University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Masters Theses Graduate School 12-2003 Evidence for an abrupt latest Miocene-earliest Pliocene climate shift preserved in a sinkhole paleolake at the Gray Fossil Site, northeastern Tennessee (Washington County) Aaron Jacob Shunk Follow this and additional works at: https://trace.tennessee.edu/utk_gradthes Recommended Citation Shunk, Aaron Jacob, "Evidence for an abrupt latest Miocene-earliest Pliocene climate shift preserved in a sinkhole paleolake at the Gray Fossil Site, northeastern Tennessee (Washington County). " Master's Thesis, University of Tennessee, 2003. https://trace.tennessee.edu/utk_gradthes/5295 This Thesis is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Masters Theses by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a thesis written by Aaron Jacob Shunk entitled "Evidence for an abrupt latest Miocene-earliest Pliocene climate shift preserved in a sinkhole paleolake at the Gray Fossil Site, northeastern Tennessee (Washington County)." I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Master of Science, with a major in Geology. Steven G. Driese, Major Professor We have read this thesis and recommend its acceptance: Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) To the Graduate Council: I am submitting herewith a thesis written by Aaron Jacob Shunkentitled "Evidence foran abruptlatest Miocene-earliestPliocene climate shiftpreserved in a sinkhole paleolakeat the Gray Fossil Site, northeasternTennessee (Washington County)." I have examined the finalpaper copy of this thesis for form and content and recommend that it be accepted in partial fulfillmentof the requirements forthe degree of Master of Science, with a major Geology. _,.Steven�b_ G. Driese, � .SAAUProfessor We have read this thesis and recommend its acceptance: G.�cllAAk G. Michael Clark Claudia I. Mora .L 11Ji11}KJ, E ILLt..t& Mari E. Uhle Acceptance forthe Council: t J ;_t 3 ,S5P Evidence for an abrupt latest Miocene-earliest Pliocene climate shiftpreserved in a sinkhole paleolake at the Gray Fossil Site, northeastern Tennessee (Washington County). A Thesis Presented for the Master of Science Degree The University of Tennessee, Knoxville Aaron Jacob Shunk December 2003 Dedication This thesis is dedicated to all those that supported me and encouraged me over the past three years. 11 Acknowledgments I wish to thank all that helped me in completing the M.S. in Geology. I would like to thank the Department for the additional financialsupport forcoring. I would like to thank Steve, Maria, Claudia, and Mike (my committee) again for all of their influence- there is no way I could have done this without them. I would like to thank Dr. McKinney, Dr. Wallace, Larry Bristol (my field partner), MartinKohl, Dr. Parmalee, Dr. Perfect, Dr. H. Delcourt, Dr. P. Delcourt, Dr. Hom, and everyone else that I bothered with a random question from time to time. 111 Abstract �ecords of Neogene terrestrial climate are rare for the eastern half of North America. The recently discovered Gray Fossil Site (GFS) in northeasternTennessee (Washington County) appears to be a sinkhole paleolake that preservessuch 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 faciescontains < I% total organic carbon (TOC), has carbon isotope composition 13 (6 C 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 gradedfacies. The transition between the two faciesis marked by: I) the development of a depositional pattern that grades into the laminated facies, 2) an abrupt increase 13 from <I % to~ 9 % TOC, and 3) the steady decrease of 6 C values to those typicalof the laminatedfacies. The laminatedfacies consists of laterally continuous sediment couplets that average 0.4-0.6 cm thick and consist of a thin, coarse-gra.ined, and organic-rich terrigenous (A) lamina added to the apparently continuous deposition of silty-clay terrigenous matrixthat comprises the (B) lamina. The couplets contain statistically significant5-couplet periodicity; the couplets are thereforeinterpreted to be annual varves with variable thickness possibly related to 13 ENSO cycles. The laminated facies averages ~ 8 % TOC with 8 C values that average -29.3%o, and is interpreted to represent a wetter overall climate with a distinct high-energy wet season. Using the varve couplets at the base