Calcareous nannofossil biostratigraphy and paleoecology of the Cretaceous–Tertiary transition in the central eastern desert of Egypt

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Marine Micropaleontology 47 (2003) 323^356 www.elsevier.com/locate/marmicro

Calcareous nannofossil biostratigraphy and paleoecology of the Cretaceous^Tertiary transition in the central eastern desert of Egypt Abdel Aziz A.M. Tantawy  Department of Geology, Faculty of Science, South Valley University, Aswan 81528, Egypt Received 2 January 2002; received in revised form 26 September 2002; accepted 26 September 2002

Abstract The Gebel Qreiya and nearby Wadi Hamama sections of the central Eastern Desert are among the most complete K/T boundary sequences known from Egypt. The two sections were analyzed spanning an interval from l.83 Myr below to about 3 Myr above the K/T boundary. A 1-cm-thick red clay layer at the K/T boundary at Gebel Qreiya contains an Ir anomaly of 5.4 ppb. The high-resolution study and well-preserved nannoflora provide good age control and the first quantitative records of calcareous nannofossil assemblages for paleoecological interpretations across the K/T transition in Egypt. Four zones (Micula murus, Micula prinsii, NP1, and NP2) were distinguished and correlated with other nannofossil and planktonic foraminiferal zonations that are broadly applicable for the eastern Tethys region. Latest Maastrichtian assemblages are abundant and diverse, though Cretaceous species richness progressively decreased across the K/T boundary. Dominant species include Arkhangelskiella cymbiformis, Micula decussata and Watznaueria barnesae, with high abundance of dissolution-resistant M. decussata reflecting periods of high environmental stress. Thoracosphaera blooms mark the K/T boundary and are followed by an acme of the opportunistic survivor Braarudosphaera bigelowii, the first appearance of the new Tertiary species Cruciplacolithus primus, and an acme of Coccolithus cavus/pelagicus. These successive abundance peaks provide the basis for subdivision of the Early Danian Zones NP1 and NP2 into five subzones. Correlation of selected nannofossil taxa from the Egyptian sections with those from various onshore marine and deep-sea sections provides insights into their paleoenvironmental and paleoecological affinities. > 2002 Elsevier Science B.V. All rights reserved. Keywords: calcareous nannofossils; biostratigraphy; paleoecology; K/T boundary; Eastern Desert; Egypt

1. Introduction In most localities throughout Egypt, Paleocene

* Corresponding author. E-mail address: [email protected] (A.A.A.M. Tantawy).

sediments unconformably overlie Maastrichtian marls. Erosion was at a maximum in the southern Nile valley and southern and central western Desert, where sediment deposition occurred in a shallow marginal sea. In these regions erosion is primarily the result of local tectonic activity and sea-level regression (El-Naggar, 1966; Issawi, 1972; Barthel and Herrmann-Degen, 1981; Her-

0377-8398 / 02 / $ ^ see front matter > 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 7 - 8 3 9 8 ( 0 2 ) 0 0 1 3 5 - 4

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mina, 1990; Hendriks et al., 1984; Tantawy et al., 2001). The K/T unconformity lies within the Dakhla Formation at the base of a thin phosphatic conglomerate (or sandy limestone) that is widespread in the Dakhla^Farafra region and marks the base of the Abu Minqar Horizon (Abbas and Habib, 1969; Barthel and Herrmann-Degen, 1981; Tantawy et al., 2001). In the central and northern parts of the Eastern Desert and the Sinai, variable erosion occurred in middle to outer shelf environments (Sestini, 1984; Hendriks and Luger, 1987; Luger, 1988; Jenkens, 1990; Kassab and Keheila, 1994; Luger et al., 1998), although hiatuses are relatively short and intra-zonal. The Gebel Qreiya and nearby Wadi Hamama sections in the central eastern Desert are among the most complete Upper Maastrichtian to Danian sequences in Egypt and among the very few localities where the Plummerita hantkeninoides (CF1) and Parvularugogloberina eugubina (P1a) planktonic foraminiferal Zones, as well as the Micula prinsii and Markalius inversus (NP1) calcareous nannofossil Zones are present (e.g. East Qena region, Luger, 1988; Tantawy, 1998; Luger et al., 1998 ; Duwi region, Tantawy, 1998 ; St. Paul, South Galala, Strougo et al., 1992; Faris, 1995a, 1997). During the K/T transition, the Gebel Qreiya and Wadi Hamama sections were located on the stable shelf of the Asyut Basin (Fig. 1) at middle to upper-shelf depths (Luger, 1988). The region was subject to global sea-level £uctuations throughout the Late Cretaceous and Early Paleocene (Hendriks et al., 1987; Luger and Gro«schke, 1989; Klitzsch et al., 1990). Calcareous nannofossil biostratigraphy and turnover across the K/T boundary have been investigated intensively during the last several years in order to understand the nature of the mass extinction that a¡ect groups in di¡erent environments and latitudes (Worsley, 1974; Monechi, 1977, 1979; Percival and Fischer, 1977; Romein, 1977; Perch-Nielsen, 1979a-c; Thierstein and Okada, 1979; Thierstein, 1981; Perch-Nielsen, 1981c; Romein and Smit, 1981; Perch-Nielsen et al., 1982; Jiang and Gartner, 1986; Seyve, 1990; Gorostidi and Lamolda, 1991; Eshet et al., 1992; Pospichal, 1991, 1994, 1995; Alcala¤-Herrera et al.,

1992; Ehrendorfer and Aubry, 1992; Lamolda and Gorostidi, 1992; Pospichal and Bralower, 1992; Gartner, 1996; Henriksson, 1996; Gardin and Monechi, 1998; Gardin, 2002). A number of studies have investigated calcareous nannofossil biostratigraphy across the K/T boundary in Egypt (e.g. El-Dawoody, 1973, 1983, 1990a,b; El-Dawoody and Barakat, 1973; El-Dawoody and Zidan, 1976; Abdelmalik et al., 1978; Faris, 1984, 1985, 1988, 1995a, 1997; Schrank and Perch-Nielsen, 1985; Faris and Abd Hamid, 1986a,b; Faris et al., 1985; Bassiouni et al., 1991), but no previous studies were quantitative in nature or carried out at high resolution. This study di¡ers from earlier reports in that an integrated quantitative database is used for calcareous nannofossils to provide improved biozonation and age control and to infer paleoenvironmental conditions during the latest Maastrichtian and earliest Danian in the central Eastern Desert of Egypt. The primary objectives are: (1) calcareous nannofossil biostratigraphy; (2) analysis of calcareous nannofossil assemblages; and (3) distribution and paleoecology of selected species.

