Marine Sediments and Bottom Communities of the Seychelles

The shoal water region of the Seychelles Bank, covering about 31 000 km², is floored by relatively thin detrital carbonate sediments. Around the granitic and coral islands at least four submarine platforms can be recognized and are tentatively related to Late-glacial and Postglacial sea levels. A shallow discontinuous rim is developed around the margin of the Bank. The sediments and bottom communities of the open Bank and of the reef flats are described in terms of nine principal environments. Sedimentary facies are distinguished by the proportions of different organic constituents, by variations in grain size and by presence or absence of quartz. Syngenetic pyrite and collophane occur locally as minor constituents. Away from the reef flats the Bank supports a fairly uniform bottom community, the main elements being mollusca and foraminifera. The reefs may be considered as large intertidal pools with many microenvironments and with a complex zonation of communities showing rapid lateral changes in composition. There is a close relation between the sedimentary facies of the reefs and the distribution of the bottom communities.