Barremian to aptian radiolarian from southwestern Iran (Dariyan Formation), Zagros basin: paleoecological implications

For the first time, moderate preserved radiolarian fauna were recovered from early Cretaceous (Dariyan Formation) cherty beds and black shales successions outcropping at Kuh-e Banesh located in high Zagros belt, southwestern Iran. Radiolarian assemblages were recovered from the lower part of Daryian Formation are described and assigned Late Barremian to Early late Aptian time interval. This study provides palaeoenvironmental interpretations of radiolarian and relationship between distribution abundance of radiolarian and calcareous planktonic foraminifera. The high abundance of radiolarian, chert beds and presence of scarce planktonic foraminifera suggest carbonate deposition under shoaling of the CCD or unfavourable conditions. Radiolarian blooms and organic-rich black shales indicate high productivity, eutrophic conditions, and regarding to age diagnostic radiolarian assemblages possibly correlate to Oceanic Anoxic Event 1a (OAE 1a). The formation of black shales with radiolarian within carbonate platform was resulted by Aptian tectonic activities in Zagros basin. The depositional trend of the Dariyan Formation represents three stages. The stage 1 and 3are defined by similar conditions that characterised by Orbitolina limestone. The stage 2 consists of radiolarian beds and marls with planktonic foraminifera that indicate abruptly deepening on the shallow water carbonates.