Published:January 01, 2012
2012. "Slope Aprons", Application of the Principles of Seismic Geomorphology to Continental Slope and Base-of-Slope Systems: Case Studies from SeaFloor and Near-Sea Floor Analogues, Bradford E. Prather, Mark E. Deptuck, David Mohrig, Berend Van Hoorn, Russell B. Wynn
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The Brazos–Trinity depositional system consists of four linked late Pleistocene intraslope basins (I–IV) located on the upper slope, offshore Texas, U.S.A. Conceptual understanding of the fill history in these basin include “fill and spill” models where basins fill sequentially in the seaward direction, to models which invoke coeval basin filling with the coarse fraction retained preferentially in the up-dip basins and synchronous early bypass of the fine fraction to down-dip basins. Integration of recent coring results with nearly complete 3D seismic coverage has improved age dating and reconstruction of infill history. Initially sediment gravity flows bypassed the upper basins, as they had not yet formed, depositing a basal sandy unit in Basin IV. Higher net/gross sands in Basin II deposited from mixed flows, with mud suspended high within the flows exiting Basin II through a tributary-like flow-gathering zone near the basin exit point. The muddy parts of these flows preferentially accumulated in the lower part of Basin IV, which was a three-dimensionally closed basin with deep ponded accommodation. In contrast, the upper fill in Basin IV comprises a submarine apron that is sourced by a continuous channel system that extends directly from a shelf-margin delta located in Basin I. Within this apron, the observed seaward tapering is controlled by lower-efficiency sandy sediment gravity flows of relatively small volume with respect to basin size. These observations allow us to distinguish perched aprons from ponded aprons, with direct implications for reservoir continuity. We further recognize that low-relief ponded aprons have lower ratios of sand net/gross than either high-relief ponded aprons or perched aprons.
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Application of the Principles of Seismic Geomorphology to Continental Slope and Base-of-Slope Systems: Case Studies from SeaFloor and Near-Sea Floor Analogues
The study of near-seafloor deepwater landscapes and the processes that form them are as important to the understanding of deeply buried marine depositional systems as the study of modern fluvial environments is to our understanding of ancient terrestrial depositional systems. In fact, these near-seafloor studies follow in the great tradition established by earlier clastic sedimentologists in the use of modern systems to understand ancient environments. The acquisition and mapping of exploration 3D seismic surveys over the last few decades allows for the study of seafloor geomorphology with a spatial resolution comparable to most deepwater multibeam bathymetric tools, and represents a significant advancement that can be used to push forward general understanding of slope and base-of-slope depositional systems through the application of the emerging science of seismic geomorphology. The papers assembled for this volume demonstrate the utility of seafloor-to-shallow subsurface data sets in studying the development of submarine landscapes and their affiliated sedimentary deposits. These contributions highlight the controls of slope morphology on patterns of both sedimentation and erosion. Many of the papers also highlight the influence of pre-existing seafloor relief on confining sediment-gravity flows specific transport pathways, thereby affecting subsequent evolution of the seafloor. The understanding of depositional processes that comes from studying deepwater analogue systems remains the best way take to knowledge from one basin or system and apply confidently to another for prediction and characterization of reservoirs for exploration and production of hydrocarbons.