Introduction

The Miocene successions in the Gulf of Suez are characterized by their vertical and lateral facies changes due to the tectonic rift events that complicated the stratigraphic correlation. An integrated planktonic foraminiferal and calcareous nannoplankton biostratigraphy may help in establishing a more accurate correlation in that area. Among the most significant recent publications on the Gulf of Suez area are El-Heiny and Martini (1981), Andrawis and Abdel Malik (1981), Evans (1988), Haggag et al. (1990), El-Azabi (2004), Moustafa (2004), Abul-Nasr et al. (2009), Mandur (2009), Mandur and Baioumi (2011), Abed El-Naby et al. (2010), and Hewaidy et al. (2012, 2013).

The present study is an attempt to integrate the planktonic foraminifera and calcareous nannoplankton biostratigraphic classifications of the Lower to Middle Miocene subsurface successions in the Gulf of Suez region. It also sheds more light on the depositional environmental conditions which prevailed during deposition of the studied successions.

Material and methods

The material of the present work includes 187 ditch samples obtained from three wells (Fig. 1), named from north to south: GS160-2 (latitude 28° 57′ 14″ N and longitude 32° 57′ 32″ E), QQ-89 (latitude 27° 47′ 55″ N and longitude 33° 33′ 36″ E), and Ras Elush (latitude 27° 53′ 29″ N and longitude 33° 33′ 08″).

Fig. 1
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Location map of the studied wells (modified after Moustafa 1976, and Salah 1994)

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The obtained residues were dried, packed, and studied under binocular Olympus stereoscopic microscope. The calcareous nannofossils were separated from the studied samples and identified by using an Olympus polarized microscope with ×100 oil immersion lens. The paleoenvironments in the present study were determined based on quantitative and qualitative foraminiferal analyses. The paleoenvironmental interpretation methods are explained by several authors (Culver 1988; Armentrout 1996; Leckie and Olson 2003; Miller et al. 2008); Hewaidy et al. 2013, and Farouk et al. 2014). The planktic/benthic ratios (P/B %) is an important tool in depth zonation (Van der Zwaan et al. 1990), which is expressed as 100 × P/(P + B). This ratio is lowest in the shallower marine waters and generally increases with depth until the carbonate compensation depth (CCD). The planktic/benthic ratios pointed out that the inner shelf (10–50 m depth) is characterized by low planktic percentages (1–5 %) with low species diversity and high benthic percentages; the middle shelf depth (50–100 m) is characterized by 8–25 % planktonic foraminifera and higher species diversity, and the outer shelf depth (100–200 m) is marked by 30-70 % planktonic foraminiferal assemblage. The species diversity is represented by the total number of foraminiferal species, which increases away from the shore up to the middle and outer shelf depths and then decreases in deeper marine. The benthic foraminiferal groups identified in the present study are the miliolid group (Spiroloculina, Quinqueloculina, and Pyrgo); nodosariid group (Nodosaria, Dentalina, and Lenticulina); buliminid group (Bolivina, Stillostomella, Bulimina, Uvigerina, and Rectuvigerina); and rotaliid group (Nonion, Chilostomella, Nonionella, Siphonina, Elphidium, Eponides, and Cibicides).

Lithostratigraphy

The Miocene successions in the Gulf of Suez region are subdivided by many workers into several rock units (Fig. 2). In the present study, the lithostratigraphic classification of the National Stratigraphic Subcommittee of the Geological Sciences of Egypt (N.C.G.S 1976) is used. The studied Lower to Middle Miocene successions are classified into the Belayim, Kareem, Rudeis, and Nukhul formations from younger to older. The following is a brief description for these units.

Fig. 2
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Comparison of the Miocene rock units used by different authors in Egypt

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The Belayim Formation

It includes the oldest part of the main Miocene evaporite cycle in the Gulf of Suez region (Ghorab 1964). It unconformably underlies South Gharib Formation and unconformably overlies Kareem Formation at its type section at Belayim well 112–12 in the Gulf of Suez area (Issawi et al. 1999). In the studied wells, the thickness of the Belayim Formation varies from 450 ft in GS 160-2 to 280 ft in Ras Elush and is much reduced to 16 ft in the QQ-89 well. It is composed of shale and siltstone interbeded with creamy white, cryptocrystalline anhydrite (Fig. 3). It is assigned to the Serravallian age based on its microfaunal constant. The pronounced changes in thickness, facies, and the development of evaporites in the Belayim Formation are probably due to the separation of the Gulf of Suez from the Mediterranean by a structural high in the northern Gulf of Suez (Patton et al. 1994).

Fig. 3
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Lithostratigraphic correlation chart of the Miocene successions in the studied wells

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The Kareem Formation

The type locality of the Kareem Formation is at Gharib North well no. 2, Gulf of Suez (Ghorab 1964). In the study area, it is composed of grey to greenish, moderately hard, richly fossilliferous, shale, interbeded with white to brown, moderately hard, crystalline limestone and anhydrite (Fig. 3).

The thickness of this formation varies from place to another according to its position in the tectonic setting. In the GS 160-2 well, the Kareem Formation is about 200 ft thick, while at the QQ-89 well, the thickness of this formation is about 254 ft and is missing in the Ras Elush well southwards. It unconformably overlies the Rudeis Formation and unconformably underlies the Belayim Formation. The age of this formation is the Middle Miocene (Langhian).

The Rudeis Formation

Ghorab (1964) described the Rudeis Formation at its type locality in the Rudeis-2 well in west central Sinai as open marine sediments. In the studied wells, it is composed of shales, sandy shales, and calcareous shales rich in microfossils, with light to dark grey, brownish grey, medium to hard sandstone interbeds and occasionally thin yellowish grey massive sandy limestone streaks. The formation is most thick (2335 ft) at the Ras Elush well; 210 ft at GS 160-2, and to about 470 ft thick at the QQ-89 well (Fig. 3). In the present study, the Rudeis Formation overlies unconformably the Nukhul Formation and underlies unconformably the Kareem Formation at GS 160-2 or unconformably the Belayim Formation at the Ras Elush well. At the QQ-89 well, the Rudeis Formation overlies unconformably the Pre-Cambrian basement paleo-high (Fig. 3). This formation is assigned to the Early Miocene (Burdigalian)–Middle Miocene (Langhian) age.

The Nukhul Formation

The Nukhul Formation at its type locality in Wadi Nukhul overlies unconformably the Oligocene Tayiba Red-Beds (Waite and Pooely 1953). At the Ras Elush well, it consists of very fine crystalline, moderately hard limestone, occasionally dolomitic and sandy limestone, interbeded with dark to greenish grey and slightly calcareous shale. In the GS 160-2 well, the Nukhul Formation consists of greenish grey shale, argillaceous sandstone, and light grey to grey, moderately hard, silty sandstone (Fig. 3). The basal Miocene sandstone recorded in the QQ-89 well is pale-yellow sandstone, fine to medium grained, moderately to well sorted, moderately hard, barren of any microplanktonic assemblages. It may be equivalent to the Nukhul Formation (Fig. 3). This formation is recorded in the Ras Elush well (about 230 ft) and GS 160-2 well (about 180 ft).

It unconformably overlies the Lower Eocene Thebes Formation and unconformably underlies the lower Miocene Rudeis Formation at the GS 160-2 and Ras Elush wells. The age of the Nukhul Formation is Early Miocene (Aquitanian).

Biostratigraphy

The biostratigraphic zonations in the present study are based on the planktonic foraminifera and calcareous nannofossil assemblages. The identified biostratigraphic units of planktonic foraminifera (Tables 1 and 2) and calcareous nannofossil (Tables 3 and 4) are correlated with other biostratigraphic units in different localities in and outside Egypt.

