Late Albian–Coniacian planktic foraminifera and biostratigraphy of the northeastern Caucasus

Abstract

This paper presents a considerably revised biostratigraphy for Upper Albian through Coniacian pelagic limestone and shale sequences in the northeastern Caucasus region based primarily on planktic foraminiferal distributions. The use of concentrated acetic acid for the extraction of microfossils from the hard limestones has yielded a much more detailed planktic foraminiferal biostratigraphy than has been documented previously. Because of the low latitude location of the study area the high diversity assemblages contain many of the biomarkers used to identify standard Tethyan biozones ranging from the Rotalipora appenninica Zone through the Dicarinella concavata Zone. A key result of this study is the recognition of an apparently continuous Cenomanian/Turonian boundary interval within a laminated, dark marl that is enriched in organic carbon. Extinction of the single-keeled rotaliporids corresponds with the onset of deposition of the laminated marl beds.