STRATIGRAPHIC EVALUATION OF THE ALLUVIAL DEPOSITS AT LAWRENCE LIVERMORE NATIONAL LABORATORY, LIVERMORE, CALIFORNIA, U.S.A

The stratigraphy of the alluvial deposits in the west/northwest portion of the Lawrence Livermore National Laboratory (LLNL), California, indicates an unexpected complex depositional history for the site. We conducted this stratigraphic evaluation to aid in hydrologic characterization of the area. Visual core descriptions included lithology, sedimentologic features, and color which came from a total of 43 wells (approximately 1500 meters of core). Four general facies were identified – gravel, sand, silty sand, and paleosols. These facies typically showed distinctive signatures on geophysical well logs (gamma ray and resistivity logs). We further categorized the paleosol facies into four types based on the amount of carbonate, amount of manganese oxide, clay content, morphology, and structure. Correlations attempted between wells focused on these paleosols since we expected them to be the most laterally continuous facies in the section. The other facies were not utilized as extensively in the correlations due to their more sporadic depositional nature. However, even the paleosols did not appear to correlate between wells, leaving the general stratigraphic structure of the area unclear. Future research is necessary to determine reasons for this stratigraphic complexity. Possible explanations for these findings may include autocyclic fan lobe switching, multiple sediment sources with distinct histories (i.e. stream piracy or capture), contemporaneous faulting and folding of the area, and other undetermined factors.