Table 1 Comparison of planktonic foraminiferal zones in the present study with the most common zones outside Egypt
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Table 2 Comparison of planktonic foraminiferal zones in the present study with the most common zones of Egypt
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Table 3 Comparison of calcareous nannoplankton zones in the present study with the most common zonations in the world
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Table 4 Comparison of calcareous nannoplankton zones in the present study with the most common zonations in Egypt
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The examination of the Miocene successions in the studied wells has led to the identification of 47 planktonic foraminiferal species (belonging to 11 genera), 54 benthonic foraminiferal species (belonging to 25 genera), and 64 calcareous nannofossil species (belonging to 21 genera).

The vertical distributions of these microfossils enabled the subdivision of the studied succession into seven planktonic and six calcareous nannofossil biozones (Figs. 4, 5, 6, 7, 8, and 9). The most important planktonic and benthic foraminiferal and calcareous nannofossil species are shown on Plates 1, 2, and 3.

Fig. 4
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Distribution chart of the planktonic foraminiferal species recorded in the Ras Elush well

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Fig. 5
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Distribution chart of the planktonic foraminiferal species recorded in the QQ-89 well

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Fig. 6
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Distribution chart of the planktonic foraminiferal species recorded in the GS160-2 well

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Fig. 7
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Distribution chart of the calcareous nannoplankton species recorded in the Ras Elush well

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Fig. 8
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Distribution chart of the calcareous nannoplankton species recorded in the QQ-89 well

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Fig. 9
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Distribution chart of the calcareous nannoplankton species recorded in the GS 160-2 well

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Plate 1
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1 Quinqueloculina cuvieriana d’Orbigny, 1839, QQ-89 well, Middle Miocene (Langhian), Kareem Formation, depth 2410 ft. 2 Quinqueloculina juleana d’Orbigny, 1846, GS 160-2 well, Middle Miocene (Langhian), Kareem Formation, depth 7690 ft. 3 Quinqueloculina seminulua (Linnaeus, 1758), GS 160-2 well, Early Miocene (Aquitanian), Nukhul Formation, depth 8080 ft. 4 Nodosaria soluta (Reuss, 1851), QQ-89 well, Middle Miocene (Langhian), Kareem Formation, depth 2500 ft. 5 Lenticulina antipodum (Stache, 1865), Ras Elush well, Early Miocene (Burdigalian), Rudeis Formation, depth 1470 ft. 6 Lenticulina iota (Cushman, 1923), Ras Elush well, Early Miocene (Aquitanian), Nukhul Formation, depth 3120 ft. 7–8 Bolivina fastigla Cushman, 1953, Ras Elush well, Early Miocene (Burdigalian), Rudeis Formation, depth 1550 ft. 9 Bolivina superba Emiliani, 1949, Ras Elush well, Early Miocene (Burdigalian), Rudeis Formation, depth 1670 ft. 10 Bulimina pupoides d’Orbigny, 1846, Ras Elush well, Early Miocene (Burdigalian), Rudeis Formation, depth 1770 ft. 11 Bulimina striata d’Orbigny, 1846, QQ-89 well, Middle Miocene (Langhian), Kareem Formation, depth 2440 ft. 12 Uvigerina barbatula barbatula Macfadyen, 1930, QQ-89 well, Middle Miocene (Langhian), Rudeis Formation, depth 2700 ft. 13 Uvigerina coastat Bieda, 1936, GS 160-2 well, Early Miocene (Aquitanian), Nukhul Formation, depth 8040 ft. 14–15 Uvigerina pygmoides Papp & Turnovsky, 1953, QQ-89 well, Middle Miocene (Langhian), Kareem Formation, depth 2440 ft. 16 Uvigerina striatissima Perconing, 1955, Ras Elush well, Early Miocene (Aquitanian), Nukhul Formation, depth 3020 ft. 17 Uvigerina venusta Franzenau, 1894, GS 160-2 well, Early Miocene (Aquitanian), Nukhul Formation, depth 8020 ft. 18 Stilostomella subspinosa (Cushman, 1943) Ras Elush well, Early Miocene (Burdigalian), Rudeis Formation, depth 1200 ft. 19–20 Eponides repandus (Fichtel & Moll, 1798), Ras Elush well, Early Miocene (Aquitanian), Nukhul Formation, depth 3030 ft. 21 Cibicides boueanus (d’Orbigny, 1826), Ras Elush well, Early Miocene (Burdigalian), Rudeis Formation, depth 1510 ft. 22 Cibicides ellisi ellisi Souaya, 1965, GS 160-2 well, Early Miocene (Burdigalian), Rudeis Formation, depth 7980 ft. 23. Cibicides ellisi graysoni Souaya, 1965, QQ-89 well, Middle Miocene (Langhian), Kareem Formation, depth 2740 ft. 24 Nonion scaphum (Fichtel and Moll, 1798), Ras Elush well, Early Miocene (Burdigalian), Rudeis Formation, depth 1950 ft. 25 Nonionella spissa Cushman, 1931, Ras Elush well, Early Miocene (Burdigalian), Rudeis Formation, depth 1990 ft. 26–27 Melonis pompiloides Fichtel and Moll, 1803, Ras Elush well, Early Miocene (Burdigalian), Rudeis Formation, depth 2940 ft. 28 Chilostomella czizecki Reuss, 1850, QQ-89 well, Middle Miocene (Langhian), Rudeis Formation, depth 2800 ft. 29 Elphidium pustullosum Cushman & Mcculloch, 1940, QQ-89 well, Middle Miocene, (Langhian), Rudeis Formation, depth 3030 ft

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Plate 2
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1–2 Globorotalia mayeri Cushman & Ellisor, 1939, QQ-89 well, Middle Miocene (Langhian), Kareem Formation, depth 2450 ft. 3–4 Globorotalia munda Jenkins, 1966, Ras Elush well, Early Miocene (Aquitanian), Nukhul Formation, depth 3030 ft. 5 Paragloborotalia kugleri Bolli 1957, Ras Elush well, Early Miocene (Aquitanian), Nukhul Formation, depth 3200. 6 Neogloboquadrina humerosa Takayanagi & Saito, 1962, QQ-89 well, Middle Miocene (Langhian), Kareem Formation, depth 2440 ft. 7 Globigerina ciperoensis Bolli 1954, Ras Elush well, Early Miocene, (Aquitanian), Nukhul Formation depth 2980 ft. 8–9 Globigerina bulloides d’Orbigny 1826 Ras Elush well, Early Miocene (Burdigalian), Nukhul Formation depth 2290 ft. 10 Globigerina nepenthes Todd 1957, Ras Elush well, Early Miocene, (Burdigalian), Rudeis Formation, depth 1710 ft. 11–12 Globigerina seminulina Schwager 1866 QQ-89 well, Middle Miocene (Langhian), Rudeis Formation, depth 2650 ft. 13 Globigerinella obesa (Bolli 1957), Ras Elush well, Early Miocene (Burdigalian), Rudeis Formation, depth 1430 ft. 14–15 Globigerinoides altiapertura (Bolli 1957), G S 160–2 well, Early Miocene (Burdigalian), Rudeis Formation, depth 2870 ft. 16–17 Globigerinoides immaturus (Le Roy, 1939) QQ-89 well, Middle Miocene (Langhian), Rudeis Formation, depth 2770 ft. 18–19 Globigerinoides primordius (Blow and Banner, 1962), GS 160-2 well, Early Miocene (Aquitanian), Nukhul Formation, depth 8120 ft. 20 Globigerinoides subquadratus Brönnimann, 1954, Ras Elush well, Middle Miocene (Langhian), Rudeis Formation, depth 800 ft. 21–22 Globigerinoides trilobus Reuss, 1850, Ras Elush well, Early Miocene (Burdigalian), Rudeis Formation, depth 2200 ft. 23 Sphaeroidinellopsis seminulina (Schwager, 1866), GS 160-2 well, Middle Miocene (Serravallian), Belayim Formation, depth 7260 ft. 24 Orbulina bilobata d’Orbigny, 1846, QQ-89 well, Middle Miocene (Langhian), Kareem Formation, depth 2380 ft. 25 Orbulina suturalis Brönnimann, 1951, QQ-89 well, Middle Miocene (Serravallian), Belayim Formation, depth 2340 ft. 26 Praeorbulina glomerosa curva Blow 1956 Ras Elush well, Middle Miocene (Langhian), Rudeis Formation, depth 670 ft. 27 Praeorbulina transitoria Blow 1956 Ras Elush well, Middle Miocene, (Langhian), Rudeis Formation, depth 700 ft

