Calcareous benthonic foraminifera across the Cretaceous/Paleocene transition of Gebel Um El-Ghanayem, Kharga Oasis, Egypt

Journal of African Earth Sciences 96 (2014) 110–121

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Calcareous benthonic foraminifera across the Cretaceous/Paleocene transition of Gebel Um El-Ghanayem, Kharga Oasis, Egypt Orabi H. Orabi a,⇑, Hamza M. Khalil b a b

University of Menoufia, Faculty of Science, Department of Geology, Egypt University of Tanta, Faculty of Science, Department of Geology, Egypt

a r t i c l e

i n f o

Article history: Received 22 November 2013 Received in revised form 17 March 2014 Accepted 18 March 2014 Available online 13 April 2014 Keywords: Egypt Benthic Foraminifera Kharga Oasis Cretaceous Paleocene

a b s t r a c t The studies of benthic calcareous foraminifera of the Maastrichtian–early Paleocene Dakhla Formation in Gebel Um El-Ghanayem (Western Desert, Egypt), improve reconstruction of depositional environments of these successions. In total, 68 taxa of benthic foraminifera were identified in the studied succession. The late Maastrichtian assemblages (Zone CF3) are dominated by calcareous foraminifera with tapered tests, this tapered taxon Loxostomum applinae, Lox. tegulatum various dentalinid taxa, and Buliminella cushmani dominate in CF3 Biozone. We thus interpret these faunas as being dominated by infaunal morphogroups, suggesting a moderately eutrophic environment. Danian assemblages are characterized by abundant epifaunal trochospiral species, such as Cibicidoides abudurbensis, Cibicidoides farafraensis, and Gyroidinoides girardanus. The infaunal morphogroups make up 25–47% of fauna in the Danian, in contrast to 62–76% in the Upper Maastrichtian. This dominance of the Danian benthic foraminiferal assemblages by epifaunal or mixed epifaunal/infaunal morphogroups suggests that the food supply to the benthos was less abundant than in the latest Cretaceous. The Cretaceous/Paleocene boundary (K/Pg) is within the upper unit of the Lower Kharga Member and marked by a hiatus in at least the top of CF3 Zone of the Upper Maastrichtian to the Lower Paleocene (base Plc Zone). Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction The benthic foraminiferal faunal turnover across the K/Pg boundary has been described from many locations worldwide (Culver, 2003). The benthic foraminifera of the Upper Cretaceous through Lower Paleogene sections have been investigated intensively because one of the largest mass extinctions of the Phanerozoic occurred at the Cretaceous/Paleogene boundary (K/Pg). Most authors accept the catastrophic mass extinctions (Alvarez et al., 1980; Smit and Hertogen, 1980) on the Yucatan peninsula, and that the anomalous concentrations of iridium, shocked quartz and microspherules in K/Pg boundary sediments reflect that impact (e.g., Alvarez et al., 1980). Meanwhile, some authors argue that the extinctions were not sudden but stepwise, starting in the Maastrichtian (e.g., Keller, 1989a,b, 2003), and linked at least in part to multiple impacts (Keller 2003). A scientific challenge is to assess the role of Deccan

⇑ Corresponding author. Tel.: +20 482236745. E-mail addresses: [email protected] (O.H. Orabi), hamzakhalil2002@ yahoo.com (H.M. Khalil). http://dx.doi.org/10.1016/j.jafrearsci.2014.03.017 1464-343X/Ó 2014 Elsevier Ltd. All rights reserved.

volcanism in the Cretaceous–Tertiary boundary (KTB) mass extinction, where Keller et al. (2011) reported on the stratigraphy and biologic effects of Deccan volcanism in eleven deep wells from the Krishna–Godavari (K–G) Basin, Andhra Pradesh, India. The main eruptions ended at or near the Cretaceous Tertiary Boundary (KTB), an interval that spans planktonic foraminiferal zones CF1– CF2, and is correlative with the rapid global warming and subsequent cooling near the end of the Maastrichtian. Unfortunately a major K/Pg hiatus is present in Gebel Um El Ghanayem, the K/Pg contact was placed at the base of a 1-m-thick tan-colored calcareous siltstone and sandy limestone sequence that is widespread in the region and marks the base of the Abu Minqar Member. In contrast to many other biotas, benthic foraminifers did not suffer significant extinction at the end of the Cretaceous (Culver, 2003). Their assemblages show temporal faunal restructuring, which has been related to the collapse of the pelagic food web, which delivers food to the benthos (e.g., Thomas, 1990a,b; Widmark and Malmgren, 1992; Coccioni et al., 1993; Kuhnt and Kaminski, 1993; Speijer and Van der Zwaan, 1996; d’Hondt et al., 1998; Alegret et al., 2001, 2002a,b, 2003; Culver, 2003). d’Hondt et al. (1998) argued that the decreased delivery of organic matter to the sea floor as the result of the extinction of pellet-producing

O.H. Orabi, H.M. Khalil / Journal of African Earth Sciences 96 (2014) 110–121

zooplankton rather than decreased productivity might also have affected the benthos. Benthic foraminifers are proxies for nutrient supply as well as for oxygenation at the sea floor, and constitute an important tool to reconstruct paleoenvironmental changes at the K/Pg boundary. Information from benthic foraminifers is particularly valuable in order to evaluate K/Pg extinction hypotheses that argue for widespread oceanic anoxia (e.g., Kaiho, 1999; Kaiho et al., 1999; Alegret and Thomas, 2005). Furthermore, benthic foraminifera can be used as a powerful tool to estimate depositional depths (e.g. Culver, 1993) as well as to infer seafloor paleoecology on the basis of their morphological similarity with recent benthic foraminifera (Olsson and Wise, 1987; Speijer and Van der Zwaan, 1996; Speijer et al., 1996; Kouwenhoven et al., 1997). The faunal and lithological variations across the K/Pg boundary in Egypt have been dealt with by many workers (e.g. Abdel Razik, 1972; Anan and Hewaidy, 1986; Hewaidy and Cherif, 1987; Hewaidy, 1990; Speijer and Van der Zwaan, 1994; Aubry et al., 1999; Bolle et al., 2000; Tantawy et al., 2000; Hewaidy and Strougo, 2001; Aubry et al., 2002; Berggren and Ouda, 2003; Knox et al., 2003; Ismail, 2012). In addition, numerous studies of benthic foraminifera have been carried out, especially on the palaeoecological interpretation of the terminal Maastrichtian, Cretaceous/Tertiary boundary (e.g., Speijer and Van der Zwaan, 1996; Alegret et al., 2001; Culver, 2003). However, no attention has been given to the benthic foraminiferal morphogroups quantitative study across the K/Pg boundary. Therefore, this paper present detailed information on the calcareous benthic morphogroups characteristic that have prevailed during the sedimentary deposition across the K/Pg boundary to evaluate the changes in the benthic foraminiferal ecosystem at Gebel Um El-Ghanayem section, Western Desert, Egypt (Fig. 1).

