106-28 A Flora from Hatchetigbee Bluff, Alabama plus North American Floral Provinciality and Climate during the Early Eocene Climatic Optimum

Session: 37th Annual Undergraduate Research Exhibition Sponsored by Sigma Gamma Epsilon (Posters)

Poster Booth No.: 114

Presenting Author:

Bailey Gervais

Authors:

Gervais, Bailey¹, Garvey, David², Polcari, Mikyle³, Fawad, Arshi⁴, Postma, James⁵, Ivany, Linda C.⁶, Arens, Nan Crystal⁷

(1) Geoscience, Hobart and William Smith Colleges, Geneva, NY, USA, (2) Math & Computer Science, Hobart and William Smith Colleges, Geneva, NY, USA, (3) Geoscience, Hobart and William Smith Colleges, Geneva, NY, USA, (4) Biology, Hobart and William Smith Colleges, Geneva, NY, USA, (5) Volunteer, Chatom, AL, USA, (6) Earth and Environmental Sciences, Syracuse University, Syracuse, NY, USA, (7) Geoscience, Hobart and William Smith Colleges, Geneva, NY, USA,

Abstract:

The early Eocene Climatic Optimum (~53-49 Ma) was marked by global warmth and, in many places, high precipitation and humidity. Fossil plants offer an important perspective on regional climate, including both temperature and hydroclimate. This study begins with a small dicot leaf flora from Hatchetigbee Bluff, an early Eocene locality on the Gulf Coastal Plain in southwestern Alabama. We collected fossil leaves from the nearshore, tidally influenced facies of the upper Hatchetigbee Formation, stratigraphically above horizons bearing earliest Eocene marine mollusks. Leaves were prepared, photographed, and grouped into 18 morphotypes based on features such as shape and venation. Morphotypes were scored and analyzed using the Climate Leaf Analysis Multivariate Program (CLAMP) and leaf margin analysis (LMA). LMA produced mean annual temperature (MAT) estimates ranging 27°C – 29°C; CLAMP-produced MAT was cooler, possibly due to incomplete coding of some morphotypes, with a warm month mean temperature of 28°C. CLAMP estimated a year-round growing season with growing season precipitation of 257 mm. Next, we reviewed published Eocene floras from the continental United States (n = 55), geolocated each, and compared the described and illustrated dicot leaf taxa with those from Hatchetigbee Bluff. Complete taxon lists from all localities were compiled and ordinated using non-metric multidimensional scaling (MDS) on presence-absence data to visualize compositional similarities and differences across different localities. The MDS analysis identified three floristic groups: one closer to Appalachian basement rocks, one across the southeastern U.S. and Mississippi Embayment, and a third restricted to the western U.S. Focusing on the Gulf Coastal Plain, we identified previously published localities (n = 10) that spanned the Paleocene-Eocene. We scored each for CLAMP and mapped the resulting climate interpretations on geolocated localities using inverse distance weighting isopleths. Interpretation of these results must be contextualized by the speed of climate change during the late Paleocene and early Eocene, limited sampling density, and uncertainties in time-stratigraphic correlation of terrestrial localities. In contrast to previous results, we reconstruct precipitation as constant across the region and through time. For MAT, we noted homogeneous temperature across the region in the Eocene.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8045

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