Abstract: Sequence Stratigraphy of the Kings River Alluvial Fan: Hydrostratigraphic Implications

WEISSMANN, GARY S., ERIC M. LABOLLE, and GRAHAM E. FOGG, University of California, Davis, CA

The Kings River forms a large, stream-dominated alluvial fan where it exits the Sierra Nevada mountains into the San Joaquin Valley southeast of Fresno, California. Sequences within the alluvial fan deposits, related to Pleistocene glaciations within the southern Sierra Nevada, consist of gray, cobbles, sand, silt, and mud bounded by red, clay-rich paleosols. Deposition of the gray sediment occurred during glacial events when increased sediment load and discharge produced accommodation space on the fan surface. Interglacial periods produced negative accommodation space and incision into a portion of the fan. Surface stability led to development the laterally continuous mature, red soils over the remainder of the alluvial fan.

The sequence stratigraphic approach allows for enhanced prediction of hydrofacies distribution within the fan deposits. When combined with a transition probability/Markov geostatistical approach, geologically plausible realizations of the subsurface facies distribution are produced. These realizations preserve the laterally continuous nature of the paleosols, facies juxtaposition tendencies (e.g., upward fining tendencies of the fluvial deposits), and known directional anisotropy and dip of units within the fan. Additionally, each sequence is modeled separately to preserve variability between sequences and to ensure facies are not crosscorrelated between the sequences.

These detailed models of subsurface heterogeneity allow development of improved contaminant transport models. Simulated plumes produced within the framework provided by this stratigraphic modeling display realistic plume geometries and will assist in developing refined remediation or mitigation strategies for this alluvial aquifer system.

AAPG Search and Discovery Article #90935©1998 AAPG Pacific Section Meeting, Ventura, California