2. Location and lithology The material used in this study was obtained from the Gebel Qreiya and nearby Wadi Hamama sections of the Qena region in the central Eastern Desert. Gebel Qreiya is located at the southern mouth of the Wadi Qena (lat. 26‡21PN, long. 33‡01PE), about 50 km northeast of Qena City and about 18 km north of km 53 of the Qena^ Safaga road. The Wadi Hamama section is located in the southwest of the Wadi Hamama, just north of the extreme eastern end of the Wadi Umm Solimat (lat. 26‡18PN, long. 33‡02PE), about 28 km south of Gebel Qreiya and 10 km south of km 44 of the Qena^Safaga road (Fig. 1). Local variations in lithology in the two sections are expressed by di¡erent members of the Dakhla Formation. The lithostratigraphic classi¢cation and equivalent ages of this succession in the Qena area are discussed by many authors (e.g. Barron and Hume, 1902; Said, 1962; Abdel Ra-

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Fig. 1. Location and geological map with the studied sections.

zik, 1969, 1972; Faris, 1974, Soliman et al., 1986). According to Abdel Razik (1972), the Dakhla Formation of Maastrichtian age comprises yellowish marls with numerous casts of Pecten farafrensis alternating with dark gray calcareous shales. They are equivalent to the upper part of Hamama marl member of Abdel Razik (1972) and are overlain by greenish-gray, laminated shales and claystones of Paleocene age (equivalent

to the Beida shale member of the Dakhla Formation, Abdel Razik, 1972; Luger, 1988). The thin red K/T boundary clay found in the Qreiya section contains an Ir anomaly of 5.4 ppb (Keller et al., in press) and represents the ¢rst such clay layer observed in Egypt. Similar thin red clay layers are present in all complete or nearly complete K/T boundary sections in low and middle latitudes (Keller et al., 1995). At the Qreiya

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P1b

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section the red clay layer is 1 cm thick with a thin gypsum layer (Fig. 2) and is devoid of calcareous microfossils. The K/T red clay layer overlies an undulating erosional surface which lies 10 cm above a second erosional surface. These erosion surfaces indicate an incomplete uppermost Maastrichtian sediment record and are characteristic of the widespread disconformities observed in many sections in central and southern Egypt (El-Naggar, 1966; Issawi, 1972; Faris, 1982, 1984, 1985; Tantawy, 1998). Nevertheless, erosion at Gebel Qreiya is relatively minor as indicated by the presence of the latest Maastrichtian Micula prinsii and Plummerita hantkeninoides zones and for this reason the section is considered one of the most complete K/T transitions in central Egypt (Luger, 1988; Luger et al., 1998; Tantawy, 1998; Tantawy et al., 2000). Similar observations are reported from the Galala plateau to the north in the Eastern Desert (Strougo et al., 1992; Faris, 1995a, 1997) and the Sinai (Faris, 1988, 1992; Shahin, 1992).

3. Methods To avoid losing small-sized coccoliths, samples were processed by smear slide preparation from raw sediment samples as described by Perch-Nielsen (1985). Smear slides were examined using a light photomicroscope with 1000^2000U magni¢cation. Each slide was observed under cross-polarized light and with a gypsum plate and phase contrast was used where necessary. Index species are illustrated in Plates 1^3. Calcareous nannofossils are generally abundant and well-preserved in both sections, which facilitates detailed quantitative analysis of the £oral assemblages. The counting technique described by Jiang and Gartner (1986) was used for quantitative analysis. All samples were prepared similarly to insure uniformity in the distribution of sample material and to minimize bias. Relative

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species abundances were determined by counting a population of about 300 specimens along a random traverse with a light microscope at a magni¢cation of about 1250U. Rare species were in two additional traverses to assure that no stratigraphic marker was overlooked. These species are marked by an X in the distribution charts. The relative abundance of dominant individual species, and the presence of specimens of all species are plotted and shown in Tables 1 and 2. The number of ¢elds of view traversed was also counted. Total nannofossil abundance was calculated as the total number of specimens counted per number of ¢elds of view traversed. The species richness (diversity) is given as the total number of species recorded in each sample. The procedure for counting broken or fragmented specimens (e.g. Thoracosphaera spp. and Braarudosphaera bigelowii) is similar to that described by Jiang and Gartner (1986), Pospichal (1991, 1995) and Pospichal and Bralower (1992). For Thoracosphaera spp., specimens larger than about one quarter to one third of the whole spherical forms are counted and added up to one. Every pentalith of B. bigelowii constructed of three or four joined elements was counted as one specimen and every four isolated elements were also counted as one whole specimen. In order to facilitate counting, the following species were combined : all Thoracosphaera spp., Arkhangelskiella cymbiformis and Arkhangelskiella speciallata ; Cyclagelosphaera alta and Cyclagelosphaera reinhardtii; Coccolithus pelagicus, Coccolithus cavus, and Coccolithus ovalis ; Prinsius tenuiculum and Prinsius dimorphosus.

4. Biostratigraphy The standard calcareous nannofossil zonations used in this study are those of Sissingh (1977) for the Maastrichtian and Martini (1971) for the Danian. In addition, the subdivisions of biozones proposed by Romein (1979) and Perch-Nielsen

Fig. 2. Lithological columns, sample intervals, integrated biostratigraphies of the studied Cretaceous^Tertiary interval in the Gebel Qreiya and Wadi Hamama sections.

