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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 976

Last Page: 976

Title: Carbonate Platform Slopes of Extensional Continental Margins: ABSTRACT

Author(s): J. F. Read

Article Type: Meeting abstract


Carbonate platforms of extensional margins may be grouped into five major categories. Homoclinal ramps have gentle slopes into deep water and may have skeletal or ooid/pellet sand shoal complexes that grade without break in slope into deep ramp nodular limestone and thence into pelagic/hemipelagic basin facies. Homoclinal ramps 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 margin 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). Most are bypass margins but accretionary and erosional margins also occur. Finally, drowned or open platforms may develop by rapid submergence of ramps, shelves, or isolated platforms. 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 wackestones. The various platform types ma be recognized from continental margin sequences ranging from Proterozoic to Holocene in age.

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