Betic Internal Zones - Springer Link

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Upper Burdigalian-Lower Langhian. Sediments of this age are scarce and poorly known. (Espejos. Formation, after Soediono 1971, and Hermes 1984; Aguilas.
Geo-Marine Letters (1992) 12:123-128

Ge0.Marine Letters 9 1992 Springer-Vedag New York Inc.

Stratigraphy and Sedimentology Onshore Neogene Stratigraphy in the North of the Alboran Sea (Betic Internal Zones): Paleogeographic Implications J. Rodriguez Fermindez and C. Sanz de Galdeano lnstituto Andaluz de GeotogfaMediteminea, Facultad de Ciencias, Universityof Granada, 18071 Granada, Spain Manuscript received 26 June 1991; revision received 12 December 1991

Abstract. The Neogene is the period in which the Betic Cordillera, the Rif, and the Alboran Sea acquired their present configuration. The Neogene sediments of the Betic Internal Zones (located directly to the North of the Alboran Sea) show the effects of important periods of deformation. Deposition was clearly controlled by tectonics. Therefore the generation, evolution, and total or partial destruction of basins and the formation of new, often superimposed, basins are common phenomena, according to the locations of the basins in the Betic Cordillera and to the different geodynamic situations.

the Alboran Sea was generated during this time as a result of the significant crustal thinning that took place (Sanz de Galdeano 1990). This was a stage of great tectonic complexity, and thus, the sedimentary record formed at that time, with major sedimentary discontinuities, is similarly complex. The stratigraphic record found in the Internal Zones of the Betic Cordillera (Fig. 1) was frequently interrupted, which means that it has to be described in successive sedimentary stages, some of which also have internal discontinuities.

Late Oligocene-Lower Aquitanian Introduction An overview is provided of the principal stratigraphic features of the Neogene basins that formed in the Internal Zones of the Betic Cordillera. Interest in this question centers partly on the fact that these Internal Zones are, from a geological point of view, the northward continuation of the Alboran Sea. Although thinner, the basement of this sea is therefore formed to a great extent by the tectonic complexes of the Internal Zones. It should be borne in mind that the Betic Internal Zones, or Betic Zone S.S., are made up of three tectonically superimposed complexes known as, from bottom to top, the Nevado-Filabride, the Alpujarride, and the Malaguide. The first two consist mainly of Triassic and Palaeozoic materials, metamorphosed during alpine orogeny, whereas the Malaguide, made up of Palaeozoic, Mesozoic, and Tertiary materials, is practically not metamorphosed at all. The superimposition of these three complexes must have taken place near the end of the Oligocene.

Main Characteristics of the Stratigraphic Record The Neogene was a very important period in the Betic Cordillera and the Rif, as it was during this time that they became definitively formed. The area at present occupied by

The formations of this age (Ciudad Granada, after Mac Gillavry and others 1963; Rfo Pliego, after Jerez 1979; Pantano de Andrade, after Bourgois 1978; Gonz~ilez Donoso and others 1983) lay unconformably on the Malaguide complex, which constituted their source area. The lithology of the formations is made up of sands, clays, and reddish conglomerates deposited in a shallow marine environment precariously connected to the sea, as shown by the benthic foraminiferal content (Jutson 1980). These formations represent the beginning of the dismantling of the first newly formed reliefs after the definitive structuring in nappes of the Internal Zones. This period coincides with the first detected cooling of the Nevado--Filabride complex (which did not outcrop at this time according to De Jong (1991).

Aquitanian-Lower Burdigalian The sediments of this age were deposited in basins that have since been destroyed by erosion and tectonics. The basement was the Malaguide and/or Alpujarride complex and both of these constituted the source areas for the formations. These transgressive deposits are breccias and angular blocks with intercalations of calcareous marls containing some turbiditic layers toward the upper part. These materials (Fuente Formation, after Mac Gillavry and others 1963, and

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the position is hypothetical). B: Simplified map of Neogeneoutcrops in the Internal Zones of the Betic Cordillera and in the area of contact between the Internal and External Zones.

