Paleoenvironmental evolution during the Early Eocene Climate Optimum in the Chicxulub impact crater

Abstract

The Early Eocene represents the warmest climate during the Cenozoic Era punctuated by transient warming events. Here, we apply for the first time biomarker and stable isotope data to describe the depositional and environmental changes at the actual Chicxulub impact crater [International Ocean Discovery Program (IODP) Site M0077A] during the Early Eocene (∼56–48 Ma) including the Early Eocene Climate Optimum (EECO; ∼53–49 Ma). TEX86-based reconstructions indicate elevated sea surface temperature around 37°C for the entire succession, punctuated by warmer and cooler periods (37.8°C, 35.7°C, respectively). Biomarker and δ13C-org data of the core sediments reveal a shift from an organic-lean lower to an organic-rich upper section of the Early Eocene interval. Embedded in the lower section is a prominent organic-rich black shale layer. The lower section, directly overlying strata deposited upon the Paleocene-Eocene Thermal Maximum (PETM), is organically lean with low biomarker concentrations indicating low primary productivity. In the upper section, higher concentrations of algal and bacterial biomarkers are ascribed to high primary productivity and nitrogen fixation in an epipelagic zone, potentially supported by upwelling. The organic-rich black shale layer exhibits a negative δ13C-org isotope excursion ascribed to recycling of 13C-depleted organic matter via upwelling attributed to a transient hyperthermal event.