanic arc formations. The reported “blueschist facies”
mineral associations in the Bou Azzer inlier are controversial. The polarity of the subduction remains also matter of debates; the same is true for the real location of the northern edge of the WAC. Along the AAMF, the oblique Pan-African collision (655 Ma to 640 Ma) generated sinistral south-vergent thrust sheets onto the cratonic margin. Elsewhere in the Anti-Atlas, the major Pan-African effects are less clearly established, being represented by folds and various ductile and brittle structures in the Lkest/Taghdout Group series; iii) The Late to Post Pan-African extensional event is recorded by the extensive volcanic and volcanoclastic series of the Ouarzazate Group (former “PIII”, 580 Ma to 560 Ma), interbedded with subaerial to lacustrine deposits, which unconformably overlie the Eburnian and/or Pan-African basement units. The Ouarzazate Group shows abrupt variations of thickness and facies controlled by extensional tectonic activity. Various high-K calc-alkaline to alkaline plutons emplaced within the Ouarzazate Group, coeval with the volcanic rocks of comparable chemistry. Considering the importance of the magmatic activity associated with the synrift sedimentation at this time, a complex tectono-metamorphic and magmatic reworking of the Precambrian basement rocks, leading to the uplift of extensional metamorphic domes, can be considered. Such exhumation processes are to be integrated within the Pan-African postcollisional collapse framework. Paleozoic series and Variscan orogeny During the Early Cambrian transgression, the sea invaded first a northwestern area where the Adoudounian "Série de base" deposited, before flooding the eastern Anti-Atlas basin. The sediments of this major transgression are virtually concordant onto the Ouarzazate Group volcanoclastic deposits and still record extensional tectonics. A significant
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subsidence in the westernmost Anti-Atlas induced the deposition of more than 4 000 m of Cambrian marine carbonates (Tiznit basin, west of the Kerdous inlier). These marine sediments evolve gradually toward thinner and more detrital deposits going eastward along the Anti-Atlas. The Precambrian-Cambrian transition (542 Ma) is thought to be located in the lower part of the Adoudounian limestones. The decline of the marine level by the end of Early Cambrian resulted in arenaceous sediments, silts and greywackes supplied by the erosion of the WAC. At the scale of the entire Anti-Atlas, Upper Cambrian deposits are reduced or lacking. During Ordovician times, a less subsident epicontinental sea occupied the Anti-Atlas domain, and clastic rocks from cratonic sources were deposited. At the end of the Ordovician, the Anti-Atlas, being located in the southern high latitudes, received periglacial sediments nourished by the icebergs coming from the Saharan inlandsis. The Silurian transgression, resulting from the melt of the Saharan inlandsis, invaded once more the entire Anti-Atlas. The Graptolite black shales, deposited in a shallow and less oxygenated sea, constitute the parent rocks of the Saharan oil. The low resistance of the Silurian shales to weathering accounts for their poor outcrops along topographic depressions (Drâa Plain) between the Ordovician J. Bani and Devonian Rich ridges. Lower Devonian formations follow those of the Silurian without hiatus, being represented by concordant bedded limestones and argillites. At that time, the low latitude location of the Anti-Atlas domain permits the installation of reefs associated with mud mounds which spread during the Middle Devonian. From the Famennian onward, sediments do not have any more a cratonic origin but originate from the uplift of the Anti-Atlas axis. Infilling takes place in basins bounded by structural highs, thus prefiguring the subsequent Variscan domains. This paleogeographic diversification is particularly clear in the Tafilalt (Eastern Anti-Atlas), with the dislocation of the carbonate platform leading to the individualisation of turbiditic basins and highs covered with condensed carbonate sediments.
The Carboniferous series, represented south of the Famennian Drâa plains, make up impressive cuestas at the northern border of the Tindouf basin. The Tournaisian schists and sandstones of the Jebel Tazout are overlain by the Betaina Visean pélites, followed upward by the Upper Visean to Namurian limestones of the Jebel Ouarkziz. Further south, the Upper Namurian to Stephanian continental deposits of the Betana plain terminate the cycle, and record the Variscan uplift of the Anti-Atlas. The 10 km thick Paleozoic series of the Western Anti-Atlas, accumulated during 200 Ma, correspond to the infilling of a huge intracratonic basin, including the undeformed Tindouf basin in its southern half. Globally, the Variscan deformation of the Anti-Atlas is much heterogeneous, and shows dominantly a thick skinned type. Deformation strongly differs from that recorded in the Meseta Block north of the South Atlas Fault, such as the tectonic vergence (SE in Western Anti-Atlas versus NW in Western Meseta), the weak metamorphic climate and the lack of granites in the Anti-Atlas. However, the major role of the basement fractures constitutes a common denominator between both Variscan areas. In the Anti-Atlas, Variscan folds are moulded around the uplifted inliers. Several décollement levels are activated within the cover series. Deformation vanishes gradually towards the south-east, being negligible at the northern edge of the Tindouf basin. ENE dextral strike-slip and/or NNW-vergent backthrust are evoked to explain the structural contrast on either sides of the cratonic edge. Towards the SW, the Zemmour and Adrar Souttouf massifs connect the Anti-Atlas to the Mauritanide belt. Mesozoic opening
series
and
Central
Atlantic
After the Variscan orogeny and the Early Permian period, during which compressional tectonics decreases and concentrates in the Meseta and Eastern Anti-Atlas, the NNE-SSW to NE-SW Variscan fractures are reactivated as normal faults during the Late Permian-Triassic rifting.
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In the central and western High Atlas (Marrakech High Atlas) and along the Atlantic margin, i.e. east and west of an uplifted ridge extending northeast-ward in the Meseta (West Moroccan Arch), hemigrabens appear, being progressively infilled by detrital sediments. This synrift sedimentation is capped by widespread tholeitic basalt flows, dated around 200 Ma. Rifting tectonics cease gradually during the Rhetian before the sedimentation of LowerMiddle Liassic marine carbonates. The Central-Eastern Atlas rift then aborts in contrast with the Atlantic one which evolves to the oceanisation. The lack of synrift deposits south of the Western High Atlas suggests a sinistral transcurrent component of motion along the Tizi n’Test fault, consistent with the NE-SW “en echelon” setting of the Triassic-Liassic dykes south of the fault. The postrift carbonates of the Lower Liassic platform seal the Triassic faults. Afterwards, the Central High Atlas gulf becomes an internally faulted trough, where the rhombic geometry of the presentday synclines and anticlines, and the intrusion of Late Jurassic gabbros in the anticlines would suggest again a sinistral transcurrent motion at that time (?). Continental sedimentation dominates during the Jurassic-Early Cretaceous, and the High Atlas – Anti-Atlas regions are converted then into a Dinosaur Natural Park. The geodynamic significance of the Late Jurassic-Early Cretaceous tectonicmagmatic activity is still unclear. From the Albian and CenomanianTuronian onward, the Africa plate operates an anti-clockwise rotation and approaches Eurasia, in relation with the opening of the South and Equatorial Atlantic Ocean. Plate convergence will now control the geodynamic evolution of Morocco. The coeval strong activity of the oceanic ridges induces a worldwide eustatic transgression. The Saharan Upper Cretaceous- sediments constitute a marine cycle which begins with Aptian-Albian and Cenomano-Turonian limestones and continues with Upper Cretaceous regressive facies. At the beginning of Senonian, the Turonian
calcareous platform disintegrates and Late Cretaceous bituminous or gypsiferous confined basins form. In the Western and Central High Atlas and Western Meseta, the Atlantic transgression stays up to the Eocene, permitting the sedimentation of the famous Maastrichtian-Ypresian phosphate series. Cenozoic series and Atlas orogeny The Atlas orogeny was contemporary with the disappearance of Tethyan oceanic spaces between Africa and Europe during the Cenozoic. Up to the Middle Eocene, confined marine environments persist in the High Atlas, being preserved in the synclines on both sides of the chain. During the Late Eocene-Oligocene and the Neogene, compressional deformation occurs within the entire chain, but concentrates particularly in the marginal zones. Two major pulses of detrital facies are recorded in the weakly subsident foredeep, indicating the uplift of the chain, first during the Oligocene, and second during the Miocene. Compressional deformation continues during the Miocene-Pliocene and Quaternary times, resulting in externally verging thrusts along the northern and southern fronts of the chain.. Subsurface data imaging the South-Atlas front has been interpreted as the emergence of a crustal detachment rooted to the north of the African plate, beneath the Rif belt. It is worth noting that the geophysical studies demonstrate that the present topography of the Atlas and Anti-Atlas is not isostatically compensated, as the existing root (34–39 kilometres) is poorly marked. In addition, structural data indicate that current topography, more than 4 km, cannot result from the only crustal shortening, which is mainly localised along the north and south borders and does not exceed 10 to 25%. Indeed, the current topography should partly result from a mantle process, i.e. an asthenospheric upwelling, evidenced also by Miocene to Quaternary alkaline volcanism (Siroua - Middle Atlas province) and high heat flux.
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ITINERARY AND STOPS
Day 1 (J1) : Marrakech-Agadir by the Argana corridor (270 km): The High Atlas traverse
From Marrakech, drive on the principal road (R.P. 10) to Essaouira (fig. 1). We drive on the Haouz Plio-Quaternary plain incised by intermittent streams or wadis (oueds, O.) which are tributaries of the O. Tensift further north and drain the High Atlas waters. One of these rivers (O. N’Fis) is crossed at km 30, after Loudaya village. Some Paleozoic outcrops occur by place in the Haouz Plain (cf. the Gueliz hills in Marrakech). The most important one is the Guemassa Carboniferous massif (barely visible on the left. More noticeable are the Devonian limestones of Mzoudia (Km 50, on the right), exploited by a cement factory. Cambrian schists crop out also on the left, a few kilometres before Chichawa (GPS: N31°34’10", W08°38’42"). The small Chichawa city is build on Turonian carbonates, and dominated by Maastrichtian to Eocene scarps (Fig. 2).
Fig. 2 - Northward view of the Eocene hill which overhangs the town of Chichawa.
From Chichawa, turn to the left at the junction and proceed to the south (R.P. 40 to Agadir). The road, up to now rather flat, gradually rises while crossing Quaternary terrasses, then Mio-Pliocene and Eocene plateaus. The High Atlas Mountains are now in front of us; we start crossing the belt in the Imi n’Tanoute gorge. The figure 3 below show the location of following stops.
- Fig. 3 - Location of - stops of day 1 (J1) in the - Western High Atlas - plotted on the geological - map of Morocco, scale: - 1/1,000,000. (hr: Permian; - T: Triassic; tß: basalts; J: - Jurassic; C: Cretaceous; Miocene; Q: - m: Quaternary).
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Stop J1.1: The North Atlasic border at Imi n’Tanoute (GPS: N31°10’04’’, W08°51’05’’)
Park at the south exit of the village, and climb a few metres uphill on the right to catch a better view to the south (Fig. 4). The Mesozoic and Tertiary series are moderately tilted to the north. From south to north, we observe (1) the thick CenomanoTuronian slab, formed by sandstone and lumachellic limestones; (2) Senonian levels characterized by chalky white marls, and (3) the Eocene marly limestones. After the cluse (« Imi » in Berber), the road crosses the north-dipping CenomanoTuronian bar, followed upward by the Lower Cretaceous marls, limestones and yellow sandstones (Barremian to Albian). Afterwards, the road turns to the W direction along the Imi n’Tanoute valley which parallels a major fault. This important
fracture separates the yellowish Cretaceous series to the north of the valley from the dark Cambrian basement to the south.
Fig. 4 - View of the Eocene, Senonian and Cretaceous series at the northern border of the High Atlas, Imi Tanoute cluse. The series are a gently dipping to the north.
Stop J1.2: The Imi n’Tanoute fault (GPS: N31°09’04’’, W08°51’55’’)
The Imi n’Tanoute fault corresponds to one of the main North-Atlas reverse faults. The Paleozoic (Cambrian) rocks are uplifted against and onto the Mesozoic series (Fig. 5). The tectonic uplift of the Cambrian block is evidenced by a “crochon” (close to the small pass to the east) which affects the reddish Jurassic beds. As most Atlas faults, the Imi n’Tanoute fault has a complex history, firstly Precambrian, then Paleozoic and Variscan (Cornée et al., 1987), and finally Mesozoic-Cenozoic. The road follows during several kilometres the E-W Imi n’Tanoute valley and its fault, separating the Aït Lahcen Cambrian massif to the south, deformed during the Variscan orogeny, and the tilted Cretaceous of Jebel Lemgo to the north (fig. 3). Then, the road climbs a gentle hill formed by faulted
Fig. 5 - Eastward view of the north Atlasic fault of Imi Tanoute which put in contact the uplifted Cambrian metamorphic substratum against the Lower Cretaceous series.
Jurassic and Lower Cretaceous red beds, turns slightly left and begins a long ascension through steeply dipping, sandyargillaceous red beds.
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Stop J1.3: Lower Cretaceous Dinosaur tracks (?) (GPS: N31°07’00’’, W08°58’57’’)
At about the beginning of the slope, park on the right shoulder and observe the left roadcut. A nearly vertical bedding surface of red sandstones shows plenty of decimetre size polygonal to oblate depressions, juxtaposed or superimposed (Fig. 6). Nonpublished interpretations span from sedimentary to biological origin (desiccation polygons or tracks of Dinosaurs), but both types of structures are probably associated here. Among the varied forms observed, some evoke the tridactyl tracks of Theropods whereas others resemble the circular tracks of Sauropods. Similar, but less mixed tracks are described in the Central High Atlas (e.g. Haddoumi et al., 2007). Proceed on the road which takes now a southern direction, crosscutting again the Imi n’Tanoute fault. We drive transversely to the chain, dominantly upon red Triassic formations. After Demssira village, our route crosses the Atlas water divide and descends into the Argana Corridor through the Foum Jerana (“Frog mouth”). Overall in the Western High Atlas, Upper Permian and Triassic outcrops are restricted to a NNE-SSW trending basin, referred to as the Argana Corridor (Fig. 4A), between the Western Paleozoic block to the east and the Agadir-Essaouira Atlantic basin to the west. In fact, the Argana Corridor represents the eastern border of the Agadir-Essaouira basin within which the series are younger and younger going westward. The Argana Triassic basin is structured by a network of ENE-WSW, NE-SW and WNW-ESE faults. The Triassic stratigraphy was carefully studied by Tixeront (1974) who distinguishes 8 formations, capped by the
Fig. 6 - Photographs of the Lower Cretaceous vertical beds with Dinosaur tracks (?). Insert: close view of the structures.
Late Triassic basaltic flow (Fig. 7A and B). The first two formations have been dated from the Permian and the next ones from the Middle and Late Triassic. The evolution of Permo-Triassic basin is closely connected with the Central Atlantic opening. It constitutes a continental rifting stage attested by the Synsedimentary extensional tectonics and the tholeitic volcanic occurrences (Manspeizer, 1988, 1994; Whittington, 1988; Medina, 1994; Piqué and Laville, 1995, 1996; Aït Chayeb et al., 1998). The Argana basin presents many similarities with those of North America, in particular that of Nova Scotia (Olsen et al., 1997). Tholeitic basalts belong to the magmatic province of the Central Atlantic (CAMP) (Knight et al., 2004), emplaced at the end of the continental rifting stage, at the Triassic-Jurassic boundary (~200 Ma).
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Fig. 7 - The Triassic Argana Corridor : (A) Structural sketch according to Tixeront (1974) and Médina (1991); (B) Simplified stratigraphical column from Tixeront (1974) and Aït Chayeb et al. (1998).
Stop J1.4: Triassic series in the Argana Corridor (GPS: N30°58’12’’, W09°02’60’’)
This stop is close to Amezri village in the Triassic sandstones and siltstones series. A WNW-ESE fault can be observed on the western flank of the Triassic corridor (Fig. 8). The fault geometry in map view suggests the occurrence of a weak decollement in the Triassic argillites. The road follows the western side of the Assif (Berber word for wadi) Mouss at about the limit between the Triassic formations F4 and 5. Further to the south, the CAMP basalts crop out uphill on the right (west), being crossed before the village of Argana (dam) by a secondary road which joins Agadir across the mountains via Imouzzer Ida Outanane. Our own road then starts a long descent within the Upper Triassic series, directed to the Souss plain in the south.
Fig. 8 - Photograph of the faulted Triassic red beds near Amezri village: an example of décollement within the Triassic sandstones and siltstones series at the western border of the Argana corridor
15
Stop J1.5: Triassic extensional tectonics (GPS: N30°37’36’’, W09°20’45’’)
Along the steep slope to the Souss plain, newly excavated trenches allow us observing the Upper Triassic dark red siltites and mudstones (T8 Fm) (Fig. 9). Several decametric normal faults with NS to NNE-SSW direction show normal offset delimiting horst and graben structures indicative of tensional stretching. Similar, but larger scale structures are frequent in the Triassic corridor. Fig. 9 - Road cut showing a system of normal faults crosscutting the Upper Triassic siltites: an exemple of Triassic extensional tectonics in the the Argana Corridor.
Stop J1.6: The southern border of High Atlas: Ameskroud Fault (GPS: N30°31’58’’, W09°19’46’’)
At the end of the descent to the Souss, on the roadcut to the right in the last turn before Ameskroud, we observe the latest outcrop of the Jurassic carbonate series which show here south verging decollement folds. We are located on the so-called Ameskroud fault, one of the faults of the complex lineament at the southern border of the High Atlas. Further explanations on this border are summarized below. Geological evolution of the Souss basin: The Souss basin constitutes the westernmost representative of the “preAfrican troughs” (Choubert and FaureMuret, 1965) that extend discontinuously south of the High Atlas front. It is separated from the Ouarzazate basin by the elevated Siroua plateau. The geometrical and geodynamic evolution of these atypical foredeep basins constitute currently one of the most debated issues. The structure of the Souss basin is complicated by the presence of the «Tizi n’Test System", a major element of the Variscan and Atlasic evolution of the High Atlas chain (Fig. 10B) (Mattauer et al., 1972; Proust et al. 1977; Ouanaimi and Petit, 1992).