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2. Material and methods Forty samples were collected from the northern side of Gebel Um El-Ghanayem, at decimeter intervals, with closer sampling across the top Maastrichtian and basal Danian strata. Samples were disaggregated in water with diluted H2O2, washed through a 63 lm sieve, and dried at 50 °C. Species richness measurement and quantitative studies were based on representative splits (using a modified Otto microsplitter) of approximately 300 specimens larger than 63 lm except for relatively poor samples from which only 50 specimens were picked. All the representative specimens were mounted on microslides for permanent record and identification. These microslides as well as the SEM-imaged (Plates 1 and 2) specimens are part of the private collection of the senior author; fresh samples and residues are stored at the Department of Geology, Faculty of Science, Menoufia University. In order to obtain general paleoenvironmental conditions and potential taphonomic alterations, the P/B ratios were calculated {expressed as 100  P/(P + B)}, benthic foraminiferal numbers expressed as the number of benthic specimens per gram dry sediments (Murray, 1991), while dominance was calculated as percentage of the frequent taxon (Walton, 1964) and the proportion of non-calcareous agglutinated taxa. The comparison of fossil and recent communities of benthic foraminifera, in addition to morphotype analysis (e.g., Corliss, 1985; Corliss and Chen, 1988; Jones and Charnock, 1985), allows us to infer probable microhabitat preferences and environmental parameters such as the nutrient supply to the sea-floor, its seasonality, and sea water oxygenation (e.g., Bernhard, 1986; Jorissen et al., 1995; Fontanier et al., 2002). One should be careful with the interpretation of these comparisons because the ecology of present foraminifera is complex and not fully understood

Fig. 1. Locality map.

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Plate 1 Scale bar = 100µm 1- Nodosaria mcneili CUSHMAN, 1944, sample no. 7 2- Nodosaria redicula (LINNE, 1956), sample no. 5 3- Dentalina colei CUSHMAN & DUSENBURY, 1934, sample no. 36 4- Lenticulina oligostegia (REUSS, 1860), sample no. 39 5- Lenticulina navicula (SCHWAGER, 1883), sample no. 35 6- Saracenaria saratogona HOW & WALLACE, 1932, sample no.4 7- Marginulinopsis tuberculata (PLUMMER, 1927), sample no. 37 8- Neoflabellina suturalis (CUSHMAN, 1935), sample no. 9 9- Vaginulina trilobata (D’ORBIGNY, 1826), sample no. 35 10-Lagena globosa (MONTAGU, 1803), sample no. 35 11-Lagena sulcata (WALKER & JACOB, 1798), sample no. 16 12-Loxostomum applinae (PLUMMER, 1927), sample no. 35 13-Buliminella cushmani (SANDIDGE, 1932), sample no. 35 14-Globobulimina suteri (CUSHMAN & RENZ, 1946), sample no. 35 15-Stainforthia farafraensis (LEROY, 1953), sample no. 39 16-Stilostomella midwayensis (CUSHMAN&TODD, 1946), sample no. 39 Plate 1. Scale bar = 100 lm. (1) Nodosaria mcneili Cushman, 1944, sample no. 7. (2) Nodosaria redicula (Linne, 1956), sample no. 5. (3) Dentalina colei Cushman & Dusenbury, 1934, sample no. 36. (4) Lenticulina oligostegia (Reuss, 1860), sample no. 39. (5) Lenticulina navicula (Schwager, 1883), sample no. 35. (6) Saracenaria saratogona How & Wallace, 1932, sample no. 4. (7) Marginulinopsis tuberculata (Plummer, 1927), sample no. 37. (8). Neoflabellina suturalis (Cushman, 1935), sample no. 9. (9) Vaginulina trilobata (d’Orbigny, 1826), sample no. 35. (10) Lagena globosa (Montagu, 1803), sample no. 35. (11) Lagena sulcata (Walker & Jacob, 1798), sample no. 16. (12) Loxostomum applinae (Plummer, 1927), sample no. 35. (13) Buliminella cushmani (Sandidge, 1932), sample no. 35. (14) Globobulimina suteri (Cushman & Renz, 1946), sample no. 35. (15) Stainforthia farafraensis (LeRoy, 1953), sample no. 39. (16) Stilostomella midwayensis (Cushman & Todd, 1946), sample no. 39.

CH-A-6). Infaunal foraminifera, living in the deeper layers of the sediment, have cylindrical or flattened tapered, spherical, rounded planispiral, flattened ovoid, globular unilocular or elongate multilocular tests (e.g., CH-B-2 CH-B-3, CH-B-4). The ratio of these morphotypes could reveal paleoxygenation of the bottom environment, especially in shallow marine and seasonally influenced areas. However, the changes in the ratio would suggest circulation and organic carbon flux changes (Wetmore, 1991). The relative abundance of morphotypes indicates infaunal taxa as an overall indicator of delivery of food to the sea floor (Gooday, 2003). 3. Litho-biostratigraphy The Upper Cretaceous–Lower Paleocene boundary in the central and southern portions of the Western Desert of Egypt is marked by a disconformity surface covered by a conglomerate rich in reworked Maastrichtian macrofossils. The following lithostratigraphical subdivision of the Late Cretaceous to Early Paleocene in Gebel Um El-Ghanayem (located about 19 km to the northeast of El Kharga Town) is mainly based on the work of Awad and Ghobrial (1965), Luger (1985, 1988), Bassiouni and Luger (1990), Orabi (1995), and Felesteen and Zakhera (1999). The Duwi Formation and the Dakhla Formation (Mawhoob, Baris Oyster, Lower Kharga, Bir Abu Munqar and Upper Kharga members) were recognized in the area under consideration (Fig. 2). The lithologic characteristics of each stratigraphic unit and their benthic foraminiferal number (BFN) and distribution (Tables 1–6) are discussed from base to top as follows:

Plate 2 Scale bar = 100µm

1- Nuttallides lotus (SCHWAGER, 1885), sample no. 4 2- Cibicidoides abudurbensis (NAKKADY, 1950), sample no. 38 3- Cibicidoides pseudoacutus (NAKKADY, 1950), sample no. 36 4- Pullenia quinqueloba (REUSS, 1851), sample no. 35 5- Osangularia plummerae BROTZEN, 1940, sample no.2 6- Cibicidoides pharaonis (LEROY, 1953), sample no. 35 7- Gyroidinoides subangulata (PLUMMER, 1927), sample no.4 8- Gyroidinoides girardanus (REUSS, 1851), sample no. 36 9- Anomalinoides affinis (HANTKEN, 1875), sample no. 2 10- Anomalinoides cf. acutus (PLUMMER, 1927), sample no. 3 11- Gavelinella danica (Brotzen, 1968), sample no. 2 Plate 2. Scale bar = 100 lm. (1) Nuttallides lotus (Schwager, 1885), sample no. 4. (2) Cibicidoides abudurbensis (Nakkady, 1950), sample no. 38. (3) Cibicidoides pseudoacutus (Nakkady, 1950), sample no. 36. (4) Pullenia quinqueloba (Reuss, 1851), sample no. 35. (5) Osangularia plummerae Brotzen, 1940, sample no. 2. (6) Cibicidoides pharaonis (LeRoy, 1953), sample no. 35. (7) Gyroidinoides subangulata (Plummer, 1927), sample no. 4. (8) Gyroidinoides girardanus (Reuss, 1851), sample no. 36. (9) Anomalinoides affinis (Hantken, 1875), sample no. 2. (10) Anomalinoides cf. acutus (Plummer, 1927), sample no. 3. (11) Gavelinella danica (Brotzen, 1968), sample no. 2.

(e.g., Murray, 2001), and we do not know to what extent to Recent faunas (e.g., Thomas et al., 2000; Alegret and Thomas, 2001; Alegret et al., 2001, 2003; Gooday, 2003). The calcareous benthic foraminiferal assemblages recovered from Upper Maastrichtian to early Paleocene in Gebel Um El-Ghanayem, Western Desert, were distinguished and subdivided according to wall structure and morphological similarity following Corliss (1985), Jones and Charnock (1985), Corliss and Chen (1988) and Koutsoukos and Hart (1990). In general, benthic foraminifera with plano-convex, biconvex and rounded trochospiral tests, tubular and coiled-flattened, are inferred to have an epifaunal mode of life, living at the sediment surface or in its uppermost layers, as seen in living faunas (e.g., CH-A-2, CH-A-3, CH-A-4, CH-A-5,

3.1. Duwi Formation (latest Campanian) (CF8a) This rock unit was established by Youssef (1975). The Phosphate Formation of Awad and Ghobrial (1965) is a synonyme. The Duwi Formation overlies the Quseir Formation and underlies the Dakhla Formation. In the study area it is composed of a succession of phosphorites, shales, marls, siltstones, mudstones, glauconitic silty mudstone beds and conglomeratic hematatic bands. The Duwi Formation is assigned to a latest Campanian age, or zone CF8a where the planktonic foraminiferal assemblages in this interval are characterized by Globotruncana aegyptiaca, G. bulloides, G. linneiana, G. fornicata and G. plummerae. Unfortunately there is no calcareous benthic foraminifera were recorded in this formation. 3.2. The Dakhla Formation (early Maastrichtian–early Danian) The Dakhla Formation was first named by Said (1962) to describe 230 m thick made up of shale and marl interbedded with siltstone, sandstone and limestone at the north scarp of Mut, Dakhla Oasis and overlying the Duwi Phosphate and underlying the Tarawan Chalk. The basal part of this unit is dark gray in color and calcareous nature. Awad and Ghobrial (1965) used the term Dakhla Formation; they subdivided it as exposed in the Kharga area, into three members: Mawhoob Member at the base, Beris Member at the middle and Kharga Member at the top, where the Kharga Member subdivided into Lower Kharga (late Maastrichtian) and Upper Kharga Member (Danian). 3.2.1. The Mawhoob Member (early Maastrichtian) (CF8b–CF7) This member is established by Awad and Ghobrial (1965); it is composed of gray to dark gray shales, mudstone and silty mudstone succession, interbedded with marly and phosphatic bands. Bioturbated surfaces and hematite bands were recognized within this succession.

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Fig. 2. Shows the agglutinated/calcareous ratio and the arenaceous agglutinated/calcareous agglutinated ratio in the Gebel Um El-Ghanayem, Kharga Oasis, Egypt.

The lowermost part of the Mawhoob Member contains wellpreserved, abundant and diverse assemblages including common rugoglobigerinids and assigned to earliest Maastrichtian zone CF8b, as suggested by the absence of Gansserina gansseri and presence of Rugoglobigerina hexacamerata. Shales and thin silt and calcareous sandstone layers characterize the lower Maastrichtian Mawhoob Member of the Dakhla Formation at Gebel Um El-Ghanayem. Microfossils are very rare in the lower Maastrichtian and indicate a CF7 Zone (Hendriks et al., 1984; Hermina, 1990). The upper part of the Mawhoob Member is devoid of planktonic foraminifera, the sediments consist of alternating layers of dark gray siltstones and thin layers of phosphatic skeletal. Table 1 shows the calcareous benthic foraminiferal assemblage of the lower part of Mawhoob Member (sample 2–4). Meanwhile, the upper part of Mawhoob Member (sample 5–9) includes Nodosaria affinis Reuss, Nod. redicula (Linne), Nod. limbata d’Orbigny, Nod. mcneili Cushman, Neoflabelina semireticulata (Cushman & Jarvis), Neo. sulturalis (Cushman), Neo. mumismalis (Wedekind), and Bulimina kickapooensis Cole (Table 2).

