Evidence for an abrupt latest Miocene-earliest Pliocene climate shift preserved in a sinkhole paleolake at the Gray Fossil Site, northeastern Tennessee (Washington County)

Records of Neogene terrestrial climate are rare for the eastern half of North America. The recently discovered Gray Fossil Site (GFS) in northeastern Tennessee (Washington County) appears to be a sinkhole paleolake that preserves such a record. Well-preserved vertebrate GFS fossils strongly suggest a Late Miocene-Early Pliocene (Hemphillian) Land Mammal Age (2:. 4.5 Ma). Three distinct facies occur within the upper 20 m of GFS lacustrine sediment. The graded facies is characterized by continuous succession of individual graded beds that average 0.8 cm thick. This facies contains \u3c I% total organic carbon (TOC), has carbon isotope composition (613C V-PDB) averaging-25.4%0 with values as positive as -24.3%o, and is interpreted to represent deposition from sporadic storm events in a water-stressed ecosystem. The laminated facies overlies the graded facies. The transition between the two facies is marked by: I) the development of a depositional pattern that grades into the laminated facies, 2) an abrupt increase fro

Late Tertiary paleoclimate and stratigraphy of the Gray Fossil Site (eastern TN) and Pipe Creek Sinkhole (northcentral IN)

Includes bibliographical references (p. 88-96).The Late Tertiary represents warm Earth conditions immediately prior to the development of extensive northern hemisphere glaciation, and this period in Earth history may therefore provide the best available analogy for the projected outcome of continued global warming. There are few interior continental sites of Late Tertiary age from the eastern half of North America and subsequently very little is known about the conditions characterizing climate. The Early Pliocene (~5 Ma) Pipe Creek Sinkhole (PCS) includes the sediment fill of a complex karst environment that developed in north-central Indiana, USA. The PCS stratigraphy has multiple facies including: 1) Terra rossa with δ¹³ C values averaging -20 ±0.7‰ PDB, which are interpreted to represent sediment deposited in a closed cave system under high summer temperatures with well-drained soils. 2) An in-situ paleosol at the top of the terra rossa, which formed after the cave opened to the land surface. 3) Dark-colored, organic-rich pond sediments cap the other facies, and include the abundant vertebrate fossils that are broadly consistent with those inhabiting an open ecosystem such as a savannah or parkland. However, pollen analysis from the pond sediments includes dominantly pine pollen and no grass pollen. The Gray Fossil Site (GFS) includes an exceptional latest Miocene to earliest Pliocene (4.5 to 7 Ma) sinkhole lake deposit that contains incredibly well-preserved sediment, fauna, and flora. The uppermost ~2.8 m of lacustrine stratigraphy is characterized by autochthonous rhythmites that regularly alternate between coarse-grained and organic-rich (A) laminae and fine-grained, silty-clay (B) laminae, and are interpreted to represent annual varves deposited in a monsoonal precipitation pattern. Equivalent periodicities at 23.0/ 24-years and 5.1/ 4.4-years were discovered from the spectral analysis of thickness measurements of annual growth bands in fossil wood and the lacustrine rhythmites, which confirms an annual association for the rhythmites. The dominant 23/ 24-year climate cycle is interpreted to represent the Hale-cycle, which is thought to have modulated precipitation. The strong expression of the Hale-cycle suggests the importance of considering the Earth-Sun climatic relationship for understanding climate change and global warming.by Aaron J. Shunk.Ph.D