Evidence for local volcanism in Mississippian continental-margin strata in southwestern Nevada, Nevada test site
- Univ. of Nevada, Reno, NV (United States)
A thick section of siltstone, shale, and quartzite at NTS records continental-margin sedimentation coeval with Antler foreland-basin clastic fill to the west. These strata are Osagean and Meramecian (palynology) through upper Chesterian and Morrowan (ammonoids) in age, and appear to contain no sediment of sand or coarser size derived from the Antler allochthon. These rocks have been referred to by previous workers as part of the Eleana Fm., but the authors regard them as more properly equivalent to the Chainman Shale. Their composition has important tectonic implications. Preliminary data suggest that swelling clays in core drilled in these strata may originally have been wind-blown bentonitic ash. A continuously cored section at the north end of Syncline Ridge (hole UE17e) contains abundant swelling clays, as well as dolomite, anhydrite, and other evaporitic minerals. This mineral assemblage, combined with a paucity of fauna and bioturbation, indicates restricted circulation. Rare quartzite intervals near the top of the section are clean, current-reworked arenites with sedimentary structures indicating shallow marine, possibly intertidal conditions. This association suggests a restricted, shallowing-upward marine basin, probably anoxic at times. The clay content indicates a significant sediment input from air-fall ash. Present plate-reconstructions place southern Nevada near 2--8[degree] N latitude, with trade winds prevailing from the paleonortheast (near present north). Volcanic detritus in Late Mississippian sediments of southern Nevada is evidence that volcanism in the Antler orogenic terrane west of the foreland basin is recorded in shelf sediments east of the foreland.
- OSTI ID:
- 5097413
- 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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