Comment on cp-2022-86

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> The Paleocene-Eocene Thermal Maximum (PETM) represents the most pronounced hyperthermal of the Cenozoic era and is hypothesized to have resulted in an intensification of the paleohydrologic cycle, including enhanced seasonality and increased sediment discharge to the coastal ocean. Although the PETM has been widely documented, there are few records from deposits that form the distal, deep-water components of large sediment routing systems. This study presents new constraints on the stratigraphic placement of the PETM in the deep-water Gulf of Mexico basin through analysis of geochemical, carbon-isotopic, and biostratigraphic data within a ~124 m cored interval of the Wilcox Group. Biostratigraphic and carbon-isotopic data indicate that the PETM extends over ~13.4 m based on acmes in the dinoflagellate<em> Apectodinium homomorphum</em> and calcareous nannoplankton <em>Rhomboaster cuspis</em> and a ~&minus;2&permil; shift in bulk organic &delta;¹³C values. A decrease in bioturbation and benthic foraminifera extinction suggest that deoxygenation of Gulf of Mexico bottom waters was coincident with the onset of the PETM. A ~2 m lag in the depositional record separates the onset of the PETM negative carbon isotope excursion (CIE) and deposition of a 5.7 m thick interval of organic-lean claystone and marlstone that reflects a shut-off of the supply of sand, silt, and terrestrial palynomorphs to the basin. An increase in CaCO₃ ~4.5 m above the CIE onset is consistent with other sites that indicate ocean acidification and shoaling of the calcite compensation depth during the early PETM. We interpret deposits of the PETM in the deep-water Gulf of Mexico to reflect the combined effects of increased erosional denudation and rising sea level that resulted in sequestration of sand and silt near the coastline but that allowed delivery of terrigenous mud to the deep-sea. The similarity of oceanographic changes observed in the Gulf of Mexico and Atlantic Ocean during the PETM supports the inference that these water masses were connected during latest Paleocene-earliest Eocene time. Although deposition of typical Wilcox Group facies resumed during and after the PETM recovery, an increased influx of terrestrial detritus (i.e., pollen, spores, organic debris) relative to marine dinoflagellates is suggestive of long-lasting effects of the PETM. This study illustrates the profound and prolonged effects of climatic warming on even the most distal reaches of large (&ge;1&times;10⁶ km²) sediment routing systems.