Driving Sediment Volume and Sand Budgets Into Shelf Margins and Beyond: Sea Level and Sediment Flux?
Examination of sea-level- and supply-drive models for the generation of stratigraphic sequences has yielded the question of ‘what is the main driver of sediment- and sand-volume partitioning into shelf margins and beyond?’ Comparative analysis of a dataset of 25 shelf margins with a spectrum of shelf-edge trajectories and a variety of depositional styles allows us to confirm that both types of margin are common and important, and can be distinguished. We suggest that accommodation-dominated margins have shelf-edge aggradation rates (Ra) of < 200 m/My, shelf-edge progradation rates (Rp) of < 10 km/My, cross-sectional net sediment flux (Fc) of < 10 km2/My, and feeding deltas restricted to the coastal region; supply-dominated margins, on the other hand, have Ra of > 200 m/My, lower Rp of > 10 km/My, lower Fc of > 10 km2/My, and large-scale feeding shelf-margin deltas. Three main styles of shelf-edge growth were recognized in both margin types, including flat to slightly descending (trajectory angles (Tse) of −4° to 0°, aggradation/progradation rates (A/P) of −0.07 to 0), low-angle ascending (Tse of 0° to 2°, A/P of 0 to 0.03) and high-angle ascending shelf-edge trajectories (Tse of 2° to 6°, A/P of 0.03 to 0.10). Descending/flat and low-angle ascending shelf-edge segments of both margin types are commonly fronted by sandy-rich submarine fan systems and mixed sand-mud depositional systems, and sand-prone systems, respectively. Strongly aggradational shelf-edge segments of accommodation- and supply-dominated margins are associated with coeval mud-dominated mass-wasting and sand-prone systems, respectively. Driven by sea-level fall, sand from even small river deltas is delivered into deep-water, accommodation-dominated margins. Driven by high sediment supply, sand of large rivers is delivered into the deep water, supply-dominated margins, and can occur at all sea-level stands. In both margin types, Tse and A/P are proportional to sediment volumes being partitioned into the shelves themselves, but are inversely proportional to sand-budget partitioning into deep-water areas. These relationships help in relating quantitative characteristics of shelf-edge growth to Source-to Sink sand-budget partitioning, assisting greatly in developing a more dynamic stratigraphy.
AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015