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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions Vol. 58 (2008), Pages 67-75

Shale Layers in the Alabama Smackover Formation and their Implications for Sea-Level Change and Regional Correlation

Lawrence R. Baria1, Ezat Heydari2, and Bradley G. Winton3

1Jura-Search Inc., P.O. Box 320426, Flowood, Mississippi 39232

2Department of Physics, Atmospheric Sciences, and Geoscience, Jackson State University, P.O. Box 17660, Jackson, Mississippi 39217

3Department of Geology, Millsaps College, 1701 N. State St., Box 151577, Jackson, Mississippi 39210

ABSTRACT

Several organic-rich, siliciclastic shale layers, ranging in thickness from 0.5-50 ft (0.1-15 m) were discovered in the nearly pure carbonates of the Smackover Formation during the recent drilling in Conecuh, Covington, and Escambia counties of Alabama. Shale layers are readily correlative across the eastern arm of the Conecuh Embayment and appear to pinch out along the rims of the basin. In the basinward direction, these shales grade into muddy outer-ramp carbonates of a normal marine Smackover sequence.

The shale beds are black, laminated, and nearly devoid of marine fauna. In some cases, they host graded silt layers. Most importantly, shales contain abundant, terrestrially derived, herbaceous organic matter.

We suggest that the deposition of these shales occurred during sea-level falls when siliciclastics and terrestrial organic matter were delivered into restricted basinal lows of the region via run off. The occurrences of these shale layers may point to as many as three sea-level falls during the deposition of the Smackover Formation in Alabama. It is also likely that the shale intervals are correlative with exposure surfaces previously described from the Smackover Formation in north-central Gulf Coast region. Therefore, it can be inferred that the observed Alabama Smackover depositional events closely correspond to the deposition of the Smackover “C,” “B,” and “A” cycles in Mississippi, Arkansas, and Louisiana.

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