TEPHROCHRONOLOGY OF MIOCENE TUFFS AND PALEOENVIRONMENTAL RECONSTRUCTION IN THE CHLORIDE HILLS, DEATH VALLEY NATIONAL PARK

Miocene tuff beds in the Death Valley and Amargosa Valley areas associated with the eruptions of the Southwestern Nevada Volcanic Field (SWNVF) have been studied individually, but have as yet to be correlated, although the possibility of their relationship has previously been suggested. Tuff beds have been described and dated in the Death Valley – Amargosa Valley area, namely in the Cottonwood Mountains, as well as in the Nevada National Security Site, previously known as the Nevada Test Site. The research area of this current study is within the eastern foothills of the Funeral Mountains within the Chloride Hills, which lay between these two previously studied regions, along the California – Nevada border. At this locality we find well exposed bedded fluvial and lacustrine sedimentary deposits with intercalated ash-fall tuff beds. The tuff beds are products of the Miocene volcanic eruptions associated with the SWNVF.

Deposits in the Chloride Hills are approximately 230 m thick and contain at least 10 tuff beds. Most of the tuff beds are more than 2 m thick and altered, containing biotite and other crystals. The tuff beds are interbedded with lacustrine mudstones and thin sandstones. These deposits are significant because they contain a record of dateable volcanic eruptions and record paleoenvironments in a spring fed lake system that preserved the remains of endemic fish, stromatolites, and plants.

The two goals of this project are to develop a detailed stratigraphic framework for this region by extending stratigraphy from the Cottonwood Mountains and Naevada National Security Site to sections in the Chloride Hills and to provide a stratigraphic context for fossil freshwater fish, including the only occurrence of fossil North American pupfish (Cyprinodon). Tephrochronology provides the unifying stratigraphic framework for the clastic lacustrine deposits and should allow correlation among similar deposits within the Death Valley and Amargosa Valley regions. Paleoenvironmental reconstruction shows the distribution of fish fossils and suggest a large lacustrine system during the Miocene.