The Souss basin constitutes a triangular depression elongated equatorially and crossed by the Wadi Souss (Fig. 10A). The plain is bordered to the north by the High Atlas and to the south by the less Anti-Atlas. Its altitude gradually raises from 0 along the Atlantic coast to about 700 m at the base of the Siroua plateau. Perpendicularly, the plain presents a dissymmetrical topography from north to south, with a relatively steep northern edge and a gentle southern edge, consistent with the contrasting tectonic activity of the bordering mountain ranges. During the Triassic - Cretaceous times, the Souss basin is part of the EssaouiraAgadir coastal basin (Medina, 1994; Hafid, 2006), whereas during the Cenozoic, it forms the tectonic foreland of the Western High Atlas. Such evolution results in a broad synclinorium structure, including two main depocentres, in the east and west respectively (Nairn et al., 1980). The northern border of the basin, which is the South Atlas front, corresponds to the WSW –ENE trending Tizi n’Test fault zone. It includes a system of four main faults (fig. 10C), from west to east, the AgadirTagragra,
16
Fig. 10 - The southern High Atlas front along the Souss basin. A: Neotectonic sketch map. Background: SRTM90 digital topography. The active faults are mapped with heavy red lines; B: Map of the tectonic structures on a LANDSAT TM image. C: Crustal scale interpreted cross-section. The former normal faults rooted at depth propagated upward during inversion with two different geometries: (1) direct propagation up to the surface; e.g. Ameskroud fault; (2) ramping off to a shallow detachment level up to the Tagragra fault bend fold.
Oued Issen, Taroudant and Oulad Berhil faults. Towards the south of the basin, the El Keléa and Biougra faults constitute noteworthy structures whose main activity took place during Triassic times. Their obliqueness compared to the Triassic rift suggests they operated as transfer faults during the extensional event. These faults seem to be rooted on detachment surfaces which controlled the Central Atlantic opening. During Africa-Europe collision, the Souss faults were reactivated after the Eocene, at least in the western areas. This tectonic inversion would be controlled by a northdipping detachement surface, probably inherited from a Variscan structure, from
which would emerge the Tizi n’Test, El Kelea and Biougra Faults (fig. 10C). With the ca. 20% shortening (Mustaphi et al., 1997) was accompanied by decollement along the Triassic evaporites. The neotectonic activity of the Souss basin is testified by the implication of the Plio-Quaternary deposits in metre to decametre size deformations, and by a regional seismicity sadly famous since the awful Agadir seism of 1960.
End of the first day Night in Agadir
17
Day 2 (J2): Agadir-Tafraoute via Aït Baha The Western Anti-Atlas Proterozoic basement: overview on the Kerdous inlier The Kerdous massif is the largest of the Western Anti-Atlas Precambrian inliers. It
displays large outcrops of both the Paleoproterozoic basement and its Neoproterozoic cover, deformed during the Pan-African orogeny. The varied Precambrian units are sealed by the Lower Cambrian onlap (Fig. 11).
Fig. 11 - Simplified geological map of the Kerdous Precambrian inlier, redrawn from the geological maps, scale 1/ 50 000 (BGS 2001a-d).
18
Paleoproterozoic basement:
According to Hassenforder (1987), an Eburnian D1 deformation is responsible for S1 foliation associated with isoclinal P1 folds. It is often transposed in another later D2 deformation assigned to the Pan-Africain event, during which retrograde metamorphism of D1 metamorphites occured. These Eburnian terrains are intruded by several plutons of calc-alkaline granitoids, leucogranites and pegmatites. The Tasserirt pluton, for instance, presents syntectonic features, whereas the Tahala and Tazerwalt plutons are post-tectonic. The E-W trending Jebel Ouiharen augen gneisses north of the Tasserirt plateau is regarded as an Eburnian granite orthogneissified during the Pan-African deformation.
It represents more than 30% of the Kerdous outcrops, being exposed mostly in the Tafraoute-Tasserirte massif to the NE, and in the Tazerwalt secondary massif to the SW (fig. 11). The Tafraoute-Tasserirte massif presents a subcircular shape, and consists of varied metamorphic rocks (Kerdous Schists, micaschists, gneiss, and migmatites), derived essentially from sandypelitic formations including locally turbiditic alternations. Several granitoid plutons of Paleoproterozoic age intrude the metamorphic units (Fig. 12). Overall, the metamorphic grade increases from the periphery (greenschist facies) to the centre of the massif (high-grade amphibolite facies and migmatite in the Tasserirt plateau).
Roches datées Granite Zawyat S. H. Omossa Granite Iguilaln Granite de Tazeroualt Granite de Tahala Granite Amarhous Granite d'Aït Daoud Granite d'Annameur
Rb/Sr
Auteurs
1906 1920
30 40
Charlot (1978) Charlot (1978)
1900 930 1510
30 65
Charlot (1978) Charlot (1978) Charlot (1978)
1906
Charlot (1978)
Granite d'Aguercif Granodiorite Tarçouate Gneiss du Jbel Ouiharem Granodiorite de Tasserhirt
604
26
Charlot (1978)
1900 1672 1670
26
Charlot 1978 Charlot (1978) Charlot (1978)
U/Pb 2187 33 2036 30
Autuers BGS 2000c BGS 2000c
2060 2044 2042
12 2 1
BGS 2000d Barbey et al. 2004 BGS 2000d
2101 2058
28 11
BGS 2000c BGS 2000d
2263 583 560
38 11 2
BGS 2000d Aït Malek (1998) Aït Malek (1998)
Orthogneiss ed Tasserirt
micaschistes injectés de Tasserirt
1900
granite d'Idikel Granite de Tafraoute Granite d'Ida Ou Cougmar Granite de Tazoulte Granite Agouni Yissène Rhyolites PIII Ignimbrite de Tagdyicht Ignimbrite Ait Wachhal Ignimbrite de Tiygdrn Ignimbritr d'Assirdrar Ignimbritr de Tifghilt Ignimbritr d'Aït Mar
549 536 760 530 625 549 522 536 580 380
989 1028 1033 345 1056 1221 1025 1339 1389 1356
23 24 24 8 24 28 24 31 32 20
soulaimani et Piqué (2004) soulaimani et Piqué (2004) soulaimani et Piqué (2004) soulaimani et Piqué (2004) soulaimani et Piqué (2004) soulaimani et Piqué (2004) soulaimani et Piqué (2004) soulaimani et Piqué (2004) soulaimani et Piqué (2004) soulaimani et Piqué (2004)
603 330 442
14 8 10
soulaimani et Piqué (2004) soulaimani et Piqué (2004) soulaimani et Piqué (2004)
341 352 316
8 8 7
soulaimani et Piqué (2004) soulaimani et Piqué (2004) soulaimani et Piqué (2004)
Charlot (1978)
Schistes de Kerdous
Granite Agouni-Ait Yahya
Auteurs
K/Ar
6 11 6 27 6 10 36
Charlot (1978) Charlot (1978) Charlot (1978) Charlot (1978) Charlot (1978) Charlot (1978) Charlot (1978) 548
11
BGS 2000a
614 570 545 555 565 600
38 36 11 7 8 50
BGS 2000d BGS 2000d BGS 2000d BGS 2000b BGS 2000b BGS 2000b
Charlot (1978) Charlot (1978) Charlot (1978)
Fig. 12 - Table of the main radiometric datings (Rb/Sr, U/Pb and K/Ar) of the Proterozoic rocks.from the Kerdous inlier
19
Neoproterozoic rocks: They are represented by two main units: i) The quarzites of the Lkest Group (equivalent to the Taghdout Group further east), and ii) the volcanoclastic formations of the Ouarzazate Group and associated plutons. - The first unit corresponds to the thick quartzitic series of the Adrar (Berber word for Jebel) Lkest, which culminates at 2359 m. They consist of epicontinental arenites, which locally host pelitic levels, conglomerates and carbonates. As everywhere in the Anti-Atlas, these platform series are intruded by doleritic dykes and sills (Toudma Suite). The contacts between the Neoproterozoic quarzites and the Eburnian crystalline rocks are faulted everywhere in the area, in particular along the Ameln valley where a broad dextralreverse shear zone affects the Kerdous schists as well as the Adrar Lkest quarzites. This major shear zone is assigned to the Pan-African deformation as it causes the folding of the Lkest quarzites and the development of a S2 subequatorial foliation in these rocks. - The second unit is made up of posttectonic volcanoclastic deposits and associated plutons sorted into several (sub)groups and suite (Tafraoute, Anezi, Feiyzirt, Tanalt, Have Baha and Oufoud) (see legend of fig. 6). The Anezi basin was infilled under periglacial conditions by polygenic conglomerates identified as tilloide deposits, sandstones, and laminated siltstones (varves). The overlaying formations are comparable and accompanied by significant volcanic activity, consisting of calc-alkaline rhyolites, ignimbrites and andesites. This major Neoproterozoic magmatism was controlled by an active extensional tectonics. It is followed upward by alkaline magmatism before and during the Lower Cambrian transgression (e.g. Ida Ougnidif intracratonic tholeitic basalt). Proterozoic deformations in the Kerdous inlier: Most previous works agree on the polycyclic character of the Proterozoic deformations in the Western Anti-Atlas in general, and in the Kerdous inlier in
particular (Hassenforder, 1987; Aït Malek et al., 1998). Indeed, two magmatic episodes are well-dated at 2 Ga. and 610-550 Ma, respectively (fig. 12). The first episode, mainly plutonic, is associated with the Eburnian orogeny responsible for the West African Craton (WAC) formation, whereas the younger, dominantly volcanic episode is related to the late Pan-Africain events (Aït Malek et al., 1998; Barney et al., 2004). However, from the structural point of view it is often difficult to distinguish the role of each episode (Nachit et al., 1996; Soulaimani and Piqué, 2004). In the Tasserirt plateau, the metamorphic foliation has been associated to the Eburnian event (Hassenforder, 1987), based mainly, as it seems, on the correlation between the metamorphism grade and the age of formation. This ancient foliation is actually refolded along the shear zones which affect the Neoproterozoic quartzites and the 2 Gaold plutons. However, outside of these shear zones, there is no evidence of reworking except retrograde metamorphism. The Tafroute-Tasserirt massif shows only one regional foliation, steeply dipping at the periphery of the massif and sub-horizontal in the centre. This foliation thus delineates a dome structure, consistent whith the centripetal metamorphism gradient. Regionally, the Tasserirt dome is limited by two EW dextral shear zones to the north and south, respectively. The core of the dome is intruded not only by Paleaoproterozoic plutons (Tahala granite), but also by several late Neoproterozoic granitoids, firstly calc-alkaline and syn- to late-tectonic (Tarçwate pluton, Pons et al., 2006), then alkaline and post-tectonic (e.g. Tafraoute pluton) (BGS, 2001a). The age of the domal foliation would be constrained by that of the Tarçwate intrusion (583-560 Ma) (Aït Malek et al., 1998). This is also the age of the volcanoclastic series of the Ouarzazate Group (Tanalt Group) deposited around the massif in extensional conditions. This suggests that the Tasserirt-Ouiharen dome would have been exhumed as a metamorphic cored dome, ending with granitoid intrusions, in a transcurrent context during the late Neoproterozoic extension which followed the Pan-African crustal thickening (Soulaimani and Piqué, 2004). This model (fig. 13) could be
20
extrapolated to the other basement inliers of Western Anti-Atlas. However, this provocative model can be regarded as a working hypothesis, and other authors favour a more classical tectonic scenario, involving a compressional ductile deformation during the main Pan-
African phase (~650 Ma), followed by extensional-transtensional, dominantly brittle deformation during the late Neoproterozoic, 610-540 Ma (Gasquet et al., 2005, 2008).
Fig. 13 - Structural evolution of the Paleoproterozoic Tafraoute-Tasserirt massif (Kerdous inlier); A Simplified geological map of Kerdous inlier; B - Structural map of the Tasserirt dome; C - Schematic cross-section; D - Kinematic model for the Late Proterozoic tectonics in the Kerdous inlier.
Route Leave Agadir (km 0) and take the bypass towards the SE. After the Wadi Souss bridge (km 8), turn left (south) on the secondary road (S 509) to BiougraTafraoute. We drive on alluvial deposits of the fertile Souss Plain. Silts and calcretes,
locally covered by sand dunes, constitute the surface formations. At 20 km from of Agadir, we traverse the agglomeration of El Keléa, known for his hydrothermal source (public fountain on the right). The El Keléa fault emerges in the area (fig. 10C). The mountainous Kerdous massif (J. Lkest) appears in the background, beyond a Cambrian plateau.
21
At Imi M’qorn (40 km from Agadir), we leave the Souss plain and enter a cluse opened in the outer Anti-Atlas. The first cliffs consist of Archeocyaths reef limestones (end of Lower Cambrian “Calcaires supérieurs”), exploited
for marble and gravels (quarry). The Cambrian layers dip gently (25°) to the north under the Souss plain. This bulk northward tilting was probably acquired during the recent surrection of the Anti-Atlas chain.
Stop J2.1: Cambrian of the southern edge of the Kerdous inlier at Imi M’qorn (GPS: N30°06’38.2’’, W09°13’48.2’’)
Stop approximately 4 km after the entrance of the cluse, once having covered around 3 km through the pelitic depression ("feija") of the Imi M’qorn basin. The road is now built upon the Cambrian Upper Limestones south of the Ait Oukrim plateau. Caution, this stop requires much vigilance (keep on the shoulders), as the road is circulated and risky. We have a large sight on the Imi M’qorn basin and Cambrian plateau in the foreground, the Souss plain and the impressive, High Atlas Mountains in the background (Fig. 14). The Imi M’qorn depression is due to vertical faulting on its northern limit (Fig. 15). In the centre of the basin, the uppermost formations of the Lower Cambrian crop out, i.e. the “Schistes et Calcaires” and “Grès terminaux” Fm., the latter being now assigned to the base of Middle Cambrian (Geyer and Landing, 2004).
In the roadcut, massive carbonate layers alternate with pelites and calcschists. The limestones show stromatolitic laminations and bedding-parallel stylolitic surfaces, developed during the diagenetic compaction process.
Fig. 14 - Northward view from the Aït Ouckrim Plateau. The Imi M’qorn depression (Lower to Middle Cambrian) extends in the foreground, separated from the Souss plain by the Lower Cambrian Upper Limestones (quarries). The High Atlas barrier can be seen in the background.
Fig. 15 - Geological cross-section of the Aït Ouckrim Cambrian Plateau at the northern edge of Kerdous inlier (From Ambroggi and Neltner, in Choubert, 1952).
22
Route: On about 15 km, we proceed on the Aït Oukrim carbonate plateau, downward in the Lower Cambrian series, from the Upper Limestones, to the Lie-de-vin pelites, to the Lower Limestones (Adoudounian). The slope is negligible until Ait Baha where we reach the volcanic rocks of the late Neoproterozoic (Ouarzazate “Supergroup”, former “PIII”), represented by the rhyolites of the Tanalt Group. At Ait Baha (54 km from Agadir), keep straight on the road (R.S. 509) to Tafraout
(another road which forks to the right (7051) across the village attains also Tafraoute, driving round the Kerdous by the west, via Tanalt). Our route runs along the eastern side of Kerdous inlier for ca. 100 km. Overall, the road meanders on the pelites and sandstones of the “Serie de base”, being dominated on the left by Lower Limestones cliffs, and bordered on the right by the precipitous escarpments of the Wadi Ait Baha, in the volcanoclastic Ouarzazate Group.
Stop J2.2: Precambrian-Cambrian transition east of the Kerdous inlier: (GPS: N30°02’41’’, W09°04’2.7’’)
After having passed the recent dam on the Wadi Aït Baha, stop at km 70, where an outstanding E-W geological cross-section illustrates the transition from the Late Neoproterozoic volcanic series (“PIII”) to the transgressive deposits of “Série de base” (Latest Neoproterozoic-Early Cambrian) (Fig. 16). The latter series, ca. 150 m thick, consists from bottom to top (fig. 17) of, i) dark basal conglomerates (5 m); ii) arkosic pelites (5 m); iii) a carbonate slab (ca. 10 m) regionally; and iv) ca. 50 m of pelites and green sandstones on which the road is built. The latter formation is capped by the Tamjout Dolomite (Lower Limestones, Adoudounian) which form a well marked cuesta. Within the Serie de base limestones, we may observe the presence of sandy layers with synsedimentary convolutions, slumping and intraformational breccias. The latter
Fig. 16 – Photograph of the transition between the Late Proterozoic rhyolites and the “Série de base” at the eastern border of the Kerdous inlier (SE of Aït Baha, looking south).
contain calcareous elements and poorly rounded, badly sorted pebbles of Neoproterozoic quartzite, sourced from the Early Neoproterozoic Lkest unit. The present-day Adrar Lkest peaks can be seen in the background to the SW.
Fig. 17 - Geological Cross section of the Precambrian-Cambrian transition at the eastern border of Kerdous inlier (SE of Aït Baha).
