MIDDLE TO UPPER DEVONIAN BASIN-TO-SHELF CORRELATIONS ACROSS THE PROTO-ANTLER FOREBULGE, CENTRAL NEVADA

The position of a Late Devonian proto-Antler forebulge that resulted from convergence of the west side of the North American continent with the Pacific plate now lies between the Northern Antelope Range (NAR) and Devils Gate. Our study of the NAR sequence permits detailed correlations between oceanic and continental-slope rocks to the west and coeval carbonate-platform rocks to the east. In late Middle Devonian (late Givetian) time, the lower tongue of the Fenstermaker Wash Formation in the NAR formed the raised outer margin of the Fox Mountain Formation carbonate platform to the east. In latest Middle Devonian time, overlying argillaceous rocks in the NAR document a connection between the moderately shallow, fish-bearing Red Hill beds of the northern Simpson Park Range and the peritidal to supratidal yellow-slope-forming unit of the Devils Gate Limestone and Guilmette Formation to the east. Beginning in earliest Late Devonian (early Frasnian) time and continuing through late Late Devonian (Famennian) time, the rising, eastward-migrating forebulge separated the continental-rise to deep-slope Woodruff basin on the west from the backbulge Pilot basin and enclosing Devils Gate and Guilmette carbonate-platform rocks to the east. Two local connections between these basins through the NAR are recorded by deeper water siltstone beds at Devils Gate. The earlier connection is the lower tongue of the Woodruff Formation, which forms the basal unit of the upper member of the type Devils Gate, and the later one is the overlying, thin lower member of the Pilot Shale. One remaining problem is the older Middle Devonian (Eifelian) sequence of the southern Fish Creek Range. Displaced Eifelian coral patch reefs there seem to fit an original position west of coeval shallow carbonate rocks in the NAR. Hence, they may represent either backbulge slope deposits on the initial forebulge or part of an overthrust nappe.