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Plate 3
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1–3 Helicosphaera ampliaperta (Bramlette and Wilcoxon 1967) 1, GS 160-2 well, Rudeis Formation, Early Miocene (Burdigalian), depth 7700 ft. 2–3 Ras Elush well, Rudeis Formation, Early Miocene (Burdigalian), depth 900 and 1740 ft. 4–5 Helicosphaera mediterranea (Muller, 1981). 4 Ras Elush well, Rudeis Formation, Early Miocene (Burdigalian), depth 2350 ft. 5 QQ-89 well, Rudeis Formation, Middle Miocene, (Langhian), depth 2590 ft. 6 Helicosphaera ampliaperta (Bramlette and Wilcoxon 1967), GS 160-2 well, Rudeis Formation, Early Miocene (Burdigalian), depth 7700 ft. 7–8 Helicosphaera carteri (Wallich 1877) Kamptner, 1954 7. GS 160-2 well, Kareem Formation, Middle Miocene (Langhian), depth 7680 ft. 8 QQ-89 well, Kareem Formation, Middle Miocene (Langhian), depth 2400 ft. 9–10 Helicosphaera euphratis (Haq, 1966). 9 Ras Elush well, Nukhul Formation, Early Miocene (Aquitanian), depth 3040 ft. 10. Ras Elush well, Rudeis Formation, Early Miocene (Burdigalian), depth 1120 ft. 11–12 Helicosphaera rhomba (Bukry, 1971), 11. Ras Elush well, Nukhul Formation, Early Miocene (Burdigalian), depth 1200 ft. 12 Ras Elush well, Rudeis Formation, Early Miocene (Burdigalian), depth 2250 ft. 13 Reticulofenestra pseudoumblica (Gartner, 1967), Ras Elush well, Rudeis Formation, Early Miocene (Burdigalian), depth 970 ft. 14 Reticulofenestra lockeri (Müller, 1970), GS 160-2 well, Nukhul Formation, Early Miocene (Aquitanian), depth 8080 ft. 15 Ericsonia robusta (Bramlette & Sullivan, 1961), GS 160-2 well, Nukhul Formation, Early Miocene (Aquitanian), depth 7800 ft. 16 Coccolithus miopelagicus (Bukry, 1971), QQ-89 well, Rudeis Formation, Middle Miocene (Langhian), depth 2800 ft. 17 Ericsonia formosa (Kamptner, 1963 Ras Elush well, Rudeis Formation, Early Miocene (Burdigalian), depth 1660 ft. 18 Sphenolithus moriformis (Bronnimann and Stradner, 1960) GS 160-2 well, Rudeis Formation, Middle Miocene (Langhian), depth 7900 ft. 19–21 Sphenolithus heteromorphus (Deflandre, 1953). 19 GS 160-2 well, Rudeis Formation, Early Miocene (Burdigalian), depth 7820 ft. 20–21 QQ-89 well, Kareem Formation, Middle Miocene (Langhian), depth 2350 and 2600 ft. 22 Micrantholithus vesper (Deflander, 1950), Ras Elush well, Kareem Formation, Middle Miocene (Langhian), depth 2600 ft. 23–25 Discoaster druggii (Bramlette and Wilcoxon 1967), 23. Ras Elush well, Nukhul Formation, Early Miocene (Aquitanian), depth 2950 ft. 24–25 GS 160-2 well, Nukhul Formation, Early Miocene (Aquitanian), depth 8010 ft. 26 Discoaster variabilis (Martini & Bramlette, 1963), Ras Elush well, Rudeis Formation, Early Miocene (Burdigalian), depth 950 ft. 27 Discoaster deflandrei (Briolette & Riedel, 1954), QQ-89 well, Kareem Formation, Middle Miocene (Langhian), depth 2400 ft. 28 Discoaster aulakos (Gartner, 1967), QQ-89 well, Rudeis Formation Middle Miocene (Langhian), depth 2780 ft. 29 Discoaster adamanteus (Bramlette and Wilcoxon 1967), Ras Elush well, Rudeis Formation, Early Miocene (Burdigalian), depth 1240 ft. 30–31 Discoaster barbadiensis (Tan, 1927), GS 160-2 well, Eocene, depth 8180 ft. 32 Discoaster exilis (Martini & Bramlette, 1963), GS 160-2 well, Belayim Formation, Middle Miocene (Serravallian), depth 7250 ft

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Planktonic foraminiferal biozones

The Miocene planktonic foraminiferal biozonation of the scheme of Iaccarino (1985) is used in the present study taking into consideration the revisions given by Berggren et al. (1995) and Wade et al. (2011). The Lower–Middle Miocene successions in the studied wells are subdivided into seven biozones as follows from older to younger.

Paragloborotalia kugleri (M1) Zone

Bolli (1957) introduced this zone as a total range of the nominate taxon. This zone is recorded only in the Ras Elush well from a depth of 3200 to 3100 ft (100 ft thick) (Fig. 4). This zone is marked by low diversity and moderately preserved planktonic foraminiferal assemblages. The first occurrence (FO) of P. kugleri (Bolli) is used to define the Oligocene/Miocene boundary (Stainforth et al. 1975; Berggren et al. 1995; Wade et al. 2011). In Egypt, due to the rarity or absence of P. kugleri, the Oligocene/Miocene boundary is defined by the FO of the large-sized and common occurrence of the genus Globigerinoides (Haggag et al. 1990; Phillip et al. 1997; Hewaidy et al. 2012; Farouk et al. 2014). On the other hand, the FO of the small- sized Globigerinoides primordius Blow and rare occurrence of Globigerina ciperoensis Bolli are considered of the Oligocene age (Ouda and Masoud 1993; Mancin et al. 2003; Kuĉenjak et al. 2006; Hewaidy et al. 2013). In the Ras Elush well, this zone is defined by the occurrence of P. kugleri.

G. primordius (M2) Zone

According to Blow (1969), this zone is defined as the interval from the last occurrence (LO) of P. kugleri (Bolli) to the LO of G. primordius Blow. This interval is characterized by abundant planktonic species (Figs. 4 and 6). The G. primordius (M2) Zone is assigned to the Aquitanian age. This zone occupies the upper part of the Nukhul Formation, in the Ras Elush well at a depth of 3100 to 2950 ft (150 ft thick), while in the GS 160-2 well it occurs between depths of 8130 to 7980 ft (150 ft) and is not recorded in the QQ-89 well (Figs. 4 and 6). It is equivalent to the Globoquadrina binaiensis (M2) partial-range Zone of Berggren et al. (1995) and Wade et al. (2011). It is also equivalent to the Globoquadrina dehiscens dehiscens subzone and lower part of the Globigerinoides altiaperturus/Catapsydrax dissimilis Zone in the Mediterranean region, by Iaccarino (1985). In Egypt, this zone is recorded from the base of the Rudeis Formation (Kerdany 1968; Andrawis and Abdel Malik 1981; El-Heiny and Martini 1981; Haggag et al. 1990; Phillip et al. 1997; Mandur 2009; Hewaidy et al. 2012).

G. altiaperturus (M3) Zone

This zone was originally established by Bolli (1957) as the interval from the LO of G. primordius Blow to the LO of G. altiaperturus Bolli. The planktonic assemblage of this zone is characterized by common occurrence of the genus Globigerinoides, in addition to the assemblage shown in Fig. 4. According to its content, this zone is assigned to the Burdigalian age. The G. altiaperturus Zone occupies the lowermost part of the Rudeis Formation at the Ras Elush well only from depths of 2950 to 2390 ft (560 ft) (Fig. 4). The LO of G. primordius and the FO of Globigerinella obesa are observed in this zone. It is equivalent to the Globigerinatella sp./C. dissimilis concurrent range Zone of Berggren et al. (1995) and Wade et al. (2011).

Globigerinoides trilobus (M4) Zone

This zone is defined as the interval from the LO of G. altiaperturus Bolli to the FO of Praeorbulina glomerosa (Blow). It is assigned to the Early Miocene (Burdigalian) according to its planktonic foraminiferal assemblage (Figs. 4, 5, and 6). This zone is recorded from the lower part of the Rudeis Formation from 2390 to 850 ft (1540 ft thick) in the Ras Elush well; at the GS 160-2 well, it is recorded from depths of 7950 to 7780 ft (170 ft thick) while in the QQ-89 well it is recorded from 3050 to 2950 ft (100 ft thick) (Figs. 4, 5, and 6). This zone is equivalent to the Globigerinoides bisphericus (M4) partial-range Zone of Berggren et al. (1995), and Wade et al. (2011). It is subdivided into two subzones based on the LO of C. dissimilis and/or Catapsydrax unicavus and the FO of the Globorotalia birnageae Zone. In Egypt, this zone is equivalent to the C. dissimilis/Praeorbulina sicana (M4) Zone recorded by Hewaidy et al. (2013) and to the G. trilobus Zone which was recorded by many authors (Haggag et al. 1990; Phillip et al. 1997; Mandur 2004).

Praeorbulina sicanus/P. glomerosa (M5) Zone

According to Iaccarino (1985), this zone is defined as the interval from the FO of P. sicana De Stefani to the LO of P. glomerosa (Blow). This zone is characterized by abundant planktonic species (Figs. 4, 5, and 6). It is assigned to the Middle Miocene (Langhian). The P. sicanus/P. glomerosa Zone is recognized from the upper part of the Rudeis Formation in the three studied wells in the Ras Elush well between 850 and 690 ft (160 ft thick), in the GS 160-2 well between 7780 and 7710 ft (70 ft thick), and in the QQ-89 well from 2950 to 2650 ft (300 ft thick), (Figs. 4, 5, and 6). It is equivalent to P. glomerosa of Iaccarino (1985). Berggren et al. (1995) classified the M5 (Globigerinoides sicanus-Orbulina suturalis) Zone into two subzones: G. sicanus-P. glomerosa (M5a) and P. glomerosa-O. suturalis (M5b). In Egypt, this zone could be equated to the P. glomerosa Zone of Kerdany (1968) in the Gulf of Suez, and Farouk et al. (2014) in the Nile Delta. This zone is correlated with the lower part of the G. sicanus/Globigerinoides transitoria Zone of Wasfi (1968), G. sicanus Zone of Beckmann et al. (1968) and P. sicanus/O. suturalis Zone (M5) of Hewaidy et al. (2013). It is equivalent to the P. glomerosa (Blow) Zone described by Bolli (1957, 1966), Stainforth et al. (1975), and Postuma (1971).

O. suturalis (M6) Zone

This zone was originally established by Blow and Banner (1966) as the interval from the FO of O. suturalis (Brönnimann) to the FO of Globorotalia peripheroronda Blow and Banner. The faunal assemblage of this zone in the present study differs from one well to another. In QQ-89, it is common and well preserved, while in GS 160-2, it is rare and poorly preserved (Figs. 5 and 6). The zone is assigned to the Middle Miocene (Langhian) age according to its planktonic foraminiferal content. This zone is recognized from the lower part of the Kareem Formation. In the GS 160-2 well, it is represented by the interval 7710 to 7640 ft (70 ft thick), while in the QQ-89 well, it is represented by the interval 2650 to 2320 ft (260 ft) (Figs. 5 and 6). It could be correlated with the O. suturalis Zone of Iaccarino (1985), Globorotalia lobata Zone (N12) of Kennett and Srinivasan (1983), Globorotalia fohsi Zone of Bolli (1966) and Stainforth et al. (1975) and G. peripheroronda (M6) Zone of Hewaidy et al. (2013). It is recorded by different authors in Egypt (Haggag et al. 1990; Abu El Enein 1990; Mandur 2004).

Globorotalia praemenardii/G. peripheroronda (M7) Zone

Berggren et al. (1995) defined this zone as the interval from the FO of G. praemenardii Cushman and Stainforth to the LO of G. peripheroronda Blow and Banner. It is characterized by low abundance and poor preservation of foraminiferal assemblages (Fig. 6). It is recognized from the upper part of the Belayim Formation at the GS 160-2 well only between 7300 and 7190 ft (110 ft thick) (Fig. 6) and is assigned to the Middle Miocene (Serravallian) age according to its planktonic foraminiferal content. It corresponds to the O. suturalis/G. peripheroronda Zone of Iaccarino (1985) and Fohsella peripheroacuta Zone of Berggren et al. (1995) and Wade et al. (2011) of the Serravallian age. In the Mediterranean region, Kennett and Srinivasan (1983) recorded the Globorotalia siakensis Zone (N15) which may be equivalent to this zone.

Calcareous nannofossil biozones

The Miocene calcareous nannofossil assemblages were studied by several workers (Bramlette and Wilcoxon 1967; Kerdany 1968; Martini 1971; Muller 1978; Okada and Bukry 1980; El-Heiny and Martini 1981; Chi 1981; Stanley and Chi 1983; Theodoridis 1984; Sadek 2001; Mandur 2004, 2009; Marzouk 2009; Soliman et al. 2012; Holcovkà 2013). Six calcareous nannofossil biozones are recognized on the basis of the zonal scheme of Martini (1971). These biozones are discussed, from base to top as follows:

Triquetrorhabdulus carinatus (NN1) Zone

This zone was assigned to the Late Oligocene to Early Miocene according to its characteristic assemblage (Fig. 7). In the present study, the T. carinatus Zone is recorded only from the lower part of the Nukhul Formation at the Ras Elush well between 3200 and 3100 ft (100 ft thick). The absence of Helicosphaera recta, Discoaster druggii, and Sphenolithus ciperoensis suggests an earliest Miocene age for this zone. This zone is recorded in the Gulf of Suez (Arafa 1991; Mandur 2004, 2009), and not recorded by others (Faris et al. 2007, 2009). This is due to the major hiatus near the base of the Nukhul Formation in the region. It is equivalent to the T. carinatus Zone of Bramlette and Wilcoxon (1967) and Martini (1971). Also, it corresponds to the Cyclicargolithus abisectus (CN1a) and Discoaster deflandrei (CN1b) subzones of Okada and Bukry (1980). This zone is equivalent to the T. carinatus/Sphenolithus belemnos (CNM2) concurrent range Zone of Backman et al. (2012). It equates also with Sphenolithus delphix of Gradstein et al. (2012) (Tables 3 and 4).

D. druggii (NN2) Zone

Martini and Worsley (1970) introduced this zone as the interval from the FO of D. druggii Bramlette and Wilcoxon to the LO of T. carinatus Martini. This zone yielded a poor nannofossil assemblage in the GS 160-2 well, while in the Ras Elush well it includes abundant assemblage (Figs. 7 and 9). It is assigned to the Early Miocene (latest Aquitanian to lower most Burdigalian). In the studied successions, this zone is recorded from the Nukhul Formation in the Ras Elush well between 3060 and 2550 ft (510 ft thick), while in the GS 160-2 well it is represented by the interval form 8130 to 7980 ft (150 ft thick). It is not recorded in the QQ-89 well as this interval is composed of barren sands (Figs. 7, 8, and 9). The FO of D. druggii is used to define (NN2) Zone in the zonal scheme of Martini (1971). In the studied wells, the presence of D. druggii, Cyclicargolithus floridanus, and Calcidiscus leptoporus refers to the NN2 Zone which is recorded by some authors in Egypt (e.g., Faris et al. 2007, 2009; Mandur 2004, 2009) (Tables 3 and 4).

