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43505-B8
Alluvial Facies Architecture and the Role of Climate and Tectonics in Basin-Fan Systems, Death Valley, California
The substantial tasks completed during 2006-07 from support by ACS-PRF grant 43505-B8 are:
a) Completion of two undergraduate research projects,
b) Tentative discovery of a new normal subchron within the Matuyama chron,
c) Mapping of two critical areas of Death Valley,
d) Collection of samples of the Wilson Creek Formation.
During 2006-07, two undergraduate students have completed theses on geomorphology of the Kit Fox Hills with the support of this grant. Two additional undergraduate students began working on projects during the year. They completed the preparation of several samples, but subsequently, due to reasons unrelated to working on the project have changed majors and are no longer working on the project. Students have contributed to writing laboratory procedures for tephrochronologic analysis as well.
At the 2006 Geological Society of America meeting, I presented the results of the initial interpretation of paleomagnetic results from 2005-06 field work. Our tentative interpretation was that this was the first evidence of the Jaramillo normal subchron in the region (Knott et al., 2006). In collaboration with Joe Liddicoat from Columbia University and an undergraduate student, we collected additional paleomagnetic samples. Based on these additional results and our examination of the stratigraphic section, we now have doubts regarding our initial interpretation that this is the Jaramillo subchron. We are now entertaining the hypothesis that we have found a short, previously undiscovered normal subchron within the Matuyama reverse chron between 0.78 and 0.8 Ma. We are trying to find additional sites to confirm this hypothesis.
I have completed initial geologic mapping of two areas. The first is in the Kit Fox Hills. Here, as an extension of previous work completed by undergraduate students, I have begun to document the development of this pressure ridge along a strike-slip fault. The stratigraphy developing through this mapping also provides the framework for interpreting climatic versus tectonic forcing of alluvial fan. The second area is at Natural Bridge. This complementary section to the Kit Fox Hills region is also yielding new information on tectonics and climate within the region. Key samples for 40Ar/39Ar analyses have been submitted for analysis.
In working out the Death Valley stratigraphy, I noted that there were Pleistocene lake deposits that contained an ash from the Wilson Creek Formation. However, geochemical identification of the ash was not possible as the ashes of the Wilson Creek Formation were not themselves characterized. As a result, accompanied by a CSUF student, and U.S. Geological Survey scientists, we collected samples of the Wilson Creek Formation for geochemical characterization. We anticipate that these results will benefit this study and many others within the western United States as well.
On a more personal note, I should state that progress has been slower than I anticipated. In January 2007, I suffered a severe stroke. My recovery has been rapid, but there was a 6-month period when my activities were restricted and travel extremely limited. I don't expect this to hamper my activities substantially during 2007-08.
Knott, J.R., Machette, M.N., Liddicoat, J.C., Sarna-Wojcicki, A.M. and Fleck, R.J., 2006. Paleomagnetics and Tephrochronology of Pleistocene and Pliocene lakes, Death Valley, California. Geological Society of America Abstracts with Programs, 38(7): 400.
