Abstract We have used terrestrial cosmogenic nuclides (TCN) to establish the age of some of the most extensive Quaternary alluvial fans in Death Valley, California.
These intermediate-age alluvial fans are most extensive on the western side of the valley, where tectonic deformation is considerably less pronounced than on the eastern side of the valley.
Surface exposure dating using terrestrial cosmogenic nuclides (TCN) is an established and reliable method to date landforms and has been applied for dating glacial advances and retreats, erosion history, lava flows, meteorite impacts, fault scarps, and other geological events.
Within landslide studies, NGU applies TCN dating to determine ages of rockslide events and the age of sliding surfaces in order to determine past long-term displacement rates Earth is constantly bombarded with cosmic rays that are high-energy charged particles.
The basic principle is that these radionuclides are produced at a known rate, and also decay at a known rate.
Accordingly, by measuring the concentration of these cosmogenic nuclides in a rock sample, and accounting for the flux of the cosmic rays and the half-life of the nuclide, it is possible to estimate how long the sample has been exposed to cosmic rays.
New and previously published luminescence ages and soil development suggest that these landforms may have formed during marine isotope stage (MIS) 2 (~ 22–18 ka), but these younger ages may reflect elluviation of material into the bar deposit long after deposition, and hence the younger ages do not record the true antiquity of the landforms.
This disparity between dates determined by different dating methods and the large spread of TCN ages suggests that the cobbles and boulders have considerable inherited Be concentrations, suggesting that the clasts have been derived from older shorelines or associated landforms.
Results from other sliding surfaces are different and suggest accelerated displacement rates today.
This suggests that the predominantly bedrock hillslopes erode very slowly and sediment is transferred very gradually in most regions within Death Valley.
A Cl depth-profile age of 170 ka suggests alluvial deposition of unit Qaio (older phase of Qao) took place prior to the MIS 6 highstand of Lake Manly.
Knowing the absolute ages (or range in ages) of the intermediate-age (Qai) surfaces in Death Valley allows us to estimate the following rates of geologic processes: (1) a lateral slip rate of 5 millimeters per year for the northern Death Valley fault zone; (2) uplift of 50 meters in roughly the past 80,000 years for parts of the Mustard Canyon hills in east-central Death Valley; and (3) an estimated 10–40 m of dip-slip thrust movement on the Echo Canyon fault in Furnace Creek Canyon. Abstract Introduction Quaternary Geologic Setting Quaternary Faulting Quaternary Stratigraphy and Soils Previous Numerical Age Control Methods Geologic and Geomorphic Mapping Cosmogenic Nuclide Dating Sampling Sites Sample Processing Parameters Used in Modeling Cl Depth-Profile Age Estimates Sampling Thickness Grain-Size Distribution Bulk Density Profile Age Computation Pedological Considerations in Profile Sampling and Analysis Modeling of Profile Age and Uncertainties Implications of Results for Cosmogenic-Nuclide Profile Dating Methodology Stratigraphic and Chronologic Interpretations Implications for Lake Manly Lake Manly Former Lake Levels Rates of Fault Slip and Uplift Offset Along the Northern Death Valley Fault Zone Uplift of the Mustard Canyon Hills, North of Furnace Creek Ranch Thrusting Along the Echo Canyon Fault, Furnace Creek Canyon Summary Acknowledgments References Cited Appendixes Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it.
These Qai fans extend to elevations of about –46 meters (150 feet below sea level) and have not been transgressed by Lake Manly, suggesting that MIS 4 or MIS 2 lakes were rather shallow in Death Valley, perhaps because they lacked inflow from surface runoff of the Sierra Nevada drainages through Panamint Valley and over Wingate Wash.