Gary S. Weissmann1,
Graham E. Fogg2
(1) Michigan State University, East Lansing, MI
(2) University of California at Davis, Davis, CA
Abstract: Correlation of sequence boundaries between continental and marine strata
Many workers have attempted to correlate sequence boundaries from marine settings into the continental realm, however results from the Kings River Alluvial Fan system, located southeast of Fresno, California, indicate that the alluvial fan depositional cycles are out-of-phase from depositional cycles noted in marine sequences. Therefore, the unconformities within the alluvial fan should not be expected to correlate directly with sequence boundaries in the marine strata.
Accommodation space on an alluvial fan is controlled by changes in base profile position (the profile of a stream at 'equilibrium') rather than changes in base level. On the Kings River alluvial fan, varying sediment load and stream discharge during Pleistocene glacial cycles of the Sierra Nevada Mountains control base profile position and accommodation. Relatively mature paleosols formed on the exposed alluvial fan surface during interglacial periods (when the river was held within an incised valley) mark the sequence boundaries within the alluvial fan strata. During the glaciations, base profile rose due to increased sediment supply, thus accommodation space was produced and deposition occurred across most of the alluvial fan.
Since the marine systems experienced base level fall, accommodation space loss, and sequence boundary formation during the Pleistocene glacial episodes, sequence boundaries in the marine setting correlate to strata formed during relatively rapid deposition on the alluvial fan. Therefore, an unconformity extension of the marine sequence boundary does not exist within the alluvial fan sediments. Conversely, sequence boundaries within the alluvial fan correlate to highstand deposits within the marine systems.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana