--> ABSTRACT: Sequence Stratigraphy and Reservoir Characteristics of the Codell Sandstone, NE Colorado, by Donna C. Caraway, Frank G. Ethridge; #91002 (1990).

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ABSTRACT: Sequence Stratigraphy and Reservoir Characteristics of the Codell Sandstone, NE Colorado

Donna C. Caraway, Frank G. Ethridge

Deposition of the Turonian Codell Sandstone member of the Carlile Shale in northeastern Colorado occurred along the western margin of the Cretaceous Epeiric Seaway. Abrupt and irregular facies relationships, gross sheetlike geometry with internal linear thickness trends, ichnofacies, and hiatal surfaces suggest an inner shelf depositional origin. Because of stratigraphic positioning, the Codell sandstone is thought to represent the shelf component of a retrogradational transgressive system tract that developed during the Niobrara transgression. Storm processes operating along the inner shelf margin produced amalgamated sheet deposits of mid-late Turonian age. Deepening of the seaway restricted sediment influx to the shelf, cannibalizing previously deposited shelf sediment . This change is marked by a marine flooding surface that separates inner shelf sediments from a winnowed condensed section above. The silica or calcite-cemented uppermost bed of the Codell Sandstone represents the winnowed cap of a condensed section produced by this starved basin condition. Further deepening of the seaway placed the shelf floor beyond the reach of episodic storm processes; a condition marked by an abrupt lithologic transition into marine limestone deposits. This contact is the basinal sequence boundary.

Codell Sandstone production is by secondary porosity. Better production rates correspond to areas of slightly thicker linear sandstone trends in the vicinity of fault systems, indicating a combined stratigraphic/structural trap.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990