THREE’S A CHARM: REASSESSING NEOPROTEROZOIC GLACIATIONS
IN DEATH VALLEY, CA*
R. Petterson
Neoproterozoic stratigraphy records shifts in climate, impacts and rifting associated with the break up of the Rodina super continent. It provides a record of the environmental conditions that immediately preceded the Cambrian explosion and the advance of multi-cellular life. Understanding the early history of life on Earth has implications for evolution, biology and the search for life elsewhere. Many unresolved problems currently prohibit understanding of the Neoproterozoic history of southwest Laurentia. These include 1) the timing of rifting and glaciations; 2) regional stratigraphic correlations; 3) uncertainty of depositional environments. Critical to addressing these issues is unraveling the stratigraphy of the Panamint Mountains, which is complicated by several deformation episodes, including Mesozoic compression, Tertiary extension, and poor age constraints due to a lack of dateable volcanics and a paucity of fossils. Key areas of the Panamints were mapped at a variety of scales, and representative stratigraphic sections were measured. Based on this mapping and previously unpublished data, new interpretations and correlations for the stratigraphic record of southwest Laurentia are presented.
On the basis of the structures and stratigraphic relations identified in this study, the Sentinel Peak Dolostone of the Noonday Fm. is interpreted as being the cap carbonate of the Wildrose glaciation. Assuming that the Redlands member of the Noonday and the Sourdough Limestone of the Kingston Peak Fm. are cap carbonates as well, we conclude that no less than three glacial intervals are recorded in the Neoproterozoic stratigraphy of the Panamint Mountains including the Surprise/Sourdough, the Wildrose/Sentinel Peak, and the Redlands Cap (which lacks an associated diamictite). Previous studies have suggested that the Redlands member of the Noonday Fm. is the cap carbonate to the glacial interval represented by the Wildrose diamictite of the Kingston Peak Formation. However, current theories to explain the formation of “cap carbonates” are inconsistent with the existence of up to 500 meters of clastic sedimentation between the Sentinel Peak (which overlies the Wildrose) and the Redlands member that is present in the Panamints. Our discovery of possible Actinian burrows (tentatively identified by A. Seilacher) in the lower Noonday provides a potential correlation with glacial successions elsewhere. It also makes the correlation of units across Death Valley substantially more complicated and emphasizes the need for more detailed stratigraphic studies and the refining of techniques for extracting reliable ages from sandstones.
If you would like more information concerning this research, please contact Ryan Petterson ( ryan@gps.caltech.edu ).
* Please note that this work is in progress, the conclusions stated here are not necessarily our final conclusions.