Location of the Lowstand Depocenters along the Shelf-Edge and Influence on Shelf Margin Stratigraphy

The location of the sedimentary depocenters during the relative low sea-level stand is inferred based on the analysis of bathymetry data in front of major modern rivers. The results suggest multiple possible locations for a single river system based on the shelf bathymetry. The multiple locations are occupied by the dispersal system during successive regressions in order to accrete the continental margin.

The bathymetry data was used form a global data set with a grid of approximate 3.5 km. The grid is coarse but appropriate for large scale studies. The gradient maps were used to delineate trajectories of the “steepest” gradient from the shoreline to the shelf-edge and infer these trajectories as possible locations for the river and associated delta during periods of low sea-level stand. The analysis was made in front of modern rivers that discharge significant sediments (more than 25 Mt/year) on “constructional” shelves that do not have a strong modern tectonic signature.

More possible locations of the lowstand system were identified, and we believe some of these paths are occupied by the fluvial channels during distinct transgressive-regressive cycles. The position of the lowstand deltas at the shelf-edge was inferred only based on bathymetry but other factors not analyzed here are important in location of the low sea-level stand depocenter such as sediment river discharge relative to basin energy dispersal (wave, tides), mud/sand content in the river sediments. While the location of the future lowstand depocenters can be inferred based on the location of the steepest gradient paths, it is more difficult to predict the position of the depocenter at the shelf-edge during normal regression. The river deltas can also reach the shelf-edge during the high sea-level stand (e.g. Mississippi, Godavari, Niger) but the importance of shelf bathymetry is more difficult to quantify.