HR: 14:00h
AN: PP53A-01    [Abstracts]
TI: Solar Periodicities and a Monsoon Climate Phase Recorded at the Latest Miocene to Earliest Pliocene Gray Fossil Site, Northeastern TN, USA.
AU: * Shunk, A J
EM: aaron_shunk@baylor.edu
AF: Baylor University, Baylor University Department of Geology One Bear Place #97354 Waco, TX 76798-7354, Waco, TX 76798-7354, United States
AU: Dunbar, J A
EM: John_Dunbar@Baylor.edu
AF: Baylor University, Baylor University Department of Geology One Bear Place #97354 Waco, TX 76798-7354, Waco, TX 76798-7354, United States
AU: Driese, S G
EM: Steven_Driese@baylor.edu
AF: Baylor University, Baylor University Department of Geology One Bear Place #97354 Waco, TX 76798-7354, Waco, TX 76798-7354, United States
AB: The latest Miocene to earliest Pliocene Gray Fossil Site (GFS) represents a paleosinkhole lake fill located in northeastern TN, USA that includes an exceptionally well-preserved record of sedimentation. The uppermost 2.8 m of lacustrine stratigraphy is characterized by rhythmites that regularly alternate between coarse-grained and organic-rich (A) laminae and fine-grained, silty clay (B) laminae. Both the (A) and (B) components are almost exclusively comprised of clastic materials. In a small, meromictic lake, the presence of laterally continuous laminated sediment that includes well-known solar periodicities in rhythmite thickness at periods of 24 (Hale cycle) and 12 (sunspot cycle) is interpreted as representing annually generated varves that correspond to seasonal variations in sedimentation. The distinctly larger fraction of medium sand-size quartz grains present dominantly within the (A) laminae, as well as the abrupt transitions between (A) and (B) components suggest that the rhythmites represent deposition during alternating high-energy and lower-energy seasons, which are consistent with a monsoonal precipitation pattern. The monsoon climate may relate to changes in the ocean circulation pattern prior to 4.6 Ma that resulted in an increased temperature and atmospheric pressure gradient between the east coast of North America and the Atlantic Ocean. Sediments underlying the 2.8 m varved sequence are characterized by a different sedimentation style comprised of thick successions of individual graded beds with low %OC and less negative stable C isotope values, which collectively suggest that the underlying sediments were likely deposited in a dryer climate phase with reduced vegetative cover. The transition from the underlying sediment to monsoon generated varves is conformable and is consistent with the expansion of a monsoon climate pattern into the GFS watershed.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1090 Field relationships (3690, 8486)
DE: 3270 Time series analysis (1872, 4277, 4475)
DE: 3309 Climatology (1616, 1620, 3305, 4215, 8408)
DE: 4901 Abrupt/rapid climate change (1605)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Joint Assembly