PLANT COMMUNITY CHANGE ACROSS THE PALEOCENE-EOCENE BOUNDARY IN THE GULF COASTAL PLAIN, CENTRAL TEXAS

During the early Paleogene (~58-53 million years ago), the Earth experienced a long-term warming trend punctuated by several short-term rapid warming events (hyperthermals). The largest hyperthermal event was the Paleocene Eocene Thermal Maximum (PETM) when global temperatures increased by ~5 °C. During this early Paleogene warmth, it has been suggested that in North America tropical biomes expanded into extra-tropical areas creating a wide band of ‘paratropical’ forests, and during the PETM these 'paratropical' forests may have extended as far north as the Bighorn Basin in Wyoming. Further, there is evidence that the PETM caused major plant community change from the tropics to high latitudes. Unfortunately, little is known about the low latitude floras in North America during this time making it difficult to assess hypotheses about the expansion of a 'paratropical' forest belt in the Paleogene, or the effect of the PETM on floras in the sub-tropics. Floras from the Gulf Coastal Plain of Texas are ideally located to help address these hypotheses.

Multiple census collections of fossil leaves were made from the upper Wilcox Group and lower Claiborne Group in central Texas that sample the late Paleocene, the early Eocene, and possibly during the PETM to assess plant community change across the Paleocene-Eocene boundary in the Gulf Coastal Plain. Seven morphotypes were present in the late Paleocene, consisting of 6 dicotyledonous (dicot) angiosperms and 1 palm. Twelve morphotypes (9 dicots, 1 fern, and 2 palms) were present in the potential PETM interval, and in the early Eocene, there were 11 morphotypes (8 dicots, 1 fern, 2 palms). One palm and two dicot morphotypes occur in all three intervals. This record documents a pattern of floral turnover across the Paleocene-Eocene boundary that is similar to the pollen record of the region. In addition to changes in morphotype occurrence, there are notable changes in morphotype abundance. Interestingly, the abundance of the two dicot morphotypes present in all intervals nearly doubles during the PETM interval, and palms become more common during the PETM interval and are most abundant in the early Eocene. These results suggest that warming associated with the PETM likely caused a significant reorganization of plant communities in the Gulf Coastal Plain in central Texas.