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Vinini Formation
The Vinini Formation is a marine, deep-water, sedimentary deposit of Ordovician to Early Silurian age in Nevada, U.S.A. It is notable for its highly varied, mainly siliceous composition, its mineral deposits, and controversies surrounding both its depositional environment and structural history. The formation was named by Merriam and Anderson (1942) for an occurrence along Vinini Creek in the Roberts Mountains of central Nevada and that name is now used extensively in the State.
== Stratigraphic relations ==
Although the name Vinini is used extensively, the Palmetto Formation in southern Nevada (Albers and Stewart, 1972) is of the same age and lithic composition and merits the name Vinini. Originally the Vinini was considered to be wholly of Ordovician age, but the unit designated as Vinini on many published maps includes, at the top, a massive chert unit, the Cherry Spring chert, now known to be of Early Silurian age (Noble et al., 1997). The formation is considered to have been deposited in relatively deep water, outboard of the contemporaneous carbonate bank to the east, because of its generally dark gray color and the near absence of a shelly fauna (Roberts et al., 1958). The identity of strata underlying the Vinini over most of its range is uncertain due to the prevalence of faults, but the equivalent Palmetto Formation is known to be underlain depositionally by Upper Cambrian limestone deposits (Ketner, 1998). The Vinini is overlain depositionally by Middle Silurian sandy strata. To the west, the Vinini grades laterally into the Valmy Formation, a somewhat similar unit, with the same age range (Ketner, 2013). Together, the Vinini and Valmi formations constitute a principal part of lower Paleozoic deep-water units in Nevada known collectively as the "western assemblage" (Roberts et al., 1958). To the east, separated by faults, is a bank of mainly shallow-water shelf carbonate rocks ranging in age from Cambrian to Devonian—the "eastern assemblage" (Roberts et al., 1958). Throughout its extent, the Vinini has been divided into two (Finney and Perry, 1991), or three (Ketner, 1991) subunits. Regardless of how it has been subdivided, the lower part of the formation, wholly of Ordovician age, is extremely heterogeneous and coarsely granular, and the upper part, of Ordovician and Early Silurian ages, is more uniform and fine-grained, reflecting very different conditions of deposition. The Vinini has remarkably similar lithic and temporal correlatives, with other names, in Idaho (Dover, 1980), Arkansas (Ketner, 1980), Oklahoma (Ketner, 1980), Texas, (King, 1937; Noble, 1994), and Mexico (Ketner and Noll, 1987).
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