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(1981a,b) are followed. Quantitative species analyses, as well as the ¢rst and last appearance of species, are used in this study to obtain high-resolution age control. The planktonic foraminiferal zonation for the Qreiya section is from Keller et al. (in press) based on the zonal scheme by Keller et al. (1995) and Li and Keller (1998a,b). 4.1. Micula murus Zone The Micula murus Zone (Bukry and Bramlette, 1970 ; emended Perch-Nielsen, 1981c) spans from the ¢rst occurrence (FO) of M. murus to the FO of Micula prinsii. This zone is equivalent to the lower part of the Nephrolithus frequens Zone (Cepek and Hay, 1969 ; emended Romein, 1979) or CC26 of Sissingh (1977). The M. murus Zone is probably restricted to low latitudes (e.g. Worsley and Martini, 1970; Worsley, 1974; Romein, 1979), whereas the N. frequens Zone is mainly applicable in higher latitudes (Perch-Nielsen, 1985). In this study, N. frequens is rare in both sections and restricted to short intervals. Micula murus spans the lower 7.5 m and 6.2 m at the Qreiya and Wadi Hamama sections, respectively, and corresponds to the CF3 planktonic foraminiferal Zone which de¢nes the interval from the FO of Plummerita hariaensis to the LO (last occurrence) of Gansserina gansseri (66.83^65.45 Ma, see Keller et al. (in press)). The calcareous nannofossil assemblages characteristics of this zone con-

tain common to abundant Arkhangelskiella cymbiformis, Micula decussata, Watznaueria barnesae, Cribrosphaerella ehrenbergii, Ahmuellerella octoradiata, Lithraphidites carniolensis, Prediscosphaera cretacea and few to rare Lithraphidites quadratus, Ei¡ellithus turrisei¡elii, Octolithus multiplus, M. murus, Rhagodiscus angustus, Thoracosphaera spp., Braarudosphaera bigelowii, and Zygodiscus spiralis. 4.2. Micula prinsii Zone The Micula prinsii Zone (Perch-Nielsen, 1979a; emended Romein and Smit, 1981) spans the interval from the FO of M. prinsii to the ¢rst common occurrence of Thoracosphaera operculata and Thoracosphaera spp. This zone is equivalent to the upper part of the Nephrolithus frequens Zone (Cepek and Hay, 1969; emended Romein, 1979) or CC26 of Sissingh (1977). The typical £oral assemblages in this zone is similar to that of the underlying Micula murus Zone, but is distinguished by the presence of M. prinsii, the youngest representative of the Micula lineage (Roth and Bowdler, 1979). At the Qreiya and Wadi Hamama sections, M. prinsii ¢rst occurs at 1.8 m and 3.6 m respectively below the K/T boundary (Fig. 2). The M. prinsii Zone encompasses the CF1 (Plummerita hantkeninoides) and CF2 planktonic foraminiferal Zones and spans the last 500 kyr of the Maastrichtian and the interval of Chron 29R

Plate I. (The scale bar for all ¢gures equals approximately 2 Wm. XPL = cross-polarized light; TL = transmitted light) 1, 2. 3, 4. 5, 10. 6, 7. 8, 9. 11, 12. 13. 14, 15. 16, 17. 18, 19. 20. 21^24. 25, 30. 26, 27. 28, 29.

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Ahmuellerella octoradiata, sample Q-34, Micula murus Zone, 1: XPL; 2: TL. Vekshinella stradneri, Q-20, Micula prinsii Zone, 3: XPL; 4: TL. Arkhangelskiella cymbiformis, sample Q-12, M. prinsii Zone, 5: XPL; 10: TL. Vekshinella crux, sample Q-14, M. prinsii Zone, 6: TL; 7: XPL. Braarudosphaera bigelowii, sample Q44, Zone NP1b, 8: TL; 9: XPL. Biscutum constans, sample S62, M. prinsii Zone, 11: XPL; 12: TL. Ei¡ellithus gorkae, sample Q-22, M. prinsii Zone, XPL. Ei¡ellithus parallelus, sample S58, M. prinsii Zone, 14: TL; 15: XPL. Ei¡ellithus turrisei¡elii, sample Q-12, M. prinsii Zone, 16: TL; 17: XPL. Cretarhabdus schizobrachiatus, sample S58, M. prinsii Zone, 18: TL; 19: XPL. Markalius inversus, sample S14, Zone NP1c, XPL. Watznaueria barnesae, sample Q-12, M. prinsii Zone, 21 and 23: XPL; 22 and 24: TL. Gartnerago obliquum, sample S87, M. murus Zone, 25: XPL; 30: TL. Chiastozygus amphipons, sample Q-12, M. prinsii Zone, 26: TL XPL; 27: XPL. Corollithion? madagaskarensis, sample Q-20, M. prinsii Zone, 28: TL; 29: XPL.

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below the K/T boundary (Henriksson, 1993; Pardo et al., 1996; Keller et al., in press). A short hiatus is present in the lower part of the M. prinsii Zone (Figs. 2 and 3), as indicated by the absence of planktonic foraminiferal Zone CF2 (Keller et al., in press). 4.3. Markalius inversus Zone (NP1) The Markalius inversus Zone (Hay and Mohler, 1967 ; emended Martini, 1970), or Zone NP1, spans from the acme of Thoracosphaera spp. to the FO of Cruciplacolithus tenuis. This zone correlates to Subzone P1a of Okada and Bukry (1980), Biantholithus sparsus Zone of Perch-Nielsen (1971), and the Zygodiscus sigmoides Zone of Perch-Nielsen (1979a). The lower boundary of this zone is characterized by the ¢rst common Thoracosphaera spp. At the Wadi Hamama section, this horizon is accompanied by the FO of Neobiscutum romeinii. At the Qreiya section, the Thoracosphaera acme starts directly above the K/T boundary clay, whereas N. romeinii appears 5 cm above the K/T boundary. The upper limit of Zone NP1 is marked by the FO of large ( s 9 Wm) C. tenuis and Cruciplacolithus primus and occurs at 6.85 m above the K/T boundary at the Wadi