S. belemnos (NN3) Zone

This zone was originally established by Bramlette and Wilcoxon (1967) and emended by Martini (1971). It is represented by the interval from the LO of T. carinatus Martini to the LO of S. belemnos Bramlette and Wilcoxon. It is assigned to the Early Miocene (Burdigalian) age based on its content from the typical Miocene nannofossil taxa, which is characterized by good preservation and common abundance (Fig. 7). This zone is recorded only from the Rudeis Formation in the Ras Elush well between 2550 and 2300 ft (250 ft thick), while this zone is not recorded in the GS 160-2 and QQ-89 wells because the Gulf of Suez was characterized by strong rifting during this time (Figs. 7, 8, and 9). This zone is equivalent to the S. belemnos NN3 Zone of Bramlette and Wilcoxon (1967), Bukry (1973), Backman et al. (2012), and Holcovkà (2013) (Table 3). Several workers have proposed the FO of Sphenolilhus belemnos as an alternative marker bioevent for the NN2/ NN3 boundary (Fornaciari et al. 1993; Fornaciari and Rio 1996; Faris et al. 2009). In the present study, the LO of this species is the marker event for the NN3/NN4 zonal boundary (Martini 1971). It is also equivalent to the D. deflandrei Zone of Kerdany (1968) and S. belemnos Zone of El-Heiny and Martini (1981), Marzouk (2009), Mandur (2004, 2009), and Faris et al. (2007, 2009) (Table 3).

Helicosphaera ampliaperta (NN4) Zone

Martini (1971) introduced this zone as the interval from the LO of S. belemnos Bramlette and Wilcoxon to the LO of H. ampliaperta Bramlette and Wilcoxon. This zone is assigned to the Early Miocene (Burdigalian)/Middle Miocene (Langhian) according to its calcareous nannofossil assemblages (Figs. 7, 8, and 9). In the present work, the H. ampliaperta Zone is recorded from the Rudeis Formation at the Ras Elush, QQ-89, GS160-2, and QQ-89 wells, with depths from 2300 to 600 ft (1700 ft thick), 3050 to 2650 ft (400 ft thick), and 7980 to 7700 ft (280 ft thick), respectively (Figs. 7, 8, and 9).

It is equivalent to the H. ampliaperta NN4 Zone of Bramlette and Wilcoxon (1967), Martini (1971), Raffi et al. (2006), and Holcovkà (2013). In the present study, H. ampliaperta Bramlette and Wilcoxon is abundant while S. belemnos disappeared. So, the LO of H. ampliaperta is considered a more reliable marker event for the H. ampliaperta Zone in the investigated subsurface sections. In Egypt, this is equivalent to the H. ampliaperta Zone of El-Heiny and Martini (1981), Marzouk 2009), Sadek (2001), Mandur (2009), Faris et al. (2007, 2009), and Soliman et al. (2012) (Tables 3 and 4).

Sphenolithus heteromorphus (NN5) Zone

According to Martini (1971), this zone includes the interval from the LO of H. ampliaperta Bramlette and Wilcoxon to the LO of S. heteromorphus Deflandre. It is assigned to the Middle Miocene (Langhian) age according to its calcareous nannofossil assemblage (Figs. 8 and 9). In the present study, this zone is recorded from the Kareem Formation at the QQ-89 well from depths of 2650 to 2320 ft (330 ft thick) and the GS 160-2 well from depths of 7700 to 7640 ft (60 ft thick) (Figs. 8 and 9). The LO of S. heteromorphus Deflandre is the marker species for the CN4/CN5a and NN5/NN6 zonal boundaries. This zone is equivalent to the S. heteromorphus Zone by different authors outside Egypt (Martini 1971; Bukry 1973; Okada and Bukry 1980; Maiorano and Monechi 1998; Backman et al. 2012; Holcovkà 2013) (Table 3). In Egypt, it is also recorded by Sadek (2001), Mandur (2004, 2009), Faris et al. (2007, 2009), and Soliman et al. (2012).

Discoaster exilis (NN6) Zone

The D. exilis (NN6) zone was introduced by Hay (1970) and emended by Martini (1974). It is represented by the interval from the LO of S. heteromorphus Deflandre and the FO of Discoaster kugleri Martini and Bramlette or LO of C. floridanus (Roth and Hay). It is assigned to the Middle Miocene (Serravallian) age (Fig. 9). This zone is well defined in the Belayim Formation at the GS160-2 well from depths of 7300 to 7180 ft (120 ft thick) and is not recorded from the other two wells (Fig. 9). It corresponds to the Discoster exilis Zone of Martini (1971), Theodoridis (1984), and Holcovkà (2013) (Table 3). In the present study, the top of the NN6 Zone is not detected due to the presence of evaporite deposits and absence of diagnostic taxa. It matches well with those recorded by Mandur (2004, 2009) and Marzouk (2009) (Table 4).

Stage boundaries

The stratigraphic distribution and integration of the calcareous nannofossil and planktonic foraminiferal assemblages in the Miocene successions of the Gulf of Suez region led to an accurate age assignment and correlation for these successions.

Paleogene/Neogene stage boundary

The Paleogene/Neogene Global boundary Stratotype Section and Point (GSSP) boundary is defined by the planktonic foraminifera at the base of the Aquitanian stage occurs slightly above the FO of P. kugleri (Gradstein et al. 2012). In the Ras Elush well, the Aquitanian stage starts at the base of the P. kugleri Zone, while in the GS160-2 well, the base of the Aquitanian stage is assigned to the G. primordius Zone recorded directly above the Middle Eocene, indicating on a major hiatus between the Paleogene and the Neogene. This was observed previously by different authors in the Gulf of Suez region (Haggag et al. 1990; Phillip et al. 1997; Mandur 2009; Hewaidy et al. 2012), indicating a major unconformity with different magnitudes. By means of calcareous nannofossil, the Paleogene/Neogene GSSP boundary is formally defined in the Lemme-Carrosio section in northern Italy at the FO of Sphenolithus capricornutus (Gradstein et al. 2012). Actually, this species is not recorded in the present study, but the base of the Aquitanian stage is defined by the LO of H. recta (Haq) and D. druggii (Bramlette and Wilcoxon). The Aquitanian stage unconformably overlies the Middle Eocene calcareous nannofossils NP15 Zone at the GS 160-2 well.

The Aquitanian stage is recognized at the Nukhul Formation between the planktonic foraminiferal zones P. kugleri (M1) and G. primordius (M2), which is equivalent to the calcareous nannofossil zones T. carinatus (NN1) and the lower part of the D. druggii (NN2) (Fig. 10).

Fig. 10
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Integrated biostratigraphy of the three studied wells

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Aquitanian/Burdigalian stage boundary

Until now, the GSSP Aquitanian/Burdigalian boundary is not defined (Gradstein et al. 2012). In the Gulf of Suez region, the distribution, lithology, and faunal content of the Burdigalian deposits indicate that a regional subsidence of the basin accompanied by an extensive transgression took place at the end of the Aquitanian (Ouda and Masoud 1993).

Berggren et al. (1995) proposed that the LO of P. kugleri can be used to define the Aquitanian/Burdigalian boundary. Actually, the P. kugleri is rarely found in the Gulf of Suez region (Hewaidy et al. 2012). They placed the Aquitanian/Burdigalian boundary at the FO Globigerinatella insueta and common occurrence of C. dissimilis. In the present study, based on the planktonic foraminifera, the base of the Burdigalian stage is delineated by the FO of G. altiaperturus and C. dissimilis near the top of the D. druggii Zone.

Burdigalian/Langhian stage boundary

Two potentially suitable sections for defining the Langhian GSSP are the downward extension of the La Vedova beach section in northern Italy and St. Peter’s Pool in Malta (Gradstein et al. 2012). The Burdigalian/Langhian stage boundary is placed at the first appearance of Paraeorbulina glomerosa Blow (Iaccarino 1985; Rögl 1985; Melillo 1988; Haggag et al. 1990; Hewaidy et al. 2013). Many authors, e.g., Blow (1969, 1979), Banner and Blow (1965), Bolli (1970), Ayyad (1983), and Kennett and Srinivasan (1983) placed the Burdigalian/Langhian boundary at the first appearance of O. suturalis Brönnimann. On the basis of calcareous nannofossil, the Burdigalian/Langhian boundary coincides with the H. ampliaperta (NN4)/S. heteromorphus (NN5) zonal boundary (Fornaciari et al. 1996; Mandur 2009; Sadek 2001; El Deeb et al. 2004; Gradstein et al. 2012).