3.2.2. The Beris Member (early/late Maastrichtian) (CF7, CF6 and CF4) Awad and Ghobrial (1965) established this rock unit. It is formed mainly of gray, greenish gray shales and silty shales, marl, phosphatic pebbles intercalated with highly fossiliferous mudstone or argillaceous dolomitic beds rich in Exogyra (Exogyra) overwegi Buch. Bioturbated surfaces and conglomeratic bands are common within this member. The presence of Exogyra (Exogyra) overwegi Buch, indicate Middle Maastrichtian age to this unit (Malchus, 1990). Hence, the presence of this oyster bed indicates deposition in an inner neritic environment. In the upper part of the calcareous sandstone layers of the Beris Member Exogyra is absent and other megafossils are abundant, bivalves, gastropods, rare solitary corals, shark teeth and reptile teeth (sample 20–23). This assemblage indicates a shallow, nearshore or lagoonal environment. The scheme of Gradstein et al. (1995) and Li and Keller (1998a,b) were used the FAD of Contusotruncana contusa as a marker species for the early/late Maastrichtian boundary (CF7/CF6) within the middle part of the Beris Member. A zone CF6 age is also suggested by the presence of the calcareous nannofossil species L. quadratus.

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Table 1 Benthic foraminiferal species counts in the studied samples from the lower part of the Mawhoob Member. Benthic foraminifera

Table 3 Benthic foraminiferal species counts in the studied samples from Beris Member. Benthic foraminifera

Sample no.

16

2 Nuttallides truempyi Lenticulina muensteri Lenticulina midwayensis Lenticulina rotulata Lenticulina naviculina Lenticulina pseudosecanus Gavelinella danica Gavelinella monterelensis Gavelinella martini Anomalinoides rubiginosus Anomalinoides affinis Anomalinoides cf. acutus Gyroidinoides girardanus Gyroidinoides depressus Gyroidinoides subangulata Osangularia plummerae Pullenia quinqueloba Sitella fabilis Gyroidina megastoma Saracenaria saratogona Total

3

4

2 13 12 21 9 12 2 6 4 4 4 1 4 2 3 2 9 6 2 3

4 14 12 7 13 10 5 3 6 3 2 – 3 1 3 – – 3 3 –

1 12 10 11 12 10 – 4 2 4 10 – 5 3 4 – – 1 2 –

121

102

91

Nodosaria affinis Nodosaria redicula Nodosaria limbata Nodosaria mcneili Neoflabelina semireticulata Neoflabelina sulturalis Neoflabelina mumismalis Sitella fabilis Bulimina kickapooensis Bulimina kugleri Praebulimina sp. Frondicularia striatula Frondicularia goldfussi Frondicularia angulosa Frondicularia phosphatica Frondicularia striatula Lagena sulcata Lagena apiculata Gavelinella monterelensis Gavelinella martini Gavelinella danica Anomalinoides affinis Anomalinoides rubiginosus Total

Table 2 Benthic foraminiferal species counts in the studied samples from the upper part of the Mawhoob Member. Benthic foraminifera

Sample no. 5

Nodosaria affinis Nodosaria redicula Nodosaria limbata Nodosaria mcneili Neoflabelina semireticulata Neoflabelina sulturalis Neoflabelina mumismalis Bulimina kickapooensis Total

6

8

9

15 12 34

14 17 28 15 25 13 22 27

16 18 19 17 13 12 10 18

– 12 27 – 20 – – 24

– 1 2 1 – – – 2

125

161

123

83

6

10 30 11 13 –

Sample no.

7

The calcareous benthic foraminiferal assemblage of zones CF7 and CF6 (sample16–19) resembles that the underlying upper part of Mawhoob Member in addition to the presence of Bulimina kugleri Cushman and Kenz, Praebulimina sp., Frondicularia striatula Reuss, Fro. goldfussi Reuss, Fro. angulosa (d’Orbigny), Fro. phosphatica Russo, Fro. striatula Reuss, Lagena sulcata (Walker & Jacob) and Lag. apiculata Reuss (Table 3). In the upper part of the Beris Member (sample 25) two graded shell hash beds are present with Thalassinoides burrows at the base and top that mark erosional surfaces. Only rare planktonic foraminifera are at the base of these shell hash beds suggests a CF4 age (sample 24). The interval from the upper Maastrichtian zone CF6 through the CF4 is missing owing to a hiatus. 3.2.3. The Lower Kharga Member (late Maastrichtian) (CF3) This subdivision is introduced by Awad and Ghobrial (1965) and recorded by Luger (1985) to designate a succession of claystones and gray to greenish gray shales containing agglutinated foraminifera. The Lower Kharga Shale Member of the Dakhla Formation consists of dark gray shale that is barren of microfossils, but contains fish scales, and rare bivalves indicating a shallow marine environment (sample 26–34). At the top of this interval, (1 m-thick) calcareous shale including low-diversity, shallow-water, late Maastrichtian planktonic foraminiferal assemblage (sample 35) and dominated by

15 15 11 20

17

18

24

– – – – –

– – – – –

16 11 18 12 15 13 2 1 27 22 1 11 18 15 2 8 10 10 – – – – –

234

276

263

212

– 8 11 13 11 – – 16 19 9 7 13 29 33

21 20 21 19 7 15 11 10 36 14

19

31 17 18 24 5 3 2 1 19 7 – 32 28 25 2 18 20 24 – – – – –

– 17 10 2 7 11 20 22

3 5 – – – – 2 3 2 3 – – – 5 – – 6 7 18 14 21 18 20 127

Table 4 Benthic foraminiferal species counts in the studied samples from the Lower Kharga Member. Benthic foraminifera Buliminella cushmani Bulimina inflate Bolivina sp. Globobulimina suteri Loxostomum tegulatum Loxostomum applinae Cibicidoides abudurbensis Cibicidoides pharaonis Cibicidoides pseudoacutus Nodosaria limbata Dentalina colei Vaginulina trilobata Anomalinoides rubiginosus Lenticulina oligostegia Lenticulina navicula Saracenaria saratogona Neoflabellina suturalis Pullenia quinqueloba Pullenia coryelli Gyroidinoides girardanus Ramulina navarroana Lagena globosa Lagena sulcata Lagena apiculata Total

Sample no. 35 19 21 1 13 17 19 16 13 14 15 16 9 7 4 10 2 7 11 12 19 2 17 10 9 283

Heterohelix dentata, H. globulosa, H. navarroensis and Guembelitria cretacea, as well as abundant benthic foraminifera All of these fossils indicate that deposition occurred in an inner neritic environment. Although there are no age-diagnostic species present, the common presence of Guembelitria cretacea along with small biserial taxa suggests a CF3 age characterized by a Guembelitria acme in the eastern Tethys (Abramovich et al., 1998). The recorded calcareous benthic assemblage (sample 35) is well diversified and shown in Table 4. Most of these forms are infaunal and able to live in an oxygen deficient environment.

