Stratigraphy of the Valanginian? to Early Paleocene succession in central Saudi Arabia outcrops: Implications for regional Arabian sequence stratigraphy

Abstract

ABSTRACT On the basis of regional lithostratigraphic field mapping, and biostratigraphic and sequence stratigraphic interpretations, the definitions and ranks of the Late Valanginian? to Paleocene rock units that crop out in central Saudi Arabia were revised. The definition of the Late Valanginian? to Early Aptian Biyadh Sandstone is inconsistent with that of the same-named formation in subsurface Saudi Arabia. In outcrop, only the lower Dughum member of the Biyadh Sandstone corresponds to the subsurface Biyadh Sandstone. Accordingly, the Biyadh Sandstone at outcrop was redefined so as to correlate to the same-named subsurface formation; the term Dughum member is considered obsolete. Above the redefined Biyadh Sandstone, the Sallah Formation at outcrop (previously Sallah member of Biyadh Sandstone) yielded the Aptian and/or earliest Albian? ammonite Hypacanthoplites cf. milletianus d’Orbigny; it correlates (in part or completely) to the undifferentiated-Aptian Shu’aiba Formation in Abu Jifan field. The overlying Huraysan Formation (previously Huraysan member of Biyadh Sandstone) is assigned an Albian age based on its stratigraphic position above the Sallah Formation and below the Upper Albian and Cenomanian Majma Formation (previously Majma member of Wasia formation). The Huraysan Formation correlates by stratigraphic position and lithology to the Khafji and Safaniya members of the Wasia Formation in subsurface Saudi Arabia. The Majma Formation may correlate to the Mauddud, Wara and lower part of the Ahmadi members of the subsurface Wasia Formation in Saudi Arabia. The successively overlying Qibah and Malihah formations (previously Qibah and Malihah members of Wasia formation) complete the Cenomanian and Early Turonian succession below the pre-Aruma unconformity. These two formations may correlate to the upper part of the Ahmadi, Rumaila and Mishrif members of the subsurface Wasia Formation in Saudi Arabia. In central Saudi Arabia, the pre-Aruma unconformity is overlain by the Upper Campanian and Lower Maastrichtian Khanasir Member of the Aruma Formation. The Upper Maastrichtian Hajajah and Paleocene Lina members form the upper part of the Aruma Formation. In contrast, the subsurface Aruma Formation in Saudi Arabia may extend to the Coniacian Stage. The Biyadh Sandstone consists of coastal-plain clastics deposited during several transgressive-regressive sequences. It overlies the pre-Biyadh unconformity, which is represented by west-cutting regional erosion that reaches down to the Jurassic Dhruma and underlying Marrat formations. The overlying Sallah Formation represents a transgressive-regressive sequence deposited in lagoonal and tidal settings, and includes limestone beds with marine fauna. The overlying Huraysan Formation consists of fluvial, fining-upward clastics and is, together with older units, regionally eroded by the pre-Majma unconformity. The associated pre-Majma hiatus probably occurred in the Late Albian and is characterized by the Az Zabirah Bauxite, a deposit that reflects a pedogenic episode that occurred in tropical humid conditions. The fluvial and marginal marine clastics of the Majma Formation, and marine clastics and carbonates of the Qibah Formation, can together be characterized in terms of three flooding events. The Malihah Formation was deposited in mixed proximal settings (tidal to fluvio-deltaic) and exposed (paleosols with bauxite). It represents a regression associated with the eastward tilting of the Arabian Plate during Turonian tectonism along the Neo-Tethyan margin. Central Saudi Arabia remained exposed during the Late Turonian through Middle Campanian, during which times the pre-Aruma Bauxite formed. The Aruma Formation is characterized by four third-order sequences; one in the Khanasir Member, two in the Hajajah Member – all of Late Cretaceous age, and the Paleogene Lina sequence.