Sequence Stratigraphic Framework of the Devonian Guilmette Formation, Pahranagat Range, Southeast Nevada

ESTES, JANE E., Colorado School of Mines, Golden, CO

The Middle to Late (Givetian through Frasnian) Devonian Guilmette Formation is a proven hydrocarbon reservoir at Grant Canyon Field, Railroad Valley, Nevada, and consists of limestones and dolomites with interbedded sandstones deposited on a broad, stable, shallow platform. The Guilmette was described and interpreted in the Pahranagat Range in Lincoln County, southeastern Nevada, approximately 64 mi southeast of Grant Canyon.

The Guilmette Formation has been informally divided into three members based on lithology and depositional environment and separated by sharp contacts. The lower member consists of interbedded carbonate mudstones and wackestones deposited as subtidal to supratidal shallowing-upward cycles. Overall the lower member deepens upward to the overlying middle member, which consists of stromatoporoid bioherms interbedded with and draped by beds of related breccia. This member appears to represent a relative sea level highstand. The upper member consists of interbedded carbonate mudstones, wackestones, and quartz sandstones deposited as peritidal shallowing-upward cycles. This member was deposited after a relative

sea level fall. Thicknesses of each member are laterally consistent within fault blocks but are variable across faults.

Interpretation of these cycles in a sequence stratigraphic framework will provide a relative sea level curve for the Middle to Upper Devonian in this area and will permit delineation of potential hydrocarbon reservoirs in the Guilmette basin wide. Preliminary analysis indicates the middle member is the best potential reservoir, while the sandstones of the upper member provide additional potential reservoirs. Within this framework, analogs to Railroad Valley may be found.

AAPG Search and Discovery Article #91010©1991 AAPG Rocky Mountain Section Meeting, Billings, Montana, July 28-31, 1991 (2009)