O.H. Orabi, H.M. Khalil / Journal of African Earth Sciences 96 (2014) 110–121 Table 5 Benthic foraminiferal species counts in the studied samples from the Upper Kharga Member. Benthic foraminifera

Sample no. 36

Anomalinoides granosa Gyroidinoides girardanus Marginulinopsis tuberculata Valvulineria scrobiculata Loxostomum tegulatum Stilostomella midwayensis Cibicidoides abudurbensis Cibicidoides praecursoria Cibicidoides pseudoacutus Nodosaria limbata Dentalina colei Lenticulina oligostegia Lagena globosa Lagena sulcata Lagena apiculata Neoflabellina suturalis Neoflabellina jarvisi Stainforthia farafraensis Cibicidoides farafraensis Nodosaria redicula Frondicularia frankei Stilostomella spinea Total

37

38

– – – – – – –

24 39 14 11 12 5 32 16 19 13 20 8 11 12 16 – – – – – – –

17 14 16 9 21 6 29 28 8 11 19 15 18 19 18 – – – – – – –

18 13 4 4 8 20 18 7 19 11 9 6 13 12 11 15 8 16 10 12 14 15

235

252

248

263

20 28 1 13 27 15 22 13 21 15 16 9 14 17 4

39

3.3. The Bir Abu Munqar Member (early Paleocene) A phosphatic-conglomerate layer marks the base of the Paleocene age. This layer marks the top of the Lower Kharga Member and is named Bir Abu Munqar Horizon by Barthel and HerrmannDegen (1981). Luger (1985) raised it to member status, which is accepted in this study. Bir Abu Munqar Member of Luger (1985) separates the Lower Kharga Member (middle Late Maastrichtian) from the Upper Kharga Member (early Paleocene) (Fig. 3). Moreover, it contains reworked Maastrichtian fossils (Luger, 1985).

3.4. The Upper Kharga Member (late Early Paleocene) (P1c) Awad and Ghobrial (1965) established this rock unit. It consists of a sequence of laminated marls with planktonic foraminifera. It has an age ranging from late Early to early Middle Paleocene as indicated by the presence of Morozovella trinidadensis and Morozovella angulata (Luger, 1985). At Gebel Um El Ghanayem, a pronounced erosional surface marks a hiatus between the top of the dark gray shale (Lower Kharga Member) and the overlying 25-cm-thick yellow calcareous sandstone that marks the base of the Bir Abu Minqar Member. The calcareous sandstone and overlying siltstone contain rounded quartz grains, phosphate nodules, glauconite and abraded benthic foraminifera. Above the K/Pg hiatus at Gebel Um El-Ghanayem section (sample 36–39) sediments contain early Danian zone (Plc) and the planktonic foraminiferal assemblages characterized by few Guembelitria cretacea and G. trifolia. Meanwhile, the common planktonic are represented by Parasubbotina pseudobulloides, Subbotina triloculinoides, and Chiloguembelina morsei. The recorded benthic assemblage (Table 5) at the base of this zone (sample 36–39) is moderately diversified (15–20). Meanwhile, at the top of this zone (sample 39) the recorded benthic is completely similar to the base except for the presence of Neoflabellina suturalis (Cushman), Neoflabellina jarvisi (Cushman), Cibicidoides farafraensis (LeRoy), C. (LeRoy), Stilostomella spinea

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(Cushman), Stainforthia farafraensis (LeRoy), Frondicularia frankei Cushman and Nodosaria redicula (Linne). The Danian assemblages (P1c) are characterized by abundant epifaunal trochospiral species, such as Cibicidoides abudurbensis, Cibicidoides farafraensis, and Gyroidinoides girardanus. The infaunal morphogroups make up 23–47% of fauna in the Danian, in contrast to 62–76% in the Upper Maastrichtian. This dominance of the Danian benthic foraminiferal assemblages by epifaunal or mixed epifaunal/infaunal morphogroups suggests that the food supply to the benthos was less abundant than in the latest Cretaceous (e.g. Jorissen et al., 1995; Van der Zwaan et al., 1999). Table 6 shows the distribution of the calcareous benthic foraminifera in the different studied rock units of Gebel Um El Ghanayem (Kharga Oasis, Egypt). 4. Ecological concepts 4.1. Benthic foraminiferal number The benthic foraminiferal number (BFN) is a useful proxy to estimate oxygen content and organic matter flux in the past (e.g., Kaiho and Hasegawa, 1994; Jorissen et al., 1995). In oxygen depleted sediments, the BFN generally decreases (Coccioni and Galeotti, 1993; Friedrich et al., 2003). In contrast, a higher BFN is observed with increasing organic matter flux to the seafloor (e.g., Kaiho, 1994; Jorissen et al., 1995; Murray, 2000). Consequently, the BFN is controlled by both oxygen content and organic matter flux. 1. The statistical analysis of the lower part of Mawhoob Member (zone CF8b and CF7) confirms Sitella, Gavelinella and Anomalinoides dominate the benthic foraminiferal morphogroups in the studied assemblages, whereas there is an increase in the percentages of deep water morphotypes (nodosariids and buliminids) of infaunal benthic foraminifera at the top of this zone. 2. The benthic foraminiferal assemblage of CF7 Zone of the Beris Member is characterized by the richness of deep water morphotypes of benthic foraminifera such as nodosariids and buliminids, where CF6 Zone of Beris Member contains abundant buliminids such as Bulimina kugleri, Bulimina kickapooensis and Praebulimina sp. 3. The foraminiferal assemblage recorded in the Lower Kharga Member is dominated by Cibicidoides abudurbensis, Cibicidoides pharaonis and Cibicidoides pseudoacutus. 4. The calcareous foraminifera of the lower part of the Upper Kharga Member represented by high content of Cibicidoides abudurbensis, Cibicidoides farafraensis, and Gyroidinoides girardanus. Meanwhile the upper part is dominated by Stainforthia farafraensis, Frondicularia frankei and Neoflabellina suturalis. 4.2. Foraminiferal morphogroups The calcareous benthic foraminifera as many organisms show a good relation between their form and the environment in which they live. Koutsoukos and Hart (1990) they illustrated morphogroups of calcareous foraminifera with their postulated life positions. On the other hand Widmark (1995) suggested that highlatitude fauna were dominated by taxa indicative of oligotrophic and high-oxygenated environments, whereas low-latitude fauna were dominated by taxa reflecting more eutrophic and less-oxygenated bottom waters. In the area under study, the distribution of calcareous benthic foraminiferal morphogroups percentage (Table 7) and the paleoecological interpretation of the calcareous benthic foraminifera for each stratigraphic unit are discussed from base to top:

