on genesis of tbilisi olistostromes

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dispersed large and small fragments mainly of andesite-basalts, porphyrites and dacites, as well as remnants of lava sheets. According to these authors clumpy ...
Труды ИГ. Нов. сер. Вып.124. 2008

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ON GENESIS OF TBILISI OLISTOSTROMES I.Gamkrelidze, G.Nadareishvili, T.Tsamalashvili, L.Basheleishvili, S.Nadareishvili On Genesis of Tbilisi Olistostromes. I.Gamkrelidze1, G.Nadareishvili1, T.Tsamalashvili2, L.Basheleishvili1, S.Nadareishvili1. 1Ministry of Education and Sciences of Georgia. Legal Entity of Public Law Alexznder Djanelidze Institute of Geology, M.Alexidze st. 1/9, Tbilisi 0193, Georgia ([email protected]); 2Seismic Monitoring Center of Georgia, Nutsubidze. st. 77; Tbilisi 0177 ([email protected]). On the basis of field observation, analysis of boring and geophysical data is shown that formation of Tbilisi olistostrmes of Middle Eocene age was connected with submeridional, long developed, consedimetation hidden deep fault (normal fault) tracing mainly along the right bank of the Kura River. Tbilisis Tbilisis olistostromebis genezisis Sesaxeb e.gamyreliZe1, g.nadareiSvili1, T.wamalaSvili2, l.baSeleiSvili1, s.nadareiSvili1. 1saqarTvelos ganaTlebisa da mecnierebis saministro. sajaro samarTlis iuridiuli piri aleqsandre janeliZis geologiis instituti, m.aleqsiZis 1/9, 0193 Tbilisi ([email protected]); 2saqarTvelos seismuri monitoringis centri, nucubiZis q. 77. 0177, Tbilisi ([email protected]). savele dakvirvebebis, burRvis da geofizikuri monacemebis analizis safuZvelze naCvenebia, rom Suaeocenuri asakis Tbilisis olistostromebis warmoSoba dakavSirebuli iyo submeridianul xangrZlivad ganviTarebad, konsedimentaciur, farul siRrmul raRvevasTan (nasxletTan), romelic gaidevneba ZiriTadad md.mtkvris marjvena napiris gaswvriv. О генезисе тбилисских олистосромов. И.П.Гамкрелидзе1, Г.Ш.Надареишвили1, Т.Н.Цамалашвили2, Л.Б.Башелеишвили1, С.Надареишвили1. 1Министерство просвещения и науки Грузии. Юридическое лицо общественного права. Институт геологии им. Александра Джанелидзе, ул. М.Алексидзе № 1/9, 0193 Тбилиси, Грузия ([email protected]); 2Центр сейсмического мониторинга Грузии, ул. Нуцубидзе 77, 0177 Тбилиси ([email protected]). На основании полевых наблюдений, анализа буровых и геофизических данных показано, что формирование тбилисских олистостромов среднеэоценового возраста связано с субмеридиональным длительно развивающимся, конседиментационным, скрытым глубинным разломом (нормальным сбросом), который прослеживается, в основном, вдоль правобережья р.Куры.

Genesis of Tbilisi olistostromes of Middle Eocene age, which first was described by H.Abich under the name “conglomerates of entangled bedding”, for a long time arouses a great interest. L.Koniushevski marked sedimentary nature of this “conglomerates”. According to V.Pakhomov (1937) deposits with entangled bedding represent the result of subaqueous slumps and downfalls. I.Kacharava (1936) connected their origin with subaqueous slumps, but P.Gamkrelidze (1949) – with volcanic explosion and throw out on the surface blocks of older sedimentary rocks. M.Varentsov (1950) spoke about denudation of cordillera. A.Janelidze (1946) prefers to speak about “coastal downfalls”. Later on A.Janelidze et al. (1955) noted that so-called “conglomerates of entangled bedding” unite two genetically different formations – clumpy breccias, consisting of chaotically oriented large blocks of rocks, and younger suite of distinctly bedded volcanogenic sandstones (microbreccias), where one can find dispersed large and small fragments mainly of andesite-basalts, porphyrites and dacites, as well as remnants of lava sheets. According to these authors clumpy breccias are products of intensive dynamic coercion of tsunami waves on coastal zone. The formation of coastal conditions according to A.Janelidze et al. (1955) favored generation of inner cordillera (Teleti, Mamadaviti and other anticlines) as a result of manifestation of Trialetian orogeny before Upper Eocene, but major source for clastic material, according to these authors, was a land situated on the east, where due to weakening of folding a basin probably was closed, and in the south-west, in Khrami massif region, that is confirmed by presence of rounded fragments of Cretaceous limestones. G.Nadareishvili et al. (1989) supposed that formation of “conglomerates of entangled bedding” was bound up with submeridional deep fault tracing along the Kura River, but the opinion was not established by corresponding factual geological material. Conducted by us field works showed that conglomerates of entangled bedding represent typical olistostromes, containing blocks and clumps (olistolithes) and plates (olistoplaks) of different age rocks

