Deep-ocean anoxia across the Pliensbachian-Toarcian boundary and the Toarcian Oceanic Anoxic Event in the Panthalassic Ocean

Abstract

The early Toarcian Oceanic Anoxic Event (T-OAE, or Jenkyns Event, ~183 million years ago) was a major hyperthermal and global carbon-cycle perturbation, likely associated with the release of a substantial volume of 12 C-enriched carbon to the Earth's surface. Seawater deoxygenation and the associated deposition of organic-rich facies during this event have been noted in many locations around the world, but evidence for pervasive and extreme oceanic anoxia has thus far been described mainly from European sections deposited in hydrographically restricted basins. Here we present new geochemical data on redox changes during the T-OAE, as well as the preceding Pliensbachian-Toarcian boundary (Pl/To) event, from a deep Panthalassic Ocean site at Inuyama, Japan. Redox-sensitive trace element data reveal an extended interval of seawater deoxygenation that began prior to the Pl/To and continued to the end of the T-OAE. A marked expansion of anoxic and possibly euxinic conditions to the seafloor occurred during both the Pl/To and T-OAE, accompanied by increased organic carbon burial. During these intervals of severe deep-ocean deoxygenation, our data suggest a global drawdown of trace elements such as Mo, U and As. Our findings highlight that: (1) the Panthalassic Ocean was likely an important locus of deoxygenation and organic carbon burial during the early Toarcian, and (2) the spread of anoxia during the T-OAE was a globally distributed phenomenon. • Anoxia in deep water Panthalassa from late Pliensbachian to early Toarcian. • A putative Oceanic Anoxic Event at the Pliensbachian-Toarcian boundary. • Global drawdown of redox-sensitive trace elements during Toarcian OAE. • Deep sea organic carbon burial at Pliensbachian-Toarcian and Toarcian OAE.