Marzouk (1998) placed the Burdigalian/Langhian boundary at the top of the H. ampliaperta (NN4) Zone. This boundary should be placed at the base of the S. heteromorphus (NN5) zone (El-Heiny and Martini 1981). Faris et al. (2007) recorded the Burdigalian/Langhian boundary at the base of the Globorotalia fohsi peripheroronda Zone by planktonic foraminifera and within the H. ampliaperta Zone (NN4) by calcareous nannofossil. Faris et al. (2009) placed the boundary at the base of the O. suturalis Zone. In the present study, the Burdigalian/Langhian boundary is recognized on the basis of planktonic foraminifera by the FO of P. glomerosa (Blow). By means of calcareous nannofossil, this boundary lies at the top of H. ampliaperta Bramlette and Wilcoxon, at the GS 160-2 and QQ-89 wells at the top of the Rudeis Formation.

The Early Langhian Kareem Formation at GS160-2 and QQ-89 includes the calcareous nannofossil H. ampliaperta Zone which is equivalent to the top of the P. sicanus/P. glomerosa (M5) Zone and the S. heteromorphus Zone matching well with the O. suturalis (M6) Zone.

Langhian/Serravallian stage boundary

The Serravallian GSSP was defined at the top of the transitional bed between the Globigerina Limestone and Blue Clay Formation in the Ras-il-Pellegrin section at Malta (Gradstein et al. 2012). On the basis of the planktonic foraminifera, the Langhian/Serravallian boundary falls within the upper part of the O. suturalis/G. peripheroronda Zone of the Mediterranean zonal scheme proposed by Iaccarino and Salvatorini (1982) which is recently emended by Iaccarino et al. (2005). In Egypt, the Langhian/Serravallian boundary by means of planktonic foraminifera is placed at the first appearance of the Orbulina universa Zone of Said and El Heiny (1967) or at the first appearance the G. fohsi and Globorotalia peripheroacuta zones (Hewaidy et al. 2013). The Langhian/Serravallian boundary is recognized by calcareous nannofossil at the LO of S. heteromorphus Deflandre (Lourens et al. 2004; Mandur 2009).

In the present study, we can expected the Langhian/Serravallian boundary between the strong vertical facies changes at the Kareem/Belayim formational boundary between interval barren below directly the FO of the calcareous nannofossil D. exilis Zone (NN6) and the FO of the planktonic foraminiferal G. peripheroronda/G. praemenardii (M7) in zone, which was recorded at the GS 160-2 well (Fig. 10).

Environmental interpretations

The paleoenvironments in the present study was determined based on integrated lithologic, biostratigraphic, gamma ray log, benthic biofacies, planktonic/benthic ratio which is expressed as 100 × P/(P + B), abundance, and diversity parameters. These procedures are explained by several authors (Culver 1988; Armentrout 1996; Leckie and Olson 2003; Miller et al. 2008); Hewaidy et al. 2013 and Farouk et al. 2014).

Environmental interpretation of the Nukhul Formation

The Nukhul Formation is bounded at the base by a major unconformity surface separating the syn-rift basal Nukhul Formation from the underlying pre-rift sediments of the Middle Eocene with different magnitudes related to the early clysmic tectonic rift event (Garfunkel and Bartov 1977; Evans 1988; El-Azabi 2004; Bosworth et al. 2005; Hewaidy et al. 2012). The Nukhul Formation includes two ecozones in the Ras Elush well (named as Ec-R1 and Ec-R2) intercalated with a barren interval, while the Nukhul Formation is not recorded in the QQ-89 well. In the GS-160-2 well, it includes only one ecozone (Ec-G1).

Environmental interpretation of the Nukhul Formation in the Ras Elush well

In the Ras Elush well, the Nukhul Formation is subdivided into two ecozones (Ec-R1 and Ec-R2) intercalated by a barren interval.

Ec-R1

The Ec-R1 ecozone is recorded from the lower part of the Nukhul Formation (P. kugleri Zone of the Aquitanian age). It consists mainly of dark shale intercalated with white limestone between 3200 and 3100 ft depth (Fig. 11). This ecozone is characterized by low diversity (8–12 species with planktic/benthic ratio of 40-60 %). It is dominated by different Lenticulina species (Lenticulina antipodum, Lenticulina budensis, and L. incrustatus), representing about 60 % of the total benthic foraminiferal groups (Fig. 12). The dominant Lenticulina group reflects a middle neritic environment (Reolid 2008). The assemblage of this ecozone includes in addition to the Lenticulina group about 40 % of other different species (Bulimina striata, Bulimina elongata, and Rectuvigerina krachemensis). The benthic foraminiferal associations are generally small sized, except the Lenticulina spp. which displays a normal size. Planktonic foraminifers include small primitive “Globigerina forms.” Based upon the abovementioned characters, a middle neritic environment is suggested for the lower part of the Nukhul Formation in the Ras Elush well (Fig. 17).

Fig. 11
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Foraminiferal paleoecologic parameters and interpretation in the Ras Elush well

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Fig. 12
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Distribution and percentage of small benthic foraminiferal species across the Miocene of the Ras Elush well

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Barren interval 1

It consists of sandstone with shale at the interval between 3100 to 3070 f. (30 f. thick) depth at Ras Elush well. The sandstone is barren of any foraminiferal tests reflecting a coastal marine environment (Fig. 11). The lithofacies characters indicate a gradual regression with increasing terrigenous influx.

Ec-R2

The Ec-R2 ecozone is recorded from the upper part of the Nukhul Formation at the Ras Elush well. This part is attributed to the G. primordius Zone of the Aquitanian age. It consists of limestone with shale and sand intercalations at the interval from 3070 to 2950 ft (120 ft thick) depth. It is characterized by dominant occurrence of unkeeled planktonic foraminiferal groups (Globigerina and Globigerinoides) with low diversity (18–22 species) (Fig. 11). It is characterized by dominant occurrence of the benthic foraminiferal assemblages as the Cibicides group 60 % (Cibicides gibbosus, Cibicides dutemplei, Cibicides ellisi), in addition to 30 % of Quinqueloculina seminulua and Q. oblonga and 10 % of B. striata (Fig. 12). Quinqueloculina seminula and Quinqueloculina spp. were recorded at water depths of 30–60 m by Gevirtz (1969) and Buck et al. (1999). A middle neritic environment is suggested for this ecozone based on the abovementioned characters (Fig. 17).

Environmental interpretation of the Nukhul Formation in the GS 160-2 well

EC-G1

Towards the tectonically paleo-low at the GS160-2 well: The EC-G1 ecozone is characterized by (1) common occurrence of unkeeled planktonic foraminifera (Globigerina and Globigerinoides), (2) high diversity of species (30–35 species), (3) dominance of the Uvigerina benthic foraminiferal group representing about 70 % (U. pygmoides, U. asperula, U. semiornata, U. venusta, and U. barbatula) in addition to 30 % of species of Bulimina, Stilostomella, and Bolivina (Figs. 13 and 14). It indicates an outer neritic environment for this ecozone (Fig. 17).

Fig. 13
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Foraminiferal paleoecologic parameters and interpretation in GS160-2 well

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Fig. 14
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Distribution and percentage of small benthic foraminiferal species across the Miocene successions of the GS-160-2 well

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Barren interval 2

The upper part of the Nukhul Formation at the GS160-2 well is found barren of foraminifera. It consists of sandstone with shale at the interval between 7980 and 7950 ft depth (30 ft thick) at the GS 160-2 well. The sandstone is barren of any foraminiferal tests reflecting a coastal marine environment (Fig. 13).

