Correlation of deep sea sediments and forereef carbonates in the Red Sea: an important clue for basin analysis

Abstract

Quaternary deep-sea stratigraphy is based on climatic changes, documented either in the frequency of planktonic and benthonic organisms or in the isotopic signal recorded in their tests. The Red Sea cores show a characteristic signal for the time of the Pleistocene-Holocene transition, which is marked by a drastic shift in the δ 18O from heavier values towards lighter values. A similar shift of the same order of magnitude is recorded in the sedimentary succession of deep forereef carbonates, but this shift is seen over a sediment thickness of only a few centimetres. Below the present water depth of − 120 m, lithified carbonate rock forming ledges several decimetres in size occur on different reef slope types. They are prominent on atoll and barrier reef slopes, while they are only subordinate on fringing reef slopes. Ledges exhibit a similar texture and fabric, independent of the actual depth and the geographical setting. Ledge formation is initiated by a basal biogenic fabric or cemented grainstone characterized by countless borings crossing each other. They are filled by a well-cemented micrite thus leading finally to a complete loss of any primary fabric. Biogenic relics and the micrite boring are unconformably overgrown by laminated micrite crusts. Remaining cavities are filled with unlithified pelagic mud. Stable isotope data on these different lithotypes of forereef carbonates reveal relatively heavy values of δ 18O for the boring micrite, intermediate values of δ 18O for micrite crusts, and the lightest values for unlithified mud. Together with radiocarbon datings of basal biota within the ledges, this shift in the δ 18O stable isotope ratio suggests a plausible stratigraphic correlation of carbonate deposits from fringing reefs, barrier reefs, atolls and their adjacent basins.