Hamama section. The upper limit of this zone is not recovered at the Qreiya section. Planktonic foraminifera indicate the presence of a hiatus in the earliest Danian (P0/P1a) interval (Figs. 2 and 3 ; Keller et al., in press). The nannofossil assemblage of Zone NP1 is characterized by Late Maastrichtian species, which may be redeposited, and by the sequential appearance of many Tertiary species (see Tables 1 and 2). The ¢rst bloom of the survivor species Braarudosphaera bigelowii is recorded within Zone NP1 in both sections. The M. inversus Zone can be divided into three subzones using the FO of the B. bigelowii acme, and the FO of C. primus as noted below. 4.4. Thoracosphaera imperforata Subzone (NP1a) The Thoracosphaera imperforata Subzone is proposed here to include the interval from the FO of Thoracosphaera spp. acme to the FO of the Braarudosphaera bigelowii bloom. This subzone can be recognized in both the Qreiya and Wadi Hamama sections where it spans 1.20 m and 1.35 m, respectively. Although Jiang and Gartner (1986) originally placed the upper boundary of this subzone at the FO of Neobiscutum

Plate II. (The scale bar for all ¢gures equals approximately 2 Wm. XPL = cross-polarized light; TL = transmitted light) 1, 2. 3, 4. 5. 6, 7. 8. 9. 10, 11. 12, 13. 14. 15, 16. 17. 18. 19. 20, 21. 22, 23. 24. 25, 26. 27. 28. 29.

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Lithraphidites carniolensis, sample Q-14, Micula prinsii Zone, 1: XPL; 2: TL. Lithraphidites praequadratus, sample Q-38, Micula murus Zone, 3: XPL; 4: TL. Microrhabdulus attenuatus, sample Q-30, M. prinsii Zone, XPL. Lithraphidites quadratus, sample Q-40, M. murus Zone, 6: TL; 7: XPL. Podorhabdus decorus, sample Q-12, M. prinsii Zone, XPL. Cretarhabdus crenulatus, sample Q-16, M. prinsii Zone, XPL. Cribrosphaerella ehrenbergii, sample Q-30, M. prinsii Zone, 10: XPL; 11: TL. Nephrolithus frequens, sample Q-30, M. murus Zone, 12: XPL; 13: TL. N. frequens, sample Q34, M. prinsii Zone, XPL. Cribrocorona gallica, sample S73, M. prinsii Zone, 15: TL; 16: XPL. Micula decussata, sample Q-22, M. prinsii Zone, XPL. Micula murus, sample Q-40, M. murus Zone, XPL. Micula murus, sample Q-12, M. prinsii Zone, XPL. Micula murus, sample, S86, M. murus Zone, 20: XPL; 21: TL. Micula prinsii, sample Q-16, M. prinsii Zone, 22: XPL; 23: TL. Thoracosphaera sp., sample S50, Zone NP1a, XPL. Prediscosphaera cretacea, sample Q-12, M. prinsii Zone, 25: TL; 26: XPL. Prediscosphaera stoveri sample Q-16, M. prinsii Zone, XPL. Rhagodiscus angustus, sample Q-34, M. murus Zone, XPL. Rhagodiscus asper, sample S66, M. prinsii Zone, XPL.

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romeinii, this study recommends its placement at the ¢rst common occurrence of B. bigelowii because N. romeinii is present (rarely) at the base of this subzone and also extends downward into the Uppermost Maastrichtian (e.g. Mai et al., 1997; Gardin and Monechi, 1998; Gardin, 2002). The T. imperforata Subzone is characterized by the abundant occurrence of Thoracosphaera spp., but only few to rare B. bigelowii. Species which have their ¢rst occurrences in this subzone include N. romeinii, Neobiscutum parvulum, Neochiastozygus primitivus and very rare Biantholithus sparsus. This subzone is equivalent to the planktonic foraminiferal Subzones P1a and P1b of Keller et al. (1995, in press, Fig. 3). 4.5. Braarudosphaera bigelowii Subzone (NP1b) The Braarudosphaera bigelowii Subzone (NP1b) is proposed here to include the interval from the FO of B. bigelowii acme to the FO of Cruciplacolithus primus. The lower boundary of this subzone occurs at about 1.3 meters above the K/T boundary at both sections and is characterized by the ¢rst bloom of B. bigelowii. The nannofossil assemblage in this subzone contains abundant B. bigelowii in addition to the same £oral assemblages present in the underlying Thoracosphaera imperforata Subzone. The B. bigelowii Subzone spans 1.50 m and 1.25 m in the Qreiya and Wadi Hamama sections, respectively, and corresponds to

the lower part of planktonic foraminiferal Subzone P1c(1) of Keller et al. (1995) (Fig. 3). 4.6. Cruciplacolithus primus Subzone (NP1c) The Cruciplacolithus primus Subzone (Romein, 1979 emend. Jiang and Gartner, 1986) spans from the FO of C. primus to the FO of Cruciplacolithus tenuis. Cruciplacolithus primus ¢rst appears at 2.85 m and 2.35 m above the K/T boundary in the Qreiya (sample 52) and Wadi Hamama sections (sample 28), respectively. At Wadi Hamama the C. primus Subzone spans 6.85 m. The top of this subzone was not recovered at the Qreiya section. This subzone is equivalent to the upper part of Subzone P1c(1) and the lower part of Subzone P1c(2) of Keller et al. (1995) (Fig. 3). The C. primus Subzone is characterized by abundant to common Thoracosphaera spp., C. primus, Braarudosphaera bigelowii and Zygodiscus sigmoides. The ¢rst appearance of Coccolithus cavus/Coccolithus pelagicus is found at the base of this subzone, and the maximum abundance of Neobiscutum parvulum occurs in the middle part of the subzone. Carbonate dissolution marks a 1.5-m-thick interval within the lower part of this subzone in the studied area. 4.7. Cruciplacolithus tenuis Zone (NP2) The Cruciplacolithus tenuis Zone or NP2 (Hay

Plate III. (The scale bar for all ¢gures equals approximately 2 Wm. XPL = cross-polarized light; TL = transmitted light) 1^3. 4, 5. 6, 7. 8. 9. 10. 11, 12. 13^15. 16. 17, 18. 19, 20. 21, 22. 23, 24. 25, 26. 27, 28. 29, 30.