Environmental interpretation of the Rudeis Formation

This formation includes two ecozones in the three studied wells, the Ras Elush well (Ec-R3 and Ec-R4), QQ-89 well (Ec-Q1 and EC-Q2), and GS-160-2 well (Ec-G2 and Ec-G3).

Environmental interpretation of the Rudeis Formation at the Ras Elush well

Ec-R3

This ecozone is recorded only from the lower part of the Rudeis Formation (G. altiaperturus Zone of the Burdigalian age) at the Ras Elush well. It consists mainly of shale with about 480 ft thick from depths of 2950 to 2420 ft. It is characterized by the dominant presence of unkeeled planktonic foraminiferal genera (Globigerina, Globigerinoides, and Catapsydrax species). It is characterized by 55–45 % of the P/B ratio with middle diversity (22–23 species, with a total of 11–13 benthic species). The dominant benthic foraminiferal groups are Lenticulina and Uvigerina representing about 80 % (L. antipodum, L. budensis L. incrustatus, Uvigerina striatissima, U. pygmoides Uvigerina fastigla, and U. barbatula), in addition to 20 % of C. dutemplei, Bolivina shukrii, and Nonion scaphum (Figs. 11 and 12). These characters reflect a middle to outer neritic paleoenvironments (Farouk et al. 2014).

Ec-R4

This ecozone is represented by the interval from 2420 to 700 ft depth and covers the middle and upper parts of the Rudeis Formation in that well and it is equivalent to the planktonic foraminiferal zones G. trilobus/Globigerinoides sicana and P. glomerosa. It is characterized by (1) presence of unkeeled planktonic foraminiferal genera (Globigerina, Globgerinoides, and Globorotalia) with notated high abundance of Globigerinoides sacculifer and G. trilobus (65–80 %), (2) high diversity of species (70–85 species), (3) dominant occurrence of the benthic foraminiferal groups Bolivina and Uvigerina which are represented by about 75 % (Bolivina dilatata, Bolivina catanensis, Bolivina superba, B. shukrii, Bolivina fastigla, B. elongata, U. striatissima, U. pygmoides, U. semiornata, and U. costata), in addition to B. elongata, B. striata, Lenticulina incrustatus, Eponides repandus, Stilostomella ovicula, S. solute, and Siphonina reticulate (Fig. 12). These characters reflect an outer neritic paleoenvironment (Figs. 11 and 17).

Environmental interpretation of the Rudeis Formation in the QQ-89 well

Ec-Q1

This ecozone is recorded from the middle part of the Rudeis Formation (G. trilobus and lower part of P. sicanus/P. glomerosa zones of the Burdigalian to Langhian ages). It consists of white limestone, highly sandy, locally cherty, from depths of 3050 to 2850 ft. It is characterized by the presence of unkeeled planktonic foraminiferal genera (Globigerina, Globgerinoides, and Globorotalia) with dominant occurrence of Globigerinoides (75 %). The Ec-Q1 ecozone is characterized by very low diversity (3–5 benthic species) represented by the dominant occurrence of Chilostomella czizecki (50 %), in addition to C. ellisi, Cibicides ellisi graysoni, Cibicides nucleates, C. dutemplei, Nodosaria soluta, (50 %),(Fig. 16). The Chilostomella, and Cibicides assemblage with low diversity reflecting an inner shelf environment (Brunner 1992).

Ec-Q2

This ecozone is recorded in the upper part of the Rudeis Formation at the interval from depths of 2850 to 2650 ft (P. sicanus/P. glomerosa Zone of the Langhian age), which consists mainly of claystone and shale rich in microfossils. It is characterized by presence of (1) dominant unkeeled planktonic foraminiferal genera (Globgerinoides and Orbulina representing about 70–80 % of the fauna), (2) high diversity (35–45 species), (3) dominant occurrence of the benthic foraminiferal groups Bolivina and Uvigerina (Uvigerina pygmoides, U. semiornata, U. asperula, U. barbatula, U. coastata, B. dilatata, B. superba, B. fasitgla, B. catanensis, B. shukrii, and B. superba) (Figs. 15 and 16). The dominant Bolivina and Uvigerina groups reflect an outer neritic paleoenvironment (Jannink et al. 1998).

Fig. 15
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Foraminiferal paleoecologic parameters and interpretation in QQ-89 well

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Fig. 16
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Distribution and percentage of small benthic foraminiferal species across the Miocene of the QQ-89 well

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Environmental interpretation of the Rudeis Formation in the GS-16-2 well

Ec-G2

This ecozone is recorded in the middle part of the Rudeis Formation (G. trilobus Zone of the Burdigalian age). It consists of shale and limestone at the interval from depths of 7980 to 7830 ft. It is characterized by presence of (1) unkeeled planktonic foraminiferal genera (Globigerina and Globgerinoides); (2) the P/(P + B) ratio, reaches 65 %; and (3) high diversity of species (40–45 species), with a total of 12–15 benthic species. The dominant benthic foraminiferal group is Bolivina which is represented by about 75 % of the B. dilatata, B. superba, B. arta, B. shukrii, Bolivina fastiglia and B. elongata, in addition to Uvigerina semiornata, Stilostomella soluta, S. ovicula, and Oolina globosa setosa (25 %) (Fig. 14). These characters indicate an outer neritic environment for this ecozone (Figs. 13, 14, and 17).

Fig. 17
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Litofacies and paleoenviromental interpretations in the three studied wells

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Ec-G3

This ecozone is recorded in the upper Rudeis Formation (P. sicana and P. glomerosa Zone of the Langhian age). It consists of shale and sandstone at the interval from depths of 7830–7750 ft. It is characterized by presence of unkeeled planktonic foraminiferal genera Globigerina, Globgerinoides, Globorotalia, and Orbulina. It is dominated by Globigerinoides (70 %). It is characterized by the P/(P + B) ratio of (45–55 %). It has a high diversity (40–45 species, with a total of 10–12 benthic species). The dominant benthic foraminiferal species are those of the genus Cibicides and represented by about 75 % of Cibicides ellisi ellisi, C. ellisi, C. ellisi graysoni, Cibicides boueanus, and C. dutemplei, in addition to Q. seminulua, Q. juleana, Bolivina elongate, and B. fastigla representing about 25 %. These characters reflect a middle neritic environment (Fig. 14).

Environmental interpretation of the Kareem Formation

This formation includes two ecozones in the QQ-89 well (Ec-Q3 and EC-Q4), while in the GS-160-2 well, it includes one ecozone (Ec-G4). The Kareem Formation is missing in the Ras Elush well due to tectonic uplifting after deposition of the Rudeis Formation.

Environmental interpretation of the Kareem Formation in the QQ-89 well

Ec-Q3

This ecozone is recorded in the upper part of the Rudeis Formation and the lower part of the Kareem Formation (P. sicana/P. glomerosa Zone and O. suturalis Zone of the Langhian age). It consists of claystone and limestone with anhydrite intercalations, and represented by the interval from depths of 2650–2530 ft. It is characterized by presence of unkeeled planktonic foraminiferal genera: (Globigerina, Globigerinoides, Globorotalia, and Orbulina). The Orbulina reaches about 65 % (Fig. 15). This ecozone is characterized by (1) high diversity (50–60 species) with a total of 17–20 benthic species, (2) dominant taxa are Cibicides which represent about 75 % (C. ellisi graysoni, C. nucleates cseguenzal, Cibicides tenellus, C. dutemplei, C. ellisi and C. boueanus), in addition to B. Striata, B. elongata, and Eponides procerus (25 %) (Fig. 16). The Cibicides biofacies is indicative of 100-m water depth (Miller et al. 2008). The benthic foraminiferal assemblage indicates an inner to middle neritic environments (Figs. 15 and 17).

