Paper No. 10
Presentation Time: 1:30 PM-5:30 PM
DEPOSITIONAL ENVIRONMENT, TECTONICS, AND ANIMAL TRACK DISTRIBUTION OF THE NEOGENE FLUVIAL-LACUSTRINE COPPER CANYON UNIT, DEATH VALLEY NATIONAL PARK
Extremely well preserved mammal and bird tracks occur throughout the fluvial-lacustrine deposits of the Copper Canyon Unit (CCU). The CCU consists of carbonates, evaporates, shales, claystones, siltstones, sandstones, conglomerates and basalt flows exposed within Copper and Coffin Canyons, Black Mountains, Death Valley National Park. The sequence includes over 3000 meters of basin sediments deposited in a tectonic setting involving large magnitude extension, normal faulting, basin formation, deposition, and subsequent uplift. The CCU can be divided into a fanglomerate, fluvial-lacustrine and basalt members. The fluvial-lacustrine member can be further divided into: evaporite facies; bioclastic carbonate facies consisting of ostracod and gastropod packstone within a calcitic micrite; conglomerate/sandstone facies; and carbonate mudstone facies that contain animal tracks, ripples, raindrops, mudcracks and other shoreline features. The lower sub-unit deposits are dominated by claystones and debris flows reflecting initial fluvial-lacustrine deposits. Up section within the lower middle sub-unit, the claystones are replaced by evaporite facies, reflecting hypersaline standing water conditions and evaporation. Further up section within the middle sub-unit the evaporite facies become rare and carbonate mudstone facies are prominent. Within the upper sub-unit bioclastic carbonate facies are prominent and beds of limestone with tufa mounds suggest spring outlets into a freshwater lake. Track distribution appears to be almost exclusive of the middle sub-unit. New age constraints confirm that the Copper Canyon Unit was deposited approximately between 6 to 3Ma, with track bearing units deposited between 5 to 4Ma. Lithology changes, along with lateral interfingering of fanglomerates within the fluvial-lacustrine member, may reflect lake system changes due to transgressions/regressions, subsidence rates, precipitation/evaporation ratio and/or regional climate changes. Additional mapping, rock analysis and track distribution models will help reconstruct the CCU depositional environment, aiding in the reconstruction of Death Valley's environment that, approximately 5 million years ago, supported an animal fauna of at least thirty-six species of cat, camel, horse, mastadon and birds.