Foraminiferal biofacies analysis and paleoecological data on Upper Cretaceous sediments of the Gagra-Java zone (Western Georgia)

The paper deals with actual questions concerning biofacies and paleoecology of the Gagra-Java zone. The Gagra-Java zone extends along the Southern slope of the Greater Caucasus, in its turn subdivided into three facies types: Abkhazia-Racha, Odishi-Okriba and Dzirula. The Cretaceous sediments have developed mainly in the junction area of the Georgian block, from the Western Georgia up to Upper Racha. The Upper Cretaceous sediments consist predominantly of terrigenous-volcanogenic (Cenomanian-Lower Turonian) and marly carbonate limestones with the layers of variegated flints (Upper Turonian-Maastrichtian). According to planktonic and benthic foraminifera in the Abkhazia-Racha sediments have been distinguished 14 foraminifera complexes. The detailed analyses have proved that: 1. The lower boundary of the Upper Turonian is connected to the massive occurrence of the genera Marginotruncana pseudolinneiana-M. schneegansi-M. lapparenti; 2. The Turonian/Coniacian boundary is based on the occurrence of Marginotruncana coronata Bolli; 3. The Coniacian/Santonian boundary - Dicarinella concavata (Brotzen); 4. The lower boundary of the Upper Santonian is based on the appearance of Contusotruncana (Rosita) fornicata (Plummer); 5. The Santonian/Campanian boundary is based on the presence of Globotruncana arca (Cushman); 6. The Campanian/Maastrichtian boundary, based on the occurrence of Globotruncanita stuarti (Lapparent). In the Odishi-Okriba facies type has been distinguished the suite “mtavari”, investigated in detail by planktonic foraminifers. The analyses made possible to establish 5 foraminiferal zones in the studied sections. These complexes have been correlated with macrofauna and nannoplankton complexes to specify the age of the suite. At present, there exists a definite methodology for the reconstruction of some parameters of the paleobasin that is based on quantitative interrelations of foraminifer associations. This technique is based on actual data of contemporary water areas. The PF (Planktonic Foraminifer) data can be used for the interpretation of the fossil material data applicable in paleogeographic reconstructions. The relation of planktonic and benthic foraminifera and the content of planktonic complex enable to define depth of the basin. According to the percentage of the leftand right-coiling species of Globotruncanidae, there have been estimated the temperature conditions of the Late Cetaceous basin. The question on the parity of left- and right-coiling foraminifera is a part of big problem of coiling directions in the nature.