PALEOCENE CRITICAL ZONE RECORDS FROM HYDRIC PALEOSOLS AND LIGNITES OF THE PALEOCENE NAHEOLA FORMATION, NORTHERN MISSISSIPPI, USA

Terrestrial records of Paleocene-Eocene hyperthermals are viewed as some of the best ancient analogs for the impacts of projected future anthropogenic climate change on Earth’s critical zone. To fully evaluate the magnitude of these climate-driven perturbations however, a more complete understanding of prevailing pre-warming background conditions is necessary. The Mississippi Embayment (MSE), a major southwest-dipping sedimentary basin in the south coastal region of North America, contains an important record of terrestrial Paleocene strata deposited prior to the onset of known warming trends. The purpose of this research is to target paleosols and lignites within the Paleocene Naheola Formation from the MSE to interpret depositional environments and paleoclimate. A continuous section of the Naheola is available in archival core collected by Mississippi Minerals Resources Institute from Tippah County, Mississippi, USA.

We focus on a ~8-m-thick interval of the Naheola Formation that contains five paleosols associated with four lignite seams. We performed a suite of initial core description methods, including visual observations (e.g., grain size and Munsell colors), and high-resolution logging of spectrophotometry, gamma density, and magnetic susceptibility.

Three types of mineral paleosols are present within the paleosol-lignite succession. An initial kaolinitic paleosol representing high rates of chemical weathering and oxidizing conditions underlies the lowermost lignite seam. Successive thick, gray gleyed paleosols associated with lignite seams represent reducing conditions in wetland settings prior to peat accumulation. A gray and purple paleosol represents waterlogged to very poorly drained conditions before deposition of the uppermost lignite. Upper contacts of most lignites are sharp and overlain by marine sand or mud containing lignite rip-up clasts, indicating that each is a marine flooding surface.

Future analyses will include high-resolution X-ray fluorescence of the entire interval and stable isotope analysis of oxygen and deuterium in pedogenic kaolinite. These will be combined with initial core description data to produce a comprehensive picture of Paleozoic coastal critical zone conditions in the MSE.