--> Abstract: Fluvial Terraces as an Autocyclic Mechanism for Incised Valley-Fill Parasequence Formation: Examples from the Late Quaternary, Northern Gulf of Mexico, U.S.A., by Antonio B. Rodriguez, John B. Anderson, Larry Greene, and Alexander R. Simms; #90039 (2005)

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Fluvial Terraces as an Autocyclic Mechanism for Incised Valley-Fill Parasequence Formation: Examples from the Late Quaternary, Northern Gulf of Mexico, U.S.A.

Antonio B. Rodriguez1, John B. Anderson2, Larry Greene1, and Alexander R. Simms2
1 University of Alabama, Tuscaloosa, AL
2 Rice University, Houston, TX

An incised valley with a bounding surface (sequence boundary) characterized by terraced morphology should inherently fill with backstepping parasequences during transgression irregardless of the rate of sea-level rise or sediment supply. Late Quaternary incised valley-fill parasequences are often attributed to changes in the rate of sea-level rise. However, sea-level rise curves created from the depth and age of associated flooding surfaces do not compare well with other sea-level curves based on corals and basal peat deposits. Inundation of flat fluvial terraces should be an autocyclic mechanism for parasequence formation. Rates of shoreline transgression and associated accommodation space will suddenly increase as flat terraces are inundated. Terrace flooding events should also change the hydrodynamics of the system and associated sedimentary facies forming parasequences. To test this model, high-resolution seismic, core, and radiocarbon data were collected from the Nueces, Corpus Christi, Galveston, eastern Mississippi Sound, and Mobile estuaries, which formed above incised-valleys. Results indicate that depths of flooding surfaces recognized in each bay correlate to depths of flat fluvial terraces. Flooding surfaces formed during a period of time when the rate of sea-level rise was decreasing and are not associated with variations in sediment supply. A complete reorganization of depositional environments within the incised valleys is observed across the flooding surfaces. While not all flooding surfaces recognized correspond to fluvial terraces those that caused the largest depositional changes do. Depositional environments that fill terraced incised valleys are inherently unstable and prone to backstepping events during transgression.

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