--> Influence of Storm Processes on Cross-Shelf Sediment Transport

AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Influence of Storm Processes on Cross-Shelf Sediment Transport

Abstract

Current models for deepwater sediment sources call upon conduit-fed slope canyons bringing sediments in to steep-sloped settings, generating turbidite-driven basinward sediment transport. However, new findings in shelf environments suggest that shelfal processes can play a large role in line-sourcing sediment plumes directly from the shelf, absent of slope conduits. In addition, distal shelf settings, once thought to be devoid of reservoir quality sediments are increasingly the target of low-net:gross exploration efforts, whose risk can be reduced through careful understanding of outer shelf sediment distributions. A series of experimental studies have been performed in a large, non-recirculating flume to test plunging hyperpycnal plumes (PHP) as a viable means for cross-shelf sand transport to middle and outer shelf locations, and potentially to deeper-water locations. PHP result from storm-flood events bringing in huge amounts of sediments into the shelf. However, these plumes are believed to die off quickly as they cannot maintain their turbulence due to the gentle nature of shelf slopes. Modern studies at Eel River, California suggest that high wave energy present during storms has a significant role in maintaining the turbulence within the wave boundary layer allowing the undercurrent to sustain its flow and keep suspended sediment from settling. In our studies, we physically model the interaction of storm-produced gravity waves and the hyperpycnal plumes generated due to storm-associated flood events, and how change in the current and wave characteristics affect the sediment transport. The results of physical models have been combined with field study, which examine the nature of hummocky cross-stratified sands in shelfal settings around the world. Current paradigms assume these sediments to be deposited above storm wave base. However, the results of preliminary experiments suggest that wave energy can get embedded into and carried forward with the current, suggesting a need to reconsider the origin of wave-formed sedimentary structures in all shelf settings. Such reconsideration has implications for interpretation of environmental settings, paleo-climate models, paleo-water depth assessments and understanding of reservoir nature and distribution in distal shelf and deepwater settings.