Sediment Volume Partitioning Into Deep Water and its Implications to Continental Margin Building

Abstract

Several decades of sequence stratigraphic studies recognized both accommodation-dominated systems and supply-dominated systems are capable to build deep-water fans. The former relied on the lowstand sea level to move river mouth close to shelf edge whereas in the latter, despite the rise of sea level high sediment fluxes bring the highstand shoreline close to shelf edge thereby the deep-water basin can receive the sediments sustainably. However, it is less clear which sediment dispersal system is more efficient to deliver the sediments to deep water and how to distinguish between the two systems. We explore sediment volume partitioning into deep-water systems by analyzing 1,600 shelf-slope geometric models with varying eustatic, morphology and sediment-supply conditions. Previous studies imply that greenhouse low-amplitude, low-frequency eustatic condition permits lower shelf accommodation and longer time for the shoreline to arrive at shelf edge. The full exploration of the eustatic and morphologic conditions indicates that this argument only works in the supply-dominated system and the deep-water sediment proportion is not correlated to the frequency of eustatic sea-level change but highly depends on the shelf width. We recommend to use the ratio between the product of shelf width and amplitude of sea-level change, and total sediment supply to determine the sediment dispersal system. This has been tested in three well-studied ancient systems (Maastrichtian, Washakie Basin, Pliocene Paleo-Orinoco, and Miocene, New Jersey Margin). The dominant control by shelf width on deep-water sediment volume also strongly suggests that continental margin building is usually rapid initially then slows down to an equilibrium status where the margin aggrades and only high-amplitude sea-level change can deliver up to ~20% total sediment supply to the deep-water basin.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019