Controls on carbonate-siliciclastic relationships in quaternary deposits of the Midyan coast of the Gulf of Aqaba, Saudi Arabia

Abstract

Quaternary deposits of the Midyan coast of Saudi Arabia include coral-bearing limestones interbedded with sheet-flow siliciclastic sands and gravels, interpreted as braid-delta fan deposits. The limestones and their contained faunas provide evidence of periodic local stabilization of gravel surfaces and effective starvation of siliciclastic supply. Some indicate growth and deposition in waters a metre or so deep whereas others were substantially deeper. An additional group reflects initial deposition in shallow waters with resedimentation downslope by storm or other ‘delta-front’ processes. The surfaces of the fans provided morphological and environmental analogues to fore- and back-reef situations in which corals, calcareous coralline algae, molluscs, and echinoderms flourished, but in this area did not form independent reefs. The dominant controls on the changes from siliciclastic- to carbonate-dominated deposition were not transitional, and primarily related to channel and fan-lobe migration rather than tectonic or eustatic sea level changes. Similar variations in the distribution of siliciclastic sediments may control carbonate occurrence in other mixed sequences.