What Conditions Are Required for Deltas to Reach the Shelf Edge During Rising Sea Level?

Abstract

It is now clear from multiple modeling and field studies that deltas can attain a shelf-edge position under conditions of rising sea level, and this is now accepted as an alternative way to form submarine fans without relative sea-level lowstand conditions. However, the relative importance and the range of controls that generate this type of shelf-edge deltas are less well known. To investigate these controls, we collect the natural range of seven accommodation and morphological variables (shelf width, shelf gradient, delta system width, delta foreset gradient, the rate of sea-level rise, the rate of shelf subsidence, and highstand duration) from 32 modern shelves, 40 subsidence curves, and 172-million-year record of eustatic sea-level variation. We input these variables into a geometric model that estimates the required sediment load to form the highstand shelf-edge delta. We conduct a one-at-a-time sensitivity analysis on each variable to determine their relative importance. Our results suggest that besides sediment supply, shelf width is the most important control in forcing deltas to the shelf edge during rising sea level. Two of the traditional ‘stratigraphic trinity’, eustatic sea-level change and shelf subsidence, most likely play a less important role than previous literature implied. This result is consistent with a recent trend in sequence stratigraphic studies, encouraging consideration of multiple controls in all interpretations, rather than assuming dominant control by relative sea level.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018