| Title: | The Terrestrial Stable Isotopic Record of Aptian-Albian OAE1b in Palustrine Carbonates of the Cedar Mountain Formation, Utah: Implications for Continental Paleohydrology |
| Author: | Greg A Ludvigson |
| Date Submitted: | 04/22/2002 |
| Address: | 109 Trowbridge Hall
Iowa City
Iowa
USA
52242-1319
|
| Phone: | 319-335-1761 |
| Email: | gregory-ludvigson@uiowa.edu |
| Co-Authors: | Gonzalez, Luis, A., Univ. Iowa, luis-gonzalez@uiowa.edu; Kirkland, Jim, I., Utah Geological Survey, nrugs.jkirklan@state.ut.us; Joeckel, Robert, M., Univ. Nebraska-Lincoln, rjoeckel3@unl.edu. |
| Affiliation: | Department of Geoscience, University of Iowa |
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| Abstract URL: | http://cis.whoi.edu/science/GG/ccod/viewAbstracts.cfm?RefNumber=19725478 |
| Author Homepage: | http://www.igsb.uiowa.edu/inforsch/climate.htm |
| Author Project webpage: | http://gsa.confex.com/gsa/2001AM/finalprogram/abstract_25866.htm |
| Keywords: | Aptian, Albian, paleosols, carbonates, carbon isotopes, oxygen isotopes hydrologic cycle hydrology precipitation |
| Abstract: | Nonmarine strata in the Cretaceous Cedar Mountain Fm (Barremian?-Albian) accumulated in the Western Interior foreland basin, preserving a record of semi-arid terrestrial paleoenvironments in the rain shadow of the Sevier mountains. We tested for coupling between marine, atmospheric, and terrestrial carbon reservoirs by analyzing the  chemostratigraphy of pedogenic carbonate glaebules in closely-spaced palustrine carbonate beds in two stratigraphic sections near Price Utah (150 m), and at Dinosaur National Monument (DNM; 60 m), looking for Aptian-Albian carbon isotope excursions. Both sections show organized structure that we have correlated to Aptian-Albian carbon isotopic segments C8 to C15 of Bralower et al. (1999, J. Foram. Res. 29:4:418-437), further supporting the use of palustrine carbonates for continental-marine correlations. The 5 per mil shifts in our continental sections exceed those reported from coeval marine sections, as in the report of Jahren et al. (2001, Geology 29:2:159-162) on Aptian changes in terrestrial C3 plants. A systematic offset of about 1.5 per mil between values in the proximal foreland section at Price (heavier), and those at the more distal section at DNM (lighter) may be related to local 13C enrichments in C3 floras that experienced greater moisture stress on the immediately leeward side of the Sevier mountains. Peak values of -3  in the section at Price occur in segments C7-C8 and C12-C13 (OAE 1b), whereas minimum values of -9.3 occur at DNM in segment C14. Peak  values of -3 VPDB occur in the Price section in segments C7-C8, with minimum values of -9.5 occurring at DNM in segments C11-C12. Mean values on the shoulders of the positive carbon isotope excursion coinciding with OAE 1b (segment C13) are the same at both sections (-8.5 ), but diverge in the C13 segment, with heavier values by about to 2 per mil in the more proximal section at Price, suggesting an intensification of aridity during OAE 1b. Individual carbonate beds are complex mixtures of micritic, microspar, and vein-filling sparry calcite components, with each showing unique diagenetic trends in C-O isotope space. Abundant microspars have trends conforming to meteoric calcite lines (MCLs), suggesting that they recrystallized in shallow meteoric phreatic groundwaters at surface MAT. Diagenetic analysis of a selected carbonate bed shows that micritic components produce a trend of covariant 13C and 18O enrichments of 1-2 per mil from the microspar MCL trend, suggesting pedogenic origin in a vadose environment. The MCL value in this bed (-7.5 ) yields a compatible groundwater estimate with that from an independent paleoprecipitation proxy (sphaerosiderite horizon with MSL value of -4.0 from the Dakota Fm of Utah reported in White et al., 2001; Geology 29:363-366). Using a zonally-averaged Cretaceous MAT of 27° C for Utah, maximum 18O enrichments in the micritic components suggest that up to 50 % of vadose fluid was lost to evaporation, exemplifying a method we are exploring for estimating evaporative fluxes from Cretaceous aridisols. |
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