Title: Carbonate platforms of passive (extensional) continental margins: Types, characteristics and evolution
Abstract: Carbonate platforms of extensional margins may be grouped into several major categories. Homoclinal ramps have gentle slopes into deep water, may have skeletal or ooid/pellet sand shoal complexes, that grade without break in slope into deep-ramp nodular limestone, and then into pelagic/hemipelagic basin facies they generally lack significant slump and sediment gravity flow deposits in the deeper-water facies. Distally steepened ramps differ from the above in having a marked increase in slope at the seaward edge of the deep ramp, and abundant slumps, slope breccias and turbidites. However, clasts of shallow platform margin facies are generally absent from breccias. Rimmed shelves have linear trends of shelf edge lime sands and reefs, a marked increase in slope into deep water, and foreslope and slope sands, breccias (with clasts of platform margin rocks) and turbidites, grading seaward into basin hemipelagic/pelagic muds. They may be divided into accretionary, bypass and erosional margins. Isolated platforms are broad flat-topped shallow platforms surrounded by deeper water (few hundred meters to 4 km deep); many are bypass margins but accretionary and erosional margins also occur. Finally, incipiently to completely drowned or open platforms may develop by rapid submergence of ramps, shelves or isolated platforms; shallow platform margin facies are shifted landward and the earlier shallow-water platform is covered with transgressive lags, and deeper-water blankets of hemipelagic or pelagic facies or open marine, whole fossil wackestone. The carbonate prisms commonly develop above a basal clastic phase. Ramps develop early, and evolve into rimmed shelves. However, with drowning, rimmed shelves may evolve up into ramps. Rimmed shelves may also develop into ramps where miogeoclinal faces prograde into filling marginal basins. Carbonate miogeocline deposition terminates when the shelf becomes a prograding clastic shelf, or where it becomes part of a collisional orogen. The various platform types may be recognized from continental margin sequences ranging from Proterozoic to Holocene in age.
Publication Year: 1982
Publication Date: 1982-01-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 284
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