GSA Connects 2021 in Portland, Oregon

Paper No. 25-8
Presentation Time: 9:00 AM-1:00 PM


ARENS, Nan1, GARCIA TOMAS, Catalina1 and IVANY, Linda2, (1)Department of Geoscience, Hobart & William Smith Colleges, Geneva, NY 14456, (2)Department of Earth and Environmental Sciences, Syracuse University, Heroy Geology Lab, Syracuse, NY 13244

The transition between the Paleocene-Eocene Thermal Maximum and the early Eocene climatic optimum is less well studied than the very warm climate extremes that bound it. The Hatchetigbee Formation of southwestern Alabama dates to the Ypresian and is characterized by fine to medium sands, micaceous silts and clays representing a variety of coastal and near-shore environments. The uppermost formation in the Wilcox Group, plant macrofossils are rare in the Hatchetigbee, with only one previous report from the underlying earliest Eocene Bashi Formation of east-central Mississippi. Here, we present initial findings on a small, fragmentary flora from the type section Hatchetigbee Bluff locality on the Tombigbee River in Washington County, AL. At this locality, the unit records nearshore marine conditions as indicated by layers of Venericardia bivalves lower in the section, and transitions to terrestrially influenced, evenly thin bedded (..lithology..) in the upper part of the bluff. Seasonally resolved oxygen isotope and clumped isotope paleothermometry on the bivalves has indicated a mean annual temperature (MAT) of ~26°C with limited seasonal variation in temperature but significant seasonal influx of fresh water, perhaps suggestive of strongly seasonal precipitation. The flora comes from fallen blocks of the upper part of the unit. While few complete specimens were recovered, leaves were abundant on bedding planes. We identify a small number of entire-margin dicot angiosperm taxa, consistent with the warm MAT and low seasonality indicated by the bivalves. Likewise, palynoflora from the matrix consists of only a handful of species, including possible Rhizophora pollen. Herbivore damage is very rare, unexpected for the early Eocene. Root casts in matrix sediment suggest estuarian or low-energy shoreface depositional environment for the leaf-bearing sediments.