AN  INTEGRATED PETROLEUM  EVALUATION OF NORTHEASTERN  NEVADA


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SHINGLE PASS TUFF

Type Section Information

The Shingle Pass Tuff has a type section at Shingle Springs, in Sect. 8, T. 8 N., R. 63 E., in the southern Egan Range (Cook, 1965).

Geologic Age

The Shingle Pass Tuff is often found overlying the Needles Range Formation, and has been dated at 24.5 +/- 1.0 Ma (Cook, 1965; Ekren and others, 1977). It straddles the Oligocene/Miocene boundary and is here considered the oldest Miocene ignimbrite exposed in the area of study.

General Lithology

At its type locality, the Shingle Pass Tuff is a pale purple, moderately to strongly welded, hard and resistant vitric-crystal tuff, that grades down into a purple-red, highly welded, crumbly weathering tuff, with a basal grayish red tuff that shows subparallel grooves on weathered surfaces (Cook, 1965). In some sections the basal portion of the Shingle Pass is an orange to brown-black glass. Phenocrysts form about 10 to 25 percent of the ignimbrite and are composed of 58 percent sanidine, 29 percent plagioclase, 11 percent quartz, and about 2 percent mafics (Cook, 1965).

As many as four separate cooling units are present in the Shingle Pass in the southern Pancake and Hot Creek Ranges. In the Pancake Range, two or three cooling units are present with an upper unit of densely welded, devitrified, reddish or gray tuff with about 12 to 32 percent phenocrysts. The phenocrysts are composed of about 25 to 47 percent alkali feldspar, 25 to 40 percent potassium feldspar, 10 to 15 percent quartz, 4 to 7 percent biotite, 1 to 2 percent hornblende, and trace clinopyroxene (Ekren and others, 1972). The lower unit is a greenish-gray and black, partially welded and vitric tuff with abundant pumice lapilli up to 3 inches across (Ekren and others, 1972; Quinlivan and others, 1974). The lower unit has about 20 percent phenocrysts with 40 percent quartz, 27 percent alkali feldspar, 27 percent potassium feldspar, 4 percent biotite, and 1 percent hornblende.

In the Hot Creek Range, Quinlivan and Rogers (1974) report one to four cooling units in the Shingle Pass Tuff, which are mainly densely welded rhyolitic vitric to devitrified tuff. These tuffs are dark red to purple and locally contain pumice lapilli and blocks in some units, and abundant shards in others. Nearly all the cooling units contain less than 10 percent phenocrysts.

In the northern Reveille Range, the Shingle Pass is composed of three cooling units (Ekren, Rogers, and Dixon, 1973). The lower unit is up to 600 feet of densely welded, brick red to red-gray, ash-flow tuff with abundant lithophyse, and an upper vapor phase zone and lower 30 to 70 foot thick black vitrophere underlain by greenish to purple, nonwelded to partially welded tuff. The middle unit is a simple cooling unit of up to 150 feet of devitrified, brick-red tuff with abundant flattened pumice lapilli, and a basal vitrophere underlain with a thin zone of vitric bedded tuff at the base. The upper unit in the Shingle Pass is a simple cooling unit of densely welded, hackly-weathering tuff with less pumice than the middle unit, common lithophyse and a well-developed vapor-phase top (Ekren, Rogers, and Dixon, 1973).

In the central and eastern portion of Lincoln County the Shingle Pass is a reddish-gray to brick red weathering tuff that is commonly composed of two or three cooling units which are nearly identical in hand sample (Ekren and others, 1977). It is typically recognized by its dense welding and low total quartz and phenocryst content. Phenocrysts form between 8 and 20 percent of the Shingle Pass Tuff in the Wilson Creek, Quinn Canyon, and Seaman Ranges, and on average are composed of about 75 to 85 percent alkali and potassium feldspar in ratios of from 1:4 to 1:6, 0 to 5 percent quartz, 0 to 2 percent hornblende and 0 to 2 percent clinopyroxene (Ekren and others, 1977).

Average Thickness

Cook (1965) reported an average thickness of 130 feet for the Shingle Pass based upon 13 measured sections. It is 125 feet thick at its type section in the southern Egan Range and 160 feet along the western flank of the Egan Range, and is 75 feet thick in the northern Seaman Range according to Cook (1965). Scott (1965) measured 1,600 and 500-foot thicknesses near Currant in the Grant Range. Hose and Blake (1976) suggest that it is not more than 75 feet thick in any section exposed in White Pine County. Scott (1969) reports 350 to 750 feet and Kleinhampl and Ziony (1985) report 750 to 950 feet of Shingle Pass in the southern Pancake Range, and about 160 feet are present in the Portuguese Mountain area of the Pancake Range (Quinlivan and others, 1974). The Shingle Pass is up to 600 feet thick in the Hot Creek Range and 800 feet in the Reveille Range (Ekren and others, 1973; Quinlivan and Rogers, 1974).

Areal Distribution

The Shingle Pass Tuff is present in the Pancake, Reveille, Hot Creek, Egan, Grant, Quinn Canyon, Golden Gate, Seaman, and Wilson Creek Ranges.


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