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Zygodiscus compactus, sample Q-14, Micula prinsii Zone, 1 and 3: XPL, 2: TL. Zygodiscus spiralis, sample Q-30, M. prinsii Zone, 4: TL; 5: XPL. Z. spiralis, sample Q-20, M. prinsii Zone, 6: XPL; 7: TL. Zygodiscus sigmoides, sample S14, Zone Np1c, XPL. Ceratolithoides kamptneri, sample Q-13, M. prinsii Zone, XPL. Neobiscutum romeinii, sample Q-11, Zone NP1a, XPL. N. romeinii, sample Q-10, Zone NP1a, 11: XPL; 12: TL. Neobiscutum parvulum, samples Q9, Q-11, Zone NP1a, 13 and 14: XPL; 15: TL. Cruciplacolithus primus, sample S14, Zone NP1c, XPL. C. primus, sample Q90, Zone NP1c. 17: XPL; 18: TL. Cruciplacolithus edwardsii, sample S3, Zone NP2b, 19: XPL; 20: TL. C. edwardsii, sample S4, Zone NP2b, 21: XPL; 22: TL. Cruciplacolithus tenuis, sample S12, S4, Zone NP2, XPL. Prinsius africanus, sample S4, Zone NP2b, 25: XPL; 26: TL. Coccolithus pelagicus, sample S2, Zone NP2b, 27: XPL; 28: TL. Neochiastozygus primitivus, sample S2, Zone NP2b, 29: XPL; 30: TL.

MARMIC 905 27-1-03

334

Table 1 Calcareous nannofossil assemblage abundance, preservation and species richness data from the Qreiya section

A.A.A.M. Tantawy / Marine Micropaleontology 47 (2003) 323^356

MARMIC 905 27-1-03 X denotes species encountered in traverses after the statistical count of V300 specimens.

Table 2 Calcareous nannofossil assemblage abundance, preservation and species richness data from the Wadi Hamama section

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MARMIC 905 27-1-03

335

X denotes species encountered in traverses after the statistical count of V300 specimens.

336

Central Eastern Desert, Egypt Datum Events

Age (Ma)

M. trinidadensis

62.2

P1d

P1c P1c(2)

P1c(2)

MARMIC 905 27-1-03

Danian

C. pelagicus Acme C. edwardsii P. af ricanus

NP2b

C. edwardsii

Cruciplacolithus tenuis (NP2)

C. edwardsii C. primus C. primus (large)

NP2a

P. petalosus P. petalosus

NP1c

CP1

C. pelagicus P1c(1)

C. primus (small)

NP1b B. bigelowii Acme

S. varianta

P. eugubina (Pα)

P1b

P1b

P1a

P1a

S. triloculinoides (>100um)

64. 5

P. eugubina

64. 7

P. logiapertura

P. eugubina G. cretacea (P 0)

G. cretacea (P 0)

Hiatus

P. hantkeninoides (CF1)

P. hantkeninoides (CF1)

C. ultimus

C. primus (small)

P1c(1)

P1b

P1a

b

63.0

P1c

P. logiapertura

N. primitivus N. parvulum N. romeinii

64. 97 65.00 Thoracosphaera Acme

Markalius inversus (NP1)

a N. parvulum

NP1a N. parvulum N. romeinii

Hiatus

Thoracosph. Acme

Micula prinsii

P. hantkeninoides

65.30 P. palpebra (CF2)

Hiatus

Abathomphalus mayaroensis

Hiatus G. gansseri

P. hariaensis (CF3)

Perch-Nielasen (1979, 1981a,b) Mediterranean

Zone

C. tenuis P. inconstans

Maastrichtian

Datum Events

Roth, (1978) Okada & Bukry (1980)

65.45

M. prinsii

Micula murus

P. hariaensis (CF3)

P. hariaensis

66.83

Nephrolithus frequens (CC26)

Tetralithus murus/ Nephrolithus frequens (NC23)

b

a

N. frequens M. murus

Fig. 3. Correlation of the proposed calcareous nannofossil and planktonic foraminiferal zonation with commonly used zonal schemes (Roth, 1978). Ages according to Berggren et al. (1995) and Li and Keller (1998a).

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P1d

P1c

Sissingh (1977) Martini (1971)

(This study) Zone

Nannofossils

Nephrolithus frequens (CC26)

Li &Keller (1998); Keller et al. (1995) Tunisia

NP2

Berggren et al. (1995)

Calcareous

Foraminifera

NP1

Stage

Planktic

A.A.A.M. Tantawy / Marine Micropaleontology 47 (2003) 323^356

and Mohler, 1967 ; emended Martini, 1970) spans the interval from the FO of C. tenuis to the FO of Chiasmolithus danicus. This zone was only recovered at the Wadi Hamama section (samples from 9^1), where the lower part of the zone is characterized by C. tenuis and common Thoracosphaera spp., Zygodiscus sigmoides, Cruciplacolithus primus (large, s 9W), few to rare Coccolithus pelagicus, Neobiscutum parvulum, Braarudosphaera bigelowii and rare re-deposited Cretaceous species (Table 2). The upper part of this zone is marked by the ¢rst appearance of Prinsius africanus, Cruciplacolithus edwardsii and dominated by C. pelagicus. The sudden increase of the latter species can be used to subdivide this zone into Subzones NP2a and NP2b. Zone NP2 corresponds to the upper two thirds of planktonic foraminiferal Subzones P1c(2) and P1d (Fig. 3).

