ABSTRACT

An extensive and thick carbonate platform complex, the Star Peak Group, is an important part of the Triassic section in north-central Nevada. Within this carbonate sequence are a few tens of meters of a distinctive and ubiquitous supratidal dolomite that forms the lower part of the Panther Canyon Member of the Augusta Mountain Formation. Owing to an unconformity beneath the Panther Canyon dolomite, in places it does not rest on carbonate rock, but where it does, as much as 75 meters of whatever limestone underlies it has been secondarily dolomitized. At China Mountain, where these rocks have been studied in the most detail, fossiliferous pelmicrites of the underlying Prida Formation have been altered to homogeneous saccharoidal dolomite. The regional coextensive occurrence of the Pant er Canyon dolomite and the altered rocks that underlie it indicates secondary dolomitization by solutions genetically associated with the overlying supratidal dolomite or the surface on which it was deposited. The secondarily dolomitized rocks have been previously treated by other workers as stratigraphic units rather than as an alteration body, and regional stratigraphic relations and nomenclature have been thereby obscured.