Late Ordovician agglutinated foraminifera from the Ra’an Shale Member, Qasim Formation of Saudi Arabia as indicators of the O40 Maximum Flooding Surface Michael A. Kaminski 1 , Pramudya Perdana 1 , Mohamed O. Abouelresh 1,2 and Lamidi Babalola 1 1 Geosciences Department, King Fahd University of Petroleum and Minerals, PO Box 701, Dhahran, 31261, Saudi Arabia 2 Faculty of Petroleum and Mining Engineering, Suez University, Suez 43528, Egypt email: kaminski@kfupm.edu.sa ABSTRACT: We report the first finding of Late Ordovician Foraminifera recovered from the Ra’an Shale Member exposed in the Qassim region of Saudi Arabia. The foraminiferal assemblages consist entirely of agglutinated forms, predominantly monothalamids dominated by the genus Thuramminoides. Additionally, rare specimens of two-chambered, pseudochambered, and multichambered forms are also found in the assemblages. The O40 maximum flooding surface is placed at the level of maximum diversity of agglutinated foraminifera. The occurrence of the genus Subreophax in the Ra’an Shale Member revises the known evolutionary history of the pseudomultichambered agglutinated foraminifera. Key words: Ordovician, Foraminifera, Ra’an Shale Member, Qasim Formation, Saudi Arabia. INTRODUCTION The Lower Paleozoic formations in Central Saudi Arabia con- sist mostly of siliciclastic sediments; sandstone interbedded with shale members that are interpreted as representing the maximum flooding surfaces (MFS) (Droste 1997; Sharland et al. 2001). In the Ordovician, the Qasim Formation contains two shale members; the Hanadir Shale Member assigned to the early Middle Ordovician and the Late Ordovician Ra’an Shale Member. These shale members contain the regional O30 and O40 maximum flooding surfaces (text-fig. 1). Foraminifera from these shale members are poorly known, yet these micro- fossils have the potential for accurately pinpointing the MFS. The only previously published study of Ordovician aggluti- nated foraminifera in the Middle East is the report by Nestell et al. (2016) from the Middle Ordovician of Iran. In this study we collected samples from the Ra’an Member near its type locality at Al-Qaraa (26° 23' 15.84" N, 43° 45' 38.50" E) in the Qassim District of central Saudi Arabia (text-fig. 2). The section selected for this study is part of the outcrop belt that trends northwest-southeast in the Qasim-Buraydah area. The purpose of this paper is to report the occurrence and taxonomy of Late Ordovician agglutinated foraminifera from Saudi Ara- bia. This study represents the first report of foraminifera recov- ered from the Ra’an Member of Saudi Arabia. Geological Setting During the Ordovician, much of present-day Saudi Arabia oc- cupied a mid-latitude position at ca. 45°S on the Gondwanan continent (Golonka et al. 2006). During the Middle to Late Or- dovician the area experienced marine stable shelf conditions that persisted until the latest Ordovician. A major marine trans- gression and maximum flooding occurred during the Middle Ordovician resulting in the deposition of the basal shale mem- ber (Hanadir Shale) of the Qasim Formation (Williams et al. 1986; Vaslet 1990). The Qasim Formation consists of two coarsening upward prograding sequences, outcropping as a northwest-southeast trending belt along the northern and northeastern margins of the Arabian Shield (e.g., Senalp and Al-Duaiji 2001). The basal ma- rine Hanadir Shale and the overlying Kahfah Sandstone Members (Williams et al. 1986; Vaslet 1990) represent the lower sequence whereas the upper sequence is comprised of the Ra’an Shale and Quwarah Sandstone Members. Each of the depositional se- quences commenced with maximum flooding surfaces. The MFS O30 is recognized close to the base of the Hanadir Shale and the MFS O40 is placed near the base of the Ra’an Shale (e.g., Sharland et al. 2001; Senalp and Al-Duaiji 2001). A long ridge of the Ra’an Shale Member outcrops in its type lo- cality in Khashm ar Ra’an cuesta in Habashi Quadrangle (e.g., Senalp and Al-Duaiji 2001). The Ra’an Shale is named after Khashm ar Raan and was first described as “the Middle shale” (e.g., Pocok and Kobb 1949), whereas Powers (1968) described it as an informal Unit 3 of the Tabuk Formation. Helal (1964; 1965) described it as the Diplograptus Shale Member. Al-Laboun (1986) proposed the name Ra’an Shale Member of the Qasim Formation. A 40-m thick succession of the Ra’an Shale Member was mea- sured at its type locality at Khashm ar Ra’an (Halwani 2001; Senalp and Al-Duaiji 2001; Saudi Stratigraphic Commission 2013), and it reaches up to 90 m thick in its reference section in the Tabuk region (Halwani 2001). The basal 3.5 m portion of the outcrop at the type locality consists of grey to dark-grey, finely laminated, fissile shale and dark brown, micaceous, graptolite- rich siltstone beds (Senalp and Al-Duaiji 2001; Saudi Strati- graphic Commission 2013). This basal unit is overlain by a 27-m thick gypsum bearing dark grey, fissile shale, silty shales and Stratigraphy, vol. 16, no. 1, text-figures 1–3, table 1, pages 27–39, 2019 27