HR: 14:45h
AN: H33E-03    [Abstracts]
TI: Isotopic and Geochemical Tracers in Terrigenous Sediments: Applications to Tectonics, Crustal Evolution and Paleoclimate
AU: * Hemming, S R
EM: sidney@ldeo.columbia.edu
AF: Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory of Columbia University Rt 9W, Palisades, NY 10964, United States
AU: McLennan, S M
EM: Scott.McLennan@sunysb.edu
AF: Department of Geosciences, State University of New York at Stony Brook, Stony Brook, NY 11794, United States
AB: The sources and sedimentary processes leading to deposition of terrigenous sedimentary rocks leave diagnostic compositional clues that make them valuable recorders of geological history. In the late 1980's through the 1990's several Stony Brook graduate students working in Gil Hanson's lab applied a variety of established petrographic and geochemical methods and developed new isotopic and geochemical approaches to study ancient tectonic histories preserved in several Paleoproterozoic and Paleozoic basins. These studies included testing Pb isotopes in detrital quartz and feldspar grains, using the Sm-Nd isotope system to identify isotopic resetting near the time of deposition, and the application of multiple tracers to unravel sources and processes in sedimentary systems. Since the early work of Goldschmidt, it has been appreciated that sedimentary rocks provide an "averaging" mechanism for large regions of exposed crust. Accordingly, sedimentary compositions, especially for elements not greatly mobilized by sedimentary processes such as weathering and diagenesis, can be used to estimate changes over geologic time in the composition of upper continental crust, and with this approach it appears that there was a profound change in the composition of exposed upper continental crust at about the Archean-post Archean boundary. Recently we have found a consistent case for this apparent change in a compilation of modern sediment data, using the Sm-Nd system as a measure of the continental age. The compositional changes that result from different source compositions and geological age as well as different degrees of chemical and mechanical weathering make the chemical and radiogenic isotope composition of sediments and their components valuable for paleoclimate studies as well. Thus the same approaches can be used to constrain such factors as wind and ocean circulation patterns and the dynamics of ice sheets in the past.
DE: 1040 Radiogenic isotope geochemistry
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 4870 Stable isotopes (0454, 1041)
DE: 4928 Global climate models (1626, 3337)
SC: Hydrology [H]
MN: 2007 Joint Assembly