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including older – Cretaceous rocks. At present it is generally accepted that olistostromes are generated either in active faults zone or in frontal parts of advancing nappes (Leonov, 1981; Khain, Lomize, 2005). One of the authors of this paper (I.Gamkrelidze) himself had an opportunity to be completely convinced in validity of this statement; he had for a long time (1976-1990) been in a position to investigate the nappe structures of the Caucasus, Alps, Western and Central East Carpathians, Rhodopian massif, Kryshtides and the Northern Pyrenees (Gamkrelidze, 1982, 1991). A.Janelidze et al. (1955) described rather in detail both separate included blocks and whole horizons and a matrix of these chaotic formation of Tbilisi region. Our investigation confirmed presence of different size mostly angular and, in places, more or less rounded inclusions of Cretaceous limestones and effusive rocks (andesites, basalts, rhyolites, dacites) typical for the Adjara-Trialeti zone, as well as terrigenous rocks (sandstone-siltstone and clastic limestone turbidites, tephroturbidites, pelagic argillites, motley clays, marls and tuffs) representing, on the basis of all signs, fragments of PaleoceneLower Eocene flysch and of the Lower part of Middle Eocene of the Adjara-Trialeti zone. Consequently all these fragments represent so-called intraclasts but olisostromes-endoolistostromes. These data undoubtedly indicate that source of removal of clastic material was within the AdjaraTrialeti zone. At the same time quite a number of signs of Tbilisi olistostromes, in particular the presence of erratic masses from underlying deposits of the same basin, relatively small thickness, the absence in them of tectonically reworked particles, availability of clearly expressed slump-downfall structures and textures, primary normal interrelations of olistostromes with enclosing deposits, the presence of normal-sedimentary rocks interbedding with olistostromes, undoubtedly concern these formations to typical gravitational olistostromes (ß-mixtites after M.Leonov, 1981). Besides, the presence of volcanic material in fragments and matrix, as well as association with volcanic formations, points to their belonging to volcanogenic-gravitational olistostromes (δß- mixtites after M.Leonov, 1981). Analysis of boring data (Fig.1,2) and field observations indicate that olistostromes with maximum thickness 100-120 m were spread from northern to southern border of this part of Adjara-Trialeti zone. To the west in southern part of this zone, on the meridian of v.Asureti they are replaced by normal sedimentary-volcanogenic Middle Eocene. In the south olistostromes, with thickness 35-40 m, are present in borehole of v.Tsalaskuri environs (bor. 12), but to the south, in Rustavi boreholes (1.3 and 16a) Middle Eocene with thickness 200 m is represented by tuffites, marls and aleurolites and not by olistostromes (Fig.1, 2). To the west from Tbilisi, in borehole Saburtalo 1 olistostromes are present. This fact points out that Middle Eocene olistostromes are spread both on anticline uplifts of Teleti, Mamadaviti and in Saburtalo synclinal fold (Fig. 4). However to the west, in boreholes Lisi 1 and Lisi 2, olistostromes are absent (see Fig. 1, 2). In the east, judging by surface outcrops of Soganlugi environs, as well as by boring data (Tabori 4, Teleti 32 and 23) between boreholes Teleti 32 and 23 olistostromes are replaced by normal-sedimentary rocks . Afore-cited data allow approximately outline Tbilisi olistostromes spreading area, occupying about 500 km2 (see Fig.1). Highly urgent is an issue of location of clastic material (especially Cretaceous rocks) disintegration area of Tbilisi olistostrome stratum. Analysis of available geological, as well as boring data indicates that this material can not come from the south as in southern part of the Adjara-Trialeti zone under the Middle Eocene is present thick flysch strata of Paleocene-Lower Eocene that is established both by surface outcrops and boring data (bor. Teleti 19, 13, Rustavi 3, 16a, Shavsakdari 5). Here thickness of these deposits increases from south to north from 1500 to 2800 m (see Fig. 2). In the north, in environs of town Mtskheta also presence rather decreased in thickness flysch deposits underlain by carbonaceous Upper Cretaceous that essentially excludes possibility of coming in the Middle Eocene sedimentary basin of Upper Cretaceous limestones and, all the more, Albian-Lower Turonian volcanogenic rocks from the north side. It should be taken into account that in borehole Teleti 19 and westwards, up to the Tedzami anticline, Upper Cretaceous is completely built up of carbonaceous deposits. Cretaceous volcanogenic rocks under carbonaceous Upper Cretaceous, judging by Rustavi boreholes (13, 16a) appear only to the east of borehole Teleti 19. Consequently, clastic material of Cretaceous volcanogenic rocks can not come from west as well. It is also confirmed by the presence of thick (more than 900 m) Paleocene-Lower Eocene deposits in borehole Tel. 19 (see Fig. 2). Boring data within the south-eastern part of Tbilisi city (bor. 1, 2, 3, 5, 7, 9, 11), indicate the presence of thick Paleocene-Lower Eocene deposits under the Middle Eocene. Consequently in this part of the city also is impossible to imply the existence of source of Cretaceous limestones and 25

