Title

Early-Cenomanian Terrestrial Facies and Paleoclimate Records of the Lower Tuscaloosa Formation, Southwestern Mississippi

Authors

David F. Ufnar

Document Type

Article

Publication Date

2007

Department

Geography and Geology

Abstract

Sphaerosiderite oxygen isotope values from the Early Cenomanian Lower Tuscaloosa Formation, or LTF, extend a mid-Cretaceous meteoric delta O-18 latitudinal gradient 9 degrees south to25 degrees N paleolatitude, and contribute to a better understanding of the hydrologic cycle in North America during a "greenhouse" period in Earth history. Sphaerosiderites have been used to reconstruct paleolatitudinal trends in meteoric O-18 values throughout western North America, and the O-18 values have been used in a stable isotope mass balance model to produce quantitative estimates of mid-Cretaceous precipitation rates and latent heat flux values. The LTF meteoric O-18 values help constrain the critical subtropical values on the coastal plain bordering Tethys and the southeastern coast of the Western Interior Seaway. The LTF, an important subsurface petroleum unit (2800-4000 m depths) in southern Mississippi, contains amalgamated pedogenicallymodified, sphaerosiderite-bearing mudstones and sandstones. Cored intervals of the Early-Cenomanian Stringer Sandstone Member of the Lower Tuscaloosa Formation (LTF) of Southwestern Misississippi are characterized by 6 lithofacies units. The descriptive lithofacies units include: (1) thickly-bedded sandstones; (2) thinly bedded sandstones; (3) carbonaceous mudstones and siltstones; (4) red-mottled rnudstones; (5) purple and yellow mottled mudstones; and (6) flaser and lenticular bedded carbonaceous muddy sandstones. The sphaerosiderites are most commonly observed in gleyed domains of the red-mottled mudstones. These mudstones were clays, and silty clay loam soils, and are characterized by prominent red mottles in a gleyed matrix with an abundance of translocated clays, pedogenic slickensides, carbonaceous debris, and root traces. The sphaerosiderites yield delta O-18 vs. delta C-18 values, meteoric sphaerosiderite lines (MSLs), that may be used as a proxy for paleoprecipitation delta O-18 values. The MSL (delta O-18) values range from -3.31% to - 5.22% (VPDB). Estimated meteoric water values for the LTF have an average value of -4.69 % VSMOW.

Publication Title

Stratigraphy

Volume

4

Issue

1

First Page

49

Last Page

65

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