23
Stop J2.3: Petrographic and structural markers of the Late Precambrian extension at Ida Ougnidif (GPS: N29°51’30’’, W08°58’15’’)
Once arrived at Ida Ougnidif (km 114), leave the Tafraout road and take a road to Tanalt on the right. The road climbs to the west on the Lkest quartzitic massif. Stop at the first pass for a global view on the Ida Ougnidif basin. The wide depression of the Ida Ougnidif basin extends on a basaltic substratum bordered to the SW by the Neoproterozoic quarzites (Adrar Lkest) and to the NE by the gently dipping Lower Cambrian series (Fig. 18). The steep slope which limits the quartzite range corresponds to a NW-trending paleofault, several kilometres long. The quartzites are affected by extensional structures (tension gashes, mini-grabens…) related to the activation of this fault (Fig. 19). In the collapsed block to the NE conglomeratic deposits accumulated (PIII), whose thickness is strongly variable as well as the nature of the reworked elements. In this region, the badly sorted pebbles are primarily angular quartzites, agglomerated in a fine grained siliceous matrix. These deposits are followed upward by tens of metres of basalts, at the top of which pillow structures can be observed (Ida Ougnidif). The transition to the “Série de base” occurs without noticeable hiatus. Therefore, the Ida Ougnidif basalts emplaced on top of the Tanalt Group prior to the Cambrian transgression. Similar basalts are known from several other places in the Anti-Atlas (Youbi, 1989; Bajja, 2001; Algouti et al.,
Fig. 18 - The Ida Ougnidif depression. The transition from the Neoproterozoic to the Lower Cambrian is marked by basaltic lava flows.
2001). Fig. 19- Interpretative geological cross-section of the eastern border of the Kerdous inlier at Ida Ougnidif locality.
Petrography and geochemistry of Ida Ougnidif basalts (Soulaimani et al., 2004): The Ida Ougnidif basalts are of greenish rocks with intersertal microgranular to sub-ophitic texture at the base, and with aphyric, microlitic fluidal to porphyritic texture upwards. Under the microscope, these basalts are completely transformed into secondary greenchist facies minerals (albite, chlorite, actinolite, epidote, sphene, calcite and quartz). Primary mineralogy would includes plagioclase, clinopyroxene, olivine, ilmenite and apatite. From a geochemical point of view, these rocks are characterized by: (i) basaltic composition; (ii) secondary albitisation of plagioclase, following an enrichment in Na2O and an impoverishment in CaO; (iii) the ratios XMg (0,40 to 0,64) added to the variability contents of Ni (64-280 ppm), Cr (77-355 ppm) and incompatible elements show that the magmas have underwent processes of fractionation and/or crustal contamination; (iv) the concentrations in TiO2 (1,70-2,78%) and P2O5 (0,22-0,46%)
Fig. 20 - Normalized multi-elemental spectra for Ida Ougnidif and Jbel Kerkar basalts.
24
are comparable with those of within plate basalts. Mantle-normalized multi-elementary spectra (fig. 20) show a negative overall slope, high contents in incompatible and light rare earth elements comparatively to the heavy rare earth elements(La/Yb = 1,79-
4,53), and weak Nb negative anomaly as in many continental tholeites (Th/Nb = 0,070,13; La/Nb = 0,86-2,26). All these chemical features confirm the tholeitic and anorogenic character of these lavas.
Route Turn back to Ida Ougnidif and take again the direction to Tafraout. Stop J2.4: Variscan inversion of the eastern edge of Kerdous inlier (GPS: N29°49’04’’, W08°53’59’’)
Immediately after the village of Tagmoute, and still along the same paleofracture alignment described above, we can observe on the right many outcrops of the Ouarzazate Group conglomerates (PIII). They are polygenic conglomerates obviously affected by a N150 directed subvertical cleavage (Fig. 21). Such cleavage is systematically observed, in the Anti-Atlas, along the fault zones (re)activated during the Variscan compression. The matrix of the conglomeratic deposits is appropriate for the cleavage development whereas the pebbles are more or less fractured according to the intensity of strain. In the present case, the pebbles long axes are simply reoriented in the cleavage. The development of the ductile deformation in the matrix of the conglomerates bordering the Adrar Lkest quartzites testifies to the reactivation of the previous paleofault, and gives evidence of the uplift of the Kerdous inlier as a pop-up structure.
Fig. 21 - Upper Neoproterozoic conglomerates affected by weak Variscan cleavage steeply dipping eastward, along the eastern border of the Kerdous inlier.
Stop J2.5: Evidences of Early Cambrian extension (GPS: N29°44’53’’, W08°49’22’’)
At km 145, turn left once in the junction at the pass and take the direction of Aït Abdellah. Stop in the descent after one kilometre. On the roadcut, we observe large synsedimentary extensional structures in the Adoudounian limestones. Decametre size slump folds are intercalated between undeformed carbonate sequences tilted
eastward (Fig. 22). The hinge of the larger recumbent fold shows a minor fold whose axial plane dips 30° to the east, whereas the normal limb of the major fold shows numerous decimetre size, synsedimentary normal faults. The co-existence of compression at the front of the major fold and extension at its tail testifies to its gravitary origin. Its synsedimentary character is confirmed by its insertion
25
between undisturbed levels, the plastic style of the deformation, the infilling of the decimetre size hemigrabens, etc. This major synsedimentary instability gives evidence for the persistence, during the Early Cambrian, of the extensional regime already active during the Late Precambrian.
About 20 m to the west, the Adoudounian carbonates are affected by a west verging fault-fold structure. However, the constant thickness of the folded beds is rather in favour of a compressive fold associated with the Variscan shortening.
Fig. 22 - Synsedimentary structures at the base of the Lower Cambrian (Adoudounian) limestones, eastern border of the Kerdous Massif. Top: view of the entire slump structure. Bottom: details of the synsedimentary normal faults backing the normal limb.
Turn back to the junction and take again the road to Tafraout. Stop J2.6: The late Neoproterozoic unconformity at Aferni Pass (GPS: N29°44’10’’, W08°50’41’’)
The Aferni Pass is the eastern entrance to the Kerdous inlier, at 1675 m a.s.l. The pass offers a fascinating view on the Ameln valley, starting from its eastern termination. The Ameln valley presents a reduced vegetable cover, dominated by almond trees (ameln) which come into flower during February. Due to the dryness of the last decades, the moussem (festival) of the Almond trees which was celebrated
on the occasion was abandoned. Several villages are built along the valley, mainly localised next to the springs at the foot of the Adrar Lkest, but their inhabitants are abnormally few as they migrated toward the other cities of Morocco or even abroad, mainly devoted there to trading activities. The E-W trending Ameln valley is opened in the Paleoproterozoic Kerdous Schists. It
26
is dominated to the north by the tightly folded, mostly verticalized Neoproterozoic quartzites (Lkest Group), and to the south by the Ouiharen orthogneiss massif (Fig. 23). A broad, right-lateral reverse shear zone separates the Kerdous Schists from the Lkest quartzites (Hassenforder, 1987; Soulaimani and Piqué, 2004). This regional shear-zone is underlined in the field by lenses of quartzites, highly elongated parallel to the general direction of the shear zone. We are located on the eastern tip of this major ductile fault zone or Ameln Valley Fault Zone (ZFVA) where it is unconformably overlain, together with the vertical quartzite beds, by volcanoclastic deposits of t he Tanalt Group (Ouarzazate Supergroup, “PIII”), gently dipping eastward. Therefore, the main Pan-African transcurrent-reverse shear deformation of
both the basement and quartzite cover occurred prior to the latest Neop roterozoic (“PIII”) sedimentation (Fig. 13).
Fig. 23 - Panorama of the Ameln valley from its eastern tip at the Aferni pass.
Stop J2.7: The Kerdous Schists (GPS: N29°44’45’’, W08°54’38’’)
The Paleoproterozoic Kerdous Schists are represented at this stop by low-grade metapelite - meta-arenite alternations, showing garnet and andalusite minerals related to contact metamorphism, but also relics of sedimentary structures. The E-W
trending metamorphic foliation dips steeply to the south, carrying steeply plunging mineral lineation, consistent with the northverging overthrust kinematics of the ZFVA (Fig. 24) (Hassenforder, 1987).
Fig. 24- Geological cross-section of the eastern Kerdous Massif, after Hassenforder, in Geological map of Tafraoute, scale: 1/100 000, Notes et Mémoires N°307 (1983).
Stop J2.8: Adrar Ouiharen orthogneiss (GPS: N29°44’27’’, W08°54’37’’)
The Adrar Ouiharen augen gneiss forms in map view an E-W band, more than 10 km long and 600 to 800 m wide, parallel to the regional foliation, the ZFVA and the
Adrar Lkest trend. To the west, the orthogneiss unit is intruded by the Late Neoproterozoic Tafraout granite whereas its eastern part is uncomformably overlain by
27
the Tanalt Group conglomerates (cf. Stop 6). The augen orthogneiss (Fig. 25) contains K-feldspar and plagioclase porphyroclasts of varied size and proportion in a quartz-two micas matrix. Regionally, the gneissic facies evolve to weakly deformed or isotropic porphyritic granite, particularly in the axial zone of the Adrar Ouiharen. Within the gneissic facies, the mylonitic foliation affects the magmatic minerals (muscovite, tourmaline, etc.) as well as the minerals of alteration (sericite, chlorite, and epidote). The K-feldspar phenocrysts are fractured at relatively low temperature, the fractures being filled with black secondary minerals. The kinematic indicators (asymmetric pressure shadows) characterize a simple shear regime consistent with top-to-thenorth thrusting, as in the juxtaposed Kerdous Schists and Lkest quartzites. This strongly suggests that the mylonitization of the Ouiharen orthogneiss is a Pan-African event. In addition, the regional dome
structure of the Tasserirt area (fig. 13C) pleads for the contemporaneity of the orthogneissification process and the exhumation of Paleoproterozoic rocks, followed by the intrusion of the Neoproterozoic granites (see discussion above).
Fig. 25 - Photograph of outcrop of foliated, medium- to coarse-grained felsic orthogneiss exposed at Jbel Ouiharen.
Stop J2.9: Tafraout granite (GPS: N29°44’57’’, W08°57’36’’)
At the crossroads, leave the road which skirts the valley toward the west and take on the left the direction of Tafraout. Stop at about 1 km before the north entrance to Tafraout city. The roadcuts (Fig. 26) show the intrusive contact of the pink Tafraout granite (Late Neoproterozoic, ~550 Ma), to the north, in the dark coloured Kerdous Schists, to the south. The isotropic granite appears to cross-cut as well augen orthogneiss which belong to the western prolongation of the Jebel Ouiharen unit. Fig. 26 - The Late Proterozoic Tafraoute pink granite (on the left) intrudes the Kerdous slates (on the right) at the northern access to Tafraoute.
End of day 3. Night in the Amandiers Hotel perched on a pink granite hill which overhangs the small and quiet Tafraout town.
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Day 3 (J3) : Tafraout-Tiznit-Goulmine Tafraout granite and its equivalents subalkaline to alkali-potassic chemical (Agouni Yessene, Tazoulte,…) aged composition. These magmatic bodies between 545 and 550 Ma, are post-tectonic represent the plutonic equivalents of the intrusions which emplaced in the widespread late Neoproterozoic volcanics of Paleoproterozoic basement of the Kerdous the Ouarzazate Supergroup series. The Late massif after the main Pan-African Proretrozoic magmatism evolves to alkaline deformation, as it occurs in the other Antiterms during the Early Cambrian. Atlas inliers. They are monzogranites with Stop J3.1: Magnificent granite landscape at Aday (GPS: N30°09’70’’, W09°13’15’’)
Leave Tafraout southwestward, direction to Tiffermit and Tiznit via Tahala (Secondary road 7074). We drive for over 10 km in the Tafraout granite massif which offers landscapes of great beauty with chaos of pink granite among palm and almond trees, small valleys and coloured villages. We can have a look on such a landscape at the picturesque village of Aday (Fig. 27). Afterwards, the road penetrates in of the much older Tahala granite, firstly dated at 1920 ± 40 Ma (Rb/Sr; Charlot, 1978), then more precisely dated by U/Pb on zircon at 2060±12 Ma (BGC 2001d) and 2044±1.8 Ma (Barbey et al., 2004). The limit between the Tafraout and Tahala granites is barely visible in the field, except through their forms of alteration, rounded boulders and prismatic blocks or slabs, respectively. Beyond Tahala village, the road twists upwards in the Kerdous Schists which constitute the country rock of the Tahala granite. Once at the pass, turn off to the right (west) on a small road and stop after 1 km before another pass.
Fig. 27 - Landscape of the Tafraoute pink granite at Aday village
Stop J3.2: The unconformity of the Upper Neoproterozoic Anezi Series on the Tahala basement (GPS: N29°36’20’’, W09°09’17’’)
This stop offers a broad sight on the Tahala plain and its mountainous borders, i.e. the Tasserirt Plateau to the east and the Adrar Lkest barrier to the north (Fig. 28). On the western and southern sides (which corresponds to our location), the Tahala
basin is bordered by gentle cliffs consisting of the Upper Neoproterozoic Anezi Formation. This volcano-sedimentary series overlies through a major discordance the Tahala Paleoproterozoic basement. The contact has been reworked as a
29
décollement level, as shown by some breccia intercalations.
Fig. 28 - Northward view of the western edge of the Tahala plain. The sedimentary sequences of Anezi formation overlie disconformably the Eburnian basement. Jbel Lkest in the background.
The Anezi Series, formerly labelled (PII3), corresponds to continental deposits resulting from the erosion of a mountainous topography in periglacial conditions (Varangian or Gaskiers glaciation; Hassenforder, 1987; Deynoux, 1987). The Anezi Series is regarded as equivalent to the Tiddiline Formation of the Bou Azzer “boutonnière” (Central Anti-Atlas). The Tiddiline Fm corresponds to molasse deposits affected by open folds and reverse faults before the accumulation of the Ouarzazate Group. At first attributed to a distinct Late Pan-African "B2" phase (Leblanc, 1975), this deformation is now assigned to the same transpressif regime which controlled the opening of syn- to latecollisional basins such as the Tidiline and Anezi basins (Hefferan et al. 1992). In the Kerdous inlier, the Anezi basin seems to be initiated and controlled by E-W dextral and NE-SW sinistral strike-slip faults, prior to the accumulation of the Tanalt (Ouarzazate) series (Hassenforder, 1987).
According to the legend of the new geological maps at scale 1: 50,000 of the Kerdous inlier (BGS, 2001a-d), both the Anezi and Tanalt formations should be grouped in the Ouarzazate Supergroup, otherwise subdivided into four Groups, i.e. from bottom to top, i) the Tafrawt (Tafraout) Group, formed by a mixture of ignimbrites, rhyolites, tuffs, sandstones and conglomerates; ii) the Anezi Group (fine grained sandstones and conglomerates); iii) the Tanalt Group (sandstones and argillaceous conglomerates), and iv) the Afoud Group formed of ignimbrites and rhyolites interlayered with conglomerates. These groups should be in turn subdivided into formations and members. The age of these non-fossiliferous series, approached by that of the associated volcanics, ranges between 620 and 544 Ma, which is close to the base of the Cambrian (542 Ma). As the explanatory notes of these maps are not yet published, the criterion for such detailed subdivisions, and their geodynamic significance remain conjectural. Route Turn back to the Tafraout-Tiffermit road and proceed to the SW. We drive on the Anezi Series. The road skirts the Wadi Ida Oussemlal which cuts deep gorges in the sandy and volcanic series, until the last cluse at Jemâa Ida Ousmlal. There we enter a narrow depression (Ait Ouafka Paleoproterozoic Schists) where the road forks. Turn right (west) to Tiznit, and proceed until reaching the Kerdous (Tifermit) Pass. The road follows the west termination of the low elevation Ait Ouafka Plateau which corresponds roughly to a Paleoproterozoic Tifermit-Tighmi anticline, as narrow by place as a few hundred metres. Stop on the Kerdous Hotel parking.
Stop J3.3: Tifermit Pass (Kerdous Pass) panorama (GPS: N29°33’04’’, W09°20’27’’)
Perched at 1232 m above sea level, the pass gives way to a surprisingly steep descent toward the plain of Tiznit. The view extends to the left on the SW part of the
Kerdous inlier (Tazeroualt massif), and in front of us (to the west), beyond the plain and the Cambrian highs, the Precambrian massif of Ifni (Fig. 29). In particularly
30
beautiful cold weather, one can see even the Atlantic Ocean at the horizon.
or faulted contact, by the volcano-detrital deposits of the Ouarzazate Supergroup. Route
Fig. 29 - The scenic view over the western border of the Kerdous massif and the Tiznit plain, from the Tifermit pass.
The hotel is built upon Paleoproterozoic mica-schists, located on the western tip of the Tighmi-Tifermite fault zone (Hassenforder, 1987). This E-W corridor is flanked on both sides, either in discordance
The descent to Tiznit follows firstly the basement/cover contact until the border of the depression of the Wadi Tizgui. Then, we drive on the ignimbrites and tuffs of the Tafrawt (Ouarzazate) Group. After Tighmi, a small village at km 60, one leaves on the left the road to the Tazerwalt massif. The road turns to the NW on the sandy and conglomeratic levels of the Anezi Group, then follows the Wadi Bou Iguechder gorges in the Latest Proterozoic volcano-detrital series, and eventually reaches the Adoudounian Serie de base and Lower Carbonates (fig. 30). This succession is slightly tilted to the west and corresponds to the cover sequence of the Kerdous massif.
Fig. 30 - Geological cross-section of the western border of the Kerdous inlier along Oued Assaka (from Choubert, 1952).
