Potential Petroleum Source Rock Deposition in the Middle Cretaceous Wasia Formation, Rub'Al Khali, Saudi Arabia

Abstract

ABSTRACT Stratigraphic correlation and regional geochemical sampling in the Rub'Al Khali (The Empty Quarter) of Saudi Arabia indicate at least two potential petroleum source rock units occur in the middle Cretaceous Wasia Formation. These two sequences, informally named the Safaniya "source rock" and the lower Mishrif, are dominated by oil-prone amorphous (Type II) organic matter, in places in excess of 10 weight percent organic carbon. Both units are fine-grained pelagic lime mudstones which were probably deposited in relatively quiet anoxic waters of large intraplatform embayments or basins. The Safaniya "source rock" and the lower Mishrif reflect strong marine transgressions on the Arabian craton in Albian to Cenomanian and Cenomanian to Turonian time, respectively. Regressive-phase sedimentary rocks overlying these two transgressive organic-rock phases are generally poor in organic carbon despite being deposited, in part, in similar forereef open-marine depositional settings. The sea-level high-stands associated with the Safaniya "source rock" and the lower Mishrif are partly synchronous with two recently described "oceanic anoxic events" respectively occurring in late Barremian to late Albian time and late Cenomanian to early Turonian time. Although there is a credible time correlation of these organic-rock units with oceanic anoxic events, their connection to oceanic anoxic events could be strengthened if they could be traced out to the vicinity of the middle Cretaceous continental margin. Unfortunately, lack of information from adjacent areas prohibits determining the complete extent of the organic-rock units. The organic richness of these sediments could therefore also be the result of euxinic conditions locally developed within silled basins of the Tethys epicontinental sea.