HR: 0800h
AN: PP41A-0584    [Abstracts]
TI: Stable Isotopic Records of the Terrestrial Paleoclimatic Consequences of mid-Cretaceous (Aptian-Albian) Oceanic Anoxic Events
AU: * Ludvigson, G A
EM: gregory-ludvigson@uiowa.edu
AF: The University of Iowa, Department of Geoscience, Iowa City, IA 52242-1379 United States
AU: Gonzalez, L A
EM: lgonzlez@ku.edu
AF: University of Kansas, Department of Geology, Lawrence, KS 66045-7613 United States
AU: Joeckel, R M
EM: rjoeckel3@unl.edu
AF: University of Nebraska-Lincoln, Conservation and Survey Division, Lincoln, NE 68588-0517 United States
AU: Carpenter, S J
EM: scott-j-carpenter@uiowa.edu
AF: The University of Iowa, Department of Geoscience, Iowa City, IA 52242-1379 United States
AU: Kirkland, J I
EM: jameskirkland@utah.gov
AF: Utah Geological Survey, 1594 W. North Temple Street, Salt Lake City, UT 84114-6100 United States
AB: Linkage between Aptian-Albian marine, atmospheric, and terrestrial carbon reservoirs is shown by the d13C chemostratigraphy of pedogenic carbonates in the Cretaceous proximal foreland basin fill of eastern Utah. Profiles from sections that accumulated in the foredeep and forebulge have a well-organized structure that we correlate to Aptian positive d13C excursions associated with Oceanic Anoxic Events (OAEs) 1a and 1b, and support the use of pedogenic carbonates for continental-marine chemostratigraphic correlations. The 5 % shifts in our continental sections exceed magnitudes reported from coeval marine carbonate sections, duplicating published results on Aptian d13C changes in terrestrial C3 plants. Peak d13C values of -3 % in the foredeep section occur in Aptian excursions associated with OAEs 1a and 1b, whereas minimum d13C values of -9.3 % occur in the forebulge section in Albian strata. A Late Albian positive excursion of 2 % in the foredeep section is correlated with the 400 Kyr OAE 1d (Wilson and Norris, 2001, Nature 412:525-429), underscoring the potential for high-resolution terrestrial correlation of Cretaceous OAEs. Pedogenic carbonates in background positions of the d13C profiles contain meteoric phreatic components that yield meteoric calcite line trends with d18O values of about -8 %. This contrasts with carbonate d18O values of about -3 % at the position of OAE 1a (segment C7 of Bralower et al., 1999, Jour. Foram. Res. 29:418-437), of about -5 % at the position of OAE 1b (segments C9-C11), and of about -4 % at the position of OAE 1d. Carbonates at the positions of these positive d13C excursions include partially dolomitized rocks composed of interlocking 50-150 micron-sized dolomite rhombs overprinting relict syntaxial inclusions of poikilotopic calcite spars. The calcite spars and overprinting dolomites have isotopic values that are arrayed along positive linear covariant trends in C & O isotope space. We interpret these strata to record the sabkha-type dolomitization of calcretes by hyperconcentrated pore fluids, resulting from local aridification of terrestrial paleoenvironments in the proximal foreland basin during Aptian-Albian OAEs.
DE: 3344 Paleoclimatology
DE: 3354 Precipitation (1854)
DE: 1833 Hydroclimatology
DE: 1045 Low-temperature geochemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting