Oligocene larger foraminifera from United Arab Emirates, Oman and Western Desert of Egypt

Abstract

An early Oligocene (Rupelian) diagnostic larger foraminiferal assemblage is described and illustrated from marls and limestones of the Asmari Formation, at Jabals Hafit and Malaqet in the UAE. An equivalent assemblage is identified in the mudstones of the Tahwah Formation, Wadi Suq, Oman. Although Nummulites intermedius (D’Archiac 1846) and N. fichteli are fully synonymous (e.g. Roveda 1970; Schaub 1981; Sirel 2003), in this study both species are biometrically differentiated, distinct and both names are valid. N. fichteli Michelotti 1841, N. intermedius (D’Archiac 1846) and N. emiratus n. sp., which are index for the early Oligocene (Rupelian), and they are replacing each others competitively and environmentally. The presence of Blondeauina bouillei n.gen., N. emiratus n.sp., N. intermedius, N. fichteli, Planoperculina complanata (Defrance 1822) and Austrotrillina asmariensis Adams 1968 ascribed the section of the Asmari Formation to the early Oligocene (Rupelian). The studied marls and limestones were deposited in outer and inner shelf environments, respectively. The Asmari Formation in the area studied consists mainly of marl in its lower portion and reefal limestone in its upper part, indicating a major marine regression. The Tahwah Formation in Oman is composed of bioturbated silty and muddy marls and is a facies equivalent to the Asmari Formation marls. The Asmari Formation facies change probably relates to a mid-Oligocene fall in global sea level. In this study, the Dabaa Formation, a subsurface unit of late Eocene–Oligocene marine shales in the northWestern Desert of Egypt, was chosen to correlate with the Oligocene of Emirates and Oman. The Dabaa Formation comprises Spiroclypeus ornatus (Henson 1937) and Eulepidina dilatata (Michelotti 1861). The environment of deposition was inner shelf to littoral, which become estuarine towards the top in many areas. This Oligocene Dabaa sequence is correlatable with Wadi El Arish sequence recently discovered by Kuss and Boukhary (2008) from Risan Aneiza, Northern Sinai, Egypt. Keywords: Oligocene; larger foraminifera;Asmari Formation (UAE); Tahwah Formation (Oman); Dabaa Formation; (Egypt) Introduction This work provides taxonomic, biostratigraphic and paleoecological data on the larger foraminifera from three Oligocene limestone outcrops in the UAE (Asmari Formation, Jabal Hafit), Oman (Tahwah Formation, Wadi Suq) and Egypt (Dabaa Formation, subsurface penetration by two petroleum exploration wells, north Western Desert) (Figure 1). The three formations are part of a broader regional sequence of Oligocene peri-reefal and pelagic carbonate sediments that extends in a narrow linear belt extending through the Arabian Gulf, Iran, Iraq, Syria, NW Egypt and Sinai Peninsula, Egypt, with isolated outcrops in southern Oman and Yemen. The formations were deposited in shallow-water environments in the central segment of the Tethyan seaway after it had become constricted as a result of late Eocene uplift (Jones and Racey 1994). The Oligocene in this region is a very important petroleum-producing sequence, so there are many studies on stratigraphy and sedimentology of these units (James and Wynd 1965; Schlumberger 1981; Cherif and El-Deeb 1984; Hasson 1985; Anan et al. 1992; Hamdan and Bahr 1992; Jones and Racey 1994; Aly and Gameil 2000; Gameil and Aly 2001; Boukhary et al. 2003, 2005, 2008 and Kuss and Boukhary 2008). This contribution achieves precise correlations and ages for these widely distributed stratigraphic units. Details of the early Oligocene paleoenvironment are also obtained from the larger foraminiferal fauna and other facies data.