HR: 11:45h
AN: PP22A-06    [Abstracts]
TI: Sr Isotope Variation in U-Pb Dated Permo-Carboniferous Carbonate Cycles of West Texas
AU: * Rasbury, E T
EM: troy.rasbury@sunysb.edu
AF: SUNY Stony Brook, Department of Geosciences, Stony Brook, NY 11794 United States
AU: Hemming, N G
EM: hemming@qc.edu
AF: Queens College CUNY, School of Earth and Environmental Science, Flushing, NY 11367 United States
AU: Dickson, J A
EM: jadd1@esc.cam.ac.uk
AF: Cambridge University, Department of Earth Science, Cambridge, CB2 3EQ United Kingdom
AU: Saller, A H
EM: asaller@unocal.com
AF: UNOCAL Corporation, 14141 SW Freeway, Sugar Land, TX 77478 United States
AU: Barrick, J E
EM: jim.barrick@ttu.edu
AF: Texas Tech University, Department of Geosciences, Lubbock, TX 79409 United States
AU: Leon, L
EM: lilyleon74@hotmail.com
AF: Queens College CUNY, School of Earth and Environmental Science, Flushing, NY 11367 United States
AB: Secular variation of Sr isotopes has an intriguing systematic relationship to supercontinental cycles and important biological and climatic events over the past billion years of Earth history. Because the Sr isotope composition of seawater is homogeneous, secular variations must represent changes in continental weathering sources or the balance between continental and mid-ocean ridge inputs into the ocean. This makes Sr isotopes an important tool for chemostratigraphic correlation, although more work is needed to demonstrate that shallow marine deposits in continental platforms are fully mixed with the global ocean. During the Permo-Carboniferous, large glacioeustatic changes in sea level produced high-frequency shallowing upward cycles. Deep water carbonates were deposited during times of highest sea level, and the tops of the cycles record subaerial exposure and meteoric diagenesis as the seas regressed. These cycles occurred on approximately a 100 ky period, based on U-Pb dating of caliches that formed on the subaerial exposure surfaces. Based on cycle stratigraphy and fusulinid biostratigraphy, cycles have been correlated among three high recovery cores of Wolfcampian (Early Permian) to Desmoinesian (middle Pennsylvanian) age from the Central Basin Platform of the Permian Basin of Texas. We selected samples of deep water facies bioclastic wackestones from the high frequency cycles of two of the cores. Two total replicates from each sampled interval were analyzed to evaluate the robustness of the Sr isotope value for recording contemporaneous seawater. Samples with indistinguishable replicate analyses fall mostly within published curves. Additionally we have included analyses of brachiopods from these cores to further evaluate the reliability of the whole rock data. Our results show a trend in Sr isotopes decreasing from 0.70825 from the Virgilian (latest Pennsylvanian) to a low of 0.70791 in the Wolfcampian. Further work on these cores will allow unprecedented resolution of Sr isotope secular variation in this climatic interval when the world was emerging from an icehouse condition similar to the Pleistocene.
DE: 1035 Geochronology
DE: 1040 Isotopic composition/chemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2005 Joint Assembly