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Paleozoic and Mesozoic succession of sediments in AI Bahra-1 well (Syria)

The vertical exploration well Al Bahra-l is located in the Hayan block in Syria. It has penetrated 4147 m of sediments ranging from the Upper Cretaceous to the Silurian. The succession of sediments began with the Markada Formation (4147-3165 m) of the Palaeozoic, identified at the bottom of the well. Sediments are composed of shale (in places sandy) with a lot of opaque materials (probably magnetite) and lenses of siltstolle and quartzarenite. The Early Carboniferous age is conflTmed on the basis of palynofloristic sporomorph composition (CingulizonLltes sp. , VaL/atisporiles sp. div., Spelacolriletes sp. div., Raistrickia sp.). Sedimentation probably took plaee in continental- marine transitional paleoenvironments, as lacustrine-swamp to tidal flat sediments, with some f1u viatilc influence. The Tanf Formation (3165-3120 m) of the Silurian, consisted of shale, sandy shale and opaque material (probably magnetite) seemed to be brought into abnormal contact with the Carboniferous sediments beneath. The Carboniferous deposits occmed below and above the Silurian deposits, therefore reverse faulting should be taken into consideration. According to the palynofloristic assemblage (MOLYNEux et aI. , 1996) represented by Multiplicisphaeridiwn sp. div., Euittia sp. div., Cymbosphaeridium sp. div., Lophosphaeridium sp. div. and Veryhachium sp. div., the sediments are dated as Silurian in age. Lithology and palynofacies characteristics indicate deposition in relatively proximal marine shelf environment with some fluviatile influence. The Markada Fonnation (3120-1060 m) of the Palaeozoic follows. The deepest part of this interval (3120-2415 m) is consisted of claystone/shale with opaque materials (probable magnetite), as well as lenses and laminae of bioclastic limestone (WfP), biomicrite (W), crystalline dolomite with anhydrite and gypsum, siltstone, quartzarenite and litharenite. The next interval (2415-1610 m) is madc of mudstone/shale in places sandy and conglomeratic, rarely altered to greywacke, with lenses or laminae of quartzarenite to subarkose, siltstone, claystone and seldom aphano to crystalline dolomite. The series ends with the hematitic mudstone/shale (in some places sandy and conglomeratic or turn into the greywacke) and sporadically with quartzarenite of the ~ast interval (16101060 m). Carboniferous age has becn defined by very rich fossil assemblages. The most significant microfossils are: Amma rchaediscus explanatus VDOVENKO, Omplullotis omphalota (RAUSER-CHERNOUSSOVA & REITLINGER), Planoendolhyra spirilliniformis (BRAZH.t'\TIKOVA & POTIEVSKA), Endothyra cf. simi/is (RAUSER-CHERNOUSSOVA & REITLINGER), Pseudoammodiscus paruus (REITLINGER), Pseudoammodiscus-sp., "Erulothyra" ex gr. bowmani PHILLIPS, Endothyra" sp., Omphalotis? sp., Tetrattlxis sp. and Bryozoa. Also, numerous sporomorph asscmblage (OWENS, 1996) are determined: Calamospora sp. div., Leiotriletes sp., Punctatisporites sp. div. , Punctatosporites sp., Retusotriletes sp., Lopholrileles sp., Anaplanisporiles sp. div., Acanthotriletes sp., Spelaeotriletes sp., Verrucosisporiles sp., Conuolwisporites sp., Reticulatisporites sp., Raistrickia grouens, Lycospora sp., Densosporiles sp., Cillgulizollates sp., Vallatisporites sp. div., Vallatisporites cf. pusilliles, Vallatisporites uerrucosus and Vallatisporites uallalus. Sediments most probably originated in the transitional (deltaic) environment with occasional short marine episodes (perireef). The Palaeozoic Amanus Sand Formation and the Mesozoic Amanus Shale Formation follow. In this interval (1060790 m) quartzarenite (in places with characteristic of sublitharenite, or subarkoze), litharenite, shale and tuff are defined. Since there are no relevant microfossils, and palynomorphs are rare and poorly preserved (? Endosporites sp., ?Densoisporites sp., ? Cyciotriletes sp., ?Veryhachium sp.), the Permian to Scythian age is just supposed on the basis of correlation with previous investigated wells, EK 'logs and