Stratigraphic architecture of the Tethyan Cenomanian-Turonian succession and OAE2 in the Dokan Area, Kurdistan Region, northeast Iraq

Abstract

This study provides a detailed examination of a condensed Cenomanian-Turonian (C-T) succession of two sections (Dokan Dam and Khalakan) in the Kurdistan Region, Northeastern Iraq, based on biostratigraphy (calcareous nannofossils and planktic foraminifera), carbon and oxygen isotope geochemistry, and facies analysis. The C/T boundary in this region is characterized by a hiatus noticeable due to the absence of the Globigerinelloides benthonensis and Dicarinella hagni subzones and the lack of positive carbon isotope excursion (CIE) peak b during the Oceanic Anoxic Event 2 (OAE2). Positive CIEs in our studied succession include three peaks (a, c, and d) from the four established positive global CIE peaks (a, b, c, and d). Peak a is recognized at the upper part of the Cenomanian Dokan Formation, while peak b is missing within the hiatus across the C/T boundary. Peak c is found within the lowest Turonian above the Gulneri/Dokan formational boundary, and peak d appears at the base of the middle Turonian Kometan Formation. Twelve microfacies and four submicrofacies types are identified and grouped by depositional paleoenvironments into five facies associations, ranging from peritidal to basinal settings. Three incomplete third-order depositional sequences (DSs) and their transgressive-regressive cyclic stacking pattern have been identified in the Cenomanian-Turonian succession studied herein. These DSs are associated with hiatuses, suggesting tectonic control combined with a global sea-level fall. Hiatuses and extreme condensation recorded in the latest Cenomanian-early Turonian successions on many Neo-Tethys platforms resulted from platform exposure, subsequent drowning, and a warming climate.