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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 55 (1971)

Issue: 2. (February)

First Page: 343

Last Page: 343

Title: Barrier Bar Sedimentation in Upper Cretaceous Facies Sequence, Southeastern USA: ABSTRACT

Author(s): Norman C. Hester

Article Type: Meeting abstract

Abstract:

Upper Cretaceous (Campanian) clastic strata in eastern Alabama indicate deposition in a shallow-marine littoral environment. Fluctuations of strand in a predominantly regressive cycle have produced at least 4 heteropic facies, one of which includes sediments of barrier-bar origin. Interpretation is based on detailed studies of sedimentary petrology supported by paleontological evidence.

Distinguishing characteristics of the facies sequence recognized from top to bottom are: (1) barrier bar (regressive)--moderately sorted, medium-grained sand; Ophiomorpha; low-angle crossbedding; lag concentrates; channels; (2) offshore clay (transgressive)--calcareous, sandy clay grading upward to clayey fine sand; high planktonic to benthonic ratio; (3) marginal shelf sands (transgressive)--fine- to medium-grained, calcareous, glauconitic sand; distinct burrows; high faunal diversity; and (4) delta front (regressive)--very poorly sorted, sandy, carbonaceous silt; bioturbate; low faunal diversity; low planktonic to benthonic ratio.

The delta-front deposits accumulated as part of a clastic wedge which was built out into eastern Alabama. Sediment source was the Appalachian Mountains and the Piedmont Plateau. A reduction in supply of detritus allowed transgression which reworked the delta-front sediments and resulted in the development of marginal-shelf sands and/or offshore clays. Sand transported from the east by longshore currents became concentrated as barrier bars wherever waves, tidal currents, and longshore currents attained a balance with available sand.

The filled channels, large-scale crossbedding, and lag concentrates suggest that some of these clean sandstone bodies of the barrier-bar facies may be complex shoal deposits or inlet channel fillings resulting from destruction and reworking of barrier islands.

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