Fragmentation, rafting, and drowning of a carbonate platform margin in a rift-basin setting

Abstract

High-resolution bathymetric and shallow seismic data along the northeast Red Sea margin reveal a previously disregarded mechanism for carbonate platform drowning at a steepflanked rift basin. At the seafloor, salt extrusions highlight the influence of extensional salt tectonics, with a salt flow from the southern flank of the Al Wajh carbonate platform that likely originates from below. Salt-flow direction, morphology, and kilometer-sized slumps and rotated blocks indicate platform-margin disintegration and rafting of platform blocks toward the southwest. The outlines of several smaller detached or semi-detached carbonate platforms to the south of the main platform can be refitted to the larger platform margin by counter-moving the direction of mass wasting. Several platforms, reaching heights above the seafloor of up to 650 m, are partially or fully submerged in the mesophotic zone and appear to be in danger of drowning. We conclude that the southern outer rim of the Al Wajh platform is breaking apart owing to salt withdrawal, which indicates that carbonate platforms on top of salt sequences grow on mobile ground, leading to platform disintegration, basinward rafts, and the demise of broken-off, smaller pieces of platform. Salt displacement also controls the growth geometries of individual platform rafts, with keep-up reef growth (growth rate equal to sea-level rise) and drowning occurring in close spatial proximity. Therefore, the interplay between salt diapirism and platform growth is not limited to platforms growing on the apexes of diapirs and is more complex than previously thought