Turonian microcrinoids from the lower Aruma Formation of Saudi Arabia

Pelagic microcrinoids assigned to the genus Roveacrinus identified in thin-sections of carbonates of the Turonian lower Aruma Formation of Saudi Arabia provide the first documented occurrence of these microfossils in the Arabian Peninsula. The species include Roveacrinus cf. alatus Douglas 1908, Roveacrinus sp., Roveacrinus geinitzi Schneider 1989, Roveacrinus cf. geinitzi, Roveacrinus aff. rugosus Douglas 1908, Roveacrinus sp. A., Roveacrinus aff. geinitzi Schneider 1989 and Roveacrinus cf. derdereensis. The Turonian range is based on the presence of planktonic foraminifera Heterohelix moremanni, H. globulosa and Marginotruncana sigali in the absence of Rotalipora spp., although possible Cenomanian forms are present within one deep marine microfacies assemblage. The biofacies containing the often abundant Roveacrinus fragments consists typically of abundant calcareous dinoflagellate cysts Calcisphaerula innominata with less common Pithonella ovalis, and rare Bonitocardiella conica, rare to common planktonic foraminifera and rare benthonic foraminifera including Marssonella turris and Gavelinella spp. This assemblage, within very fine-grained packstones, suggests a deep marine depositional environment with low energy, normal salinity conditions. Deep marine sediments, that include Heterohelix moremanni and forms that may be transitional to H. globulosa, include roveacrinids that compare with the Cenomanian species R. derdereensis and these may prove to be supplementary useful age indicators in such environments. Although their association with pelagic microfossils would suggest a planktonic lifestyle, a definite paleoenvironmental interpretation seems elusive by most authors although there is a direct association between the roveacrinoid abundance and flooding surfaces and high-productivity events. Roveacrinid fragments have been recovered from calcareous mudstones of the Ruwaydha and Tuwayil members of the Aruma Formation that overlie upper Cenomanian grainstones of the Mishrif Member of the Wasia Formation. A regionally significant unconformity separates the Mishrif Formation from the Aruma Formation, of which the basal Aruma represents a significant deep marine transgression. The episodic microcrinoid distribution potentially provides regionally correlative bioevents in addition to their possible relationship with the oceanic anoxic event OAE 2.