[B-PT02] Biotic History

[BPT02-P03] Oceanic anoxic event 2 observed in Southwestern Newfoundland Ridge

*Kazuyoshi Moriya¹, Yasuko Miyakura², Takashi Hasegawa³, Akiko S. Goto⁴ (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, 3.Faculty of Earth Science and Civil Engineering, Institute of Science and Engineering, Kanazawa University, 4.Center for Ecological Research, Kyoto University)

We have re-examined Oceanic Anoxic Event 2 (OAE2) at Southwestern Newfoundland Ridge. Mid-Cretaceous sequences including a major black shale approximately 40 cm thick and a few minor black shale layers were recovered by Integrated Ocean Drilling Program Expedition 342 at Site U1407. Shipboard and shore-based biostratigraphy indicates that the sections including these black shales are correlated to the Cenomanian through Turonian. Here, we report total organic carbon content (TOC), organic carbon/total nitrogen ratio (C/N ratio), and organic stable carbon isotope ratio (δ¹³C_org). Maximum TOC observed becomes more than 20 wt% at the major black shale, while background TOC is less than 1 wt%. δ¹³C_org stratigraphy suggests well-known isotope signature at OAE2, namely, first build-up (FB), trough interval (TI), second build-up (SB), plateau (PT), and recovery (RV), is preserved at this site. At the PT interval, δ¹³C_org shows an approximately 5‰ positive excursion from the pre-excursion background. The magnitude of this positive excursion is comparable to that observed in Oceanic Drilling Program Site 1276 at Newfoundland Basin. On the other hand, stratigraphic distribution of Black shales in Site U1407 is different from those in Site 1276. In Site 1276, the deposition of black shales started at the base of FB and continued up to PT. However, the major black shale in Site U1407 observed only at SB and PT. Estimated paleodepth at the mid-Cretaceous is deeper than 2000 m for both sites, indicating depths may not regulate the timing of the black shale deposition. Considering bathymetry of western north Atlantic and position of Grand Banks, we hypothesize that these two sites were under the different bottom water current system at the Cenomanian through Turonian.