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