volcanites clastic material (see Fig. 2). Very thick Paleocene-Lower Eocene deposits are present to the south-west from Tbilisi, in borehole Tel. 19 as well.

Fig. 1.Geological map of eastern termination of Ajara-Trialeti zone and adjacent areas. 1 – Quaternary alluvial-proluvial and talus deposits, 2 – Upper Pliocene-Lower Quaternary continental subalkalic basalts, andesite-basalts, andesites, 3 -Upper Pliocene (Aghchagil and Apsheron stages) - continental and marine molasse, 4 – Neogene (Meotian and Pontian stages) marine and continental molasses, 5 – Middle and Upper Miocene (Sarmatian) marine and continental molasses, 6 – Oligocene and Lower Miocene marine molasses, 7 – Upper Eocene terrigenous deposits, 8 – Exposure of Middle Eocene olistostrone stratum, 9 – Middle Eocene volcanogenic suite (subalkaline basalts, dacites and their tuffs), 10 – Paleocene and Lower Eocene sandstone – siltstone and clastic limestone flysch, 11 – Campanian-Maastrichtian carbonaceous deposits, 12- Upper Turonian-Maastrichtian carbonaceous deposits, 13- Aptian and Albian sandstone-siltstone flysch, 14 -Turonian-Santonian calc-alkalic basalts, andesite-basalts, their tuffs and limestones, 15-nappes, 16-reversed faults and thrusts, 17-old hidden deep fault, 18-Boundary of Middle Eocene olistostromes spreading area 19 – boreholes.

Hence, the presence of washing out land and considerable scarp in relief, which was necessary for the formation of Middle Eocene olistostromes, one can assume only between the Tbilisi boreholes 1,2,3 in the east and the borehole Tel.19 in the west (see fig. 1, 2). It is natural to connect this scarp with the existence of consedimentation fault of submeridional direction with changed facies (see below) and apparently reduced thicknesses of deposits in its upthrown west side. Summary vertical separation of this fault seemingly reached 4000-4500 m (Fig. 3). The existence of submeridional deep fault along the Kura River supposed earlier investigators. In particular during the interpretation of seismic cross sections compiled on the basis of correlation method of refracted seismic waves, in crystalline basement and Cretaceous deposits of the AdjaraTrialeti zone the existence of deep fault of north-western strike, with north-eastern downthrown side, 26

tracing roughly along the Kura River was established (N.Gamkrelidze, 1976). Besides according to G.E.Gugunava’s data (1989) along the profile Black Sea-Caspian Sea in Tbilisi environs enormous gradient of vertical thermodisplacement is observed, which indicates the existence of submeridional fault going deep down up to 70 km. and more.

Fig. 2. Boreholes data of Tbilisi environs (conventional signs see in Fig.1.)