Ec-Q4

This ecozone is recorded in the upper part of the Kareem Formation (O. suturalis Zone of the Langhian age). It consists of claystone and siltstone and represented by the interval from 2530 to 2350 ft depth. It is characterized by presence of unkeeled planktonic foraminiferal genera (Globigerina, Globgerinoides, Globorotalia, Orbulina, and Neogloboquadrina). It is dominated by Orbulina (60 %). It is characterized by a P/(P + B) ratio of 80–90 % with high diversity (25–30 species), with a total of 11–13 benthic species. The dominant benthic foraminiferal genera Uvigerina is represented by about 60 % (Uvigerina barbatula, Uvigerina rutila, Uvigerina coastat, U. pygmoides, U. semiornata, Uvigerina venusta,) in addition to S. soluta, Stilostomella corporosa, S. paleocenica, S. subspinosa, S. ovicula, Nodosaria catenulate, B. elongata, and B. striata) (Fig. 16). These parameters reflect outer neritic paleoenvironment (Figs. 15 and 17).

Environmental interpretation of the Kareem Formation in the GS 160-2 well

Ec-G4

This ecozone is recorded in the lower part of the Kareem Formation (O. suturalis Zone of the Langhian age). It consists of siltstone and anhydrite and represented by the interval from 7750–7680 ft depth. It is characterized by presence of unkeeled planktonic foraminiferal genera Globigerina, Globigerinoides, Globorotalia, and Orbulina. It is dominated by Globigerinoides (60 %). It is characterized by a P/(P + B) of 60–70 % with low diversity (15–20 species), with a total of 10–12 benthic species. It is characterized by presence of Bolivina and Stilostomella which represent about 15 %. The dominant benthic foraminiferal genera are Bolivina (B. dilatata, B. superba, B. shukrii, B. fastiglia, and B. elongata) (50 %), in addition to Stilostomella (S. solutea, Stilostomella verneullia, and S. ovicula), L. incrustatus, Lenticulina iota, C. ellisi ellisi, and N. soluta which represent about 50 % (Fig. 14). The high P/B ratio and dominance of Bolivina and Cibicides groups reflect a middle neritic environment (Figs. 13 and 17).

Environmental interpretation of the Belayim Formation

The Belayim Formation was found barren of foraminifera in the Ras Elush and QQ-89 wells, while in the GS-160-2 well, it is subdivided into three units: a lower barren interval, middle Ec-G5 ecozone, and upper barren interval. The following is the description of these two units, the barren interval and Ec-G5:

Barren interval 3

This interval is represented by the whole Belayim Formation in the Ras Elush and QQ-89 wells or the lower part of the Belayim Formation at GS-160-2. It is represented by the whole lower part of the Belayim Formation (Serravallian age). It is represented by anhydrite and sandstone. These sediments reflect a lagoonal environment (Figs. 11, 13, and 15).

Environmental interpretation of the Belayim Formation in the GS-160-2 well

Ec-G5

This ecozone is recorded in the Serravallian Belayim Formation of the G. praemenardii/G. peripheroronda Zone. It consists of limestone and shale and represented by the interval between depths of 7260 and 7120 ft. It is characterized by presence of unkeeled planktonic foraminiferal genera Globigerina, Globigerinoides, Globorotalia, Orbulina, and Hastegerina. It is characterized by a P/(P + B) of 45 % with high diversity (22–30 species), with a total of 7–10 benthic species.

The dominant benthic foraminiferal group is Uvigerina (Fig. 14) representing about 60 % (U. barbatula, U. pygmoides, U. semiornata, and Uvigerina asperula) in addition to Cibicides, Rectuvigeruna which represent about 40 % (C. ellisi ellisi, C. boueanus, C. dutemplei, Rectuvigeruna kraohemensis, and R. tenuistriata). These parameters reflect middle to outer neritic environments (Figs. 14 and 17).

Barren interval 4

This interval is recorded from the upper part of the Serravallian Belayim Formation in the GS-160-2 well. It consists of mainly anhydrite which is completely barren of any Foraminifera genera. These sediments reflect a lagoonal environment (Fig. 13).

Summary and conclusions

Three offshore wells (GS 160-2, QQ-89, and Ras Elush) from north to south representing the subsurface Miocene successions in central and southern parts of the Gulf of Suez, Egypt, were selected to study the foraminifera and calcareous nannofossil contents and paleoenvironments. Lithostratigraphically, the lower Middle Miocene succession is classified from older to younger into Nukhul (Aquitanian), Rudies (Burdigalian-Langhian), Kareem (Langhian), and Belayim (Serravallian) formations.

The identified foraminifera includes 54 benthonic species belonging to 25 genera and 47 planktonic species belonging to 11 genera with moderate to good preservation and relatively high diversity, in addition to 64 calcareous nannofossil species. These assemblages allowed to classify the studied successions into seven planktonic foraminiferal biozones arranged from older to younger into P. kugleri (M1) (Early Miocene, Aquitanian), Globigerninodes primordius (M2) (Early Miocene, Aquitanian), Globigerinoides altiapertura (M3) (Early Miocene, Burdigalian), G. trilobus (M4) (Early Miocene, Burdigalian), P. sicanus/P. glomerosa (M5) (Middle Miocene, Langhian), O. suturalis (M6) (Middle Miocene, Langhian), and G. praemenardii/G. peripheroronda (M7) (Middle Miocene, Serravallian); in addition to six nannofossil biozones from older to younger: T. carinatus (NN1) (Early Miocene, Aquitanian), D. druggii (NN2) (Early Miocene, Aquitanian), S. belemnos (NN3) (Early Miocene, Burdigalian), H. ampliaperta (NN4) (Early Miocene, Burdigalian), S. heteromorphus (NN5) (Middle Miocene, Langhian), and D. exilis (NN6) (Middle Miocene, Serravallian).

The ranges of both planktonic foraminifera and calcareous nannofossil zones proved to match reasonably with each other. These biozones were correlated with those recorded in Egypt and in other parts of the world.

Based on the planktonic foraminifera, the Aquitanian/Burdigalian boundary in the investigated wells is delineated with the FO of G. altiaperturus and C. dissimilis near the top of the D. druggii Zone of calcareous nannofossil. The Burdigalian/Langhian boundary is placed at the first appearance of P. sicanus/P. glomerosa planktonic foraminiferal zone. The Langhian/Serravallian boundary is recognized by the FO of the planktonic foraminiferal G. peripheroronda/G. praemenardii (M7) Zone and the FO of the calcareous nannofossil D. exilis Zone (NN6).

The environments of deposition of the studied units were analyzed based on the lithologic characters and faunal contents. The Nukhul Formation is recorded in the Ras Elush and GS 160-2 wells, while it is missing in the QQ-89 well. In the Ras Elush well, it is subdivided into two ecozones (Ec-R1 and Ec-R2) separated by a barren interval 1. These ecozones are supposed to be deposited in a middle neritic environment followed by a regressive phase and then back to the middle neritic environment again. In GS 160-2, the Nukhul Formation is classified into one ecozone (Ec-G1) followed by a barren interval, which were interpreted to be deposited in a deeper outer neritic environment followed by a regressive phase.

The Rudeis Formation was recorded in the three studied wells. In the Ras Elush well, it is classified into two ecozones (Ec-R3 and Ec-R4) which may be deposited in a middle to outer neritic environments. In the QQ-89 well, the Rudeis Formation is classified into one ecozone (Ec-Q1) bottomed by a barren interval which may be deposited in an inner neritic environment changed to outer neritic upwards. In the GS 160-2 well, the Rudeis Formation is classified into two ecozones (Ec-G2 and Ec-G3), which may be deposited in an outer neritic environment changed to inner to middle neritic environments at the top.

The Kareem Formation is represented in the QQ-89 and GS160-2 wells and missing in the Ras Elush well due to tectonic activity after the deposition of the Rudeis Formation. At the QQ-89 well, the Ec-Q3 ecozone reflects an inner to middle neritic paleoenvironments grades to middle to outer neritic environments in the central part of the study area at the GS 160-2 well.

The Belayim Formation is detected in all the studied wells represented by a regressive phase which consists of evaporites intercalated with shale. At the GS 160-2 well, it consists of evaporites intercalated at the middle part of the Belayim Formation by deeper shale with sandstone of middle to outer neritic environments.