Dinoflagellate cyst biostratigraphy of the upper Eocene and lower Oligocene of the Kirmizitepe Section, Azerbaijan, South Caspian Basin

Abstract

The South Caspian Basin is a deep Cenozoic basin located in eastern Paratethys along the northern margin of the Arabia–Eurasia collision zone. The basin, with its proven oil and gas reserves, has been the subject of numerous biostratigraphic studies, but most of these studies have concentrated on the Pliocene reservoir rocks. Precise chronological correlations between Paratethyan sedimentary successions and Mediterranean stages have not yet been achieved, although detailed local foraminiferal and non-foraminiferal biostratigraphic studies allow chronostratigraphic division and accurate regional correlations. As a pioneering work, this paper provides a detailed dinoflagellate cyst biostratigraphy of the upper Eocene and lower Oligocene deposits in the South Caspian Basin. A total of 127 dinoflagellate cyst taxa have been studied for the first time from the Eocene Koun Formation and the Oligocene part of the Maykop Formation exposed in the Kirmizitepe Section, Azerbaijan. Three dinoflagellate cyst biozones known from classic areas in central Italy are recognizable in the South Caspian Basin. One (Aal zone) is uppermost Eocene and two (Gse and Adi zones) are lower Oligocene. Thus, although some dinoflagellate cyst species from the studied section have stratigraphic ranges different from those of mid and higher latitudes, others provide correlations with previously defined biozones and dinoflagellate cyst events in the Tethyan realm and northwestern Europe. Dinoflagellate cyst assemblages indicate shallow marine depositional conditions for the latest Eocene. Deeper conditions prevailed during the earliest part of the early Oligocene, succeeded by a pronounced shallowing later in the early Oligocene.