lithology. Depositional environment was most probably transitional to continental. Next is the Kurrachine Dolomite Formation of the Middle Triassic (790-570 m) composed ofdolomite (very finely to medium, sporadically coarsely, crystaHine), in places sandy and recrystalized dolomicrite (aphanocrystalline to very finely crystalline dolomite) and sporadically volcanoclastic ('1) breccia and shale. Microfossil association is very poor or almost absent. Sporomorphs are abundant: Punclalisporiles sp., Todisporires sp. div., Heliosaccus dimorpi1us, Cannanaropollis scheuringii, Vilreisporiles pallidus, Brachysaccus neomundanus, Brachysaccus ovalis, Sulcalisporiles kraeuseli, Alisporiles sp. div., Falcisporiles sp. div., Platysaccus queenslandiae, Minulosaccus crenulalus, Samaropolieniles specioslls, Parilliniles sp., Anguslisulciles sp., Vollziaceaesporiles heleromorpha, Triadispora sp. div., cf. Sleliapollenires lhiergarlii, Lunalisporiles aculUS, LUllalisporiles pellucidus, Slria/oahieiles balmei, Aulisporiles aSligmosus. Phytoplankton (Leiosphaeridia sp., Michryslridillm sp. div.) and Chlorophyceae (Botryoeoeeus sp.) are represented rarely. Based on the palynofloristic assemblages (730-720 m) the Late Anisian to Early Ladinian age is defined. Lithology and palynofloristic assemblages indicate peritidal - supratidal environment. The Kurrachine Dolomite (570-311 m) Formation consisted of very finely to coarsely crystalline dolomite with laminae of organic matter and early diagenetic acicular and nodular anhydrite, micrite (M) in places dolomitized, dolomitized ooidic bioclastic limestone (WfP) and claystone to c'Iayshale continues into the Uppcr Triassic as well (LUCIe et aI., 2003). Microfossils are rare. Besides fragments of echinoderms, ostracods and thin molJusc shells, togcther with Middle to Late Triassic benthic foraminifera have been found: Frondieularia xiphoidea KRlSTAN-TOLLMANN, Frondicularia sp., Agalhamminoides sp., Semiinvolulina sp. and AulolOr/uS sp. On the basis of the recovered palynofloristic assemblages reprcsented by MinulOsaecus erenulatus, Salllaropollelliles specioslls, Patinas poriles dells~lS, Pseudenzonalasporiles swnmus, Froehliehsporiles lraversei, Parlilisporiles sp., Parlilisporiles verrueosa, Duplieisporiles sp., Camerosporiles seealus, the deposits of the analysed samples are dated more precisely as Carnian in age (YAROSHENKO & BASH IMAM, 1995). Sediments are deposited in supratidal with sabhka environment. Discordantly follows the Judea Formation of the Upper Cretaceous (311-202 m) composed of dolomite (aphanocrystalline, very finely crystalline and coarsely crystalline Knjiga sazetaka -Abstracts Book with visible vugy porosity). Only rare undeterminable small benthic foraminifera, thin mollusc shells, gastropods and ostracods have been found. On the basis of correlation with previously investigated wells, EK logs, and lithology the age of whole interval has been estimated as Late Cenomanian -Turonian. Sedimentation took place in thc shallow subtidalsupratidal environment. The Soukhne Formation of the Upper Cretaceous (202150 m), consisted of fossiliferous marls to calcareous marlstones came after. Both planktonic and benthic foraminifera (Helerohelix globulosa (EHRENBERG), Arclweoglobigerina blowi PESSAGNO, Murieohedbergella sp.) have been identified. On account of recovered microfossi I assemblages and EK logs, deposits a.re dated as Coniacian - Early Campanian in age. Environment of deposition is outer shelf to deep marine. The Shiranish Formation of The Upper Cretaceous (15045 m) made of fossiliferous clay marl and fossiliferous marl to calcareous marlstone ends thc succession of sedimelilts in AI Bahra-l wcll. The microfossil association of rare planktonic foraminifera Maeroglobigerinelloidcs prairiehi/lensis (PESSAGNO), Muricohedbelgelia sp. and Bulimina sp. defines Late Campanian to Maastrichtian age. Sedimentation took place in outer shelf to deep marine depositional environment.

Silurian; Carboniferous; Permian; Triassic; Cretaceous; Lithostratigraphic Formations

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