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Table 6 Distribution of the calcareous benthic foraminifera in the studied rock units of Gebel Um El Ghanayem (Kharga Oasis, Egypt). Benthic foraminifera

Rock units Mawhoob Member Lower

Nuttallides truempyi Lenticulina muensteri Lenticulina midwayensis Lenticulina rotulata Lenticulina naviculina Lenticulina pseudosecanus Gavelinella danica Gavelinella monterelensis Gavelinella martini Anomalinoides rubiginosus Anomalinoides affinis Anomalinoides cf. acutus Gyroidinoides girardanus Gyroidinoides depressus Gyroidinoides subangulata Osangularia plummerae Pullenia quinqueloba Sitella fabilis Gyroidina megastoma Saracenaria saratogona Nodosaria affinis Nodosaria redicula Nodosaria limbata Nodosaria mcneili Neoflabelina semireticulata Neoflabelina sulturalis Neoflabelina mumismalis Bulimina kickapooensis Bulimina kugleri Praebulimina sp. Frondicularia striatula Frondicularia goldfussi Frondicularia angulosa Frondicularia phosphatica Lagena sulcata Lagena apiculata Lagena globosa Gavelinella monterelensis Gavelinella danica Anomalinoides affinis Anomalinoides rubiginosus Buliminella cushmani Bulimina inflate Bolivina sp. Globobulimina suteri Loxostomum tegulatum Loxostomum applinae Cibicidoides abudurbensis Cibicidoides pharaonis Cibicidoides pseudoacutus Dentalina colei Vaginulina trilobata Lenticulina oligostegia Lenticulina navicula Pullenia coryelli Ramulina navarroana Anomalinoides granosa Marginulinopsis tuberculata Valvulineria scrobiculata Stilostomella midwayensis Cibicidoides praecursoria Lenticulina oligostegia Neoflabellina suturalis Neoflabellina jarvisi Stainforthia farafraensis Cibicidoides farafraensis Frondicularia frankei Stilostomella spinea

Beris Member

Lowe Kharga Member

Upper Kharga Member

Upper

x x x x x x x x x x x x x x x x x x x x

x x

x

x

x x x x x x x x x x x

x x x x x x x x x x x x x x x x

x

x x x

x x x x x x x x x x x x x x x x x x x

x

x x x x x x x x x x x x

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4.2.1. Duwi Formation (Campanian–Early Maastrichtian) Unfortunately no calcareous benthic foraminifera were found in this formation. 4.2.2. Mawhoob Member (early Maastrichtian) (CF8b–CF7) At the lower part of Mawhoob Member (zone CF8b and CF7) the planktonic foraminifera are nearly absent (max. 5 specimens/g) with P/B ratios well below 1% in most samples. These low numbers persist in intervals which are considered hardly affected by postmortem dissolution. In comparison with data on modern continental margins, planktonic percentages lower than 4% correspond to water depths less than 30 m in the Gulf of Mexico and less than 70 m in the semi-enclosed Adriatic Sea (Van der Zwaan et al., 1990). Furthermore, Sitella, Gavelinella and Anomalinoides dominate the benthic foraminiferal morphogroups, where these morphogroups are absent in more deep-sea assemblages (Speijer and Van der Zwaan, 1996). Consequently, our data point to deposition in a restricted shallow basin with connections to the open marine Tethys as can be judged from the common presence of calcareous planktonic fossils (sample 2–4). The upper part of Mawhoob Member (sample 5–9) is characterized by a decreasing trend in the percentage of planktonic foraminifera (51.2–39.4%) and increasing trend in the calcareous morphogroups at the top (27%). On the other hand there is an increase in the percentages of deep water morphotypes (nodosariids and buliminaceans) of infaunal benthic foraminifera at the top of this zone suggests an inner–outer neritic environment as pointed by Ernst et al. (2006). 4.2.3. Beris Member (early/late Maastrichtian) (CF7, CF6 and CF4) There is an increase in the percentages of deep water morphotypes of benthic foraminifera such as nodosariids and buliminids. Koutsoukos et al. (1990) argued that the presence of Praebulimina spp suggests an inner–outer shelf environment. Therefore, the presence of buliminids and planktonic non-keeled morphogroup in this unit (CF7) suggests there is also progressive increase in the depth of the sea (sample 16–17). There is a progressive increase in the depth of the sea from the CF7 to the CF6 zones as indicated by increasing the percentage of planktonic taxa (non-keeled and double-keeled). The doublekeeled taxa were float deeper than non-keeled forams (Hart and Bailey, 1979). Benthic foraminiferal assemblages at CF6 Zone of Beris Member contain abundant buliminids such as Bulimina kugleri Cushman and Kenz, Bulimina kickapooensis Cole and Praebulimina sp., which proliferate at deep-bathyal and abyssal depths (e.g., Tjalsma and Lohmann, 1983; Thomas, 2003). Further, the increasing percentage of buliminids in the CF6 Zone (sample 18–19) suggests deeper environment than the CF7 Zone.

