COMPARATIVE SEDIMENTOLOGY OF CARBONATE RAMPS

Carbonate ramps dominate much of today's modern carbonate shelves and were equally widespread in ancient systems. Models for carbonate ramp shelves have come from tropical settings in the Yucatan, Persian Gulf, west Florida Shelf, and subtropical to cool-water shelves surrounding the south and northwestern margins of Australia. Ancient ramps are the single dominant hydrocarbon system in carbonates, yet the level of maturity of comparative studies of modern carbonate ramps lags far behind their rimmed platform counterparts.

Shaw's (1965) concept of eperic seas, followed by Ahr's (1973) definition of a new type of carbonate depositional system, the carbonate ramp, highlighted a distinct and volumetrically dominant style of carbonate sedimentation that was distinct from the better known reef-rimmed carbonate platforms of the Bahama Bank and similar provinces. The carbonate ramp model has proved a valuable model for predicting facies distributions/architecture in examples ranging from Proterozoic through Cenozoic. Regardless, the need to update models or modern ramp systems for use as analogues is now clear. Detailed analysis of superb ancient systems have shown that ramps are rarely homoclinal but in fact can be easily differentiated physiographically by dominant physical parameters such as position of fair-weather and storm wave-base. Some ramps have extensive interior hypersaline shelves occurring behind the main shoal complexes analogous to portions of the Shark Bay profile where others have welded foreshore-shoreface systems similar to today's better-accepted Persian Gulf and Yucatan models. There is a dearth of data addressing process/product in the deeper areas of ramps below fair-weather wave base but still within the influence of tide, storm, and oceanic currents. Where do sediment gravity flow processes begin to take over from traction currents on modern shelves and where are storm processes dominant over background currents?

The need for a new generation of modern carbonate ramp comparative studies is pressing. The potential is great, with ever increasing seismic resolution, side-scan data, better monitoring of current regimes, and the ability to understand the evolution of oceanic currents through time.