It should be noted also that on the bases of geomorphic, hydrogeologic and seismic data, as well as of distribution of rocks’ temperature field very close to this fault, along the Kura River very young seismogenerating fault is established, which arose close to old fault at the boundary between the thick shatter zone, that is typical for such deep faults, and the monolithic rocks (Gamkrelidze et al, 2007). Taking into account peculiarities of geological structure of the eastern part of the Adjara-Trialeti zone and boring data, one can assume that generation of this old deep normal fault took place seemingly already at the close of Early Cretaceous and it continued to develop during the accumulation of thick Albian-Lower Turonian volcanogenic suite, which developed mainly in eastern lying side of this fault (normal fault), but in hanging wall it replaced by carbonaceous deposits (see Fig. 3.I). The fault developed or underwent rejuvenation in the second half of Middle Eocene (see Fig. 3.II). Formation of scarp in relief and coastal land was connected apparently with manifestation of Trialetian orogeny in the second half of Middle Eocene. With these tectonic movement apparently frequent earthquakes were connected, which triggered rocks disintegration and downfall – slump processes (It is generally known that some investigators olistostromes include in shock-induced socalled seismites, Seilacher, 1992). As a result, at the very end of Middle Eocene all this highly elevated land has been completely disintegrated, washed out and overlain by olistostrome stratum, which is built up of clastic material of this land consistent rocks, and then – by transgressive Upper Eocene (see Fig. 3 III).

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Fig. 3. Paleogeographic geologic sections of Tbilisi environs. I – Albian – Early Turonian time, II – Middle Eocene time, III – ending of Middle and beginning of Late Eocene. 1-Upper Jurassic – Lower Cretaceous carbonaceous rocks, 2-pre-Alpine crystalline basement (other conventional signs see in Fig. 1,2).

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References Gamkrelidze I. (1982) Nappe structures of the Caucasus. In: Alpine structural elements: CarpathianBalkan-Caucasus-Pamir orogene zone //Veda, Bratislava. PP. 95-114. Gamkrelidze I. (1991) Tectonic nappes and horizontal layering of the Earth’s crust in Mediterranean belt (Carpathians, Balkanides and Caucasus) //Tectonophysics. Vol. 196. PP. 385-396. Gamkrelidze I., Giorgobiani T., Kuloshvili S., Lobzhanidze G., Shengelaia G. (1998) Active deep faults map and catalogue for the territory of Georgia //Bull. of the Georgian Acad. of Science. 157. №1. PP. 80-88. Gamkrelidze I., Tsamalashvili T., Nikolaeva E., Godoladze T., Djavakhishvili Z., Elashvili M. (2007) Tbilisi fault and seismic activity of Tbilisi environs (Georgia) //Proceedings of A.Janelidze Geological Institute. New ser. Vol.... PP..... Gamkrelidze N. (1976) Separation of highvelocity refracted seismic waves belonging to different lithologic-stratigrafic horizons in Tbilisi environs //In: Geophysical investigations. Tbilisi: Metsniereba.PP.226-235 (in Russian). Gamkrelidze P. (1949) Geological structure of Adjara-Trialeti foldsystem. Georgian Acad. of Science. 508 p. (in Russian). Gugunava G. (1989) Interrelation of some geophysical fields and deep structure of the Caucasus. Doct. thesis. Baku. 316 p. (in Russian). Janelidze A. (1946) Landslides of Tbilisi and geological significance of geologic events. Proceedings of Tb. St. University. T. XXXIV (in Georgian). Janelidze A., Skhirtladze N., Rubinstein M. (1955) On Tbilisi Eocene conglomerates of entangled bedding //Proceedings of Geol. Institute of Acad. of Science. T.VIII (XIII). PP. 97-112 (in Georgian). Kacharava V. (1936) Paleogene of Tbilisi environs. //Proceedings of Georgian Geological Institute. T. II. V. 1 (in Georgian). Khain V., Lomize M. (2005) Geotectonics with bases of Geodynamics //Moscow State University. 559 p. (in Russian). Kitovani Sh., Shatirishvili T., Imnadze P., Omadze I., Mikaia L., Omiadze N. (1970) Complex study of Paleogene and Cretaceous diposits of the eastern part of Adjara-Trialeti foldsystem. Moscow, funds of “VNIGNI”. 130 p. (in Russian). Leonov M. (1981) Olistostromes in the structure of foldbelts //Moscow: Nauka. 175 p. (in Russian). Nadareishvili G., Gamkrelidze I., Maisadze F., Gogoladze D. (1989). Investigation of core material of Cretaceous – Paleogene volcanosedimentary and sedimentary formations of oil-bearing areas of Georgia, funds of “Grusneft”. 102p. (in Russian). Pakhomov V. (1937) Geomorphology of Dzegvi – Dalliar part Kura valley //Bull. of State Geographic Society. T. 69, V. 5. (in Russian). Seilacher A. (1992) Event stratigrafy: a dynamic view of the sedimentary record. In: Understanding the Earth //Cambridge University Press. PP.375-385 Varentsov M. (1950) Geological structure of western part of Kura depression //Acad. of Sci. of USSR. Moscow – Leningrad (in Russian).

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