Though stream-dominated alluvial fans comprise a large percentage of important aquifer systems, detailed three-dimensional characterizations of these deposits are notably lacking in the literature. Successful application of sequence stratigraphic concepts in petroleum research to predict subsurface facies distributions strongly suggests that, when modified for purely continental strata, sequence stratigraphy can be applied to characterize alluvial fan systems. This project involves the fusion of several disciplines, including hydrology, geology, geophysics, and soil science, to develop a sequence stratigraphic framework from which a more advanced, tractable model of heterogeneity can be produced for typical, stream-dominated alluvial fans. Significance of this research is three-fold. First, it will create some needed "order" in our understanding of heterogeneity in many alluvial fan groundwater systems through development of continental sequence stratigraphic concepts. Second, the research will provide a method to incorporate geostatistical simulation into a sequence stratigraphic framework, thus providing a detailed characterization of the aquifer system. Finally, the research will provide a large step forward in our ability to characterize and model regional groundwater flow and transport in many types of alluvial deposits. Such an advance is sorely needed for estimating long-term impacts of agricultural and urban pollution on sustainability of groundwater quality.
Central to the proposed research is the recognition of sequences, related to Quaternary climate cycles, bounded by laterally extensive, mature paleosols. These paleosols mark fan exposure during interglacial periods, and form laterally extensive aquitards in the aquifer system. Strata within the sequences represents deposition that occurred on the fan during glacial episodes, when accommodation space was made available by increased discharge and sediment supply. Within these sequences, systems tracts (e.g., linked assemblage of lithofacies deposited during one time period of the climatic cycle) have also been recognized in core, driller's logs, and geomorphic mapping of the Kings River fan. It is proposed that additional continuous core will be collected specific systems tracts (e.g., incised valley fill deposits) to examine these differences. The systems tracts will be compared through use of environmental magnetism, facies morphology, and petrographic analysis. Calibration of relatively abundant drillers logs to the core data, already successfully accomplished in other portions of the Kings River alluvial fan, will provide a means to define systems tract geometry in the subsurface. A new Markov-chain technique for geostatistical modeling of spatial distribution in sedimentary units with greater geologic rigor (Carle and Fogg, 1996a, 1997) will be used to produce stochastic simulations of textural units within the sequence stratigraphic framework.