It is worth mention that the upper part of the Beris Member (sample 20–23) two graded shell hash beds are present with Thalassinoides burrows at the base and top that mark erosional surfaces and there are abundant of bivalves, gastropods, rare solitary corals, shark teeth and reptile teeth, which indicates a shallow, nearshore or lagoonal environment. The presence of abundant macrofossils, vertebrate bones, Fe-rich sand and very abundant benthic foraminifera (95% relative to planktonic foraminifera) in the upper part of the Beris Member indicates that deposition occurred in a very shallow, high-energy, inner neritic to littoral environment. The barren intervals (sample 9–15) and (sample 20–23) below and above the two biozone (CF7 and CF6) is devoid of microfossils (Fig. 2), and suggests that deposition alternated between neritic and lagoonal to brackish environments. Latest Early Maastrichtian and Late Maastrichtian (sample 24) show shallower conditions through zone CF4, which indicated by the dominance of Gavelinella and Anomalina and the decreasing order of planktonic foraminifera. The predominance of benthic foraminifera (>95%) in the upper part of Beris Member suggests that deposition occurred within a shallow, high-energy, inner neritic to littoral environment, with either periodic marine incursions transporting open marine planktonic foraminiferal assemblages into the coastal areas. 4.2.4. Lower Kharga Member (late Maastrichtian) (CF3) The recorded planktonic assemblage is well diversified (sample 35) and shows high values, which expressed by a gradual deepening at the advent of Zone CF3. The abundance ratio of buliminids (this group includes Bolivina, Bolivinoides, Loxostomum, Praebulimina) to rotaliids (this group includes Cibicidoides, Cibicides, Gavelinella, Anomalinoides, Gyroidinoides, Osangularia) were used for estimating the variability in bottom water aeration. The buliminids to rotaliids ratio is often used to determine the oxygenation level of the bottom water in modern and ancient sediments (Nyong and Olsson, 1984; Almogi-Labin et al., 1993). Within the buliminids group, triserial buliminids are regarded as infaunal species, indicative of a very low-oxygenated seafloor and higher organic matter fluxes (e.g., Holbourn et al., 1999a,b, 2001; Friedrich et al., 2006; Friedrich, 2009). The late Maastrichtian assemblages (Zone CF3) are dominated by calcareous foraminifera with tapered tests, this tapered taxon Loxostomum applinae, Lox. tegulatum various dentalinid taxa, and Buliminella cushmani dominate in CF3 Biozone. These fauna is interpreted as being dominated by infaunal morphogroups, suggesting a moderately eutrophic environment. 4.2.5. Bir Abu Munqar Member (early Paleocene) Bir Abu Munqar Member separates the Lower Kharga Member (middle Late Maastrichtian) from the Upper Kharga Member (early Paleocene). Moreover, it contains reworked Maastrichtian fossils.

Table 7 Percentage distribution of calcareous benthic foraminiferal morphogroups characterizing the Cretaceous/Paleocene boundary in Gebel Um El Ghanayem (Kharga Oasis, Egypt). Morphogroups, %

Rock units Dakhla Formation Mawhoob Member

CH-A-2 epifaunal CH-A-3 epifaunal CH-A-4 epifaunal CH-A-5 epifaunal CH-A-6 epifaunal CH-B-2 infaunal CH-B-3 infaunal CH-B-4 infaunal

L. Kharga Member

U. Kharga Member

Lower part (CF8a–CF7)

Upper part

Beris Member CF7

CF6

CF4

CF3

P1c

30 30 – 2 38 – – –

– – – – – 30 45 25

10 10 – 2 – 20 40 18

20 14 – – – 20 16 30

15 15 – – – 32 38 –

– 8 10 – 10 30 22 20

7 25 37 – 12 9 10 –

100%

100%

100%

100%

100%

100%

100%

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Fig. 3. Field photograph shows the contact between the K/Pg, the Lower Kharga Member (Maastrichtian) and the Upper Kharga Member (Danian) at Gebel Um ElGhanayem, Kharga Oasis, Egypt.

4.2.6. Upper Kharga Member (late Early Paleocene) (P1c) Paleocene assemblages have a significant component of typical neritic taxa, where this component is characterized by various species of Anomalinoides, Bulimina, Lenticulina and Cibicidoides, i.e. taxa that are generally abundant in the neritic deposits of central Egypt (e.g., LeRoy, 1953; Luger, 1985; Speijer and Van der Zwaan, 1996; Speijer and Schmitz, 1998; Schnack, 2000). A morphologically small and low-diversity benthic foraminiferal assemblage indicates a low oxygen environment. These foraminifera suggest that sediment deposition occurred within a lowenergy, low-oxygen middle neritic environment. 4.3. Abundance and species diversity In total, 68 taxa of benthic foraminifera were identified in the studied succession. The fauna is strongly dominated by calcareous forms (more than 73% in all samples), indicating deposition well above the calcite compensation depth. The succession exhibits high BFN (Abundance) and benthic foraminiferal diversity fluctuations. The lower part of the Mawhoob Member (shales) characterized by low fluctuations in benthic foraminiferal number, followed by solid and high fluctuations within the marls of Beris Member. Benthic foraminiferal numbers show strong fluctuations between 6 and 283 individuals. High numbers generally are found in the Lower Kharga Member of the succession in the gray marl beds.

the benthos was less abundant in the latest Cretaceous (following Jorissen et al., 1995; Van der Zwaan et al., 1999). Benthic foraminiferal assemblages from the uppermost Maastrichtian CF3 Biozone are diverse, contain abundant rotalids and consist of both infaunal and epifaunal morphogroups. According to Jorissen et al. (1995) and Gooday (2003), assemblages composed of mixed infaunal and epifaunal morphogroups may well have lived under moderately eutrophic conditions, with enough organic matter not only at the sediment surface, but also in the deeper layers of the sediment. At the Mawhoob Member (zone CF8b and CF7) of the studied section is characterized by high abundance of rotalids (above 95%), and low abundance of buliminids, (below 5%). The buliminids have been found in association with high and fairly stable food supply and/or low levels of oxygen at the seafloor, contrary to rotalids, which favored oxygenated bottom water (Kaiho, 1994; Bernhard et al., 1997; Leckie et al., 1998). In the studied samples of Mawhoob Member low abundance of Bulimina also indicate oligotrophic and low oxygen condition. The benthic foraminiferal assemblages of Gebel Um El Ghanayem section are quite similar to their Late Cretaceous counterparts in oligotrophic shelf and open ocean environments, such as those found in Mexico, Tunisia, North Atlantic North Pacific and Iran (Li and Keller, 1999; Alegret et al., 2001; Frank et al., 2005; Friedrich and Hemleben, 2007; Ghoorchaei et al., 2012). The benthic foraminiferal assemblages at these localities are more diverse and consist mostly of epifaunal and shallow infaunal species. The benthic assemblage of the studied section is dominated by epifaunal species. It has been suggested that Maastrichtian species of the genus Buliminia reflects a high organic matter flux to the seafloor, combined with low oxygen contents in bottom waters (e.g., Coccioni et al., 1993; Widmark, 1997). The lenticulinids are common taxa of lower part of the Mawhoob Member assemblages and dominate in several low-oxygen environments (Bernhard, 1986; Coccioni and Galeotti, 1993; Friedrich et al., 2003, 2005). This is indicated that Cretaceous lenticulinids association with black shales suggest certain adaptational mechanisms, including tolerance in dysoxia and have the ability to use degraded organic matter as a potential food source. Thus, Cretaceous Lenticulina species may have occupied a deep infaunal microhabitat. Samples from the middle part of the section show extremely low BFN, while abundance in thick-walled species such as lenticulinids increases. This probably reflects dissolution of the tests, because decrease in BFN could be a result of high sedimentation rate and/or the selective preservation of dissolution-resistant taxa. Late Cretaceous Gyroidinoides is limited to abyssal depth and regarded also as a shallow infaunal taxon that thrived under mesotrophic (Alegret et al., 2001; Alegret and Thomas, 2005; Friedrich et al., 2005; Florisbal et al., 2013). In the relative abundanc curve, these species show the shortest peaks, except in the base of the section, possibly reflecting high-oxygen conditions as well as environmental instability.

