--> Abstract: Controls on Accommodation in Fluvial Depositional Systems: Fluvial Fan Sequence Stratigraphy, by Gary Stephen Weissmann; #90039 (2005)

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Controls on Accommodation in Fluvial Depositional Systems: Fluvial Fan Sequence Stratigraphy

Gary Stephen Weissmann
Michigan State University, East Lansing, MI

Variable geometry and distribution of stratigraphic sequences of fluvial fans in the eastern San Joaquin Basin, California, were controlled by tectonics (e.g., basin subsidence and basin width) and response to Quaternary climate change, reflected in the degree of change in sediment supply to discharge ratios and local base level elevation changes. Several fluvial fans illustrate the influence of these factors on ultimate sequence geometry. In areas of the basin with high subsidence rates, sequences are relatively thick and apexes of subsequenct sequences are vertically stacked. Areas that experience relatively low subsidence rates produced laterally stacked sequences. Rivers that experienced significant increase in sediment supply to stream discharge ratios due to direct connection to outwash from glaciated portions of the Sierra Nevada developed high accommodation space and relatively thick sequences with deep incised valleys. Conversely, rivers that were not connected to glaciated regions and, thus, experienced relatively minor change in sediment supply to discharge ratios, produced thinner sequences that lack deep incised valleys. Local base level connection to sea level, via the axial San Joaquin River, produced deeper incised valleys than those of internally-drained rivers. Finally, narrow basin width allowed glacially-connected fans to completely fill available accommodation, thus producing smaller fans that lack preservation of distal, interglacial deposits. Evaluation of these controls allows prediction of sequence geometries and facies distributions for future hydrogeologic models.

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