Enhanced chemical weathering and organic carbon burial as environmental recovery factors of the OAE2; a case study in the Koppeh-Dagh Basin (NE Iran)

A late Cenomanian-early Turonian interval (Hamam-ghaleh section) adjusted with the transition of Aitamir and Abderaz formations has been investigated in the east of Koppeh-Dagh Basin to examine environmental perturbations related to the oceanic anoxic event 2. The dark shale of the upper Aitamir Formation indicate higher organic matter concentrations especially in the two intervals at the end of Rotalipora cushmani biozone and the middle part of Whiteinella archaeocretacea biozone. These intervals are characterized by higher detrital input (quartz and feldspar) and chemical alteration (high kaolinite/illite ratios), which suggest a warm-humid condition coeval with high productivity during the OAE2. The Aitamir Formation also shows higher total sulfur values associated with deposition of framboidal pyrite reflecting an oxygen deficiency.The warm and humid periods in the study section were followed by the cooler and drier intervals associated with decreased TOC values and chemical weathering. These cooling periods might be caused by falling of atmospheric CO2 due to large amount of carbon burial in sediments and high silicate weathering. The δ13Corg positive excursions of around 1‰ are other characteristics of these cooler-drier intervals, which were result of high burial of light carbon in the organic matter and lower isotopic differentiation in low atmospheric pCO2.