AN INTEGRATED PETROLEUM EVALUATION OF NORTHEASTERN NEVADA

ANTELOPE RANGE FORMATION

Type Section Information

The type section for the Antelope Range Formation is in Sec. 22, T. 16 N., R. 51 E., in the northern Antelope Range (Hose and others, 1982). The upper portion of the formation is either eroded away or thrusted, and is often exceedingly poorly exposed. It is questionable whether this formation has any significance since it is so poorly defined and structurally complicated. It may represent dismembered portions of other units. It is essentially lithologically indistinguishable from the Webb Formation in most exposures at the type area, and may well be the Webb. We have mapped the Antelope Range and Webb Formations together.

Geologic Age

The Antelope Range Formation unconformably overlaps the Kinkead Spring Limestone in the Antelope Range. It rests on the Devils Gate Limestone or the Pilot Formation in the southern Fish Creek Range, where it is either overlain unconformably by Cretaceous Newark Canyon Formation or overthrust by beds of Mississippian (Osagean age) which are in turn overthrust by Late Devonian beds of the Woodruff Formation (Hose and others, 1983).

Devonian through Mississippian fossils have been recovered from the formation and the age should be considered cryptic. The formation is considered Osagean or younger Mississippian in age.

General Lithology

Sequence has been poorly determined for the Antelope Range Formation. The base of the formation is marked by as much as 100 feet of yellowish‑orange to light‑brown weathering, fine to coarse‑grained, angular to well‑rounded sandstone (Hose, 1983). Quartz and feldspar commonly compose more than 50 percent of the sands, with 5 to 35 percent chert, and 20 to 40 percent lithic clasts which are dominantly grey shale. Pebbly zones are also locally present within the sands. Grey, silty shale and platy siltstone, and tan limestone beds are present above the sandstone (Hose, 1983). Poorly sorted pebble, cobble and boulder conglomerate, with Devonian carbonate and Ordovician Valmy quartzite clasts, is present locally in the Fish Creek Range and intertoungues with the silty shales (Hose, 1983).

Hose (1983) suggests that the basal contact of the Antelope Range Formation is an unconformity, but that it may be a low‑angle fault since the underlying Kinkead Spring Limestone appears to be structurally thinned (Hose, 1983). The Antelope Range Formation was considered to be an autochthonous lower plate unit by Hose (1983). Our observations in the Cockalorum Wash Quadrangle suggest that the formation may well be allochthonous, and is probably correlative with the Webb Formation.

Average Thickness

The Antelope Range Formation is about 795 feet at the type section (Hose and others, 1982).

Areal Distribution

The Antelope Range Formation is exposed within the Northern Antelope and southern Fish Creek Ranges.

Depositional Setting

An estuarine or deltaic environment has been suggested by Hose and others (1982) based upon plant remains and nearshore marine and nonmarine spores recovered from the Antelope Range Formation. They feel an environment where marine and nonmarine waters could mix is the most plausible depositional setting.