Description
A rare, complete and well-exposed section of the Cambrian Bonanza King Formation occurs at the Desert Range of northwestern Clark County, Nevada. The section was measured, described, and sampled for fossils and lithologies. Measurements were taken following the metric system, but are presented in both metric and British units. Carbonate lithologies dominate the 1395 meter (4577 foot) thick sequence, with varieties of limestone accounting for 64% of the strata while dolostone comprises 34% of the section. The remaining 2% of studied strata are siltstone and shale. Sporadic chert-bearing intervals and rare silty horizons facilitate correlation to other published sections. Based on gross differences in weathering and lithology, 11 units ("members") are recognized within the formation. These, in turn, are comprised of 184 subunits. Analysis of lithologic, paleontologic, and primary structural features indicates that this sequence of rock was deposited in supratidal, intertidal, and shallow subtidal marine waters. These environments were behind and within a carbonate bank complex, on the extremely low gradient southwestern edge of the Cordilleran miogeocline. Trilobites and brachiopods are locally abundant, and include 56 species of trilobites, representing 36 genera, and five species (four genera) of inarticulate brachiopods. In addition, a possible articulate brachiopod, problematical fossils, and fragments of crinoid or eocrinoid occur. Thirty fossil collections were made for this study and provide valuable biostratigraphic control. Collections bracketing the base of the formation indicate a middle Middle Cambrian Glossopleura Zone Age for that boundary. Trilobites and brachiopods of the Bathyuriscus-Elrathina Zone occur at the base of the Banded Mountain Member; in unit Cbk 5. Abundant trilobites and brachiopods near the top of the formation represent four early Late Cambrian zones and allow placement of the top of the formation within the Dicanthopyge Zone.
