Palaeocene–Eocene paratropical floral change in North America: responses to climate change and plant immigration

Abstract

The Initial Eocene Thermal Maximum (IETM) at c. 55 Ma represents a period of rapid global warming that lasted less than 200 ka. The response of vegetation to such an event, and particularly warmadapted highly diverse vegetation types, is poorly understood. Using pollen floral, clay mineral and stable carbon isotope analyses of sediments from the upper Tuscahoma Formation on the eastern US Gulf Coast (eastern Mississippi and western Alabama), we document paratropical floral changes across the PalaeoceneEocene boundary from the Wahalak #2 and lower Harrell cores. Data indicate strong changes in the abundance of kaolinite that correlate with changes in relative abundance of native pollen taxa. There is no evidence for a transient, extra-tropical flora on the US Gulf Coast that may characterize the IETM. Immigration and extinction are not associated with this event. Instead, Early Eocene plant immigration occurs in pulses and therefore is not associated directly with climate change during the IETM. The two cores share the same regional species pool but compositional differences are stronger between cores than they are either through changes in environment, increased soil erosion or chemical weathering, or through the introduction of nonnative plants. Our data suggest that vegetation change across the Palaeocene-Eocene boundary is not a single event but rather a sequence of cascading events.

Paratropical floral extinction in the Late Palaeocene–Early Eocene

“…Stratigraphy of the eastern US Gulf Coast presented against (a) magnetostratigraphic time scale (Rhodes 1995;Rhodes et al 1999), (b) sequence stratigraphy (Mancini & Tew 1995), (c) planktonic foraminiferal zones (Mancini & Oliver 1981;Berggren et al 1985), (d) nannoplankton zones (Gibson & Bybell 1994) 1999) and sequence stratigraphy (Mancini & Tew 1995). The exact position of the PETM is still unknown, although Harrington et al (2004) 1973;Elsik 1974;Frederiksen 1980;Harrington 20036 (Gibson & Bybell 1994), although a short unconformity separates the Tuscahoma Formation from the Bashi and Hatchetigbee formations (Frederiksen et al 1982;Ingram 1991;Mancini & Tew 1995;Frederiksen 1998). The general depositional environments on the eastern US Gulf Coast are muddy strand-line, very shallow marine settings that periodically became emergent and formed swamps that are now preserved as lignites in the upper Tuscahoma and Hatchetigbee formations (Mancini 1981;Gibson et al 1982;Mancini & Tew 1995).…”

“…The Eocene sporomorph suite includes the following sporomorph taxa: Granulatisporites luteticwa, Mapo//ewf« spp., CeA» &cAw#', /Mf#po//M micnwwpplingensis, Thomsonipollis sabinetownensis, Brosipollis spp., and Platycarya spp. (Tschudy 1973;Elsik 1974;Frederiksen 1980Frederiksen , 1998Harrington 2001Harrington , 2003aHarrington et al 2004). …”

“…1 (Harrington 2001, 2003a, Harrington & Kemp 2001Harrington et al 2004). Ackerman Mine and Fort Gaines may be age equivalent and span the boundary between the Nanafalia-Tuscahoma formations (Fig.…”

“…Wing 1998;Jaramillo 2002;Harrington 2003a, b;Wing et al 2005), several regions globally have excellent plant records both immediately before and after the PETM. For example, in North America, plant and pollen records are documented from different vegetation types from the warm-temperate Bighorn Basin in Wyoming (43°N, 107°W), which had a mean annual background temperature of c. 16-17 °C (Wing 1998;Wing & Harrington 2001), to the paratropical eastern US Gulf Coast (32°N, 87°W) (Frederiksen 1994(Frederiksen , 1995Harrington 2003a;Harrington et al 2004), which had a Late Palaeocene-Early Eocene background mean annual temperature of c. 26-27 °C (Wolfe & Dilcher 2000;Ivany et al 2004). The changes of the US Gulf Coast floras provide an example of the responses of a warm-adapted, taxonomically diverse vegetation type to the impact of rapid climate warming.…”

Short-term fluctuations in vegetation and phytoplankton during the Middle Eocene greenhouse climate: a 640-kyr record from the Messel oil shale (Germany)

“…Numerous climate-related palaeobotanical studies on the Palaeocene and the Eocene focused on these so-called hyperthermal events, particularly on the question whether an important floral turnover was associated with the PETM in mid-latitudes of Europe (Beerling and Jolley 1998;Collinson et al 2003) and North America (Wing et al 2005, Harrington et al 2004, Harrington and Jaramillo 2007. However, their conclusions appear to be somewhat inconsistent and generally range from significant to moderate vegetation responses depending on the palaeogeographic position of the studied sections.…”