Pacific Section AAPG, SPE and SEPM Joint Technical Conference

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Evaluation Of Calleguas Creek As A Source Of Sand At ODP Site 1015 On The Hueneme-Mugu Submarine Fan, Santa Monica Basin


Thorough and accurate models of modern potential sand sources to the Santa Monica Basin, offshore southern California, are needed to facilitate the interpretation of the Hueneme-Mugu fan, the largest submarine fan within the basin. Bathymetry and seismic isopach mapping of basin fill indicates that dominant sources of sand are channels that enter the basin from the northwest which are likely fed by the Santa Clara River or Calleguas Creek with possible input from the Santa Monica Mountains as well. Definition of sand composition from the previously unstudied Calleguas Creek was necessary to differentiate its potential contribution to basin fill from the other two sources as defined by Valles (1995) and Critelli and Ingersoll (1997). We found downstream Calleguas Creek sand to be uniquely enriched in volcanic lithics but with subequal amounts of plagioclase and potassium feldspar. The abundance of volcanic material and lack of metamorphic grains is a stark contrast to the Santa Clara River's relative abundant metamorphic lithic content. In addition, Calleguas Creek sand can be further differentiated from Santa Clara River and Santa Monica Mountain stream sands by its higher potassium feldspar and lower plagioclase content. Petrographic analysis of 15 samples of Pleistocene (<60ka) sand recovered in cores at Ocean Drilling Program Site 1015 on the Hueneme-Mugu submarine fan within the Santa Monica Basin appears to validate Calleguas Creek's deep marine contribution. Downhole trends in sand composition at Site 1015 are potentially related to changes is sea level, alternating between a Santa Clara River provenance during lowstands and a Calleguas Creek provenance during highstands. None of the sand samples analyzed exhibited a Santa Monica provenance.