A regional marker unit within the Upper Paleozoic Bird Spring Formation, southern Nevada: Evidence for a slope facies
- Geological Survey, Denver, CO (United States)
A distinctive unit within the latest Mississippian to Permian Bird Spring Formation of southern Nevada is interpreted as a slope facies between the Lower Permian eastern shelf margin and interior sea. Members of the Bird Spring are difficult to define and correlate across southern Nevada because of the formation's great thickness, lithologic heterogeneity, and structural complexity. The newly identified unit, about 35 to 130 m thick and 1,000 m above the base of the Bird Spring, is a prominent marker unit that will facilitate regional stratigraphic and structural studies in southern Nevada. Outcrops of the marker unit can be traced for 100 km from the north, in the southern Delamar Mountains, Lincoln County, to the south in the northern Spring Mountains, Clark County, where it is offset approximately 45 km along the right-lateral Las Vegas Valley shear zone. The marker unit consists of laminated micritic limestone and chert interbedded with calcareous siltstone. The limestone is spiculitic and organic rich, and radiolarians were identified in some samples. Sedimentary structures include convoluted bedding and minor slumps, and at the top of the marker unit in the southern Arrow Canyon Range, submarine debris flows consist of cobble-size clasts of shelf-facies rocks in a silty, micritic limestone matrix. The spiculitic limestone, radiolarians, soft-sediment deformation, and debris flows suggest rapid deposition in deep water, characteristic of a slope depositional environment. The marker unit is late Wolfcampian in age.
- OSTI ID:
- 5129467
- Report Number(s):
- CONF-9305259--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 25:5; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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