Soediono 1971; Alamo Formation, after Votk and Rondeel 1964; Alamillos Formation, after Rodr/guez Fernfindez 1982; Vifiuela Formation, after Boulin and others 1973, and Rivi6re 1988; Las Millanas Formation, after Bourgois and others 1972; San Pedro de Alc~intara Formation, after Aguado and others 1990) witness the denudation of the partially emerged Betic reliefs. Acid tuffite and flint levels are also characteristic of these formations. The vigorous beginning of the westward movements of the Betic-Riffian Internal Zones took place during this period, while to the east the oceanic floor of the Algerian Basin began to form. In the western prolongation of this basin (present Alboran Sea) the thinning of the continental crust began. This moment coincides with the second cooling peak of the micas in the Nevado-Filabride complex as shown by De Jong (1991). Another deposit, also Burdigalian in age, is the Neonumidian (Bourgois 1978). It is basically made up of remains inherited from the Flysch trough and was subject to a widescale resedimentation process. [This Flysch trough stretched from Calabria to the present day Rif in North Africa (Wildi 1983). Part of its deposits were pushed westward and now outcrop in the Campo de Gibraltar, where Aquitanian age Numidian sandstones are well developed. Significant resedimentation processes also took place, giving rise to the above mentioned Neonumidian.] The Neonumidian also contains numerous large olistoliths, in some cases over 1 km in size. At present it is located, apparently as a result of

tectonics, over both the External and the Internal Zones and also extends to some sectors of the Alboran Sea.

Upper Burdigalian-Lower Langhian Sediments of this age are scarce and poorly known. (Espejos Formation, after Soediono 1971, and Hermes 1984; Aguilas deposits, after Montenat and others 1978). They are gray calcareous marls, conglomerates, and turbiditic sandstones formed from Alpujarride and Malaguide materials. The basement is normally Alpujarride and, in some cases, Malaguide. The scarcity of preserved sediments may be related to the intense tectonic activity of this period. During this interval a foredeep basin was formed in the External Zones, in which large olisthostromic masses were deposited, whereas the Internal Zones received sedimentation in smaller areas (back and intra-deep basins). The end of this period seems to coincide with the last recorded cooling peak of the micas in the Nevado-Filabride complex. It also marks the beginning of brittle deformation of this complex (De Jong 1991 ; Monie and others 1991). Throughout the contact between the Internal and External Zones it is relatively frequent to find that the sedimentary record of this interval (Upper Burdigalian-Lower Langhian) is missing. In its place, tectonically positioned, Neonumidian materials appear thrusting toward the south or southwest. These materials are discordantly covered by Middle

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Miocene materials from the next stage of sedimentation. These backthrusts may be related to the transpressive situation affecting the contact between the Internal and External Zones.

These basins were controlled by dextral strike-slip displacements moving within an approximately northwest-southeast to west-northwest-east-southeast direction of compression.

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A complete transgressive and regressive sedimentary cycle is recorded in the sedimentary basins of this age. It begins with a succession of gray pelagic marls (normally preserved under fault planes) and conglomeratic formations usually deposited on an Alpujarride basement (made up of the Alpujarride and Malaguide materials). The Lower Serravallian transgression advanced over these materials or directly over the Alpujarride basement with the appearance of bioclastic platforms that changed laterally to yellow marly facies with intercalated turbiditic sandstone levels. The regressive semicycle appears over these deposits or on the basement and is represented by thick formations of breccias and either continental or marine conglomerates, depending on the location. The succession ends with the development of some lutitic lacustrine formations with intercalations of gypsum, limestone, and some clastic formations at the edges of the basins (La Peza Formation, after Rodrfguez Fern~indez 1982; Umbrfa Formation, after Volk and Rondeel 1964). These basins are mainly situated along two large fracture lines. The more northerly of these runs in an approximately N70~ direction and coincides with the contact between the Internal and External Zones, which at this time was practically sutured. The more southerly fracture line runs in an approximately east-west direction and is located toward the central part of the Internal Zone (Alpujarran Corridor, after Rodriguez Fernfindez and others 1990) (Figs. 1 and 2).

The geodynamic situation changed during the Tortonian. The westward movements of the Internal Zones, which were very subdued during the Middle Miocene, became practically inactive. Similarly, the extension and thinning of Alboran ceased. The entire region was subjected to approximately north-northwest-south-southeast compression linked to almost perpendicular distension. In all of the Cordillera, and especially in the Internal Zones, new Neogene basins with polygonal morphologies were formed (Rodrfguez Fern~indez and Sanz de Galdeano 1990), which were particularly controlled by northwestsoutheast and northeast-southwest to north-northeastsouth-southwest fractures (Fig. 3). These are typically intramontane basins, although some were subjected to strong control by important strike-slip movements. Thus, in the southeast, the north-northeast-south-southwest left-lateral Palomares fault and the northeast-southwest Carboneras fault moved actively, displaced previous structures, and formed the Aguilas curvature. However, in most of the other basins vertical movements of the faults were predominant. Important reliefs were formed and some basins became continental at the end of the Upper Tortonian. At the same time, a process of uplift and radial extension of the Cordillera began, which was superimposed on the north-northwest-south-southeast compression and the approximately east-west extension.

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