Acarinina rohri (Bronnimann and Bermudez, 1953)

Salama, Yasser, Sayed, Mostafa, Saber, Shaban & El-Gaied, Ibrahim Abd, 2021, Eocene planktonic foraminifera from the north Eastern Desert, Egypt: Biostratigraphic, paleoenvironmental and sequence stratigraphy implications, Palaeontologia Electronica (a 11) 24 (1), pp. 1-29 : 15-16

Acarinina rohri (Bronnimann and Bermudez, 1953)

Acarinina spinuloinflata (Bandy, 1949)

Acarinina topilensis (Cushman, 1925)

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acterized by an absence of planktonic species. It is equivalent to the benthic foraminiferal Pyrgo elongata zone recorded by Abd El-Gaied et al. (2019) from the studied section. The identified benthic species in this interval includes miliolid, textularid, and nummulitid foraminifera. This interval assigned the Late Eocene age based on its stratigraphic position and the occurrence of the marker small and large benthic foraminifera ( Nummulites and Operculina ) and macrofossils ( Carolia placunoides and other bivalves; large and small size of gastropods, corals and echinoids). The abundance of the miliolids, textularids, and nummulitids with a remarkable extinction of the planktonic foraminifera at this interval of the studied succession was related to fall of the eustatic sea-level that took place at the end of the Late Eocene (Berggren et al., 1985; Keller et al., 1987; Anan 1995, 2007).

Middle / Upper Eocene (Bartonian / Priabonian) Boundary

Up until now, the Global Stratotype Section and Point (GSSP) for the Middle /Upper Eocene (Bartonian/Priabonian) boundary has not been designated. Generally, in Egypt the Middle -Upper Eocene (Bartonian/Priabonian) boundary was traced at the lowest occurrence of Globigerinatheka semiinvoluta (Strougo, 1992 and 2008; Abd El-Shafy et al., 2007; Strougo et al., 2013 and Marzouk et al., 2014). Some authors placed this boundary at the last appearance of Truncorotaloides (Acarinina) rohri and the associated spinose forms (Haggag, 1986, 1989a, 1989b; Haggag and Luterbacher, 1991; Abd El-Aziz, 2002; Abdallah et al., 2003; Abd El-Gaied and Abd El-Aziz, 2005). Haggag (1992a, b) studied the planktonic foraminiferal groups in the Middle and Upper Eocene succession in different localities of Egypt and recognized that the Middle /Upper Eocene (Bartonian / Priabonian) boundary traced at the top of the Turborotalia pseudoampliapertura zone. However, Aly et al. (2011) and Abd El-Gaied et al. (2019) placed this boundary between the benthic foramineferal Palmula ansaryi zone and the Bulimina jacksonensis zone. Some authors (Blow, 1979; Toumarkine and Luterbacher, 1985; Shahin, 1992; Berggren et al., 1995; Haggag and Bolli, 1996; Mukhopadhyay, 2003 and others) considered the extinction of the middle Eocene spinose planktonic foraminifera as a marker for the boundary between the late Middle and the earliest Upper Eocene in the tropical and Mediterranean reagions. Others considered the first appearance of the Globigerinatheka semiinvoluta simultaneously with the disappearance of the Middle Eocene Truncorotaloides, Morozovellids , and the large Acarinina distinguished the Middle /Upper Eocene boundary (Strougo, 1992, 2008). According to the standard chronostratigraphic scale, the Bartonian/ Priabonian boundary is located either at the P14/ P15 zonal boundary or at the lower part of zone P15 (Toumarkine and Luterbacher, 1985; Berggren et al., 1995). In Egypt and the Middle East, Anan (1994, 2011), Hussein (1998), Helal (2002), Aly et al. (2011), and Abd El-Gaied et al. (2019) placed the Bartonian/Priabonian boundary at the last appearance of the benthic foraminiferal species palmula ansaryi . In the present study, the boundary between the Middle Eocene (Bartonian) and Upper Eocene (Priabonian) was located within the Globigerinatheka semiinvoluta zone (according to the works of Berggren and Pearson (2005), Wade et al., (2011), and Karoui-Yaakoubi (2017). The sedimentary succession at this boundary was characterized by shale and marl intercalations.