US Gulf Coast vegetation dynamics during the latest Palaeocene

Pollen and spore floras from the Bear Creek section in western Alabama (US Gulf Coast) record vegetation events from the lower to middle Tuscahoma Formation (late Palaeocene mid NP9). Sporomorphs are abundant and well preserved in these sediments and are used as a proxy to record vegetation change over time. We present results from both palynofloral and clay mineral analyses in the interval approximately 0.4–0.1 my before the Paleocene/Eocene thermal maximum (PETM); a period of transient and intense global warming that had a profound effect on animal and plant groups in high latitudes. An important factor that has a significant bearing on our understanding of turnover across the PETM is that of climate/environmental stability prior to the PETM in terrestrial ecosystems. Palynological analysis with a between sample resolution of <10 ky suggests that the vegetation type characterising the US Gulf Coastal plains was highly stable with no significant changes in composition and diversity that can be successfully correlated with orbital oscillations. Our results indicate considerable stability of the vegetation type on time-scales of 104–105 yr. Clay mineral suites show the dominance of smectite and illite throughout the studied section with minor fluctuations in the abundance of kaolinite (ranging from 2 to 10%) that indicates a high seasonality of precipitation throughout our studied section. The exact stratigraphic position of the PETM is unknown on the US Gulf Coast but data from existing publications suggests there is little change in the vegetation type across the Palaeocene/Eocene boundary with no major immigration or turnover events. Dinocysts are restricted in both diversity and occurrence but Apectodinium homomorphum is present with ∼30% abundance throughout the studied section and provides some evidence that the Apectodinium acme is not correlative with the PETM at middle latitudes.