Preprints
https://doi.org/10.5194/cp-2022-86
https://doi.org/10.5194/cp-2022-86
 
09 Dec 2022
09 Dec 2022
Status: this preprint is currently under review for the journal CP.

Carbon-isotope chemostratigraphy, geochemistry, and biostratigraphy of the Paleocene-Eocene Thermal Maximum, deep-water Wilcox Group, Gulf of Mexico (U.S.A.)

Glenn R. Sharman1, Eugene Szymanski1,2, Rebecca A. Hackworth3, Alicia C. M. Kahn3, Lawrence A. Febo3, Jordan Oefinger1, and Gunnar M. Gregory1 Glenn R. Sharman et al.
  • 1Department of Geosciences, University of Arkansas, Fayetteville, AR 72701, United States of America
  • 2Utah Geological Survey, 1594 W. North Temple, Suite 3110, Salt Lake City, UT 84116, United States of America
  • 3Chevron Technology Center, 1500 Louisiana St, Houston, TX 77002, United States of America

Abstract. 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 Apectodinium homomorphum and calcareous nannoplankton Rhomboaster cuspis and a ~−2‰ shift in bulk organic δ13C 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 (≥1×106 km2) sediment routing systems.

Glenn R. Sharman et al.

Status: open (until 01 Mar 2023)

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  • RC1: 'Comment on cp-2022-86', Anonymous Referee #1, 01 Feb 2023 reply

Glenn R. Sharman et al.

Data sets

Carbon-isotope, geochemical, and biostratigraphic data from the Anchor 3 well, Green Canyon protraction area, Gulf of Mexico Glenn R. Sharman, Eugene Szymanski, Rebecca A. Hackworth, Alicia C. M. Kahn, Lawrence A. Febo, Jordan Oefinger, Gunnar M. Gregory https://doi.org/10.5281/zenodo.7291552

Glenn R. Sharman et al.

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Short summary
This study examines deep-water deposits within the Gulf of Mexico (U.S.A.) that record an episode of pronounced global warming that occurred ~56 million years ago. We show that the supply of sand and silt into the basin shut off after a delay of about 30,000 years, followed by an influx of clay derived from deep erosion of central North America. Our results are consistent with other studies that indicate rapid sea level rise, ocean acidification, and decreased oxygen during this warming event.