Stop J3.4: The western border of Kerdous inlier (GPS: N29°37’4.5’’, W09°29’24’’)
The Wadi Assaka is deeply cut in the Lower Ordovician pelites (Tachilla Formation), and sided by fluvial terraces. After crossing the Wadi, and beyond the village of Bouchtil, a beautiful cross-section of the southern termination of J Ouarzemine-Tachilla syncline can be observed on the right in the panorama (fig. 31). The entire Ordovician succession is regarded as parautochthonous, being pushed eastward and detached by the Variscan compression.
Route:
Fig. 31 - The Ordovician stratigraphic succession of the southern side of Jbel Warezmine along the western flank of the Kerdous inlier.
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From there, we enter in the Tiznit Plain which corresponds to the southern prolongation of the Souss Plain, covered by Quaternary deposits: dunes, silts, gravels and calcretes Coffee break at Tiznit Leave Tiznit to the south, en route to Goulimine via road P30. From Tiznit, (260 m a.s.l.), we can observe to the southwest the border of the Ifni Precambrian massif, and to the southeast the Kerdous massif. Between the two Precambrian massifs, the Jbel Inter progressively emerges. This is the frontal relief of the Lakhssas Plateau which closes the plain to the south. The road remains on the Quaternary plain, underlain by lacustrine limestones and carved here and there by small wadis. We cross the famous Wadi Adoudou (taken as eponym of the Adoudounian formation by G. Choubert, 1952) at the foot of Jbel Inter. Then, we drive on Middle Cambrian pelites (“Schistes à Paradoxides”) in the core of the northtrending Talainte syncline, bordered by the Lower Cambrian “Calcaires supérieurs” on both the western and eastern sides.
Kerdous inliers, being affected in its axis by the Jbel Inter and Ida Yahia anticlines, to the north and south respectively (Fig. 32c). Variscan deformation is much heterogeneous, being particularly intense in the centre of the plateau close to subvertical shear zones, such as those which limit the Jbel Inter. On both sides of these ductile fault zones, the intensity of the deformation decreases rapidly. The N-trending folds range from open to isoclinal and from centimetre to kilometre scale. They show axes plunging slightly either north or south. A nearly vertical, axial planar foliation develops, being affected in the north by sinistral N160 and dextral N10-20 virgation zones. Subvertical stretching lineation is locally observed, and the associated kinematic indicators suggest an upward movement of the Jbel Inter during the Variscan compression between the Ifni and Kerdous basement massifs (fig. 32c).
Variscan deformation in the Cambrian of the Lakhssas Plateau The Lakhssas Plateau, about 1000 m high, separates the Tiznit plain from that of Bou-Izakarn (fig. 32). It is underlain by Late Proterozoic and Lower Cambrian series overlying unconformably the Paleoproterozoic basement. The Adoudounian-Lower Cambrian sequence includes, from bottom to top, the green siltites and pelitic sandstones of the "Série de base ", the dolomites and marls of the "Lower Limestones", the dolomitic limestones with reddish sandy levels of the "Lie-de-vin Series". The latter series crops out in the core of the Jbel Inter anticlinorium, in the axis of the plateau, Fig. 32 - Structural map of the Lakhssas being otherwise surmounted by the "Upper Plateau area and E-W geological crossLimestones", followed by the "Schistosection (C-C' in the map). Stereograms calcaire Series" with Archeocyaths and (Wulff stereonet, lower hemisphere) Trilobites, topping the Lower Cambrian represent bedding (S0) and foliation data succession. (S1). Insert: Location of the Lakhssas The Lakhssas Plateau occupies the core Plateau area. of a wide synclinorium between the basement culminations of the Ifni and Stop J3.5: Variscan deformation at the base of Jbel Inter
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(GPS: N29°24’58’’, W09°43’04’’)
Before the rise on Lahkssas Plateau, the southern termination of Talainte syncline (1st order fold) shows a conspicuous ductile deformation. The Upper Limestones are affected by a subvertical foliation, axial planar to sub-meridian 2nd order upright folds (Fig. 33). The thin sedimentary layering, underlined by carbonate-silicified silts alternations, is affected by 3rd order
folds (Fig. 33B), whose limbs are strongly sheared, resulting in the specific “schiste à trous” facies due to the weathering of the carbonate layers (Fig. 33C). The limestones contain syncinematic pyrite crystals, bordered by symetrical pressure shadows filled up with vertical fibres, thus testifying to a dominant vertical component of strain.
Stop J3.6: Variscan deformation in the Lakhssas Plateau (GPS: N29°23’57’’, W09°44’5.8’’)
The stop is located at the km-marker Guelmim 70 in the Tizi Mighert (Mighert Pass). It corresponds to one of the more intensely strained area of the Paleozoic Anti-Atlas. The layering of the Cambrian marbles is overprinted by an N-S trending, steeply dipping foliation, as observed already in the previous stop. The lack of visible sedimentary layering is substituted by tightly folded stylolitic surfaces likely originated from diagenetic compaction (see J2.1 stop) (Fig. 33D). The fold axes are nearly horizontal to steeply plunging, either northward or southward, thus indicating intense shearing in the foliation plane. Careful observation permits to observe vertical shear bands (C/S structures) associated with steeply plunging lineation which indicate a reverse, top-to-the-east sense of motion (Fig. 33E). This suggests that the Jbel Inter Precambrian basement and its Paleozoic cover have been ejected as a "pop-up" structure more or less contemporary with the uplift of the Ifni and Kerdous blocks. The Jbel Inter appears as a potential inlier which is still covered by the Lower Cambrian layers. The gravimetric data confirm the uplift of the crystalline basement beneath the Jbel Inter (Soulaimani, 1989). It should be noted that the Variscan ductile faults bounding the Jbel Inter pop-up have been reactivated during the Atlas orogeny, as evidenced by their current seismic activity.
Fig. 42 33- Panorama - Variscanofdeformation the Western of Anti-Atlas the as seen fro Lower north, one Cambrian can see limestones the ridgesofofthe J. Tazout Lakhssas (foreground), J. R Plateau. separated A)by foliated the Betaïna, carbonate, Drâasouthern and Assa-Aouinat end Torkoz pla of Talaïnt syncline; B) Close view of a normal limb associated with minor folds; C) incipient transposition of stratification in foliation planes; D) isoclinal fold with thickened hinge, Jbel Inter bordering fault ; E) ductile shear zone with dominant vertical motion.
Route:
33
Over more than 15 km, the road remains on the Lakhssas Plateau, covered by argan trees and euphorbs. The vegetation is relatively dense because it benefits from marine breeze and rather abundant precipitations. However, only water reserves and fontains allow the local inhabitants to live on this karstic plateau.
The Village of Tlata Lakhssas is the administrative Center and the principal agglomeration of the Aït Baâmrane tribes, known for their brave resistance to French colonial forces. After the Agni Imgharen Pass, the descent to Bou Izakarn follows the Wadi Imgharen in the Lie-de-vin series.
Stop J 3.7: The southern border of the Lakhssas Plateau (GPS: N29°11’04’’, W09°44’64’’)
The carbonate series of the southern part of the Lakhssas plateau are obviously less deformed than those of its northern part. Bedding is deformed into large folds with southward plunging axes (Fig. 34). The stop offers a panorama on the Cambrian highs of the folded ridge of the Jebel Taiert, which displays now the NE-SW trend of Jbel Bani belt. Beyond the Cambrian, if the atmosphere is limpid, we can see higher ridges which correspond to the Jbel Bani Ordovician quartzites. The mountain ridges to the west correspond to the Ifni massif, with the Jbel Fogo ignimbrites at 1250 m a.s.l. Route:
At Bou Izakarne, turn right on road P41 to Guelmim (Goulimine). From Bou Izakarne to Guelmim we drive on the Middle Cambrian pelites and greywackes (Schistes à Paradoxides) which form the Adrar Akenbouch cliff on the left, and more to the SW, beyond the village of Tagante, the
western side of the Jbel Taiert faulted syncline, topped by the Goulimine bar (Tabanit or Lingula Sandstones).
Fig. 34 - The Andja perianticline, south of the Lakhssas plateau in the Agni Imgharen pass, towards the Bou Izakarn plain.
End of day 4 Night at Goulimine
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Day 4 (J4): Goulmine-Assa-Tata (270 km): Paleozoic fold belt and WAC border The folded Paleozoic cover in the Western Bani The Western Anti-Atlas can be regarded as the foreland fold belt of the Variscan Appalachian-Mauritanides chain, broadly symmetrical to the "Valley and Ridge" belt (Soulaimani, 1998; Burkhard et al., 2001; Soulaimani and Burkhard, 2007). However, the Anti-Atlas is characterized by the presence of broad Precambrian outcrops which correspond to faulted antiforms surrounded by the folded Paleozoic cover. Consequently, the belt offers a thick-skinned tectonic style contrasting with the thin-skinned tectonics of the Valley-and-Ridge (Soulaimani et al., 1997; Helg et al., 2004; Burkhard et al., 2006). Significant duplications and tangential structures occur only in the westernmost Anti-Atlas, in the Ifni and Bas Draa area (Soulaimani, 1998; Belfoul et al., 2002). Therefore, in most of the Western AntiAtlas, the Variscan folds observed in the 10 km thick Paleozoic cover are upright, strongly disharmonic, decoupled along several incompetent horizons, but not associated with duplex structures. The most significant decollement levels are the Liede-vin Series and the Silurian black shales. In the varied competent levels, folds are dominantly cylindrical and upright, contrasting with the more “internal”, south westernmost regions where the structures are clearly verging craton-ward. The fold amplitude and wavelength are specific to each competent formation, being controlled by its thickness (Fig. 35). For instance, the thick Ordovician quartzites of the Jbel Bani
show fold amplitude of 3 to 5 km whereas the thinner Devonian limestones and sandstones of the Jbel Rich are folded with amplitude of 100 to 200 m. The total shortening has been estimated at 15-20% (Caritg et al. 2004; Helg et al., 2004). The basement remobilisation, whose implication in Variscan shortening is obvious, takes place by the inversion of old fractures which previously controlled the Late Proterozoic extensional event. At the southeastern border of the folded domain, the striking contrast between the Jbel Rich folds and the undeformed Tindouf basin (Jbel Ouarkziz monoclinal series), clearly shown on the satellite images, has been subject to different interpretations, included that of a Neogene shear zone (Weijermars, 1993)! The "en échelon" disposition of the Jbel Rich folds along the Ouarkziz border suggests a weak dextral motion along the N70 direction of this border (Piqué and Michard, 1989), combined with the southwestward attenuation of the shortening (Soulaimani et al. 1997). The very rapid decrease of the deformation along the J. Ouarkziz has been interpreted as the surface expression of a cryptic triangle structure under the J. Ouarkziz which would overlap the Rich folds along a blind thrust (Burkhard et al. 2001, 2006). Route: The first part of the day is devoted to the folded Paleozoic series of the western Bani, observed along a section nearly normal to the fold axes (fig. 35 and 36). Leaving Guelmim (Goulmine) to the SE, we will
Fig. 35 - Schematic geological cross-section of the Paleozoic series of the Western Anti-Atlas (Goulmine-Assa transect) (From Soulaimani, 1998).
35
cross the beautiful J. Bani folds (Fig. 36), then the Devonian ridges of the Rich, scattered in the Assa-Aouinat Torkoz plain whose substratum is formed by the Silurian black shales. We will afterwards cross the plain of the Wadi Drâa, underlain by the Upper Devonian slates, until reaching the Carboniferous series of the J. TazouteJ.Ouarkziz, which form an imposing ENEWSW monoclinal crest more than 400 km long. This crest constitutes the northern boundary of the Tindouf basin, i.e. the southern half of the large Paleozoic intracratonic basin, whose northern half corresponds to the Western Anti-Atlas. In the second part of the day we will follow to the northeast the Devonian Rich folds from Assa to Tata. The town of Goulmine is built on the Middle Cambrian sandy shales of the internal “Feija” (“combe”). The sandy-
quartzitic Conocoryphe bar of Tabanit (discovered here by Bondon), also called the Goulmine bar, caps the Jbel Ras Anessar which overhangs the town and constitutes the SW tip of the Jbel Taïert that we have seen yesterday along its other face. Take the direction of Assa by crossing the downtown area via the souk, direction to the east. Until Fask village, on 15 km, the road follows the right bank of the palm plantation of the Wadi Seyyad which crosses the Middle Cambrian plain of Fask. On the right, south of the plain, we observe the periclinal termination of the Jbel Taïssa anticline formed in the northern envelop of the Bas Drâa Precambrian massif. To the north, the Tabanit ridge appears to be formed by more than 8 sandy bars, on the SE side of Jbel Taïert.
Fig. 36 - Field stop location for the first half of day 4 superposed on the Landsat 7 image of the western Anti-Atlas.
36
Stop J4-1: The Fask fault (GPS: N28°57’1.7’’, W09°46’56’’)
Stop at 20 km from Guelmim. We observe in the panorama in front of Fask that the series of the Jbel Taïert are disturbed by a fault, probably connected with those observed further north in the Lakhssas Plateau. East of the fault, an anticlinal fold affects the Middle Cambrian formations, seemingly overthrust by the Jbel Taïert unit, and pushed onto the Ordovician folds further east. Consistently, the first outcrops of the Ordovician series show folded quartzites thrust towards the SE over more pelitic levels (fig. 37). Route: The road takes a SSE direction and goes around the synclines of Adrar Taïloukst (831 m), Adrar Amesmardane
Fig. 37 - Folding and décollements of the western Bani Ordovician series at Fask
(985 m), and more to the east that of Adrar Oumrhajjid (1036 m). These summits correspond to perched synclines separated by slightly wider anticlines.
Stop J4-2: Deformation of the "Schistes à Paradoxides" (GPS: N28°50’25’’, W09°42’55’’)
Stop at 46 km from Guelmim. Opposite to Adrar Tanselfoute, the road crosses the Paradoxides Schists of Middle Cambrian age, which show a welldeveloped spaced cleavage trending N 35 and dipping 50° to the NW. In the NE direction, the Ordovician quartzites form a scenic fold train (Adrar Oumrhajjid). At the Targmaïte village (60 km from Goulmine), a beautiful NW-SE section of a
broad syncline can be seen on the left of the road, on the southern side of Adrar Tiouargâne (1091) which is topped by a thick quartzitic bar of Upper Ordovician age. Lower in the slope, the competent layers form asymmetrical minor folds overturned either to the SE or the NW, consistent with the box-fold geometry of the major fold (Fig.38A).
Stop J4-3: Amazloug Pass (GPS: N28°49’24’’, W09°32’23’’)
7 km after Targmaïte (67 km from Guelmim), stop in the Amazloug Pass on the NW flank of the Adrar Oui-n-Tigunite ridge. This ridge consists of steeply dipping Ordovician quartzites which form the southeast side of an elongated, NE-trending syncline (Fig. 38C). We can also observe to the north the conical periclinal termination of
the Adrar Tiouargâne anticline (of which we have previously observed the southern flank) with its NE plunging axis (Fig. 38B). To the south-west, another anticlinal closing can be seen between the verticalized layers of Adrar Oua-n-Noûmes and Ouamalou Tzegzaouine, left and right, respectively.
37
Fig. 38 - Deformations of the Ordovician quartzite series in Targmaïte locality; A) disharmonic folds at the base of the massive quartzite of Adrar Tiouargane; B) box anticline in the north of Targmaïte; C) steeply deeping quartzite of Adrar oua-n-Noûmes, seen from the Amazloug pass, and; D) closing anticline in its NW part.
Route: Beyond the pass, we enter a broad depression excavated in a large anticline cored by the Middle Cambrian series (Paradoxides Schists and Tabanit Sandstones). The road follows the southern side of the structure then crosses the last gorge leading to the plain of Assa-Aouinat Torkoz. The plain is underlain by a Silurian and lowermost Devonian substratum, covered by Quaternary stony deposits, strewn with much dispersed acacias. In front of us, the Early-Middle Devonian series of J.Rich dominates the town of Assa. After Assa, the road crosses the plain of the Lower Wadi Drâa, then the wadi itself, barely hemmed in the plain. The latter is covered by Quaternary regs which mask the Upper Devonian formations of the Drâa Group, 2000 to 2500 m thick, formed by
Fig. 39 - Frontal view of the Carboniferous series of J. Tazout and J. Ouarkziz from the Drâa plain south of Assa.
mudstones with sandy or carbonate intercalations in the upper levels. South of the Drâa, two staged cuestas appear in front of us, from bottom to top, the J. Tazout (Tournaisian) in the foreground, and the J. Ouarkziz (Visean) in the background (fig. 39).
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Stop J4-4 - Jbel Tazout: Upper Devonian -Tournaisian (GPS: N28°27’16.7’’, W09°21’46.4’’)
Stop on top of the Tazout slope, and climb upon the crest east of the “pass”. The monoclinal cuesta, slightly dipping to the SSE, corresponds to the Uppermost Devonian -Tournaisian series, and consists of 400 to 500 m of mudstones intercalated with three sandy bars (Fig. 40). The lower bar (Tazout 1), rich in brachiopods, is still part of the Late Devonian. The "Tazout 2" is allotted to Strunian whereas the ultimate bar (Tazout 3) is dated from the lower Tournaisian. These sandy bars constitute successive filling sequences sourced from the south. Beyond the Jbel Tazout, the Betaïna arrow depression is underlain by 700-1100
m thick Lower (goniatites) which transgression.
Visean mudstones record a renewed
Route: The road follows the Betaina plain for nearly 2 km towards the SW, turns to the south to cross the last barrier before the Tindouf Basin, i.e. the Jbel Ouarkziz, the crest of which supports a big antenna. After meandering across the thick Ouarkziz Formation, the road reaches the Betana plain.
Fig. 40- Geological cross-section of the northern border of the Tindouf basin, south of Assa (From Choubert, 1952, modified).