5. Calcareous nannofossil assemblages Sixty-three calcareous nannofossil species from 40 genera were found in the course of this study (Tables 1 and 2). Among these, three distinct species groups can be recognized : (a) vanishing or Cretaceous species, (b) persistent or survivor species, and (c) incoming or Tertiary species (Figs. 4 and 5). Similar species groups have been distinguished by other workers (e.g. Percival and Fischer, 1977; Perch-Nielsen et al., 1982; Jiang and Gartner, 1986; Pospichal, 1991, 1995; Pospichal and Bralower, 1992). 5.1. Vanishing species Vanishing species include taxa that are considered to have become extinct before or at the end of the Maastrichtian. About 40 typical Cretaceous species were recorded in both sections (Tables 1, 2). The most abundant are Arkhangelskiella cymbiformis, Micula decussata, Watznaueria barnesae, Prediscosphaera cretacea, and Cribrosphaerella ehrenbergii. Species that are common include Ei¡ellithus turrisei¡elii, Chiastozygus amphipons, Lithraphidites carniolensis, Ahmuellerella octoradiata, and Zygodiscus spiralis. All other species are quantitatively insigni¢cant. The vanishing Creta-

337

ceous nannofossil assemblages encompass 93% to 95% of the total assemblages in the Micula murus Zone and gradually decrease in the Micula prinsii Zone by about 10% (Figs. 4 and 5). Previous studies reported little or no changes in Cretaceous nannofossil assemblages below the K/T boundary (e.g. Perch-Nielsen et al., 1982; Romein, 1977; Thierstein, 1981; Jiang and Gartner, 1986; Pospichal, 1994). Thus the decrease in the Eastern Desert of Egypt may be a local phenomenon. A major change is observed in calcareous nannofossil assemblages across the K/T boundary as observed in other sections worldwide (e.g. Pospichal, 1994, 1995). In the Qreiya and Hamama sections, this £oral turnover is marked by a dramatic decrease in the relative abundance of combined Cretaceous species and a corresponding increase in the survivor group. At the Hamama section, Cretaceous nannofossils are reduced by 50% at the K/T boundary, average 40% in Subzone NP1a and 10^20% in Subzones NP1b and c and Zone NP2 (Fig. 4). But at the Qreiya section a more gradual transition is indicated by a decrease of 25% in the Cretaceous nannofossil assemblage in the 15 cm overlying the K/T boundary, and a gradual decrease to 40% in Subzone NP1a (Fig. 5). The di¡erence between the two sections is likely to be due to erosion and reworking in the Early Danian. For example, the basal Danian foraminiferal Zone P0 and most of Subzone P1a (Parvularugogloberina eugubina Zone), which span the lower part of Subzone NP1a, are missing at the Hamama section, whereas at Qreiya Zone P0 is reduced to the red clay layer and P1a is only 50 cm thick (Figs. 4 and 5 ; Keller et al., in press). Reworked planktonic foraminifera are abundant immediately above the K/T boundary at the Qreiya section, and similar reworking of calcareous nannofossils may partly account for the overall higher percentage of nannofossil assemblages relative to Hamama. Reworking in this interval is indicated by abundant reworked foraminifera (Keller et al., in press). Anomalous Lower Danian peaks in Cretaceous assemblages at both sections are also due to reworking and re-deposition particularly in intervals of hiatuses (e.g. at 11.5 m at Qreiya and 11 m at Wadi Hamama).

MARMIC 905 27-1-03

P1C(2)

40

60

80

Tertiary species

c

Q80 11

Dissolution

Q70 Q60

NP1 b

Q50 Q40

9

Survivors

Q30

a

Q20 Q-1 8

Q-5

7

Q-15

6

Q-25

P1a

Q-10

M.prinsii

CF1

20

Q90

P1C(1) P1C(1)

Danian Formatio n

Percent Abundance (%)

12

10

P1b

Gebel Qreiya

Sample No.

Thickness Lithology

Planktic Foraminifera Calcareous Nannofossils

A.A.A.M. Tantawy / Marine Micropaleontology 47 (2003) 323^356

Stage Formation

338

K/T

Q-20

Q-30

M. murus

4

CF3

Maastrichtian Dakhla

5

Cretaceous species Q-35

3

2

1

Q-40

(m) 0

Q-42

Fig. 4. Percent abundance of Cretaceous, survivor and Tertiary nannofossil assemblages across the K/T boundary in the Gebel Qreiya section.

The observed pattern of K/T and Lower Danian Cretaceous species assemblage variations is consistent with previous quantitative studies that show a gradual decrease up-section within NP1 and NP2. For example, Pospichal and Wise (1990) documented this pattern at the Antarctic Ocean ODP Site 690 Perch-Nielsen et al. (1982), and Keller and von Salis-Perch-Nielsen (1995) at El Kef, and Jiang and Gartner (1986) at Brazos River, Texas. 5.2. Survivors Survivors are de¢ned as Cretaceous species that

survived into the Paleocene or have direct descendants surviving into the Paleocene (PerchNielsen et al., 1982). Eleven survivor species were recorded in Danian sediments at Qreiya and Hamama, including Biscutum constans, Biscutum sp., Braarudosphaera bigelowii, Cyclagelosphaera reinhardtii, Markalius inversus, Neobiscutum parvulum, Neobiscutum romeinii, Neocrepidolithus neocrassus, Octolithus multiplus, Thoracosphaera spp., and Zygodiscus sigmoides (Tables 1 and 2). The rare occurrence of N. romeinii and N. parvulum were previously recorded in the Maastrichtian sediment by several authors, e.g. in the Geulhemmerberg section, the Netherlands

MARMIC 905 27-1-03

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339

Wadi Hamama Percent Abundance (%) 20

40

60

80

1 21 20

Tertiary 5

19

Survivors

18 10

17 16 15

15

14

20

13

25

12

30

11

35 40

10

50 60

9 8 7

Dissolution

K/T

70 75

80

Cretaceous

6 5

85

4 3 2 1 90

Fig. 5. Percent abundance of Cretaceous, survivors and Tertiary nannofossil assemblages across the K/T boundary in the Wadi Hamama section.

