Variability of Shelf Delta-Estuary Complexes on Shelf-Margin and Ramp Platforms

Carlos A. Uroza, The University of Texas at Austin, Department of Geological Sciences Austin, TX, [email protected]

In pre-Modern coastline successions repeated regression and transgression produce clastic tongues that are deltas/strandplains in their lower part and estuary/barrier in their upper part. This research will build and analyze a database of such tongues, developed in both shelf-break and ramp settings. The main research hypotheses to be tested from this database are: (1) As deltas regress on shelf platforms towards their outer edge there is a tendency towards more wave dominance in shelf-break settings, and more tide influence in ramp basins, as would be predicted from theory, (2) Deltas tend to be more wave influenced in sea-level ‘rise’ regime, and more tide influenced in ‘fall’ conditions, (3) In basins differing subsidence regime there is a discernible difference in the facies and architecture of the deltas and estuaries, (4) Estuary-Barrier systems developed on the transgressive limbs of clastic tongues are thicker and more complex in shelf-edge settings than when they arrive farther landward on the inner shelf.

This research involves outcrop analysis from four different locations: 1- Eocene Battfjellet Formation, West Spitsbergen, Norway, where two clinoforms showing shelf to slope transition are targeted; 2- Campanian McCourt Tongue, Rock Springs Formation, Wyoming-Utah (deposited on an inner-shelf ramp setting); 3- Pliocene Paleo-Orinoco Delta, Trinidad, which represent thick shelf-edge deltas developed on a growth fault province (the impact of high subsidence on the architecture and geometry of the sandbodies will be examined); and 4- Campanian Haystack Mountains Formation, Wyoming, where the character of lowstand deltas developed on a ramp setting will be evaluated.