AN INTEGRATED PETROLEUM EVALUATION OF NORTHEASTERN NEVADA
FISH HAVEN DOLOMITE
Type Section Information
The Fish Haven Dolomite was named by Richardson (1913) for exposures along Fish Haven Creek, in the Bear River Range, in the Randolph Quadrangle some two miles north of the Utah-Idaho state Line.
As described in detail under the Hanson Creek Formation, the Fish Haven is equivalent to both the Ely Springs and Hanson Creek Dolomites. The Fish Haven gradationally overlies the Eureka Quartzite and is in turn gradationally overlain by the Laketown Dolomite, from which it is difficult to distinguish.
Several geologists have mapped the Fish Haven and overlying Laketown as a single unit, both because of their gradational lithologic nature making contact placement a matter of interpretation, and because the boundary between the Upper Ordovician and Silurian lies within the Fish Haven-Laketown Dolomite sequence. Placement of the contact between the Fish Haven Dolomite and Laketown Dolomite determines whether the Fish Haven is all Ordovician or partly Ordovician and partly lower Silurian in age.
At the type section the Fish Haven is described as a "fine textured, medium-bedded, dark gray to blue-black, locally cherty dolomite about 500 feet thick and containing a Richmond Fauna" (Richardson, 1913).
Detailed descriptions of the Fish Haven Dolomites are rare, with most descriptions being quite brief, or an aggregate of units representing Fish Haven plus the Laketown Dolomite (Woodward, 1964; Hose and Blake, 1976; Moores and others, 1968; Whitebread, 1969). In general, the unit is described as a light to dark gray, medium-bedded, fine to coarse-grained dolomite with nodular chert concentrated in the lower portion of the dolomite. The dolomite is laminated to thickly bedded, with beds commonly 3 to 10 feet in thickness, and often unconformably underlies the Laketown Dolomite.
In the Kingsley Range, Buckley (1967) mapped a unit he originally assigned to the Hanson Creek Formation which Coats (1985) has reassigned to the Fish Haven Dolomite. It consists of dark-brown to medium-gray, massive and non-fossiliferous dolomite which gradationally overlies the Eureka Quartzite.
In the Goshute and Toana Ranges, the Fish Haven is medium- to dark-gray, very fine-grained to sublithographic, massive dolomite with thin, light gray dolomite streaks and brachiopod-crinoid hash beds (Coats, 1985). In the Pequop Mountains and Wood Hills, the Fish Haven is medium-bedded, alternating light and dark gray dolomite with a basal 80 foot thick section of dark gray dolomite and black chert (Thorman, 1970).
Dechert (1967) mapped the Fish Haven-Laketown Dolomites as one sequence in the Schell Creek Range. This sequence is also apparently structurally complicated by at least some duplication of section since thicknesses for the combined unit greatly exceed those in surrounding areas (Dechert, 1967). The basal portion of the section is composed of about 270 feet of dark brownish gray to black, massive dolomite which is here considered the Fish Haven portion of the section. In the northern Schell Creek Range, Young (1960) described the Fish Haven as a highly faulted sequence of medium to dark-gray, well-bedded dolomite which is both cherty and fossiliferous in the upper portion of the unit.
In the western portion of the Red Hills, west of the Kern Mountains, the Fish Haven Dolomite is tectonically thinned and brecciated. It is composed of dark gray to black, fine-grained dolomite with a sooty weathered surface. The dolomite contains poorly preserved corals, gastropods, and brachiopods (Bartel, 1968).
In the southern Deep Creek Range, the Fish Haven is composed of bluish-black crystalline dolomite with bleached zones parallel to bedding (Nelson, 1959). In the Pilot Range, the Fish Haven is massive, medium-gray to black, black weathering, medium to fine-grained, calcareous dolomite. Blue (1960) described an upper unit of 100 feet of thick-bedded, cherty, medium and dark-gray, arenaceous dolomite underlain by about 275 feet of massive, dark gray dolomite, with chert nodules and stringers in both units. O'Neill (1968), described three units in the Fish Haven in the southern Pilot Range. The basal member is 195 feet of black to gray, thin-bedded, fine to medium-grained, calcareous dolomite with chert stringers and nodules. The middle member is a 135 feet of gray to brown, argillaceous, thin-bedded calcareous dolomite. The upper member of the Fish Haven is 120 feet of platy, gray to black, red-orange weathering, fine to medium-grained, dolomitic limestone which is locally cherty.
Thicknesses reported in the Fish Haven include 200 to 350 feet in the central Egan Range (Woodward, 1964; Hose and Blake, 1976), 618 feet near Heusser Mountain in the northern Egan Range (Young, 1960), 510 feet near Currant (Wire, 1961), and 570 feet in the Pequop Mountains (Thorman, 1970). In the Snake Range, the Laketown and Fish Haven have been lumped together for a thickness of about 1500 feet (Whitebread, 1969) with 250 feet estimated for the Fish Haven interval by Drewes (1958). In the Schell Creek Range the Fish Haven-Laketown interval is about 2,150 feet thick with about 270 feet representing the Fish Haven interval (Dechert, 1967), about 0 to 60 feet in the western part of the Red Hills (Bartel, 1968), 150 to 200 feet in the southern Deep Creek Range (Nelson, 1959), 200 feet in a faulted section in the Kingsley Range (Buckley, 1967; Coats, 1985), 320 feet thick in the Goshute Range (Coats, 1985), 375 feet in the northern Toana Range and 700 feet in the southern Toana Range (Coats, 1985), 370 to 440 feet in the Pilot Range (Blue, 1960; O'Neill, 1968), and 570 feet in the Pequop Mountains (Thorman, 1970).
The Fish Haven Dolomite has been described in the southern Egan and Schell Creek, Snake, Deep Creek, Kingsley, Silver Island and Pilot Ranges, the Pequop, Goshute and Toana Ranges, and the Wood Hills and Red Hills.
The Fish Haven Dolomite, like the Ely Springs Dolomite, represents subtidal to intertidal, shallow restricted shelf carbonates, deposited in water depths of 100 feet or less in lagoonal and shallow shoal settings (Chamberlin, 1975; Ross, 1977).