603-pp18 - The Record of Pliocene Sea-Level Change At...

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Unformatted text preview: The Record of Pliocene Sea-Level Change At SeaEnewetak Atoll Bruce W. Wardlaw and Terrence M. Quinn When? Pleistocene: 1.8 Ma to 11.5 Ka Pleistocene: Pliocene: 5.3 Ma to 1.8 Ma Pliocene: Quarternary Science Reviews, Vol. 10, pp. 247-258, 1991. 247Steven Scyphers Geological Oceanography 3/20/2008 Where is PEACE? Purpose Reconstruct sea level based upon stratigraphic distribution of major disconformities that coincide with resolvable age differences in the biochronology Stratigraphy= study of distributions, Stratigraphy= deposition, and age of sedimentary rocks Litho= physical and petrographic properties Litho= Chemo= dating marine sediments/rocks using trace Chemo= elements, molecular fossils, isotopic ratios Seismic= Reflection character analysis Seismic= Bio= based upon fossil content Bio= Overview Previous studies: Previous Single Bore Hole Single Isotope (Sr) (Sr) Discrepancies due with intra-lagoon variability when Discrepancies intracompared with biochronology Disconformities= surface between successive Disconformities= strata, representing a missing interval in geologic time This study: Six Bore Holes This Multiple Approaches - Sequence Stratigraphy Model - Isotope Model 1 Seismic Stratigraphy Seismic Stratigraphy Results: 9 Major Disconformities in Results: PEACE Boreholes 6 within the Plio-Pleistocene within Plio2 Shallow Reflections correlate exactly with Shallow disconformities -utilizes equipment that produces vibrations and allows their behavior in the substrate to be recorded Chemostratigraphy Literature on sediments states: Literature Holocene = unaltered aragonite Holocene Plio-Pleistocene= mixed mineralogy of Plioaragonite/calcite Pliocene= altered calcite Pliocene= Chemostratigraphy Low δ13 C and δ18 O relate to meteoric Low calcitization Biostratigraphy ------ Upper and Lower Paleo Lines of Correlation _____ Line of Correlation Windows of Correlation define distance between disconformities Sea Level HighStand Models 25 and 40 m/Ma Subsidence Rates for Isotope Proxy Model and Sequence Stratigraphy Model 2 Sea Level Estimates Considering minor disconformities, Sea Level Falls were probably less than the depth of the Lagoon. Plio-Pleistocene Ice Volume, Antarctic PlioClimate, and the Global δ18 O Record M.E. Raymo, L.E. Lisiecki, K.H. Nisancioglu Raymo, Lisiecki, Science. Vol. 313. 28 July 2006 Vol. Steven Scyphers Geological Oceanography 3/20/2008 Objectives Present a simple model of ice volume Present change that predicts sea level change and δ18 O that matches geological record. Evaluate the relative importances of Evaluate obliquity and precession to cyclicity. cyclicity. Assertions 23k year orbital precession cancels out 23k globally. 41k year in-phase obiquity is the 41k incomponent of insolation that dominates the records. Obliquity The angle of axial tilt The Lower Obliquity Lower Lower Solar Radation at Poles Increased Glaciation 3 Precession -dV/dt = (i + V)/ t Relationship of Relationship accumulation and abrasion Milankovitch Model Output Conclusions Obliquity and Precession are both factors Obliquity Obliquity in phase between poles Obliquity Precession out of phase between poles Precession Long-term cooling could transition Longprimarily land based to marine based East Anarctica Ice Sheet Conclusion Small Changes in Anarctic Ice Mass could Small cancel out much larger changes in N.H. The Terrestrial-Marine Shift could result in The Terrestrialstrengthening of the 23k cycle in the marine δ18 O 4 ...
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