Stop J4-5: The Carboniferous of Jbel Ouarkziz and Betana; dating the Variscan folding (GPS: N28°22’50’’, W09°23’11’’) This is our southernmost stop, located at the boundary between the Ouarkziz and Betana Formations. The ca. 650 m thick Ouarkziz Formation, just crossed, has been subdivided into two units. The lower unit (which constitutes the Jbel Ouarkziz escarpment) (Fig. 41) consists of
Lower Visean limestones and clays, rich in corals and brachiopods, intercalated with sandstones and sandy clays. The higher unit is dominated by gypsum clays in the west and evolves to the east to brown and green clays with layers of black dolomitic limestones. This unit corresponds to the
Fig. 41 - Photograph of a N-S natural cross-section of the Visean formations of Jbel Ouarkziz. Note the gentle southward dip of the bedding.
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Fig. 42 - Panorama of the Western Anti-Atlas as seen from the Jbel Ouarkziz. From south to north, one can see the ridges of J. Tazout (foreground), J. Rich and J. Bani (in the background), separated by the Betaïna, Drâa and Assa-Aouinat Torkoz plains, respectively.
Late Visean and Early Namurian. On top of the latter unit, the Betana series crop out until the hills at the horizon. They consist of approximately 1500 m of continental sandstones and mudstones, which contain plants of Namurian age at the base (Jbel Reouina Series), and Westphalian to Lower Stephanian towards the top (Merkala Series). These formations were deposited by braided streams sourced in the NW, i.e. in the Western Anti-Atlas (cf. Favre, 2005). Further south, these series are capped by the Hamada of Tindouf (Neogene). The limit between the Ouarkziz marine series and the Betana continental formations is underlined by an erosional discontinuity, which records the emersion of the entire area and the folding and uplift of the Western Anti-Atlas. The outcome of this tectonic phase is negligible at the northern edge of the Tindouf basin, slightly tilted southward due, possibly, to a north-verging triangle structure underneath (Burkhard et al., 2006). Note that the Late Carboniferous age of the folding event in Western AntiAtlas has been also recognized through K/Ar dating of fine grained recrystallized micas from the base of the Paleozoic sequence (Bonhomme & Hassenforder, 1985) and underlying basement (Margoum, 2001, in Soulaimani and Piqué, 2004). Zircon fission track analyses on Kerdous
granites yield similar dates (Saddiqi et al., 2007). Route Backtrack to Assa and take the road of Foum El Hisn (Foum el Hassan) toward the NE. Cross the Wadi Assa and proceed to the NE until to reach the Rich peak of Sidi Boulasrar. The Lower-Middle Devonian Rich Group and the Variscan folds south of Jbel Bani The Rich Group is defined as a succession of four sedimentary formations, almost identical, called Rich (Hollard, 1967, 1981). Each Rich consists of a thin basal calcareous level, followed by rythmites (sandy pelites), and finally by sandstones. These formations are named as follows (Fig. 43): Rich 1 (Assa Fm), Rich 2 (Merzâ Akhsai Fm), Rich 3 (El Annsar or Mdaouer El Kbir or lower Timrhanrhart Fm), and Rich 4 (Nkheila or Khebchia Fm). Hollard (1981) attributes the Rich Group to the Upper Siegenian-Lower Eifelian period. This was confirmed by recent paleontological datings (Lazreq and Ouanaimi, 1998; Weddige, 1998; Jansen, 2000 and. 2001, Becker et al., 2004) summarized in the synthesis edited by El Hassani (2004). The ages would be as follows: Rich 1, Upper Lochkovian to Praguian; Rich 2, Late Praguian to Lower Emsian; Rich 3, Lower to
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Middle Emsian, and Rich 4, Late Emsian to Lower Eifelian. In addition, the Rich Group presents great ENE-WSW lateral variations, along the Drâa plain. An interpretation of these variations, in terms of sequence stratigraphy and tectonics, is presented in fig. 44 (Ouanaimi, 2004; Ouanaimi and Lazreq, 2007).
Fig. 43 - Location of the J4-1 to J4-6 stops on the satellite image (Landsat 7) of the western Jbel Bani and Jbel Ouarkziz area.
In addition, the Rich Group presents great ENE-WSW lateral variations, along the Drâa plain. An interpretation of these variations, in terms of sequence stratigraphy and tectonics, is presented in fig. 41 (Ouanaimi, 2004; Ouanaimi and Lazreq, 2007).
Fig. 44 - Lateral variations of the Rich Group sequences (R) in the Drâa basin, compared to the neighbouring areas (Hollard, 1967; Ouanaimi; 2004 and Ouanaimi & Lazreq, in press). D: major discontinuities, TST: Transgressive system tract, HST: High stand system tract.
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Stop J4.6: The Lower Devonian Rich: Rich 1 and Rich 2 (GPS: N28°37’27, 5’’, W09°24’23,5’’)
The Sidi Boulasrar Rich 1 and 2 are exposed along a NW-SE natural crosssection. The sequence steeply dips to the south and develops on ca. 50 m thick (Fig. 45). The succession, observed from distance, begins with the high stand system tract (HSST) of the Rich 1 sequence, represented from bottom to top, by siltstones, sandy siltstones and sandstones. This sequence is overlain by the Rich 2 sequence, which begins with a calcareous transgressive interval and continues upward with sandy siltstones, then sandstones corresponding, respectively, to Lower and Upper HSST. All the facies on this outcrop would deserve more detailed observation. We can note particularly the very fossiliferous character of the deposits, and the varied sedimentary structures which attest to a shallow marine shelf, influenced by tide and wave dynamics.
Route:
Proceed north-eastward on the same road along the eastern flank of the Rich 1 ridge. On the left, the dejections of the vast Quaternary glacis originate from the Jbel Bani. At ca. 27 km from Assa, we cross the Rich 1 to Rich 3 series, close to Wadi Infguene (optional stop, GPS: W09°11' 32"/N28°44' 07). Then, the road penetrates in a large syncline, and follows its core, formed by Middle Devonian incompetent series, often masked by Quaternary alluvium. We leave this structure rather quickly and approach the faulted eastern flank of Jbel Bani, in the foot of which the Upper Silurian fossiliferous limestones, mudstones and sandstones crop out. A few kilometres further north-west, the road reaches the gorgeous palm plantation of Foum El Hiçn along the large Wadi Tamanart which has its source in the Kerdous massif and flows into the Wadi Drâa. At the crossroad, turn off left (NW), direction to Bou Izakarn. The Icht oasis is located in a cluse (“foum”) which crosscuts the SE-dipping flank of J. Bani. A curious anticlinal hinge appears progressively on the NE side of the cluse, which is the target of the next stop.
Fig. 45- Photograph of Rich 1 and 2 of Sidi Bou Lasrar (north of Assa).
Stop J4.7: The minor fault-ramp fold in the Bani at Icht (GPS: N29°03’36’’, W8°51’32’’)
Park immediately after Icht village, close to the km-marker “Tighjijt 61”. The sandstones of the “1st Bani” (Llandeilo) are folded into a minor conical anticline included in the SE-dipping limb of the major Bani fold. The base of the minor fold is truncated by a fault parallel to the bedding of the major fold (Fig. 46). The minor structure disappears toward the NE along strike, probably due to its axial plunge. Two alternative interpretations can be proposed: i) the minor fold could have formed on a NW directed ramp-flat thrust, before being tilted during the subsequent stage of deformation;
or ii) the minor fold developed as a “rabbit ear” during the main folding process in relation with bedding-parallel flexural slip (Fig. 47). The first hypothesis is not consistent with the expected craton-ward sense of shear during the early stages of shortening. Then, the second and simpler hypothesis has to be retained (cf. CaritgMonnot, 2003). Route: Do a U-turn back to the junction of Icht and turn left on the road to Akka. We follow a northern branch of the Siluro-Devonian Drâa plain, limited to the south-east by the
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Fig. 46 - The eastern side of the Icht cluse where the Ordovician quartzites show a minor ramp-anticline structure in the SE dipping limb of the major Bani fold..
Addana-Adrar Zouggar anticlinorium (old Pb mine). This Ordovician ridge trends NE-SW, parallel to the regional fold axis. During a few kilometres, the road runs aside a vertical bar which corresponds to the transgressive interval of the Rich 1 ferruginous calcarenites. This long barrier which appears initially north of the road will constitute afterwards the base of the series of the southern limb of the Tissenral anticline.
Fig. 47 - Interpretative scheme Fig. 43- Interpretative scheme of the Icht ramp-anticline, formed by an intra-Ordovician overthrust followed by Variscan folding. The fold axis orientation is ENE-WSW.
Stop J4.8, optional - the Tissenral Rich 1 and 2 (GPS: N29°07'00’’, W07°39'43’’)
Close to “Bou Izakarn 122 km” (Fig. 48) milestone, the transgressive calcarenitic beds of Rich 1 becomes much fossiliferous and presents large cross-stratifications, typical of shallow water deposits in a high energy context. They are covered by siltstones and sandy siltstones interlayered by some nodular limestones of the lower HSST. The Rich 1 sequence is truncated and does not comprise any more the Upper HSST sandstones, disappeared already SW of Foum El Hiçn. The Rich 2 sequence starts with the same transgressive calcareous level as seen at Assa, followed upward by sandy siltstones, then by sandstones, representing respectively the Lower and Upper parts of a HSST.
Fig. 48 - Lower Devonian beds of the southeast limb of the Tissenral anticline.
Thereafter, the road turns toward the NE and approaches the structural surfaces of Jbel Bani, close to Ait Oubelli village. Rare outcrops of Silurian black shales are indicated here on the geological map (1 / 200 000). Toward the south, we can see the south-eastern end of the Addana-Adrar Zouggar Anticlinorium which can be reached by varied tracks (one of them starts from Douar Tizounine). Akka is a relatively wide village known for its outstanding palm plantation irrigated with khettaras and other traditional channels (seguias). The old village of Akka, now deserted, is perched on an Ordovician cliff at the foot of Jbel Bani. The Wadi Akka directly flows into the Drâa River, whereas a western tributary has been responsible for the large muddy plain of Tizzounine. After Akka, the road passes close to the village of Om El Aàlg (GPS: W08°11' 24 " / N29°21' 33"), built on sub-reef limestones of the base of the Rich 2 sequence. The siltstones and sandstones of the infilling sequence (HSST) are seen to the east. The road continues toward Tata, taking progressively a north direction, and skirting kilometre scale folds, often in Middle and Upper Devonian marls and mudstones.
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Stop J4.9: Optional: the Sellanarcestes calcareous level of Oued Maskaou (GPS: W08°04’04"/N29°25’48")
Immediately close to the bridge above the Wadi Maskaou, HSST dark sandstones of the Rich 3 sequence constitute the SE side of a tight, faulted anticline striking N35. The sandstones are overlain by a calcareous level which records the large marine transgression of the Late Emsian. This level begins with a thin trilobitic horizon of ferruginous calcarenites, followed by grey massive limestones and capped by goniatite calcschists. This facies association is named Sellanarcestes Wenckenbachi limestones (Hollard, 1967, 1981) and constitutes a remarkably extended stratigraphic level. At a sequential point of view, it corresponds to the transgressive interval of the Rich 4 sequence, whose clastic HSST, well developed in the SW of the Drâa plain (Assa-Torkoz), does not exist here. The remainder of the sequence merges with the marls and mudstones of the Middle Devonian which form the eastern synclinal depression. For more information, a comprehensive stratigraphic study of this level is described close to Tata by Ebbighausen et al. (2004).
Once passed the Wadi Maksaou, the road turns towards the west, and then joins the Rich 3 sandy bar (HSST) which corresponds to the NW flank of 10 km long syncline. The bar presents steep to vertical dip, and abrupt strike virgations easily observed in the landscape. Its southern prolongation will be observed tomorrow. End of Day J4 Night at Tata: "Le Relais des Sables" Hotel Tata is a small city and a regional administrative centre. The city is dominated by a Middle Cambrian hill on which the prefectoral building is located. The Tata oasis is located in a canyon watered by the Tata and Tagmoute wadis descending from the northern highs of the Tagragra de Tata and Irherm inliers. The oasis contains many ksars (fortified villages) with stunning houses built out of pink clay. The inhabitants of the region are exclusively Berbers (Imazighen). Famous sites of rupestral engravings are announced by signposts along the road.
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Day 5 (J5) : Tata-Taroudant via Tagmoute-Irherm The folded domain south of Tata: examples of fractured reservoirs and fold interferences During the first half-day, in the southern zone of Tata, we will focus on two principal topics: the interference of two superimposed Variscan fold orientations, and the relation between folding and fracturing, respectively. As we saw before, the SE side of the Ordovician Jbel Bani presents large NE- trending folds often associated with relatively minor thrusts organized as flat and ramp structures. To the SE, Ordovician folds reappears in the Addana anticlinorium (Agueliz, A. Zouggar, Bou Oudaden), within the large folded Silurian-Devonian area. Between Akka and Tata, the Jbel Bani shows a constant NNESSW trend, but this regular direction of folds changes brutally in the approach of Tata, acquiring an equatorial direction referred to as the Tata fault direction. This new direction is due to the incorporation of the Jbel Bani series in a vast E-W anticlinorium whose core corresponds to the Proterozoic “Tagragra de Tata” inlier. South-west of the Tata region, the Devonian units are characterized by many regional folds, directed generally NE-SW to NNE-SSW, mainly individualized in the Rich Group (Fig. 49). The short wavelengths of the Rich folds contrast clearly with the large wavelengths of the Bani folds. This discrepancy suggests the occurrence of detachments plans in the Silurian and Lochkovian argillaceous series. Indeed, in some places, the folds are accompanied by some thrust systems which lead sometimes to amplify the thickness of the series (Cortès, 2000). This style of deformation is often expressed also on smaller scale, that of the beds. Generally, the alternation of soft and endured levels supports such folding/thrusting processes of deformation. However, the observable fold interferences in the Tata area, to the east of the Western Anti-Atlas is in fact the result of two successive episodes of deformation. Consistent with the E-W virgation of the Bani, the Rich series is also folded in the EW direction, transversally to the regional ENE-WSW folds. This interference is at the
Fig. 49 - Location of the B4 stops south of Tata on Landsat 7 image. Stops J5.1 to J5.4 are in the Rich 3 sequence and J5.5 and J5.6 in the Ordovician. White features correspond to the regional, early folds and the yellow ones to the latest folds.
origin of domes and pans structures. The structural and microtectonic studies show clearly two successive phases of folding (Ouanaimi 2002, Caritg et al., 2004, Ouanaimi, 2004) where the E-W folds are superimposed to the NE-SW ones. Triassic-Lower Liassic doleritic dykes and sills are located in the southeast prolongation of the large Foum Zguid dyke and cross obliquely the Variscan structures. They are regarded as a side effect of the Atlas and Central Atlantic rifting. The moderate folding and the relatively well understanding of the regional tectonic context are favourable to a thematic study of the fracture porosity in this folded zone. We will examine in particular the relationship between folding and jointing, a problem debated for a long time (Stearns, 1964; Ramsay, 1967, Ramsay & Huber, 1987) (Fig. 50), but which continues to fuel field researches, experimental tests and simulations. A particular attention is accorded to the problem of the oblique fractures (O fractures) often considered as shearing whereas the field reality shows that they are often a “mode I” fractures.
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al., 2003) and were integrated in a large field study (Ouanaimi, 2002 and 2004). The Tata circuit
Fig. 50 - The ATO classification of the fractures associated with a cylindrical fold (from Ramsay and Huber, 1987; modified). A: axial fractures (longitudinal), T: transversal fractures, O1: left oblique fractures, and O2: right oblique fractures.
At the regional scale, Donzeau (1971) already tackles this problem in the Ougarta aulacogen; followed by Desthieux (1977) on the Jbel Addana mineralized anticline. The Rich folds appear as a good field illustration of subsurface folded-fractured reservoirs studied by the IFP geologists (Gaulier et al., 1994; IFP, 1995) with the contribution of one of us (H. Ouanaimi). Some of these examples are used for experimental and simulation arguing (Cortès, 2000; Guiton et
Retrace the route of yesterday toward Akka. The road crosses first the prominent mountain of Ordovician quartzite (Jbel Bani) which lies as an E-W wall south of Tata. Stops 5.5 and 5.6 are devoted to this outstanding natural barrier. After the Tiiti village, at the junction of the road and TataAkka bar, close to the locality Oufrane (GPS: W08°00' 10"/N29°35' 36"), a beautiful sight is offered showing the virgation of this bar, due to the refolding along a subequatorial axis. We leave the asphalt road and take the track on the left, which crosses the Wadi Adis and continues along the syncline core whose substratum, hidden by thick Quaternary deposits, consists primarily of Middle Devonien. After approximately 2,5 km, the Wadi Adis sinks a narrow canyon normal to the hinge of El Bouir anticline (or Jbel Al Touzy).
