Light at the end of the funnel: coupled carbonate shelves and terrigenous catchments in the hyperarid northern Red Sea

Abstract Along the Egyptian and Saudi Arabian rifted margins of the northern Red Sea, the near-absence of a continental shelf forces photozoan-dominated carbonate-producing ecosystems to develop directly along siliciclastic shoreline. These coastlines are dissected by ephemeral desert stream networks (wadis), which episodically deliver high volumes of siliciclastic sediment during rare but intense flash flood events. These floods form coastal-fan deltas that episodically prograde into the shallow marine zone. Over centennial to millennial time scales, these intermittent pulses of siliciclastic sedimentation create new shallow-water substrate, which forms essential real estate for colonization by photozoan carbonate ecosystems. Crucially, the intervals between flash flood events, which may span decades or longer, provide prolonged periods of reduced turbidity and sedimentation and are necessary for recovery, growth, and lateral expansion of carbonate ecosystems. Paradoxically, the same siliciclastic inputs that are often viewed as disruptive to carbonate production can, over the long term and at the basin scale, facilitate the growth of carbonate shelves in steep, narrow-margin settings in arid environments. The broadest areas of carbonate shelf sedimentation in fact, occur on the subaqueous parts of fan deltas adjacent to the largest wadi catchments. This dynamic is most pronounced where large wadi catchments generate extensive subaqueous fan deltas—zones where carbonate sedimentation can occur at scales more than three orders of magnitude greater than the regional shelf average. Traditional paradigms that portray siliciclastic influx as uniformly suppressive to carbonate accumulation fail to capture the nuanced relationships and complex sedimentary dynamics inherent in mixed depositional systems. In arid settings characterized by episodic but intense siliciclastic input delivered through high-magnitude, low-frequency flash flood events, separated by protracted intervals of reduced or negligible terrigenous sedimentation, the periodicity and magnitude of sediment supply become fundamental controls on carbonate-platform evolution. These discrete pulses of sedimentation promote progradation of fan deltas and create transient accommodation in proximal shallow-marine settings, which, during inter-flood intervals, are exploited by photozoan carbonate-producing communities. Consequently, the temporal distribution of siliciclastic delivery exerts a first-order influence on carbonate-shelf expansion in steep and narrow-margin settings, constituting a previously underappreciated control on the spatial and temporal development of carbonate systems.