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Temporal Evolution of the San Fernando Deep Marine Channel System

Thompson, Philip 1; Kneller, Benjamin C.1; Dykstra, Mason 2
1 Geology and Petroleum Geology, University of Aberdeen, Aberdeen, United Kingdom.
2 Geology and Geological Engineering, Colorado School of Mines, Golden, CO.

The Upper Maastrichtian San Fernando Channel System is one of numerous deep marine channel systems in the Cenomanian - Danian age Peninsular Ranges Forearc basin, located on the western margin of Baja California, Mexico. The 650m thick channel succession consists of 5 stacked, erosively based channel complex sets (sensu Sprague et al., 2002). The lowest of these shows the effects of confinement within a system-bounding erosion surface. However each subsequent channel complex set is marked by a basal erosion surface, and shows a similar stratigraphic evolution, consisting of 2 distinct stages: the lower part of each channel complex set (Stage 1) contains thick, erosionally-bounded amalgamated conglomerate and sandstone packages; the conglomerate is typically poor to moderately sorted, disorganized to organized and dominantly clast supported. Even though distinct bed and bar forms occur within the conglomerate packages, individual deposits are commonly separated by complex erosion surfaces which are the manifestation of multiple erosive and bypassing flows. Stage 1 deposits are overlain by a thick (10's of meters) package of thin bedded heterolithics containing thin (few meters), laterally persistent conglomerate bodies (Stage 2), commonly characterized by sigmoidal inclined stratification, and show more organized (commonly imbricated) conglomerate deposits compared to the deposits in Stage 1. Pebbly mudstones are common in the stage 2 deposits. They are pinch out laterally suggesting that they lie within a larger erosional confinement. Also they are commonly eroded in the axial area. The thin bedded heterolithic deposits which lie between the conglomerate bodies of Stage 2 show a thinning fining upwards trend but are punctuated by laterally persistent sandstone with locally scoured bases. The uppermost deposits of each CCS are capped by thick mudstone packages inter-bedded with calcareous mudstone bands; these deposits are only preserved on the margins of the system due to erosion in the axial regions. These channel complex sets and their basal erosion surfaces illustrate cycles of progressive strengthening then weakening of turbidity flows through the channel system, superimposed on a longer-term diminution of flow energy. These might be interpreted in terms of 4th and 3rd order sea level cycles, but other externally-imposed changes in flow strength might also be responsible.

Sprague et al. (2002) - AAPG Ann. Meeting Abstracts, Houston, TX, pp. 10-13

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009