Stop J5-1- Folding interferences and fracturation: the El Bouir Anticline (GPS: W07°59' 00"/N29°34' 40")
The outstanding El Bouir fold is a perfectly cylindrical anticline, with subhorizontal axis striking N 40, parallel to the Tata-Akka Bani. It affects the Rich 3 sandstones, and the overlaying Sellanarcestes horizon which pass upward to Middle Devonian marls, siltstones and platy limestones. The joint network comprises the regional transverse set (T, N135) and the longitudinal set (A, N40). As secondary oblique fractures, there are especially a subequatorial set (O) and sometimes the orthogonal N-S fractures. This distribution is observed in the entire fold (fig. 51A). In the northwestern flank, the fracture planes are visibly opened and infilled with calcite; shearing displacements are testified by en echelons tension gashes. Walk to the hinge, preferably on the southern bank of the canyon, to get a wide view on the open anticline. The canyon section shows the higher part of the Rich 3 sandstones (20 to 25 m) constituting a
mechanical unit, crossed by longitudinal and transverse HPF (High Persistent Fractures). The disposition of these two major families of fractures probably made easy the digging of the canyon. One of the most important points here is the arched or oblique geometry of the longitudinal fractures (Fig; 51D). The observation of the structures in a section along the canyon will make possible to see fractured corridors “of connected type", organized in tails of horse, indicating a normal movement on these fractures, as a result of the curvature accommodation. On the southern flank (GPS: W07°59' 01, 2"; N29°34' 40, 5"), the longitudinal joint set constitutes a good marker for the superposed tectonic movements of the region: i) it is firstly crossed by an early phase of thrusting, probably related to the folding (Fig. 51B), ii) it is reactivated as normal faults, and finally iii) as sinistral faults related to the late N-S shortening (Fig. 51C). These following movements are
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Fig. 51 – El Bouir Anticline (top of Rich 3); A) general view of the anticline, looking to the north, white circles indicate the location of the following photographs; B) late thrust crosscuting the longitudinal diaclases (L); C) sinistral reactivation of a longitudinal fracture during the subsequent N-S shortening event; D) longitudinal fractures F4 (N40) oblique to the stratification within a sandy unit. Note the “horse tail” connected fractures.
moreover confirmed by mirrors with superimposed striae. The tectonic events chronology is synthesized in the interpretative diagram (Fig. 52).
Backtrack to Oufrane, close to the tarred road, and then proceed to north on the track bordering the Tata-Akka bar. After a few hundreds metres, an optional stop may be considered Here
Fig. 52 - Summary of the evolution of the El Bouir fold. 1) folding and formation of the transverse set; 2) folding, formation of the longitudinal set, and thrusting; 3) Increase of the curvature, L set densification, normal fault accommodation and thrusting in the flanks; 4) N-S Shortening, sinistral reactivation of the L set, warping of the fold hinge and oblique secondary fractures O (enlarging).
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Stop J5-2- optional: The Tata-Akka bar at Oufrane: Folding interferences and fracturation (GPS: W08°00'00"/N29°36'40")
The Devonian bar of Tata-Akka, followed over a long distance yesterday, is now located in a different structural setting characterized by two phases of shortening, with an early NW-SE compression and a late one directed N-S. This interference determines the individualisation of dome structures (e.g. Wadi Addis dome) adjacent to subcircular syncline (e.g. Tiggane and Tazzoult), and a virgation of the Devonian bar (Ouanaimi, 2002, 2004; Caritg et al., 2004) (fig. 46). It is worth noting that the fracture network in this bar is similar to that of the El Bouir anticline (Fig. 53). The fractures affect the sandy structural surfaces of the Rich 3, which strikes NE-SW and dips 50° toward the southeast, and forms the north-western limb of a long syncline. The common sets ATO are easily identified, whose geometrical characteristics (length, spacing, abutting criterion) show
clearly that they predate the two oblique near-orthogonal sets (O1 and O2). However, the longitudinal outline of the set L (axial), usually near-horizontal on the flank of the folds, plunges definitely here towards the north. That testifies, on the one hand, to a disturbance of this family at the approach of the pericline represented by the virgation and, on the other hand, to the late occurrence of the virgation event (controlled by the 2nd phase of folding).
Fig. 53 Thetrack ATOnorthward joint distribution Proceed on - the until the stereograms main virgation (Lower of JbaïrHemisphere) in stops J5-1 (A), J5-2 (B) and J5-3 (C).
Stop J5-3: The virgation of the Tata-Akka bar at Jbaïr (GPS: N29°37'34", W07°58'50")
The Tata-Akka bar turns abruptly from the NNE-SSW to E-W direction, then constituting a flank with an average dip of 55° toward north. The configuration of the joint sets is classic, with a principal and a secondary network, both perpendicular to the layering (fig. 54). Nonetheless, the family which was transverse in the preceding stop becomes now longitudinal, whereas the family which was longitudinal before becomes transverse here. The oblique secondary sets remain appreciably constant. Afterwards, the bar turns again to a NNE-SSW orientation parallel to the regional folds. Route: Continue the track toward Jbaïr village, srrounded by a beautiful palm
Fig. 54 - Westward sight of Jbair virgation.
plantation. Avoid the track toward the east to Oum El Gourdane, and follow right that of Anorhrif. This one goes up and crosses the Tata-Akka bar at GPS W07°55' 05,5"/N29°38' 42". Park close to the well on the peak of the bar, then walk down, on the sand dune, along the water pipes until a small artificial basin downstream.
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Stop J5-4: South Tata: lithological control on jointing at Jbaïr (GPS: N29°38' 43 ", W07°55' 05")
The structural surface of the Rich 3 sandstones is plated with sandy dune. The thin Sellanarcestes calcareous level is shown on the surface at the bottom of the outcrop (Fig. 55). The two facies (sandstone and limestone) do not have the same behaviour vis-à-vis the fractures. On the sandy part, only joints network of T and O sets are expressed, whereas in the limestone layers, the longitudinal set (A) is well individualized. This discrepancy is probably due to a lithological control on the fracturing process. Such factor must be taken into account in the interpretation of fracturation in terms of tectonics (Auzias, 1996). Additionally, observe the presence of non-systematic fractures (polygonal) in the sandstone layers. This type of fractures corresponds to the effect of residual stresses, contrary to the adjoining systematic network which is of tectonic origin (oriented stress fields). Route: From here, two road solutions are offered: Backtrack and take the asphalt road run this morning or follow the same track toward the Anorhrif village. In this last case, continue toward Wadi Adis and the beautiful
Fig. 55 - Variation of the diaclases networks according to lithology in the northern tip of the Tata-Akka bar close to Jbair (view to the North, GPS: W07°58' 05,5"/N29°38' 42,9").
perched village of Anorhrif. Before Anorhrif, a small peak of Rich 2 rises on the left. This site is ideal to produce a section of the HSST of the Rich 2 sequence. The sandy layers are very fossiliferous and show beautiful sedimentary structures (nipples, gutters, waves ripples, HCS), often illustrating typical elementary sequences and testifying to storm-dominated sedimentation. On the opposite side of the Rich 2 peak, rupestral engravings are announced. Cross the agglomerations of the Anorhrif oasis and join the tarred road which gets back to Tata. It crosses the Jbel Bani at Tiiti where the Ordovician sandstones are steeply dipping or even upside down.
Stop J5-5- Variscan thrust faults in the Jbel Bani: section view (GPS: N29°42’1.4", W07°59’5.5")
Park along the tarred road close to the Adis village at the milestone “Akesbi 60 km”. The Cambrian-Ordovician formations constitute a prominent barrier with an E-W orientation and a steep southward dip. The succession shows from north to south (Fig. 56): i) the Tabanit Sandstone (Middle Cambrian); ii) the “Feija externe” siltstones (Arenigian-Llanvirn), and iii) the 1st Bani (Llandeilo) and Ktaoua (Caradoc) sandstones. Along the southern side of the Jbel, the Ktaoua siltstones and the 2nd Bani sandstones crop out.
This succession corresponds to the southern flank of the vast E-W anticlinorium cored to the north by the Agueliz and Tata Proterozoic inliers. From the distance, we can detect a detachment plane which induces the thickening of the Ordovician bars, being associated with an overturned fold. This structure compares with that observed at Icht and testifies to the importance of the internal deformation of the J. Bani multilayered sequence. Proceed toward Tata and park approximately 1,5 km away from stop 5.
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Fig. 56 - Eastward view of a N-S natural cross-section of the Bani of Tata, across the Tiiti cluse.1-4: Ordovician formations Tachilla to Ktaoua. See text for explanations.
Stop J5-6: Variscan thrusts in Jbel Bani: front view (GPS: N29°43’5.7", W07°58’13.2")
In the front view (due south), the 1st Bani bars appear clearly affected by two opposite west- and east-directed thrusts of flat/ramp geometry, (C1) and (C2), respectively (Fig. 57). We observed of C1 in cross-section at the preceding stop. As indicated in the interpretative diagram of fig. 58, these thrusts could be related to the earliest ESE-WNW shortening phase (1). They were tilted and integrated in the southern side of the E-W Tata anticline during the N-S shortening (2). The second folding phase is also responsible for the Devonian interferences and virgations seen in south of Tata. Route:
circumventing to the west the Issafene Cambrian syncline, or the recently tarred road of Tagmoute. We favour the latter road which crosses the Adoudounian-Lower Cambrian carbonate series, rich in spectacular fold trains. These series constitute a broad synclinal structure between the Agouliz, Tagragra de Tata and Irhem inliers to the south, east and north, respectively. The road to Tagmoute follows the gorge of the wadi Tata, sunk in the Lower Cambrian limestones. A multitude of folds with decametre to hectometre size wavelength and amplitude can be observed on both sides of the road, and merit certainly some stops for photographs.
To join Taroudant from Tata, via Irherm, we can either take the old road
Fig. 57 - Panorama showing southward view of the 1st Bani of Tata. Two layer-parallel décollement with opposite vergence, to the west (C1) and to east (C2). The C1 fault corresponds to the one of the previous stop. Numbering corresponds to the previously levels reference marks.
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Fig. 58- Schematic diagram showing the interference of two Variscan folding phases (1 and 2) in the Tata area.
Stop J5-7: Detachment folds in the Adoudounian limestones (NW of Tagragra de Tata (GPS): N29°55’14", W08°06’46")
Along the eastern frontage (on the right of the road), we can see, in the backgound, the dark Precambrian rocks of the Tagragra de Tata inlier, which contrast with the clear limestones of the Cambrian cover. The thick limestone formations show several dysharmonic levels framed by more competent layers (Fig. 59). Regionally, and according to structural measuring, the Variscan folds show two orthogonal, E-W and N-S axial directions, which interfere and form “egg-board” structures (Faïk et al., 2003, Caritg et al., 2004). Contrary to the preceding stops, it is more difficult to tell for certainty the actual chronology between these two folding episodes. Route: The road leaves temporarily the limy landscapes crossed from Tata, and enters the broad Tagmoute syncline, with Middle Cambrian siltstones and sandstones in its core. Hills of the latter Tabanit sandstones are preserved in the centre of the basin, otherwise covered by alluvium. The Souk
Fig. 59 - Fold disharmony in the Lower Cambrian limestones at the north-western border of the Tagragra de Tata inlier
Tleta Tagmoute village is located on the NW flank of the syncline, in a verdant cluse, carved in the Lower Cambrian Upper limestones that reappear here with a steep SE dip. The road crosses this century-old village and goes up along the wadi Tagmoute which has its source further north in the Irherm massif.
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Stop J5-8: Detachment levels between the “Serie de base” and Cambrian Lower limestones in the Wadi Tagmoute (GPS: N29°59’30", W08°16’45")
The option of only one stop in the splendid gorges along the Wadi Tagmoute meanders is not an easy decision. So it is desirable to go up for ca. 10 km to reach a very beautiful section exposed to the right (NE) beyond the river (Fig. 60). It shows an excellent example of repeated detachment layers between the Lower Limestones (Adoudounian) and the underlying, dark sandy bars of the “Serie de base”. The latter is affected only by large open folds, whereas a spectacular disharmony develops above within the lower levels of the Lower Limestones. During the end of the afternoon, we have to drive to Taroudant through the Irherm inlier and its picturesque landscapes. After a coffee-break at Irherm village, the crossing of the Precambrian Irherm and Wawfengha inliers will be done unfortunately without stops - not for lack of geological interest, but simply for lack of time.
Fig. 60 - Photograph showing detachement folds in the Lower Cambrian between the Lower Limestones and the “Série de base”, south of the Irherm inlier
Taroudant is a rich and old city in the central part of the Souss plain. End of day 5. Night at Taroudant (Hotel Salam)
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Day 6 (J6) : Taroudant-Marrakech via the Tizi n’Test Pass The permanent dynamics of the northern edge of the Western Anti-Atlas: the Tizi n’Test Fault Zone (TTFZ) It is now widely accepted that the High Atlas chain is structured mainly by the post-Cretaceous inversion of Mesozoic normal faults, inherited from the Paleozoic and Proterozoic basement faults. In the High Atlas Paleozoic massif (Massif Ancien du Haut Atlas, MAHA), the intraplate Atlas chain, oriented ENE-WSW, crosses and superimposes the NE-SW trending Variscan chain of the Meseta domain. The southern boundary of this “poly-orogenic” area corresponds to the Tizi Test Fault Zone (TTFZ) (fig. 61). The MAHA is characterized by a vast axial zone made up of ante-Mesozoic rocks, including two distinct blocks: a Precambrian eastern Block (Ouzellarh Block, Choubert, 1942) and a western Paleozoic block. Our route will follow approximately the limit between these two blocks (fig. 62). The MAHA is surrounded by two narrow Subatlasic zones, consisting primarily of Cretaceous and Eocene pre-orogenic deposites and syn-orogenic Mio-Pliocene molasses. In the axis of the chain, narrow Triassic basins are preserved along the TTFZ.
Fig. 61 - Location of the Tizi n’Test Fault zone (ZFTT or TTFZ), as the Variscan structural limit between the Meseta and Sahara (Anti-Atlas) domains (after Hoepffner et al. 2006).
The Ouzellarh block constitutes an AntiAtlas promontory within the High Atlas chain (Ouanaimi, 1989; Ouanaimi and Petit, 1992). It consists of a vast Proterozoic and Pan-African substratum, surmounted by reduced Paleozoic series, recording repeated uplift events and erosional gaps. It corresponds to an important paleogeographic highland area at least since the Late Proterozoic times (Proust, 1961; Ouanaimi, 1989). Generally, the influence of the Variscan compression is very moderate within this area, mainly reactived as rigid blocks. Open folds affect the Visean flyschs along its northern and eastern borders, without development of any penetrative schistosity or metamorphism. The MAHA separates two Paleozoic areas, western and eastern respectively, whose stratigraphy extends from Cambrian to Devonian. The divergent stratigraphic polarity in the two Paleozoic compartments suggests that the Ouzellarh block acts as a NNE-SSW to N-S
Fig. 62- Location of the B4 stops on the geological map of Morocco, scale 1/1,000,000 (continuation).
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individualised antiform at least since the Cambrian. This antiform is affected by an important ante-Carboniferous erosional phase, prior to the widespread Visean transgression, by place down to the Cambrian. The Western Paleozoic compartment is bounded to the south-east by the TTFZ, whereas to the west, it encroaches on the West Meseta Shear Zone (Piqué et al., 1980). It is infilled essentially by several km thick Cambrian series with interlayered volcanic lavas. Geodynamic interpretations based on the nature of magmatic rocks are still discussed (Badra et al., 1992, Ouazzani et al., 1998 and 2001, Jouhari et al., 2001; El Archi et al., 2004, Aarab et al., 2005). The youngest Paleozoic formations (Ordovician to Carboniferous) occur only at the western border, towards the Argana corridor. The whole of these series is affected by syn-metamorphic deformation and intruded by Upper Carboniferous granitoids. Therefore, the western part of the MAHA compare with the neighbouring Western Meseta domain, in spite of their opposite structural vergence (to the east and west, respectively), due probably to the opposite dip of the inherited faults. The sedimentary and structural contrast between the Meseta-type Western Paleozoic Block and the AntiAtlas/Ouzellarh domain implies (in the absence of major Mesozoic-Cenozoic displacements) a major and composite activity of a Paleozoic Tizi n’Test Fault Zone (TTFZh, “h” for Hercynian). Note that the latter lineament is often confused with the so-called South Atlas Fault, defined as a basically Alpine (Mesozoic-Cenozoic) fracture zone. The TTFZh is considered as a dextral, Variscan (Hercynian) to Late Variscan fault zone (Mattauer et al., 1972; Petit, 1976; Proust et al., 1978). It strikes to the west along an Atlasic ENE direction, but acquires eastward a Mesetan NNE-SSW orientation (Ouanaimi and Petit, 1992 and Fig. 63). The latter NNE-SSW part of the fault is broken up by subsequent Atlasic faults (Fig. 64).
Fig. 63 - Reconstitution of the MAHA Variscan blocks before the Atlasic orogeny (From Ouanaimi and Petit, 1992).
