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The continental margin of central Venezuela is a borderland similar to the area off California. Major east-west faults separate tilted crustal blocks which form horsts and grabens. Gravity gliding on these blocks has developed folds and secondary faults. The shelf east of Margarita Island is a shallow terrace topographically, but seismic profiles show an underlying system of sediment-filled horsts and grabens. The Antilles arc can be traced from Grenada to Testigos Island and on through Margarita and Tortuga Islands.
Sediment-size distribution is related to bathymetry. Sands are restricted to the Tortuga-Margarita rise and the broad terrace east of Margarita. These sands are high in carbonate content and have abundant glauconite. They are mainly relict sediments that were reworked during lower sea level of the last glacial episode. Silts and clays cover the continental slope, Cariaco basin, and the inner shelf between Cumana and Cape Codero, marking deeper areas of the sea floor and areas where only fine sediments are available.
Sand composition also is related to bathymetry west of Margarita. The Tortuga-Margarita Rise sediments are reef-related material. The rest of the shelf is dominated by a benthonic Foraminifera-Mollusca shell-fragment facies. The continental slope and Cariaco basin sands consist of planktonic Foraminifera. The eastern terrace sands are more complex. Reworked detrital sands surround Margarita. Around Testigos and in the south, there is a reef debris facies. Except for a pellet facies north of Araya Peninsula and Carupano, the rest of the area has a benthonic Foraminifera-shell-fragment facies.
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