(Mai et al., 1997), and the Elles section, Tunisia (Gardin, 2002). These species are present only above the K/T boundary at the Qreiya and Hamama sections. The survivor species are generally rare ( 6 3%) in the Micula murus Zone, though a marked increase in the upper Micula prinsii Zone immediately below the K/T boundary is observed in both sections (Figs. 4 and 5). Above the boundary, the survivor assemblage (here mainly Thoracosphaera and B. bigelowii) shows a rapid and

progressive increase in the relative abundance to about 40% near the NP1a/b Subzonal boundary and a further increase in Subzone NP1c to about 70% in both sections (Figs. 4 and 5). 5.3. Tertiary species Tertiary species are de¢ned as species that ¢rst appear at or above the K/T boundary. A total of eleven Tertiary species are identi¢ed (Tables 1 and

MARMIC 905 27-1-03

340

A.A.A.M. Tantawy / Marine Micropaleontology 47 (2003) 323^356

Gebel Qreiya section

Species Richness

Nannofossil Abundance

(Species/Sample)

(Specimens/Field of view)

10

20

5

10

15

Q90

12 Q80

11

Dissolution

Q70

Q60

10

Q50 Q40

9

Q30 Q20 Q-1

8

Q-5 Q-10 Q-1.5

7

Q-15 Q-20

6

Q-25 Q-30

Survivor + Tertiary species

5

4

Cretaceous species

Q-35

3

2

1

Q-40

(m)

0

Q-42

Fig. 6. Calcareous nannofossil abundance and species richness across the K/T boundary in the Gebel Qreiya section.

2), including common to abundant Cruciplacolithus primus and Coccolithus cavus/pelagicus. Other species are rare or occur sporadically, including Cruciplacolithus tenuis, Cruciplacolithus edwardsii, Cyclagelosphaera alta, Neochiastozygus ultimus, Neochiastozygus primitivus, Prinsius dimorphosus/ tenuiculum, Prinsius africanus, and Toweius petalosus. The Tertiary assemblage is a minor component (V2^3%) of the Danian nannofossil assemblages in Subzones NP1a and NP1b, increases to about 20% in the upper part of Subzones NP1c and NP2a, and a rapid increase to 56% in the upper part of Zone NP2 (Figs. 4 and 5).

6. Nannofossil abundance and species richness 6.1. Species richness (number of species per sample) 6.1.1. Cretaceous species Species richness in the Cretaceous assemblage varies considerably below the K/T boundary. At the Qreiya section, the species richness of the Cretaceous assemblage decreases gradually from 27 at the base of the section to 14 species within the middle part of Micula murus Zone, then returns gradually to 27 species at the top of this

MARMIC 905 27-1-03

A.A.A.M. Tantawy / Marine Micropaleontology 47 (2003) 323^356

341

Wadi Hamama section Species Richness

Nannofossil Abundance

(Species/Sample) 10 20

(Specimens/Field of view) 5 10

1 21 20

5

19

Survivor + Tertiary species

18 10

17 16 15

15 20

14 13

25

12

30

11

35

Dissolution

40 10

9 8 7

50 60 70 75

80

6

5

85

Cretaceous species

4

3 2 1 90

Fig. 7. Calcareous nannofossil abundance and species richness across the K/T boundary in the Wadi Hamama section.

zone. Within the Micula prinsii Zone, the species richness shows a gradual decrease in the lower part, an abrupt increase at 85 cm below the K/T boundary, and £uctuates around 25 species up to just below the boundary. At the Wadi Hamama section, the species richness increases slightly from the base upward and averages 18 species within the Micula murus Zone and 21 species within the Micula prinsii Zone with a peak of 27 species at 45 cm below the K/T boundary. The di¡erences in species richness recorded at the Gebel Qreiya and Wadi Hamama

sections may be due to the lithologic changes, preservation and more shallow-water conditions in the Wadi Hamama area during the Late Maastrichtian M. murus and M. prinsii Zones. Species richness at Qreiya shows a progressive decrease from 27 to 17 species within the uppermost 20 cm of the Maastrichtian, then increases again to 22 species at 5 cm above the K/T boundary (Figs. 6 and 7). This trend is not recorded at Wadi Hamama, where the species richness remained similar below and above the boundary. This di¡erence may be due to the hiatus in the

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342

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basal Danian, where most of Subzone P1a and lowermost part of Subzone NP1a are missing (see Figs. 2 and 7). In both sections, the species richness of the Cretaceous assemblage shows a general decreasing trend with a strong oscillation in the Lower Danian and the presence of nine species at the top of both sections (Figs. 8 and 9). The species abundance changes possibly as a result of dissolution, and intermittent reworking and re-deposition within the lower part of Zone NP1. 6.1.2. Survivors and Tertiary species The species richness of the survivor assemblage averages about 2.5 species in the Maastrichtian at both sections and increases slightly just below the K/T boundary (Figs. 6 and 7). Survivor and Tertiary species combined at the Qreiya section show an abrupt increase in species richness across the boundary and £uctuate between 5 and 10 species in the Danian. However, at Wadi Hamama, the survivors and Tertiary species show a more gradual increase in the species richness across the boundary and an increase from two species at 45 cm below the K/T boundary to 13 species at 45 cm above the boundary (Fig. 7). Fluctuations in the combined survivor and Tertiary species richness parallel to those of Cretaceous species are also observed in the upper part of Subzone NP1a and lower part of Subzone NP1b. Carbonate dissolution and poor preservation appear to be responsible for these £uctuations. In the upper part of Subzone NP1b and Zone NP2, species richness is constant, averaging nine species per sample (Fig. 7). 6.2. Nannofossil abundance (specimens per ¢eld of view) The relative abundance of nannofossils, calculated by counting the number of specimens per ¢eld of view (s/fv), provides a measure of environmental change. At Qreiya the relative abundance of the Cretaceous assemblages in the Upper Maastrichtian Micula murus Zone £uctuates between four and ¢ve specimens per ¢eld of view. In two intervals in the Micula prinsii Zone at 1.25 m and 1.85 m, the relative abundance reaches

