--> ABSTRACT: What Happened to My Marine Reservoir? Implications of Falling Stage and Lowstand Fluvial Sediment Storage during “Sequence-Boundary” Scour for Sand Starvation of Coastal Marine Reservoirs, by Holbrook, John M.; Bhattacharya, Janok; #90142 (2012)

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What Happened to My Marine Reservoir? Implications of Falling Stage and Lowstand Fluvial Sediment Storage during “Sequence-Boundary” Scour for Sand Starvation of Coastal Marine Reservoirs

Holbrook, John M.*1; Bhattacharya, Janok 2
(1) School of Geology, Energy, and the Envirnment, Texas Christian University, Ft Worth, TX.
(2) Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX.

Recent flume and field studies show that sediment may be stored by fluvial aggradation and lateral migration during regression, resulting in sediment starvation in coeval marine environments. In extreme cases, this may result in storage of all sediment within the fluvial system and complete starvation, or “autodetachment,” of the contemporary marine shoreline. Complete sediment starvation of the shore is still theoretical, and likely rare. Several recent field studies, coupled with new ideas regarding the scour processes of sequence boundaries, however, suggest that significant falling and lowstand fluvial sand storage commonly results in diminished to near total reduction of marine reservoir sand.

Newer views on scour of the “subaerial unconformity” sequence boundary show that it does not actually record a surface of exposure and near complete bypass of sediment at lowstand as originally presumed, but rather records a composite surface formed by lateral migration and incision of rivers that ‘carve-and-cover’ the subaerial unconformity throughout regression. This carve-and-cover process means that fluvial sediment is deposited above this surface throughout the regressive phase. Since transport of sand lags transport of suspended load, regressive fluvial sediments disproportionally sequester the sandy fraction. Coastal Quaternary systems and the Cretaceous of the Western Interior provide several examples where coastal systems were deprived of sandy sediment to varying degrees during regression. Sand starvation ranges from minimal, resulting in prominent regressive coastal sand reservoirs, to near complete, in which case lowstand terminal estuaries with negligible coastal sand deposition result. Partial to near complete "sand autodetachment", in which there is sand starvation of marine reservoirs, appears more pronounced where regressive slopes are low compared to river profiles and in where base-level remains relatively stable during regression. Such minimally-incised systems are common where stable base level promote lateral migration of channels during falling and lowstand stage enhancing fluvial sand storage.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California