There and back again; on dinoflagellate cyst index events of the Eocene - Oligocene Transition in the (Para)Tethyan Realm

Abstract

A recent biochronostratigraphic (coccolithophorids, dinoflagellate cysts) and paleoenvironmental analysis of the hemipelagic deposits of the İhsaniye Formation, exposed along the cliffs in the Karaburun area (Black Sea coast, NW Turkey) provided new insights into the paleoceanographic and paleoclimatic evolution of the central (Para-)Tethyan region across the Eocene–Oligocene Transition (EOT). Among others, the study identified the Earliest Oligocene Stable Isotope Step (EOIS) marking the inception of Antarctica's first continental-scale ice sheets since the mid-Permian and coinciding with a major eustatic lowering, followed by the Early Oligocene Glacial Maximum (EOGM) period with its peak δ¹⁸O values. The study showed apparent (quasi) continuity of the EOT succession at Karaburun, a notion that is not a 100% obvious from the organic walled dinoflagellate cyst (or dinocyst) record. This is mainly because the iconic Eocene – earliest Oligocene taxon Areosphaeridium diktyoplokum, in coeval sections in the region quite abundant near the end of the Eocene, is virtually absent. Here, we focus on obtaining a more detailed picture of correlative secondary dinocyst and other EOT bioevents allowing an even more robust chronostratigraphic assessment of the succession, including correlation to the Italian type sections. Particularly the ranges of the (herein taxonomically revised) species Explodinium priabonensis gen. and comb. nov. and the new species Glaphyrocysta peterbijlii sp. nov. may be regarded as additional criteria to correlate EOT strata within the (Para)Tethyan realm. Combined evidence now suggests that the Karaburun section may not be as complete as previously assumed and that a small part of the succession correlative to the base of the EOGM, representing a portion of the Adi dinocyst Zone may be missing. This aspect does not affect the overall outcome and significance of the studies at Karaburun. In fact, a brief hiatus may well be driven by the major EOT sea level lowering.