Biostratigraphy and palaeoenvironment of the Upper Cretaceous flysch sediments of the Mestia-Tianeti Zone of the Greater Caucasus Fold System

For the detailed stratigraphic division of the Upper Cretaceous sediments of the Zhinvali-Gombori subzone of the Mestia-Tianeti zone GCFS, and for specifying the volume and age of the formations, in the facies of Sadzeguri-Shakhveli and Zhinvali-Pkhoveli nappes the sections of the Ksani and Aragvi river basins (the rivers Aleura, Sakanaphe, Arkala, Didi Jakha, Patara Jakha; near the villages Sadzeguri, Korinta, Ananuri, Muguda, Avenisi, Pavleuri) have been studied.
   Detailed study of the assemblage composition of calcareous plankton contents (calcareous nannofossil and planktonic foraminifera) of the Late Cretaceous sediments of the Zhinvali-Gombori subzone of the Mestia-Tianeti zone of the Greater Caucasus fold system (GCFS) has been carried out for the first time in this region to define biozonation. Within the limits of the Cenomanian-Maastrichtian 9 small foraminiferal and 19 nannoplankton biostratigraphic units (zones and subzones) have been established. Here are specified volume and age of lithostratigraphic units (successions) composing the Upper Cretaceous of the Mestia-Tianeti zone of GCFS: the Ukughmarti succession – СС9 (Early Cenomanian); the Ananuri succession – СС9-СС11 (Early Cenomanian-Early Turonian); the Margalitisklde succession – СС12-СС13 and planktonic foraminifera zones Marginotruncana pseudolineiana-M. lapparenti and Marginotruncata sigali. (Late Turonian-Early Coniacian); the Eshmakishevi succession - СС14-CC19 (Late Coniacian-Early Campanian) and zones Archaeoglobigerina basquensis and Globotruncana arca (upper part of the succession); the Jorchi succession – СС20-СС25а (Middle Campanian-Lower Maastrichtian), in the sediments of СС22с is established the small foraminiferal zone Globotruncana ventricosa-Rugoglobigerina rugosa; the Sabue succession – СС25b-СС26 and foraminiferal zone Gansserina gansseri (Late Maastrichtian).
   The analysis of the Late Cretaceous nannoplankton and foraminifers association of the Zhinvali-Gombori subzone of the Mestia-Tianeti zone of GCFS has shown the existence of four sedimentary cycles: Cenomanian-Early Turonian, Middle Turonian-Early Campanian, Late Campanian-Early Maastrichtian and Late Maastrichtian On the territory of Georgia contained in the Late Albian pool there were is established some large sites of a land, where the Cenomanian sediments with the washout rest on the underlying formations. In the Cenomanian-Early Turonian there was a basin of isolated, regressive sea in the southern part of the moderately cold-water belt. From the Late Turonian the boundary between the warmand moderately cold-water belts moved to the north. Transgression that started in the Late Turonian lasted till the Early Coniacian. In the middle part of the Early Coniacian is outlined shoaling of the basin. From the Late Coniacian to the end of the Santonian sedimentation took place in the shallow, calm marine basin. The omission of the nannoplankton СС19, СС20, СС21 and СС22a, b zones from the sections of the Zhinvali-Pkhoveli nappe and the analysis of the redeposited forms enables to admit break in sedimentation caused by Early Campanian regression and Late Campanian transgression. At the end of the Middle Maastrichtian took place a short-term regression that was replaced by the Late Maastrichtian transgression.