[B-PT04] Biotic History

[BPT04-P02] Diachronic extinction of planktic foraminifers at the mid-Cretaceous Cenomanian/Turonian boundary

Soichi Shirakawa², *Kazuyoshi Moriya¹, Yasuko Miyakura² (1.Department of Earth Sciences, Faculty of Education and Integrated Arts and Sciences, Waseda University, 2.Major in Earth Sciences, Resources and Environmental Engineering, Graduate School of Creative Science and Engineering, Waseda University)

Keywords:Cenomanian/Turonian boundary, Planktic foraminifers, Extinction

Planktic foraminifers, appeared in Earth history in the late Jurassic, are known as one of major carbonate producers in modern pelagic ocean. They have flourished from the late Mesozoic through Cenozoic with two major diversity crises, at the Cretaceous/Paleogene and Eocene/Oligocene boundaries. The former and latter crises were induced by an extraterrestrial impact on Earth and a shift in Earth’s climate mode from greenhouse to icehouse, respectively. On the other hand, another minor but substantial extinction event is identified at the mid-Cretaceous thermal maximum, which is called the Cenomanian/Turonian boundary event (CTBE). This event was, obviously, accompanied by extensive warming of Earth’s climate and plausible expansion of oxygen depleted water mass.
Here, we examined extinction levels of each planktic foraminiferal taxon across the CTBE. Our sediment samples were recovered by Integrated Ocean Drilling Program Expedition 342 at Newfoundland Ridge, northwestern Atlantic. Sediments were mostly composed of nannofossil chalk excluding a distinctive black shale layer at the Cenomanian/Turonian boundary. Except for the CTBE interval, planktic foraminifers abundantly occurred. As seen in many localities, Rotalipora spp. and Thalmanninella spp. went extinct approximately at the CTBE. In return, Marginotruncana spp. arose in the early Turonian. A few species of Dicarinella, Muricohedbergella, Praeglobotruncana, and Whiteinella were observed from the late Cenomanian through early Turonian. An extinction level of Rotalipora cushmanni can be correlated with those in UK, France, and US. On the other hand, comparing to records in UK and France, the last appearance datum of Thalmanninella in Newfoundland Ridge is well higher/younger. Possible diachronism of the last appearance datum of Thalmanninella between Atlantic and Western Interior Seaway has recently been reported. Our results indicate this diachronism may exist even within north Atlantic.