Mineralogy, geochemistry and microfacies of late Quaternary periplatform sediments : Carbonate export cycles and secondary processes - Sanganeb Atoll and Abington Reef, Sudan, Central Red Sea
A set of sediment cores was obtained in the periplatform realm close to Sanganeb Atoll and Abington Reef, about 20 miles offshore the Sudanese coast in the central Red Sea. Microfacies, mineralogy and geochemistry of periplatform sediments were analysed to quantify glacial-interglacial variations in carbonate production and sediment export of the reefs in response to late Quaternary sealevel fluctuations. The present study showed that the periplatform sediments from the Sudanese shelf to great extend record variations in sediment export of the offshore reefs in tune with sealevel changes. This is clearly visible in the increased input of fine-grained, strontium- and aragonite-rich shallow-water derived sediment during the Holocene sealevel highstand, which is in good accordance with the highstand shedding model of carbonate systems. However, during the last interglacial sealevel highstands (marine isotope stage 5) this pattern is not clearly developed and generally no characteristic highstand bundling in the frequency of calciturbidites was observed in the Red Sea. Syn- and post-depositional processes play a significant role in the nearly isolated Red Sea basin with its unusual paleoceanographic and climatic conditions during the late Quaternary. Those processes to some extend changed the sealevel controlled sediment export signal. Of major importance is the submarine precipitation of aragonite and Mg-Calcite at the seafloor, which even led to the formation of a hard layer during marine isotope stage 2 when salinities of Red Sea surface- and bottom-waters rose over 50 ‰ during the sealevel lowstand. During high salinity phases of glacial sealevel lowstands biogenic carbonate production was drastically reduced because reefs and planktic organisms vanished nearly entirely from the Red Sea. Furthermore, glacial-interglacial changes in carbonate dissolution- and preservation at the seafloor occurred, partially in phase with monsoonal climate variations. Carbonate (aragonite) dissolution is generally increased during interglacials and a better preservation of this mineral was observed during humid phases (prevailing SW-monsoon) when stagnation of the basin led to oxygen depletion of the deeper water masses.
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