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Depositional Analysis of Hill Sand of Rodessa Formation (Lower Cretaceous) in North Shongaloo-Red Rock Field, Webster Parish, Louisiana

John A. Adamick, Austin A. Sartin

Hill sand is an informal subdivision of the Lower Cretaceous Rodessa Formation and is a common hydrocarbon reservoir in northeastern Texas, northern Louisiana, and southern Arkansas. The Hill sand is lithologically variable within the study area and consists of conglomerate, fine-grained sandstone, siltstone, mottled red-green clay-stone, black shale, and limestone.

Five depositional Previous HitenvironmentsNext Hit were interpreted for lithofacies present in Hill sand cores from the North Shongaloo-Red Rock field. These include facies A, fluvial point bar; facies B, crevasse system; facies C, interdistributary bay; facies D, swamp; and facies E, carbonate interdistributary bay. Fluvial point bar and crevasse deposits commonly form hydrocarbon reservoirs in the field.

On a regional scale, depositional Previous HitenvironmentsNext Hit observed in the Hill sand include several fluvial deposystems trending northeast-southwest through Webster Parish. These deposystems terminate into Previous HitdeltaicNext Hit distributary mouth bars along a northwest-southeast-trending coastline. Areas west of the coastline were occupied by shallow marine Previous HitenvironmentsNext Hit. Interchannel areas east of the coastline were occupied by interdistributary bay, lake, and crevasse Previous HitenvironmentsNext Hit in lower Previous HitdeltaicNext Hit areas, and by lake, swamp, and crevasse Previous HitenvironmentsNext Hit in upper Previous HitdeltaicNext Hit areas.

Lowermost deposits of the Hill sand throughout the region are interpreted to consist of shallow marine Previous HitenvironmentsNext Hit. These marine deposits were overlain by thick, predominantly nonmarine sediments. Near the end of Hill sand deposition, the entire region was covered by very shallow marine Previous HitenvironmentsTop, prior to deposition of the overlying First Lower Anhydrite Stringer.

AAPG Search and Discovery Article #91036©1988 GCAGS and SEPM Gulf Coast Section Meeting; New Orleans, Louisiana, 19-21 October 1988.