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GATECLIFF FORMATION

Type Section Information

The Gatecliff Formation was named for exposures at Gatecliff, about 1 mile from the mouth of Mill Canyon in the northern Toquima Range (Kay, 1960). The best exposures of the formation are about 1 mile west of the mouth of Mill Canyon (McKee, 1976b).

Geologic Age

The Gatecliff is Early Silurian (Llandoverian) in age based on poorly preserved coralline and graptolite faunas and pelmatazoans (Kay and Crawford, 1964: McKee, 1976b). The black cherts present in the upper portion of the Gatecliff are equivalent to the basal black cherts in the Roberts Mountains Formation (McKee, 1976b) and the underlying sandy dolomites may correlate with the Diana Formation and the upper portion of the Hanson Creek Formation (McKee, 1976b).

In the Toquima Range, the Gatecliff commonly rests on the Caesar Canyon Limestone (upper Copenhagen Formation) with apparent conformity, however, fossil evidence suggest a considerable hiatus between the two formations (McKee, 1976b). The upper contact is conformable with the overlying Masket Shale.

General Lithology

The Gatecliff consists of a basal, light gray, medium to thin-bedded dolomite about 60 feet thick; a middle, massive, sandy, cross-bedded to finely laminated, dolomite to dolomitic quartzite 25 to 50 feet thick; and an upper thin-bedded light gray dolomite irregularly replaced with black thin-bedded cliff-forming chert up to 70 feet in thickness (Kay and Crawford, 1964; McKee, 1976b). All three members vary in thickness and are not present in all exposures.

Kay and Crawford (1964) also reported the Gatecliff Formation along Pablo Canyon in the southern Toiyabe Range within rocks mapped as the Ordovician Palmetto Shale by Ferguson and Cathcart (1954). The Gatecliff is composed of 70 feet of massive laminated dolomite overlain by 90 feet of laminated black dolomite and carbonaceous argillite which contains abundant graptolites.

Average Thickness

The Gatecliff Formation is about 200 feet thick in the northern Toquima Range, and 160 feet in the southern Toiyabe Range (Kay and Crawford, 1964). Areal Distribution

The Gatecliff is limited to a few small exposures in the northern Toquima and southern Toiyabe Ranges.

Depositional Setting

The details of sedimentation are poorly understood for this limited and poorly exposed transitional facies. Poorly preserved corals, brachiopods, crinoid columnals, and abundant pelmatazoan debris have been reported within various members of the formation suggesting shallow marine deposition (McKee, 1976b; Kleinhampl and Ziony, 1985). The Gatecliff Formation probably represents quiet and relatively deep water outer shelf to upper slope deposition similar to the Roberts Mountains and Masket Formations (Matti and McKee, 1977).


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