Planktonic Foraminifera of the Dariyan formation and implications of Oceanic Anoxic Event 1a

Abstract

The investigated section cropping out in Kuh-e-Banesh, Zagros basin (southern Iran) is represented by limestone, Cherty beds and marl levels bearing abundant Planktonic foraminifers, radiolarian microfaunas, and ammonite imprints. For the first time, well to moderately preserved forms of Planktonic foraminifera have been extracted from black shale and marls levels. Extracted biota was studied with regard to relationship with abundances of radiolarian and total organic carbon. Rock Eval analysis shows high total organic carbon content within Daryian Formation (lower part). The presence of high abundances of planktonic foraminifers and radiolarian associated with high total organic carbon content in the lower part of the Dariyan Formation suggest a high productivity event, eutrophication, and warming phenomena of the ocean during early Cretaceous. Biostratigraphical ranges of planktonic foraminifera in the studied section indicate Early Aptian to early Late Aptian age. It is, therefore, implicated that the oceanic anoxic event 1a (OAE 1a) interval be regarded as equivalent levels in Tethys domains. The black shale of oceanic anoxic event is characterized by the widespread existence of regionally organic-rich beds in the Tethys basins. Micro-paleontological and geochemical results provide new insights into the paleogeography of the Tethys realm and better correlation with well-studied worldwide successions.