UNRAVELING δ13CBULK CHANGES ACROSS THE PETM AND K/PG BOUNDARIES: SEAWATER OR ARTIFACT?

Drilling onshore New Jersey by ODP Leg 174AX has provided an unparalleled paleoshelf transect from Wilson Lake (40 m Paleocene paleodepth), Ancora (50 m paleodepth), Millville (70 m paleodepth), and Bass River (90 m paleodepth) that allows reconstruction of water column, surface to deep, and along shelf gradients in stable isotope, trace metals, and organic markers for the Paleocene-Eocene thermal maximum (PETM) and the Cretaceous/Paleogene (K/Pg) boundary. The K/Pg boundary in the shelf is associated with a ~2.5‰ δ¹³C decrease in bulk carbonate, a ~0.8‰ δ¹³C decrease in organic carbon, and a collapse of the surface to bottom δ¹³C gradient due to reduced export productivity. Monospecific analyses of Heterohelix globulosa across the boundary show a 0.9‰ decrease, suggesting that the DIC decrease of seawater was ~0.8-0.9‰, and that the bulk carbonate change primarily reflects vital effects associated with the mass extinction in calcareous nannoplankton. A progressively higher amplitude of the δ¹³C change landward (varying from 3 to 6‰) across the PETM was reported by Wright and Schaller (2013). The difference between bulk carbonate and the thermocline dwelling Subbotina δ¹³C appears to mirror the abundance of the nannofossil D. araneus, D. anartios, and Rhomboaster spp. (RD) assemblage, suggesting that bulk δ¹³C is overprinted by vital effects. There is an apparent precursor increase in bulk carbonate δ¹³C that progressively increases landward from Bass River to Wilson Lake, with the largest change at Wilson Lake (2‰). This change is not recorded by Subbotina, though it is in bulk organic δ¹³C, suggesting that it was not due to a change in DIC, but rather due to a change in sediment input associated with a transition zone from glauconitic sandy silts of the Paleocene Vincentown Formation to kaolinitic clayey silts of the Eocene Marlboro Formation.