Carbonate Ramp--Alternative to Shelf Model: ABSTRACT

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One of the most common depositional models for carbonate rocks is the shallow shelf. This model typically is constructed to show a nearly flat platform and a clearly defined shelf-slope break. Typically, there are detrital carbonates on the platforms, reefs or banks at the shelf-margin and basinal rocks seaward of the reefs. The usual analogs are the Florida-Bahamas (recent), the Cretaceous of Texas and northern Mexico (Edwards-El Abra), and the Permian of West Texas-New Mexico (Capitan model). Less commonly presented, but very important, is the ramp depositional model. The ramp model is an inclined platform that extends basinward without a pronounced break in slope. Carbonate facies, therefore, are not protected necessarily by a shelf-margin barrier. Reefs and facies patterns of the detrital carbonates tend to be distributed in bands which parallel the coastline and reflect the greater wave and current activity near the mainland shore. A modern example of the ramp model is the Campeche Bank. The detrital carbonates of the Campeche Bank are in concentric bands which range from grainstones and boundstones in shallow, agitated water to mudstones and wackestones on the seaward reaches of the ramp. Coral-algal reefs are common, but they do not occupy a position at the margin of the ramp. The ramp model is appropriate to explain the Jurassic carbonates of the Smackover and Cotton Valley around the ancestral Gulf of Mexico. The Jurassic ramp is modified by, and facies patterns are complicated by, salt tectonics. End_of_Article - Last_Page 1826------------