Fig. 64- The main Variscan Tizi n’Test fault fragmented during the Atlasic orogeny into four segments: 1: ZFTT, 2: Tizien fault, 3: Nfis fault, 4: Ait Khaled fault (supposed). The field trip itinerary is represented in red (from Ouanaimi and Petit, 1992)
The abrupt change in the Variscan deformation from the Western Paleozoic Block and the Ouzellarh massif is assigned to the shortening induced by a major transpressional dextral slip on the TTFZh, post-dating its extensional activity during the accumulation of the Paleozoic series. The NNE-SSW prolongation of the TTFZh limits this deformation to the east and was activated as a dextral-thrust fault (Ouanaimi, 1989; Eddif, 2002), whereas the Ouzellarh massif acted as a rigid block. Note that the TTFZh is part of the larger Atlas Paleozoic Transform Zone (APTZ; Michard, 1983; Piqué and Michard, 1989; Hoepffner et al., 2006) which separates the Meseta Block from the Anti-Atlas domain during the Paleozoic. During the Atlasic cycle, the evolution of the MAHA is conditioned by the inherited
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Variscan faults, notably by the “TTFZa”. Upon the post-Variscan peneplain, the Permian and/or Triassic series are deposited directly on the Cambrian or even on the Proterozoic basement units, during the rifting evolution (Fig. 65). But, contrary to the Paleozoic times, the subsidence is more pronounced in the northern (instead of western) part of the Ouzellarh block. The extended area is limited by the TTFZ (h and a) to the west and the south. At the same time, the surrounding zones (Western Paleozoic block, Siroua, Anti-Atlas) were raised, with the Cretaceous directly
Fig. 65- Compared distribution of the preCretaceous lithostratigraphic series of the “Massif Ancien du Haut Atlas (MAHA), after Ouanaimi and Petit (1992), modified.
transgressive on the crystalline basement (Proust, 1973; Petit, 1976). Elsewhere, the Triassic sequence develops in the adjacent Souss and Ouarzazate basins (Fig. 5C), in the eastern and western sides of the Siroua high. The Jurassic constitutes only a thin level in the Subatlasic borders of the MAHA (Ferrandini and Ferrandini, 1984). Hence, before the Cretaceous time, the MAHA is globally a high zone separating the Atlantic and Tethyan marine domains: it is part of the vast, NNE-trending West Moroccan Arch (Medina, 1995; cf. Terre des Almohades, Choubert and Faure-Muret, 1962). The Triassic-Jurassic extensional and transtensional events induce some sinistral kilometre scale movements mostly concentrated along the TTFZa. The faults are affected by post-Cretaceous and postEocene and Neogene inversions, separated by quiescence periods. The Atlasic movements (controlled by the Africa-Iberia convergence) are still active within the MAHA and its borders (Dutour and Ferrandini, 1985; Morel et al., 2000; Sébrier et al., 2006), but a significant part of the high elevation of the area is dependant on the occurrence of active asthenosphere uplift underneath (e.g. Missenard et al., 2006).
Stop J6-1: The southern Subatlasic Zone NE of Taroudant and the southern flank of the High Atlas. (GPS: N30°35’15", W08°32’34")
While leaving Taroudant eastward, the principal road (P32) follows the eastern part of the Souss plain, bordered to the north by the High Atlas, and to the south by the less elevated Anti-Atlas. A stop can be done at a free emplacement, for instance at Km 35 (Figs. 62 and 67). From here we may observe the three topographic levels of the Atlas (Fig. 66). The advanced anticline of the southern Subatlasic Zone is mainly formed by Upper Cretaceous, Eocene and Oligocene formations. This structure is crossed by the Ida-ou-Gailal valley and plunges eastward under the Souss plain alluvium. In the core of the anticline, Jurassic and Cretaceous deposits unconformably overlie the Cambrian substratum which outcrops in several “inliers”. The Cambrian rocks are not
strongly deformed and metamorphism is lacking, contrary to the series of the Atlas Axial Zone further north, which are strongly deformed, metamorphosed and intruded by the Late Carboniferous Jbel Tichka granite. A few leucogranite dikes linked to the latter granite appear in the background. The TTFZ is located between the two contrasted Cambrian compartments.
Fig. 66 - The southern flank of the High Atlas and the South Subatlasic Zone, as seen from NE of Taroudant.
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Fig.67 - Structural sketch map of the Tizi n’Test lineament in the high valley of N’Fis (Petit, 1976, modified). ZFTTh: southern ,Variscan segment, ZFTTa: northern segment, essentially Atlasic. Turn off to the left at the Tafingoult intersection. The road starts to climb the long rise on the much disturbed Cretaceous
series belonging to the TafingouIt anticline that opens up eastward, around a slaty-limy Lower Cambrian core. The road goes through Senonian levels (red marls and clays, fossiliferous limestones), then gets round the Cenomanian-Turonian limestone bench above Aït-Ou-Blal. From this turn (GPS W 08°24'00"/N 30°49'13"), the structural relationships between the varied Atlasic zones are better observable (Fig. 67 and 68), from north to south: i) the deformed and metamorphic Cambrian of the Axial Zone; ii) the Triassic red beds of Tirknit (northern branch of TTFZa); iii) Upper Neoproterozoic (PIII)Lower to Middle Cambrian still belonging to the deformed, Meseta-type compartment; iv) the Variscan branch of FZTTh; v) the undeformed, Anti-Atlas-type Lower Cambrian, in a reverse fault bend, and finally, vi) the flexured Cretaceous series of the Subatlasic Zone.
Fig. 68 - Geological cross-sections through the Tizi n’Test lineament (see locations and legend in Fig. 33).
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Toward the NE, the Adrar n’Guinnous cliffs rise, with their Upper Proterozoic and Lower Cambrian succession (shales and massive dolomites). Then, the road crosses red and green marls located in the faulted Paleozoic-Cretaceous contact. At the Indras inn (GPS: W08°23'32"/N30°51'37"), the road goes up steeply in a very deformed set assigned to the Ouarzazate Group (PIII) and capped by massive dolerites with pillow lavas (Petit, 1976). This sub-aquatic volcanics (not shown on the geological maps) belong to the Anti-Atlas volcanic province (J2.3), represented also in the high Agoundis valley
by sub-aquatic intraplate tholeites (Aarab et al., 2005). Down to the west in the valley, close to AitTyouga village, the TTFZh (Variscan limit) can be clearly observed north of the recumbent fold which affects the Lower Cambrian (Fig. 68A). Thereafter, the road takes an eastward U curve on nearly 3 Km, and then forms a second U near Targa Izrane village. A narrow track fork eastward and takes to the old mine of Assais (Aït Ibourk), in the high valley of the Wadi Tafingoult. The track follows the Cambrian-Upper Proterozoic contact (Fig. 68B). The main stop will be done about 7 Km farther, in the last curve of the road before the Tizi n’Test Pass.
Stop J6-2- "Belle Vue" Inn: The main segments of the TTFZ and the tectonic blocks of the Atlas southern flank (GPS: N30°51’46", W08°22’43")
This stop offers a fine-looking view, extended on the entire southern flank of the Atlas, the Souss plain, and the Anti-Atlas beyond the plain (Fig. 69). Westward, the two main branches of the Tizi n’Test fault zone (TTFZh and TTFZa) may be differentiated. The southern branch (ZFFTh) separates the northern, deformed compartment (Meseta-type Proterozoic to Cambrian) from the undeformed Cambrian of the southern, Anti-Atlas-type compartment. This branch presents a long and complex history, being a normal fault during the Lower to Middle Cambrian rifting, then activated as a reverse, right-lateral strike-slip fault during the Variscan
(Hercynian) orogeny, again normal, then inverted during the Alpine (Atlas) cycle. The northern branch (TTFZa), outlined by Triassic red beds strips, is a Mesozoic normal (-sinistral?) fault, inverted as a reverse-sinistral fault during the Atlas orogeny. Far away, toward the top of Iggui Ifri, the two branches merge into a single fault at the southern limit of the Variscan block intruded by the Jbel Tichka granite. This fault continues farther west up to the Argana corridor. South of the TTFZh, the Cretaceous series are transgressive on the Cambrian substrate as in all the southern Subatlasic zone and Ounein massif. In contrast, to the
Fig. 69 - Northwestern view of the Tizi n'Test Fault Zone from the U curves of the road. Triassic red beds (rt) are pinched in the Atlasic branch (ZFTTa) into Proterozoic (PIII) and Cambrian (k) series. PIII: Upper Neoproterozoic, Ki: Lower Cambrian (a: schists, b: dolomites), β: basalts, Km: Middle Cambrian, rt: Trias.
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north, one of the Triassic basins of the Tizi n’Test lineament is shown (Tirknit basin). It was infilled with red detrital beds constituted by basal conglomerate (Fm 3), sandy siltstones (Fm 4) and sandstones (Fm 5 cf. the Oukaïmeden sandstones farther east) (Fig. 70). According to Quarbous et al. (2003), the Tirkint basin forms a northward tilted half-graben extended enough westward, but without connection with the Triassic Argana corridor (1st Day). The absence of Triassic deposits in the southern (Anti-Atlas) block suggests the existence of emerged lands there during the Triassic epoch, and the Triassic remobilisation of the TTFZh. The abundance of granite pebbles in the basal conglomerate (Fm 3) suggests that the Jebel Tichka granite has been exhumed at the beginning of the Triassic, before being covered by the onlapping red beds (Petit, 1976). Just at the back of the “Belle vue” inn, the vertical roadcut shows a beautiful example of satellite fault affecting Cambrian series. Route: About 1 Km later, the road reaches the Tizi n’Test Pass.
Fig. 70 - Lithostratigraphic comparison of the Cambrian/Adoudounian along the ZFTTh. Note the remarkably abundance of the volcanism in the Western block and the northward reduction of the series. The lithostratigraphy is summarized after: (1) Viland, 1972 ; Petit, 1976 ; Aarab, 2005 et Landing et al., 2006; (2, 4 et 5) Ouanaimi, 1989 et (3) Petit, 1976.
Stop J6-3: The Tizi n’Test Pass (GPS : N30°52’14", W08°22’48")
Just to the pass, a decrepit inn, with two rudimentary rooms and a small space barrestaurant, is currently the unique refuge. However the enormous local hospitality makes forget this dilapidated framework, where one can in addition get fossils, ornamental rocks and minerals, and potteries. A commemorative plaque pays homage to the engineers and top French officers who supervised the work of the old Tizi n’Test track during years 1924-1932… neglecting the indigenous Berber who carried out this hard task!
(Fig. 71) and review under another angle the TTFZ and its two branches, Variscan (Hercynian, h) and Atlasic (a), because the Variscan branch will henceforth move away from our trip, circumventing by the south the Cambrian massif of Wijddane. Now, we are going to follow continuously the Atlasic branch (a), which is clearly underlined by the reverse fault carrying the western Cambrian block onto the Triassic series. To the west, the high summits of the Jebel Tichka massif in the backgrounds (Tiflillis) overhang the Tirknit Triassic basin.
The Permo-Triassic rocks outcrop along a narrow, pinched strip which is linked to the N’fis Triassic basin, which we will go along downwards. As long as we still stand in altitude, admire the landscape westwards
From the Tizi n’ Test inn, a track forks westward on the left, and goes up toward the TV antenna. It offers a detailed section of the Lower to Middle Cambrian transition. In this section, described in detail by Petit
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Fig. 71 - "Belle Vue" Inn panorama, showing the main segments of the Tizi n'Test Fault Zone and the tectonic blocks of the Atlas southern flank. ZFTTh: Variscan fault, ZFTTa: atlasic fault, PIII: Upper Neoproterozoic, Ki: Lower Cambrian (a: schists, b: dolomites), Km: Middle Cambrian, rt: Trias.
(1976), deformed Lower Cambrian cipolin facies are surmounted by basalt flows and volcano-detritic rocks. Coeval volcanic activity is portrayed elsewhere along the TTFZh, in the Ouzellarh, notably in the Ounein-Agoundis zone. But farther in the Ourika valley, it is rather andesitic and trachy-andesitic (Proust, 1961; Ouanaimi, 1989). As a general rule, the Cambrian volcanism (Lower and Middle Cambrian, Ki and Km), which is barely developed in the Anti-Atlas (except at the base of Ki near Bou Azzer, and top of Km in easternmost Anti-Atlas) is well developed around the TTFZ and especially in the Lower Cambrian of the Western Paleozoic Block (Fig. 67). However, its age and geodynamic significance are still under debate (Badra et al., 1992, Ouazzani et al. 1998 and 2001, Jouhari et al., 2001 El Archi et al., 2004, Aarab et al., 2005). From the pass, the winding road goes down following the Oued N’fis Valley. On the left (NW), the Lower Cambrian shales and metamorphic limestones of Adrar n’Guinnous are flanked by Triassic siltstones and sandstones along the TTFZa.
At about 6 Km from the pass (GPS: W08°20'46"/N30°55'35"), the Triassic outcrops enlarge, forming the Idni basin (Fig. 36). Close to the former forest house of Iguer, the Triassic series are NE dipping and show basal conglomerates (Fm 3), siltstones and sandstones (Fm 4), and a powerful “Oukaimeden sandstone” formation (Fm 5). Some Cambrian shale lenses underline the TTFZa, which is composed of several braided faults. Numerous striated mirrors attest to the sinistral throw of these faults (GPS: W08°20'26"/N30°54'03 "). Westward, in the landscape, the Triassic series (Agadir Ouqoun) lean against the Cambrian horst of Jbel Tadafelt, while a scenic view opens up due NE on the high Precambrian summits of the Toubkal massif (Jbel Ouanoukrim). Then, the road goes down quickly on multiple S-bends along Triassic outcrops. Along the TTFZa fault, the Cambrian horsts overlap eastwards and westwards the Triassic formations. It is difficult to consider a halt in this dangerous descent, but we will make it down, keeping in mind the main elements of the panorama.
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Stop J6-4- Idni Inn: The Atlasic TTFZa fault and the Tadafelt horst (GPS ~ N30°55’05", W08°17’34")
The stop is on Triassic outcrops in the vicinity of the Idni inn. Toward the northeast (Mouldikht), the panorama shows a narrow band of Triassic red beds along the TTFZa (Fig. 72). To the east and the southeast, the high summits (2500 to 2800 ms) of Adrar Aoulim and Azrou Irghane consist of deformed Lower Cambrian limestones and shales, surmounted locally by basaltic volcanics and Middle Cambrian greywackes (Tanzat-Mouldikht). The latter unit clearly overthrust the Triassic red beds through a SE-dipping fault (TTFZa). To the northwest, the Triassic series are also overthrust (in an opposite direction) by the Middle Cambrian series of the Tadafelt horst. In the eastern backgrounds the high Toubkal massif (often snow-covered) is formed by Precambrian rocks.
In the Idni red sandstones, some beautiful examples of small syn-sedimentary grabens and striated reverse faults have been observed. The road joins the Wadi N’fis, offering a beautiful sight toward the west on the southern reverse fault of the Tadafelt Horst rose up against the Triassic series which display a characteristic level of pinky sandstones. The road follows the meanders of the Wadi N’fis, sunk in Middle Cambrian schist and sandstones, then goes along the Cambrian-Triassic contact, before reaching, at Mzouzit, the junction with the narrow western valley of the Wadi Ogdemt. This valley marks the end of the Cambrian Tadafelt horst and the beginning of the Triassic basin (or graben) of Talat n’Yâqoub. On the left side of the Wadi N’fis, the famous Tinemal Mosque appears, standing on the Triassic red beds upright close to the bordering fault of the eastern Middle Cambrian block. Downhill, leave the main road and take, on the left, the appointed road to the recently restored Mosque on the other side of the river (GPS: W08°13' 53"/N30°59' 00 ").
Fig. 72 - Idni Inn: The Wijddane and Tadafelt Cambrian horsts (Ki, Km) along of the Tizi n'Test Atlasic fault (ZFTTa). In the box: Detailed view of the ZFFTa in the right side of the road.
Stop J6-5: The Triassic basin of Talat n’Yâqoub at Tinemal (GPS: N30°59’24", W08°13’45")
Tinemal village (Fig. 73) is the cradle of the Almohade Dynasty (XII century) which reigned on the Maghreb and a large part of southernmost Europe. Beyond its historical interest, this site gives the occasion to observe some Triassic facies and to admire the stunning extensive view of Talat n’Yâqoub basin.
The Talat n’Yâqoub basin constitutes the prolongation of those of Tirknit and Idni (fig. 75). It comprises the same Triassic series
as those of the Precambrian block of the MAHA (Oukaïmeden, Yagour...), with the classical formations “F”: (F3) basal conglomerates and sandstones, (F4) lower siltstones, (F5) “Oukaïmeden” sandstones and (F6) upper Siltstones (Carnian). The CAMP basalts do not outcrop here, but some doleritic dykes intrude the Triassic series.
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Fig. 74 - NW–SE geological cross-section of the Tinemal Triassic graben and its reconstitution before Atlasic compression.
Fig. 73 - The Talat n'Yâqoub Triassic basin: Unconformable Triassic series on the Middle Cambrian near the Tinemal Mosque.
The basin displays great thickness variations, with the depocentre near Douar Mzouzit and reduced thicknesses toward the eastern and western edges, in a horst and graben geometry which was inverted during the Atlas shortening (Fig. 74). During the inversion, some ancestral normal faults were tilted and became flat. However, their synsedimentay character is still attested by abrupt thickness changes, slumps, sealed faults and "hydroplastic" striated planes.
The Oukaïmeden sandstones (F5) can be observed behind the Mosque. They show frequent rippled surfaces and various cross stratifications of shallow water setting, probably in a deltaic environment. The paleocurrent measurements suggest a tectonic control of the sedimentation (Petit and Beauchamp, 1986; Quarbous et al., 2002). Around the site, we can notice that the Triassic series unconformably overlay the Cambrian substrate and dip towards the wadi N’fis. Towards the SW, the small Ogdemt valley follows the north Tadafelt reverse fault. Towards the north and NE, the Talat-n-Yâqoub depression corresponds to the extension of the Upper Triassic siltstones. The eastern, reduced series are separated from the Cambrian of Wijddane by the TTFZa.
Fig. 75 - The main Triassic outcrops of the Tizi n’Test lineament between the Ouzellarh and the Western block of the MAHA.
