T121 Quantitative Reconstructions of the Large-Scale Cenozoic Terrestrial Climate Change

Monday, 28 October 2013
8:00 AM - 12:00 PM
Room 507

LATE NEOGENE DRY CLIMATE CONDITION IN THE SOUTHERN APPALACHIANS

Paper number: T121-10
Program: Technical Sessions
Time: 10:15 AM – 10:30 AM

Authors

Abstract

A Neogene site from northeast Tennessee has yielded well preserved floral and mammal remains, demonstrating a unique combination of North American and Eurasian biota in a forest-woodland and a window for understanding the terrestrial Neogene climate conditions in southeastern North America. Fossil vertebrates from the site support the late Hemphillian Land Mammal Age (the latest Miocene to earliest Pliocene, viz. 7 ~ 4.5 my). The site consists of about 40 m of dark colored sediment of lacustrine origin, in which the top 4 m-thick fossiliferous laminated facies preserves excellent record of plant fossils, represented by wood, seeds, leaves, and pollen grains. Forty-eight palynological samples from seven different test-pits were analyzed. All pits exhibit a low pollen yield, a result of basic pH levels, drought, and fire events that occurred during the deposition. The palynofloral assemblage has a low to moderate diversity and is largely dominated by a Quercus–Carya–Pinus assemblage (~ 90% of the palynoflora). Floristically, we have recognized at least 55 genera, representing more than 25 families of seed plants. Based on the nearest living counterpart comparisons, these fossils can be identified with certainty to their specific modern genera. Therefore, the Coexistence Approach, a well-established quantitative paleoclimate reconstruction method, was used to reconstruct the paleoclimate condition. Seven climatic parameters are calculated as follows:

Temperature (oC)

Precipitation (mm)

Mean annual

ColdMonth

WarmMonth

Mean annual

WettestMonth

DriestMonth

WarmestMonth

Paleoclimate at the site

13.6-17.6

5.5-7.1

24-27.5

979-1551

148-195

18-24

120-176

Current climate of site

13

-4 -1

24

1034

109

81

109

The comparison clearly indicates that the southern Appalachians in the late Neogene was under a climate quite different from the modern; especially its winter in the late Neogene was much warmer (above freezing), which could explain the occurrence of alligators and beaded lizards in the fossil record. Furthermore, the much drier month (likely last fall to winter) in the past might be responsible to intensive forest fires, which contribute the common occurrence of charcoals all over the site. In general, the paleoclimate in the southern Appalachians appears much more seasonal in the late Neogene than that of today.