4.4. The Epifaunal–Infaunal ratio Table 7 shows the epifaunal–infaunal morphogroups percentage in the different litho-stratigraphic units, which marked the dominance of epifaunal species through the studied succession. In the studied section assemblages are highly diverse, and contain both infaunal (Praebulimina, Globobulimina, Bulimina) and epifaunal morphogroups (Gyroidinoides, Anomalinoides). Epifaunal morphotypes make up 40–100% of the assemblages fluctuation. Dominance of epifaunal species often indicates high oxygen condition and/or low nutrient concentration (Bernhard, 1986). Benthic foraminiferal assemblages dominated by epifaunal or mixed epifaunal–infaunal morphogroups suggest that the food supply to

5. K/Pg boundary studies A major K/Pg hiatus is present in Gebel Um El Ghanayem, the K/ Pg contact was placed at the base of a 1-m-thick tan-colored calcareous siltstone and sandy limestone sequence that is widespread in the region and marks the base of the Abu Minqar Member. The strong reduction of surface-water productivity and the collapse of the pelagic ecosystem have been suggested the faunal changes across the K/Pg boundary (e.g. Keller, 1992; Kuhnt and Kaminski, 1993; Speijer and Van der Zwaan, 1996). Some morphologically epifaunal taxa, such as Bulimina and Bolivina flourish

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temporarily during deposition of the basal part of the boundary (low-oxygen conditions) at the most K/Pg boundary (Speijer and Van der Zwaan, 1996). However, the infaunal morphogroups which, represented by Bulimina, Praebulimina and Sitella declined in relative abundance or become extinct following the K/Pg boundary (Keller, 1992; Widmark and Malmgren, 1992; Speijer and Van der Zwaan, 1996). Meanwhile, taxa with epifaunal morphogroups which, represented by Gavelinella spp. and Cibicidoides spp. is largely unaffected and occasionally increasing in relative abundances following the K/Pg boundary (Thomas, 1990a,b; Widmark and Malmgren, 1992; Speijer and Van der Zwaan, 1996). Major depositional hiatuses span the upper Maastrichtian through lower Paleocene in Gebel Um El Ghanayem section appear to be linked primarily to major sea-level regressions and secondarily to regional tectonic activity (Bahariya arch uplift). The major eustatic sea-level changes may have been the primary controlling factors for widespread erosion and hiatuses, which is known eustatic sea-level changes detailed by Haq et al. (1987) and Li et al. (1999). Berggren et al. (2012) pointed out that the Late Cretaceous (Maastrichtian) depositional environment of the Dababiya Quarry (Upper Nile Valley, Egypt and lies eastern south of the Dakhla Oasis), was nearshore, tropical–sub tropical and nutrient rich; the latest Maastrichtian somewhat more restricted (coastal); and the early Danian cooler, low(er) salinity with increasing warmth and depth of water (i.e., more open water). Meanwhile, the Paleocene is further characterized by outer shelf (200 m), warm water environments as supported by foraminifera P/B ratios >85% (79– 28 m). 6. Summary and conclusion 1. The upper part of the Mawhoob Member (early Maastrichtian) is characterized by an increase in the percentages of deep water infaunal morphotypes of calcareous benthic foraminifera than the lower part which characterized by epifaunal morphotypes. This dominance benthic foraminiferal assemblage by infaunal morphogroups suggests that the food supply to the benthos was high abundant. 2. The Beris Member (zone CF7, CF6 and CF6) is characterized by an increase in the percentages of deep water morphotypes of benthic foraminifera such as nodosariids and buliminids, which suggests an inner–outer shelf environment and also progressive increase in the depth of the sea. 3. The Latest Early Maastrichtian and Late Maastrichtian show shallower conditions through zone CF4, which indicated by the dominance of Gavelinella and Anomalinoides and the decreasing order of planktonic foraminifera. The predominance of benthic foraminifera (>95%) in the upper part of Beris Member suggests that deposition occurred within a shallow, highenergy, inner neritic to littoral environment. 4. The calcareous benthic foraminiferal assemblage of Lower Kharga Member (Zone CF3 of late Maastrichtian) is similar to that recorded from the underlying zone (CF4) in addition to the presence of Pullenia quaternaria. The Lower Kharga Member is characterized by an increase in the percentages of infaunal calcareous benthic morphotypes and low abundance of epifaunal morphotypes. This dominance of benthic foraminiferal assemblage by infaunal or mixed epifaunal/infaunal morphogroups suggests that the food supply to the benthos was high abundant. 5. A morphologically small and low-diversity benthic foraminiferal assemblage of the Upper Kharga Member (Paleocene, Zone P1c) indicates a low oxygen environment, where this component is characterized by various species of Anomalinoides, Bulimina, Lenticulina and Cibicidoides, these foraminifera suggest

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that sediment deposition occurred within a low-energy, lowoxygen middle neritic environment. The dominance of epifaunal calcareous morphogroups suggests that the food supply to benthos was less abundant. 6. The benthic foraminiferal turnover across the K/Pg boundary within the studied section is characterized by a decrease in relative abundance of infaunal morphogroups, probably reflecting a decrease in food supply to the benthos as the result of a decrease in primary productivity and/or of food delivery to the sea bottom.

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