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Route: Backtrack and proceed on the main road to Marrakech. The valley widens in the Upper Triassic fine grained facies of Talatn-Yâqoub, being dominated on the right by the old perched Goundafi Kasbah. Now, a short incursion to the east may allow us to cross the TTFZh and reach the Ouzellarh block. At the south exit of Ijoukak (W08°13'45"/N30°59'24”), a track forks to the right and goes along the valley of the wadi Agoundis. This valley is attractive for the splendour of its landscapes, through the Precambrian-Adoudounian-Cambrian series of the Ouzellarh block, east of the TTFZh (Proust 1961; Viland, 1972; Petit, 1976; Aarab et al., 2005) (Figs. 64 and 70). It is preferable to observe this section starting from the higher part of the valley, at Ighir village (GPS: W08°11'32"/N30°59'34 "), north of the Tanfit Mine (Cu, Ag). Above the Neoproterozoic volcanic basement capped by tholeitic basalt flows (Aarab et al., 2005), the sedimentary succession includes: i) “Série de base”: gray and green mudstones and siltstones, with sandy lenses; ii) Lower dolomite (so-called Tamjout dolomites); iii)
“Lie-de-vin” horizon; iv) Lower slates and dolomites, green mudstones, limy beds, pyroclastics and conglomerates ; v) massive limestones (with Archeocyaths), surmounted by massive dolomites with stromatolites and including sills of microdiorites (or basalts flows; Aarab et al., 2005); vi) upper slates and limestones. The latter Lower Cambrian series are not significantly deformed, being merely tilted, and they show well preserved sedimentary structures (Killick, 1988) and strong subsidence (Fig. 76).
We join again the main road (and the Triassic basin) at Ijoukak, and proceed to Marrakech. The road crosscuts soon the Triassic unconformity onto the Middle Cambrian of the Western Paleozoic Block. The latter constitutes a nearly monotonous series (Fig. 73) that we follow without stopping for more than 30 km.
Fig. 76 - Distribution and thickness variations of the Lower Adoudounian-Cambrian series along the TTFZ lineament, in the Agoundis area. Simplified from Killick (1986).
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Fig. 77 - Sketch map of the northern part of the trip with optional stop locations. Geological map at 1/100,000, Amizmiz sheet, with additional data from Ouanaimi (1989) and Eddif (2002).
Stop J6-6: A NNE-SSW active segment of the TTFZh at Imidel, N'Fis Valley (GPS: N31°06’44", W08°08’09")
Imidel village is built on the Middle Cambrian slates and sandstones. It is located at the junction of the western Assif (wadi) Ait Hsain with the N’fis valley. The Triassic silts are collapsed along the complex NNE-SSW N'Fis fault zone (connected to the ENE-WSW major faults of Azegour (Medinet) and Sid Fars - Erdouz).
On the left bank of the N’fis, a fault mirror up to 20 m high is underlined by its white alteration (Fig. 78). This fault zone appears to have been remobilized most recently as the Quaternary terraces are clearly disturbed (Bhiry, 1985).
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Fig. 78 – Photograph of a NNE-SSW active segment of the ZFTTh at Imidel, in the N'fis Valley
Route: The Triassic outcrops continue along the valley, often hidden by the Quaternary deposits. A few kilometres after Imigdal (GPS: W08°06'28"/N31°07'00 "), one can observe again the Triassic unconformity over the Middle Cambrian metagreywackes. Farther, to the west of Timesguine, the Triassic is represented only by a small scarp along of the N’fis fault. Just before Wirgane, the road leaves the eastern side of Wadi N'Fis and penetrates the Triassic basin of Wirgane. The contact of the Triassic deposits and the basement, formerly visible here, with striated planes of reverse faults, is now drowning under the water reserves of the Wirgane dam. North
of the dam, the Oued N’fis runs toward the NW alond deep gorges that cross the Proterozoic-Cambrian formations and the Cretaceous of Ouchlifène. After Tagadirt n’Bour (GPS: W08°06'04"/N31°09'31 "), the N'Fis fault separates the eastern Middle Cambrian of Takherkhort from the western PrecambrianCambrian of Tighardine (Fig.40). It corresponds to a segment of the TTFZh (Fig. 31) marked by a ductile deformation which converted the Precambrian granodiorite and acidic lavas into orthogneisses (the Precambrian age of the protolith has been confirmed by U-Pb zircon dating; Eddif et al., 2007). In the western block, contact (or Buchan-type?) metamorphism is well expressed in the Middle Cambrian formations. This major Paleozoic ductile fault (probably inherited from Precambrian) has been reactivated before the Cretaceous, as it marks the eastern limit of an area, devoid of Triassic deposits, which extends westward up to the Argana Corridor. As usual, the fault was also remobilized during the Atlas shortening. The road leaves definitely the Wadi N’fis and goes up again in the Triassic series of the Wirgane basin, first in the upper siltstones (F6), then in the Lower Liassic basalts, where the next stop may be done.
Stop J6-7: The northern Subatlasic Zone: The Upper Triassic – Cretaceous series of the Kik plateau (GPS: ~ N31°11'30", W08°03'43")
In the slope, we can observe from the distance the weakly tilted Mesozoic series as follow, from bottom to top (Fig. 79): Triassic upper siltstones, basalts, mudstones, reddish pink sandstone and conglomerates (Neocomian), yellow marls, sandy limestones (Barremian-Albian), limestones, marls, mudstones and red sandstones (Cenomanian), and the Turonian limestones on the crest. On the Kik plateau itself, some Senonian outcrops occur, consisting of limestones, marls and red mudstones with gypsum.
Northwards, the road runs on the Quaternary deposits until the Tizi n’Wadou Pass between the N’fis basin and the Asni. The latter basin corresponds to a large N-S anticline cored by the Upper Triassic argillites, bordered east and west by the Triassic-Liassic basalts and the Cretaceous succession described at the last stop. To the east, the beautiful Imlil valley offers an excellent stratigraphic section of the Precambrian block, crossed by several regional faults (Sidi Fars fault, Tizi Oussem fault…). After the Imlil crossroad, we pass the small village of Asni (souk) and drive down
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the wadi Rerhaia, east of the Kik Plateau (Moulay Brahim village on the east tip of the Turonian cuesta). After the turn to the left, we cut across the reverse fault (N110) that raises the Souktana Carboniferous (northern block) against the Cretaceous syncline of the Kik Plateau. The meandring cliff road will cross this Carboniferous compartment over ca. 5 km along the Rerhaia valley. After an ultimate ca. 180° turn, park nearby the Rerhaia bridge.
Fig. 79 – View of the northern Subatlasic Zone and the Upper Triassic-Cretaceous series of the Kik Plateau.
Stop J6-8 – Rerhaia bridge: the Visean of Souktana (Ouzellarh Block) (GPS : N31°19'03", W07°57'33")
The Carboniferous of Souktana (~1500 m of thickness) contains three essential formations (Beauchamp et al., 1985): i) conglomerates, sandstone and limestones (coastal and shallow platform facies); ii) sandy-silty flysch with local limestones; iii) shales and marls with calcareous olistolites (originating from a platform) (Fig. 80).
Fig. 80 – Photograph of the Visean deposits of the Souktana massif (Ouzellarh Block) at the Rérhaia bridge.
The greyish sediments, locally folded and faulted, belong to a globally northward dipping monoclinal series, Upper Visean in age. Huvelin (1970) described the onlap of these deposits over the Cambrian slates at the km-marker “Asni 5”. This set did not undergo noticeable Variscan deformation (lack of penetrative schistosity and metamorphism) as in the remainder of the Ouzellarh block. To the north, a N70 striking fault separates the Visean series from Triassic red beds. In the border of the old bridge, a big calcareous block, surrounded by greyish flysch, is representative of the frequent olistolites that testify to gravity dismantling of a Visean carbonate platform inside the Ouzellarh. Thereafter, the road follows some Triassic conglomerates and sandstones unconformable on the Visean. It passes the old track of Tadmamt forest, and then goes up windingly to Douar Sour.
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Stop J6-9 : Douar Sour panorama; the northern Subatlasic Zone and the Haouz Plain (GPS: N31°20’43", W07°57’14")
At Dour Sour, the view due east, toward the eastern side the Wadi Rerhaia, gives an outline of the northern front of the Atlas Mountains along the Haouz foreland plain. From south to north we can distinguish (Beauchamp et al., 1985 and Fig. 81): 8 - greyish rounded mountains of Visean flysch (Souktana massif); 7 - bordering reverse fault; 6 Upper Triassic basal conglomerates and sandy siltstones; 5 Liassic calcareous siltites (Ferrandini and Ferrandini, 1984). Layering dips roughly to the north, and an angular unconformity separates the Triassic red beds from the yellow marine Liassic limestones (post-rift unconformity); 4 Dogger red continental sandstones ;
3 Lower Eocene phosphatic limestones upon which Douar Sour is built. The lack of the Cretaceous deposits can be assigned to the earliest compressive phase of the Atlas orogeny, also evidenced further west (Herbig, 1984) ; 2 - Mio-Pliocene (MP1) yellowish conglomeratic sandstones, overlying unconformably the preceding formations and dipping to the north. 1 - Quaternary conglomeratic glacisterraces truncating the Mio-Pliocene and slightly dipping to the plain. Route:
After the Tahanaoute agglomeration, located at the piedmont of the High Atlas, we enter the Haouz plain and drive on the Quaternary terraces for 30 km before arriving at Marrakech.
Fig. 81 - Panorama of the northern front of the High Atlas Mountains along the Haouz plain seen from Douar Sour.
Marrakech, end of the field trip.
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ACKNOWLEDGEMENTS
We thank André Michard for helpful comments in the field and on an early draft of the present guide book.
FIGURE CAPTIONS Cover :
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Front cover page: Landsat Image 7 ETM+ (Enhanced Thematic Mapper). Available in : https://zullu.ssc.nasa.gov/mrsid/ Inside cover page: Geological map of the Western High Atlas and Anti-Atlas (from Geological map of Morocco, scale : 1/1,000,000, Notes et Mémoires du Service Géologique du Maroc, 260 (1985). Third cover page: synthetic Stratigraphical columns of: A) Precambrian formations; B) Paleozoic formations, and C) Mesozoic-Cenozoic formations. Last cover page: Digital topographic model (MNT) from GTOPO 30 model (Global 30 Arc Second Elevation Data) available on http://edc.usgs.gov/products/elevation/gtopo30/gtopo30.html
Figures : - Fig. 1: Simplified geological map of the Western High Atlas and Anti-Atlas, redrawn from the geological map of Morocco, scale 1/1000 000. Black line with arrows indicates the itinerary and direction of the trip. Stops are indicated in the white circles. - Fig. 2- Location of stops of day 1 (J1) in the Western High Atlas plotted on the geological map of Morocco, scale: 1/1,000,000. (hr: Permian; T: Triassic; tß: basalts; J: Jurassic; C: Cretaceous; m: Miocene; Q: Quaternary). - Fig. 3- Location map of the stops along the northern front of the High Atlas, extracted from the geological map of Imi n’Tanoute, scale 1/100,000 (J: Jurassic; C: Cretaceous; mc: Miocene). - Fig. 4- The Triassic Argana Corridor: (A) Structural sketch according to Tixeront (1974) and Médina (1991); (B) Simplified stratigraphical column from Tixeront (1974) and Aït Chayeb et al. (1998). - Fig. 5- The southern High Atlas front along the Souss basin. A: Neotectonic sketch map. Background: SRTM90 digital topography. The active faults are mapped with heavy red lines; B: Map of the tectonic structures on a LANDSAT TM image. C: Crustal scale interpreted crosssection. The former normal faults rooted at depth propagated upward during inversion with two different geometries: (1) direct propagation up to the surface; e.g. Ameskroud fault; (2) ramping off to a shallow detachment level up to the Tagragra fault bend fold. - Fig. 6- Simplified geological map of the Kerdous Precambrian inlier, redrawn from the geological maps, scale 1/ 50 000 (BGS 2001a-d). - Fig. 7- Table of the main radiometric datings (Rb/Sr, U/Pb and K/Ar) of the Proterozoic rocks.from the Kerdous inlier - Fig. 8- Structural evolution of the Paleoproterozoic Tafraoute-Tasserirt massif (Kerdous inlier); ASimplified geological map of Kerdous inlier; B- Structural map of the Tasserirt dome; CSchematic cross-section; D- Kinematic model for the Late Proterozoic tectonics in the Kerdous inlier. - Fig. 9- Geological cross-section of the Aït Ouckrim Cambrian Plateau at the northern edge of Kerdous inlier (From Ambroggi and Neltner, in Choubert, 1952). - Fig. 10- Geological cross-section of the Precambrian-Cambrian boundary at the eastern border of the Kerdous inlier (SE of Aït Baha). - Fig. 11- Interpretative geological cross-section of the eastern border of the Kerdous inlier at Ida Ougnidif locality. - Fig. 12- Normalized multi-elemental spectra for Ida Ougnidif and Jbel Kerkar basalts. - Fig. 13- Geological cross-section of the eastern Kerdous Massif, after Hassenforder, in Geological map of Tafraoute, scale : 1/100,000, Notes et Mémoires N°307 (1983) - Fig. 14- Geological cross-section of the western border of the Kerdous inlier along Oued Assaka (from Choubert, 1952).
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- Fig. 15- Structural map of the Lakhssas Plateau area and E-W geological cross-section (C-C' in -
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the map). Stereograms (Wulff stereonet, lower hemisphere) represent bedding (S0) and foliation data (S1). Insert: Location of the Lakhssas Plateau area. Fig. 16 Location of the J4-1 to J4-6 stops on the satellite image (Landsat 7) of the western Jbel Bani and Jbel Ouarkziz area. Fig. 17- Schematic geological cross-section of the Palaeozoic series of the Western Anti-Atlas (Goulmine-Assa transect) (From Soulaimani, 1998). Fig. 18- Geological cross-section of the northern border of the Tindouf basin, south of Assa (From Choubert, 1952, modified). Fig. 19- Location of the B4 stops on the stratigraphic column of the Rich Group (Lower Devonian) (from Becker et al., 2004, modified). Fig. 20- Lateral variations of the Rich Group sequences (R) in the Drâa basin, compared to the neighbouring areas (Hollard, 1967; Ouanaimi; 2004 and Ouanaimi & Lazreq, in press). D: major discontinuities, TST: Transgressive system tract, HST: High stand system tract. Fig. 21- Interpretative scheme of the Icht ramp-anticline, formed by an intra-Ordovician overthrust followed by Variscan folding. The fold axis orientation is ENE-WSW. Fig. 22- Location of the B4 stops south of Tata on Landsat 7 image. Stops J5.1 to J5.4 are in the Rich 3 sequence and J5.5 and J5.6 in the Ordovician. White features correspond to the regional, early folds and the yellow ones to the latest folds. Fig. 23- The ATO classification of the fractures associated with a cylindrical fold (from Ramsay and Huber, 1987; modified). A: axial fractures (longitudinal), T: transversal fractures, O1: left oblique fractures, and O2: right oblique fractures. Fig. 25 – Summary of the evolution of the El Bouir fold. 1) folding and formation of the transverse set; 2) folding, formation of the longitudinal set, and thrusting; 3) Increase of the curvature, L set densification, normal fault accommodation and thrusting in the flanks; 4) N-S Shortening, sinistral reactivation of the L set, warping of the fold hinge and oblique secondary fractures O (enlarging). Fig. 26- Schematic diagram showing the interference of two Variscan folding phases (1 and 2) in the Tata area. Fig. 27- Location of the Tizi n’Test Fault zone (ZFTT or TTFZ), as the Variscan structural limit between the Meseta and Sahara (Anti-Atlas) domains (after Hoepffner et al. 2006). Fig. 28- Location of the B4 stops on the geological map of Morocco, scale 1/1,000,000 (continuation). Fig. 29- Compared distribution of the pre-Cretaceous lithostratigraphic series of the “Massif Ancien du Haut Atlas (MAHA), after Ouanaimi and Petit (1992), modified. Fig. 30- Reconstitution of the MAHA Variscan blocks before the Atlasic orogeny (From Ouanaimi and Petit, 1992). Fig. 31- The main Variscan Tizi n’Test fault fragmented during the Atlasic orogeny into four segments: 1: ZFTT, 2: Tizien fault, 3: Nfis fault, 4: Ait Khaled fault (supposed). The field trip itinerary is represented in red (from Ouanaimi and Petit, 1992) Fig. 32- A) Structural skech map of the southern Subatlasic Zone in the Ida Ou Gailal area; B) The frontal anticline north-east of the Souss basin. (After Missenard, 2005). Fig.33 - Structural sketch map of the Tizi n’Test lineament in the high valley of N’Fis (Petit, 1976, modified). ZFTTh: southern Variscan segment, ZFTTa: northern segment, essentially Atlasic. Fig. 34 - Geological cross-sections through the Tizi n’Test lineament (see locations and legend in Fig. 33). Fig. 35- Lithostratigraphic comparison of the Cambrian/Adoudounian along the ZFTTh. Note the remarkably abundance of the volcanism in the Western block and the northward reduction of the series. The lithostratigraphy is summarized after: (1) Viland, 1972 ; Petit, 1976 ; Aarab, 2005 et Landing et al., 2006; (2, 4 et 5) Ouanaimi,1989 et (3) Petit, 1976. Fig. 36 - The main Triassic outcrops of the Tizi n’Test lineament between the Ouzellarh and the Western block of the MAHA. Fig. 37 - NW–SE geological cross-section of the Tinemal Triassic graben and its reconstitution before Atlasic compression. Fig. 38 - Distribution and thickness variations of the Lower Adoudounian-Cambrian series along the TTFZ lineament, in the Agoundis area. Simplified from Killick (1986). Fig. 39 - Sketch map of the northern part of the trip with optional stop locations. Geological map at 1/100,000, Amizmiz sheet, with additional data from Ouanaimi (1989) and Eddif (2002). Fig. 40 - Schematic geological cross-section showing the E-W variations of the Paleozoic series in the northern TTFZ zone (Ouanaimi, 1989; modified). See Legend in Fig.39.
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- Fig. 41 - Geological sketch map of the northern Subatlasic Zone and Souktana Carboniferous massif, with stop locations. Extract and modified from the geological map of Tahannawt, scale 1/100,000. - Fig.42 - Panorama of the northern front of the High Atlas Mountains along the Haouz plain seen from Douar Sour.
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