Fluvial Sediment Supply in a Cool Lowstand World: Modeling Results for the Late Quaternary Gulf of Mexico Passive Margin

Fluvial systems are point sources for sediment delivery from hinterlands to the depositional basin. This paper evaluates the impact of climate and sea-level change on fluvial sediment supply to shelf and deepwater systems for the last glacial-interglacial cycle of the northern Gulf of Mexico passive margin offshore Texas.

Numerous studies show that fluvial sediment supply is a function of hinterland drainage area, relief, lithology, climate, and sediment storage enroute to the discharge point. Over time scales of <10^6 yrs, drainage area, relief and lithology are steady, but climate and storage terms vary, such that supply will be unsteady. Moreover, climate-driven sea-level fall forces rivers to extend across emergent shelves, which changes the discharge point: some river systems simply get longer, with only marginal increases in drainage area, whereas others merge as they traverse the shelf, significantly increasing drainage area that contributes to a single point source.

Previous workers have suggested that fluvial sediment supply along the Texas coast and shelf was significantly greater during the last glacial period, as compared with the Holocene. We test this interpretation, using an empirical model to predict supply with glacial period climates, and with sea-level fall and merging of fluvial systems. Sediment yield (supply per unit drainage area) would have been less under either a cool and dry or cool and wet glacial period climate when compared with present values (pre-dam). However, merging of drainages on the shelf would have increased point-source sediment loads, such that volumes of sediment documented in falling stage and lowstand deltas could have been produced within a few thousand years, less time than the same deltas are thought to represent. Hence, even with lower yields, glacial climates would have produced sediment volumes sufficient to construct observed shelf-margin deltas and disperse sediments to slope and deepwater systems.