Latest Miocene to earliest Pliocene sedimentation and climate record derived from paleosinkhole fill deposits, Gray Fossil Site, northeastern Tennessee, U.S.A. Aaron J. Shunk a , Steven G. Driese a, * , G. Michael Clark b a Department of Geology, Baylor University, One Bear Place #97354, Waco, TX 76798-7354, USA b Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996-1410, USA Received 2 November 2004; received in revised form 29 July 2005; accepted 22 August 2005 Abstract Lacustrine sediments deposited within a paleosinkhole at the Gray Fossil Site (GFS) in northeastern Tennessee, USA, provide a latest Miocene and earliest Pliocene (4.5–7 Ma) record of sedimentation and paleoclimate. The basal graded facies consists of mm- to cm-thick, normally graded layers of primarily locally derived terrigenous silts and fine sands with low organic content, which record storm flow influxes into a 40 m-deep paleosinkhole lake. The graded facies is overlain by the laminated facies , which is characterized by mm thick, non-graded bA–B coupletsQ of abundant macerated terrestrial organic matter and fine to coarse quartz sand (A), alternating with quartz and carbonate silt (B). Isotopic evidence for establishment of either C4-dominated or mixed C3/C4 terrestrial ecosystems is not evident at this site; d 13 C values of bulk organic matter from the basal graded facies range from À 24x to À 26x PDB, and decrease upsection to À 28x to À 30x in the organic-rich laminated facies. Isotope values covary with changes in both total organic content (TOC: 0.25–1 wt.% in graded facies, 2–12 wt.% in laminated facies) and in carbon–nitrogen ratio (C / N: 1–2 in graded facies, 20–50 in laminated facies). These upsection changes in sedimentary facies and organic geochemistry within the GFS are attributed to either: (1) a climate shift characterized by increased precipitation and concomitant increased vegetation within the paleosinkhole watershed over time, or (2) progressive shallowing and eutrophication of the paleosinkhole lake, coupled with organic diagenesis within either the watershed or the paleosinkhole sediments, in which there was isotopic discrimination associated with organic matter decomposition. Subaerial exposure of the paleosinkhole lake is recorded by paleosol development. D 2005 Elsevier B.V. All rights reserved. Keywords: Paleosinkhole; Paleoclimate; Pliocene; Tennessee; Gray Fossil Site 1. Introduction The Late Miocene to Early Pliocene was character- ized by major climate, faunal, and floral changes. A global increase in C4 grassland ecosystems occurred during the Late Miocene (8 to 6 Ma), which expanded into middle and high latitudes and was accompanied by a significant Cenozoic faunal turnover (Cerling et al., 1997, 1998). Ungulate survivorship patterns from the Late Miocene extinction indicate that North American climate changes involved some combination of cooling, drying, and an increase in the seasonality of temperature and/or precipitation (Janis, 1989). Gomphotherium-tusk growth patterns suggest development of a wet season 0031-0182/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2005.08.001 * Corresponding author. Tel.: +1 254 710 2177; fax: +1 254 710 2673. E-mail address: Steven _ Driese@baylor.edu (S.G. Driese). Palaeogeography, Palaeoclimatology, Palaeoecology 231 (2006) 265– 278 www.elsevier.com/locate/palaeo