--> Abstract: Structure Controls on Paleosol Development at Lawrence Livermore National Laboratory, California, U.S.A., by Leslie R. Mikesell and Gary Stephen Weissmann; #90039 (2005)
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Structure Controls on Paleosol Development at Previous HitLawrenceNext Hit Livermore National Laboratory, California, U.S.A.

Leslie R. Mikesell and Gary Stephen Weissmann
Michigan State University, East Lansing, MI

Paleosols at Previous HitLawrenceTop Livermore National Laboratory (LLNL), located east of San Francisco, California, reflect the complex structural and depositional history in the Livermore Basin. This transextensional basin is currently undergoing compression and closure; however, at the LLNL location, subsidence is still occurring. Local subsidence rates at LLNL are strongly affected by position above developing structures, and this subsidence rate variability is reflected in paleosol distribution and development. For example, an anticline-syncline pair plunges below the western portion of the LLNL site. Over the anticline, paleosols display a relatively mature morphology (i.e. reddish color, thick clay coats on peds, thick to moderate manganese oxide coatings, and well preserved prismatic structure.) Paleosols in this area show moderate correlation. In contrast, paleosols developed over the syncline are rare and display a lesser degree of development (i.e. thinner clay coats on peds and grains, thinner preserved B-horizons, and brownish color rather than red.) Though wells are closely spaced, little correlation between these paleosols is observed. Paleosols in northeastern LLNL site show greater correlation, most-likely due to the more proximal position on the fan. The depositional history at this site is equally complex. Two streams, Arroyo Seco and Arroyo Las Positas, are currently the primary sources of sediment at the LLNL site. Provenance studies, along with geomorphic evidence, support the hypothesis that past stream capture influenced the position of Arroyo Seco. The stream capture event allows correlation of stratigraphic units across the complex basin, offering a tool to recognize the underlying structure of this site.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005