5:15 PM - 6:45 PM
[BCG06-P13] Carbon cycle and deep-sea redox conditions during the Toarcian oceanic anoxic event
Keywords:paleoclimate, Oceanic Anoxic Events, Jurassic
The Toarcian oceanic anoxic event (T-OAE; ~183 Ma) was caused by global warming due to degassing from the Karro-Ferrar volcanisms and orbital-scale methane emissions characterized by repeated negative carbon isotope excursions (NCIEs) in Tethys ocean deposits. However, effect of methane emission on oceanic redox condition is still largely unknown.
In this study, to examine carbon cycle and redox condition of bottom water, we measured high-resolution δ13Corg and degree of bioturbation of a deep-sea chert of the Sakahogi section of the Mino Terrane. This succession was deposited at a low-latitude several hundreds kilometers away from the subduction zone in Pantharassa ocean, the largest ocean at that time.
At the Pliensbachian/Toarcian (Pl/To) boundary, bioturbation was decreased with NCIE at the onset of black chert and shale deposition. In the T-OAE stage, δ13C shifted negatively in the gray chert interval a few cm below the bottom of black chert and shale deposition, and bioturbation also began to decrease. In addition, the overlain black shale shows several hundred µm-scale lamination, while no such laminae were observed in the black chert.
Periodic fluctuations in δ13C values corresponding to the Milankovitch cycle have been identified in the coastal sediments, and methane release and absorption are associated with ice sheet shrinkage and expansion, which may have affected ocean circulation and deep-sea redox condition across the T-OAE.
In this study, to examine carbon cycle and redox condition of bottom water, we measured high-resolution δ13Corg and degree of bioturbation of a deep-sea chert of the Sakahogi section of the Mino Terrane. This succession was deposited at a low-latitude several hundreds kilometers away from the subduction zone in Pantharassa ocean, the largest ocean at that time.
At the Pliensbachian/Toarcian (Pl/To) boundary, bioturbation was decreased with NCIE at the onset of black chert and shale deposition. In the T-OAE stage, δ13C shifted negatively in the gray chert interval a few cm below the bottom of black chert and shale deposition, and bioturbation also began to decrease. In addition, the overlain black shale shows several hundred µm-scale lamination, while no such laminae were observed in the black chert.
Periodic fluctuations in δ13C values corresponding to the Milankovitch cycle have been identified in the coastal sediments, and methane release and absorption are associated with ice sheet shrinkage and expansion, which may have affected ocean circulation and deep-sea redox condition across the T-OAE.