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Correlation Trends in Thin-Bedded Turbidites, Jackfork Sandstone, DeGray Lake, Arkansas

DE VRIES, M. B., and A. H. BOUMA, Louisiana State University, Baton Rouge, LA

Detailed sandstone and shale-bed thickness measurements at the two walls of the DeGray Lake spillway and one on the outcrop at the intake for the dam reveal that these Jackfork sandstones consist of turbidite, slurry, and debris-flow deposits. These deposits are situated between massive channel-fill deposits. The term "thin-bedded" refers to all bedded and recognizable turbidite layers occurring in levee, overbank, bedded fill in a dying channelway and depositional lobe deposits. The measured sections are divided into units with similar lithofacies and can be correlated across the 200-ft distance between spillway walls. Units in the upper part of the spillway can be correlated with the intake section 5500 ft away.

A bed-to-bed correlation can be accomplished between the east and west walls of the spillway by plotting successive bed thickness values on a vertical scale. The result looks much like a well log. Recognition of thinning- or thickening-upward cycles within each unit eases bed-to-bed correlation. This detailed correlation increases the resolution of the quantitative understanding of these type deposits.

Units of similar lithofacies show similar trends in unit thickness change and sandstone/shale ratio change. Units identified as overbank deposits showed the lowest change in correlation between measured sections. Lobe deposits have a unit-to-unit thickness compensating nature and are lenticular in geometry. Units showing the greatest change contain large-scale cross-beds and scouring, suggesting that these are small, perhaps meandering channel deposits.

 

AAPG Search and Discovery Article #91006 © 1991 GCAGS and GC-SEPM Meeting, Houston, Texas, October 16-18, 1991 (2009)