of the laminatedfacies to establish a sedimentation rate (which likely underestimates the sedimentation rate at the top of the graded facies), the majority of the facies change appears to have been deposited in less than 500 years. A subaerial facies records soil formation and filling of the sinkhole lake. The possible shiftfrom a drier climate to. a �etter, seasonal climate documented in the changing paleolake sediment facies at the GFS may have been caused by a eustatic sea level rise documented at ~ 5 Ma. Sea level rise is proposed to have caused a brief period of upwelling along the Atlantic coast of North Carolina. iv TABLE OF CONTENTS Section Page 1. INTRODUCTION................................................................ 1-2 2. SITE DESCRIPTION............................................................. 3-4 3. METHODS I. SAMPLIN"G................................................................ 5 II. PETROGRAPHICANALYSIS......................... ..... .. .. .. 5 ill. SEDIMENTACCUMULATION............................ ........... 5-6 IV. STABLEISOTOPES ANDESTIMATION OF %TOC........... .. 6 V. TIMESERIES ANALYSIS .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 7 4. RESULTS I. PETROGRAPHIC ANALYSIS.......................................... 8-11 II. SEDIMENTACCUMULATION....................... .................. 11-12 ill. STABLEISOTOPES ANDESTIMATION OF %TOC .............. 12-13 IV. TIMESERIES ANALYSIS .. .. .. ... ... .. .... ... .. .. .. .. .. .. ........... 13 5. INTERPRETATION ANDDISCUSSION I. GFS BASIN"CHARACTER....................................... ........ 14-15 II. SEDIMENTOLOGY II a. Graded Facies ......................................................... 15-19 II b. Transition from the Laminated to Graded Facies ............. 19-21 II c. Laminated Facies............................... ....................... 21-26 II d. Experimental modeling of GFS depositional patterns ........ 26-27 II e. Sedimentation rates and rate of faciestransition .............. 27-28 II f. Subaerial Facies ....................................................... 28 m APPROXIMATE %TOC AND STABLECARBON ISOTOPES ill a. Approximate o/oTOC............................................... 29-30 illb. Stable carbon isotopes......................... ................. 30-33 IV. POSSIBLEMECHANISM FOR RAPIDCLIMATE SHIFT IV a. Climate shift.......................................................... 34-35 IV b. Possible mechanism of climate shift............................. 35-36 6. CONCLUSIONS................................................................... 37-38 REFERENCES CITED......................................................... 39-41 APPENDIX.......................................................................... 42-78 VITA................................................................................... 79 V LIST OF TABLES Table Page 1. Stable carbon isotope compositions and % TOC fromstratigraphic column 43 2. Stable carbon isotope compositions and % TOC frommechanically separated (A) and (B) laminae in sediment couplets from /aminatedfacies .............. 44 3. Periodicityraw data .................................................................. 45-47 4. Couplet thicknessof laminatedfacies .. .................................. 48 5. Thicknessof (A) and (B) laminae......................................... 48 6. Raw data forsediment accumulation tests 1-4 in cm ........................... 49-50 7. Settling time forGFS clay component...................................... 51 8. Comparisonof GFS, Green River Formation, and modem Arabian Sea varved depositional patterns....................................................... .. 52 V1 LIST OF FIGURES R� h� Fig. 1. Maps ofthe Gray Fossil Site (GFS), Tennessee............................. 53 Fig. 2. Gray Fossil Site (GFS) research sampling locations....................... 54 Fig. 3. Gray Fossil Site (GFS) unlithifiedlacustrine sediment.................. 55 Fig. 4. Field photographsof Cut-One and Cut-Two............................... 56 Fig. 5. Gray Fossil Site (GFS) fossilsand preservation............................. 57 Fig. 6. Stratigraphy of the GrayF ossil Site (GFS).... .... .. ... .. .... .. .... .. ..... ... 58-59 Fig. 7. Settling Column ...........•...................................................... .. 60 Fig. 8. Petrographyof