JURASSIC AND CRETACEOUS SEA BASINS IN THE SOUTHEASTERN PART OF THE LESSER CAUCASUS: SEDIMENTATION SETTINGS AND FORAMINIFERAL ASSEMBLAGES

Abstract

Structural features and composition of Jurassic deposits in the Kafan tectonic block that is located in the southeastern part of the Lesser Caucasus are considered. Three carbonate members bearing foraminifers are distinguished in the Upper Jurassic-Valanginian sequence of volcanogenic-sedimentary rocks of the Zangezur Group. The overlying Hauterivian-middle Aptian stratigraphic interval is also subdivided into three carbonate members that yield foraminifers. Changes in composition of foraminiferal communities and in lithological features are established below the base of the Valanginian Stage and at the appearance level of orbitolinids within the Barremian interval. As is shown, the lower (Oxfordian-Tithonian) and upper (Valanginian-Aptian) parts of the whole sequence accumulated in different paleolandscape settings. The analyzed paleocoenoses suggest that there were two types of foraminiferal communities: the older (Oxfordian-Tithonian) one with dominant cosmopolitan genera and the subsequent population with prevailing endemic genera of Tethyan affinity. The facies structure of investigated sequence and compositions of foraminiferal assemblages are used to elucidate the evolution history of sea basin that existed in the southeastern part of the Lesser Caucasus during the Late Jurassic-Early Cretaceous time.