AGE, STRATIGRAPHY, DEPOSITIONAL ENVIRONMENT AND VERTEBRATE ICHNOLOGY OF THE MIOCENE-PLIOCENE COPPER CANYON FORMATION, DEATH VALLEY, CALIFORNIA

The Copper Canyon Formation (CCF), a fluivial-lacustrine deposit exposed within the Black Mountains of Death Valley National Park, has only previously been broadly included in regional tectonic and depositional analyses. The CCF is significant because it preserves numerous shoreline-playa features including highly abundant and diverse mammal and bird tracks. The CCF represents a basin fill sequence consisting of 1800 meters of fanglomerates, fluvial-lacustrine sediments, basalt flows, and tuffs. A measured type section along with x-ray diffraction and isotopic analysis, shows an evolution of the ancient Copper Canyon Lake from an under-filled (evaporitic facies) to a balanced-filled (fluctuating profundal) lake. Tufa mounds reflecting active spring deposition are numerous within the upper two-thirds of the formation. Stable isotope data (δ¹⁸O ranges from -10.15 to -10.96‰ PDB) from the tufa mounds indicate the lake was fed by relatively fresh groundwater. Tracing beds laterally demonstrates that the tufa mounds formed around the margin of the ancient Copper Canyon Lake. Vertebrate track diversity and abundance is tied to the appearance and distribution of the tufa mounds. The spring water allowed a more abundant and diverse fauna/flora population to thrive. Radiometric age dating from three basalt flows within the CCF and magnetostratigraphic analysis of interbedded sedimentary rocks constrain deposition between ~5 and 3 Ma. Further stratigraphic works limits the upper CCF fluvial-lacustrine deposition in Copper Canyon to between 4.73 and about 3.2 Ma, which is significant because it constrains the timing of the most prevalent animal activity. Age, measurement of a type section, sedimentary petrology along with review of shoreline features and fauna/flora, establishes timing and interpretation of the depositional environment of the ancient Copper Canyon Lake. In addition, a better understanding of the distribution of the animal tracks within the CCF is understood. Temporal placement of the CCF within the other Cenozoic basin fill deposits of Death Valley is also now possible.