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Estimating the oxygen isotopic composition of equatorial precipitation during the Mid-Cretaceous

Marina B. Suarez, Luis A. Gonzalez and Gregory A. Ludvigson
Estimating the oxygen isotopic composition of equatorial precipitation during the Mid-Cretaceous
Journal of Sedimentary Research (May 2010) 80 (5): 480-491


Recent studies utilize the oxygen isotopic composition of pedogenic carbonates (siderite and calcite) to evaluate empirically the global hydrologic cycle during the Cretaceous. Pedogenic carbonates are used as a proxy for the isotopic composition of meteoric waters in order to estimate precipitation rates in the Aptian-Albian via a mass-balance model. These modeling studies have previously been limited to mid-latitude to high-latitude data, and thus a more extensive latitudinal data set is needed to produce a more globally constrained model. This study provides an equatorial ( approximately 2 degrees S paleolatitude) data set from pedogenic sphaerosiderites of the Caballos Formation from the Upper Magdalena Valley, Colombia. In addition, macroscopic and microscopic morphological features of paleosols were used to identify ancient soil conditions. The gleyed appearance and presence of sphaerosiderites suggest that soils were dominated by water-saturated conditions, with occasional incursions of marine-influenced water resulting in pyrite precipitation. This observation constrains the sampling sites to paleoelevations near sea level. Paleosols are interpreted to have been Entisols, Inceptisols, and Ultisols similar to soils in coastal equatorial regions of modern Colombia. Relatively invariant delta (super 18) O values and more variable delta (super 13) C values produce vertical trends in delta (super 13) C vs. delta (super 18) O space called meteoric sphaerosiderite lines. The average oxygen isotopic composition for these trends is -4.41+ or -0.37 per mil (VPDB). The average oxygen isotopic composition of meteoric waters precipitating the sphaerosiderites is estimated at -4.56+ or -0.38 per mil (VSMOW). These are slightly more enriched than modern and modeled Cretaceous estimates of equatorial precipitation delta (super 18) O but are generally in agreement with expected oxygen isotopic compositions of precipitation for this paleolatitude.

ISSN: 1527-1404
EISSN: 1938-3681
Serial Title: Journal of Sedimentary Research
Serial Volume: 80
Serial Issue: 5
Title: Estimating the oxygen isotopic composition of equatorial precipitation during the Mid-Cretaceous
Affiliation: University of Kansas, Department of Geology, Lawrence, KS, United States
Pages: 480-491
Published: 201005
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
References: 54
Accession Number: 2010-053668
Categories: Isotope geochemistryStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, geol. sketch maps
N02°00'00" - N03°00'00", W75°30'00" - W75°00'00"
Secondary Affiliation: Kansas Geological Survey, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 201029
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