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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 57 (1973)

Issue: 4. (April)

First Page: 810

Last Page: 810

Title: Sediment Distribution in Southwestern Indian Ocean: ABSTRACT

Author(s): Edith Vincent

Article Type: Meeting abstract


Sediment distribution patterns in the southern Mozambique Channel and adjacent southwest Indian Ocean were investigated from short gravity cores and surface bottom samples. These shelves are covered by terrigenous sediments of varying grain sizes, chiefly silty, and upper slopes by hemipelagic calcareous mud. Areas of nondeposition on parts of the African shelf and upper slope reflect the winnowing action of the Mozambique-Agulhas Current. Relict foraminiferal faunas and exposed beachrock on the African shelf indicate a former lowered sea level. Lower continental slopes (below 1,500 m), continental rises, and plateaus are covered by foraminiferal marl and chalk oozes whose distribution correlates in part with the grain-size distribution. A size analysis of planktonic Fora inifera indicates that concentrations of small and large tests in some oozes are due to sorting. Manganese nodules are abundant on the Mozambique Plateau, which is swept by an eddy of Antarctic Intermediate Water. Natal basin sediments include turbidites, derived from neritic and bathyal depths, which are dispersed from northwest to southeast. Surficial turbidite layers did not reach the southern part of the basin floor, which is covered by pelagic clay and manganese nodules.

Average sedimentation rates of sediments younger than approximately 4,000-6,000 years range from 1 to 9 cm/1,000 years, depending on topographic position and distance from land. The average rate of accumulation for undisturbed deep-sea ooze during the entire late Quaternary is 1.5-2.5 cm/1,000 years.

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Copyright 1997 American Association of Petroleum Geologists