17 and 12 s/fv, respectively (Fig. 6). These peak values were not observed at the Wadi Hamama section, in which the Cretaceous assemblages show variable abundances below the K/T boundary parallel to the lithologic changes. In the latter section, the minimum abundance is recorded within a sandstone marker bed at the base of the section at the base of M. murus Zone, sample 90, 3.4 s/fv, and appears to be due to poor preservation. Maximum abundance of 13.5 s/fv is reached in the marls within the uppermost two meters of the M. murus Zone (Fig. 7). An abrupt decrease in the Cretaceous assemblage abundance from seven to one s/fv occurs in the 25-cm interval above the K/T boundary at the Qreiya section (Fig. 6). On the other hand, a gradual decline in nannofossil abundance from six s/fv at 45 cm below the K/T boundary (sample 62) to 0.5 s/fv at 60 cm above the boundary (sample 39) is observed at the Wadi Hamama (uppermost Micula prinsii Zone and Subzone NP1a, Fig. 7). Up-section in the Danian, the abundance of the Cretaceous assemblage is very low and £uctuates between 0 and 1.5 s/fv. The combined relative abundance of survivor and Tertiary assemblages is very low ( 6 1 s/fv) below the K/T boundary, and peaks just above the boundary (2 s/fv) at Qreiya and (5 s/fv) at Wadi Hamama. This di¡erence may be due to the shallower depositional environment and possibly higher salinity in the southern Wadi Hamama area, which resulted in the bloom of survivor and opportunistic Thoracosphaera spp. during the earliest Danian. The relative abundance of survivors and Tertiary species combined at Wadi Hamama increases gradually upward to reach eight s/fv with minor £uctuations at the top of the section (upper part of Zone NP2, Fig. 7).

7. Paleoecology of selected species 7.1. Late Maastrichtian During the Late Maastrichtian, calcareous nannofossil assemblages in central Egypt are similar to assemblages reported from low to mid-latitudes

MARMIC 905 27-1-03

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MARMIC 905 27-1-03 Fig. 8. Relative abundances of selected calcareous nannofossil species across the K/T boundary in the Gebel Qreiya section.

343

344 A.A.A.M. Tantawy / Marine Micropaleontology 47 (2003) 323^356

MARMIC 905 27-1-03 Fig. 9. Relative abundances of selected calcareous nannofossil species across the K/T boundary in the Wadi Hamama section.

A.A.A.M. Tantawy / Marine Micropaleontology 47 (2003) 323^356

(Thierstein, 1981) in that they contain a mixture of low and high-latitude species. Micula decussata, the dominant species, averages between 20% and 30% of the total nannofossil assemblage (Figs. 8 and 9). Four well-developed peaks of M. decussata are observed at Qreiya and Hamama. The lower two peaks occur in the middle and upper Micula murus Zone, and the upper two peaks within the middle and upper Micula prinsii Zone (Figs. 8 and 9). The M. decussata blooms below the K/T boundary have also been recognized in other Upper Maastrichtian sections (e.g. Braggs, Alabama (Worsley, 1974); San Tolmo, Spain (Percival and Fischer, 1977); Brazos River and Littig Quarry, Texas (Jiang and Gartner, 1986); Hor Hahar, Israel (Eshet et al., 1992; Eshet and Almogi Labin, 1996); Gubbio, Italy, and DSDP site 577A (Gardin and Monechi, 1998); Elles, Tunisia (Gardin, 2002)). Micula decussata has been reported as a major constituent of Late Cretaceous tropical and subtropical assemblages (Thierstein and Haq, 1977; Wind, 1979). Its distribution may in fact be the result of latitudinal preservation patterns, possibly related to fertility. According to Thierstein (1980, 1981), M. decussata is a highly dissolution-resistant form and is considered a good indicator of poor nannofossil preservation and diagenetic enhancement (see also Roth, 1983; Pospichal, 1991; Eshet and Almogi Labin, 1996). However, in the two sections examined from central Egypt, the high abundance of M. decussata does not appear to be an artifact of dissolution because most other species, including dissolution-prone forms (e.g. Biscutum constans, Prediscosphaera cretacea and Cribrosphaerella ehrenbergii), are well-preserved. Similarly, abundant M. decussata was reported by Moshkovitz and Eshet (1989) and Eshet et al. (1992) from Israel in samples with good preservation and no evidence of strong dissolution or overgrowth. Hence, the high abundances of M. decussata in well-preserved assemblages in Uppermost Maastrichtian sediments in sections in the Negev, Egypt and elsewhere could re£ect a natural increase in abundance (Pospichal, 1991) due to high-stress marine environments (Eshet et al., 1992). There is other support for this interpre-

345

tation. Stable isotope data from the Qreiya section indicate very low surface productivity for most of the Micula murus and the lower and uppermost parts of the Micula prinsii Zones (Fig. 10; Keller et al., in press), and planktonic foraminiferal assemblages are dominated by the disaster species Guembelitria cretacea. Following Thierstein (1980), the studied sections show the presence of some warm-water indicators such as Micula murus, Micula prinsii, Lithraphidites quadratus, and Watznaueria barnesae. Watznaueria barnesae comprises up to about 29% of the nannofossil assemblage in the Uppermost Maastrichtian Micula prinsii Zone at Qreiya (Figs. 8 and 9), and re£ects a global warming trend identi¢ed in planktonic foraminiferal Zone CF1 based on oxygen isotopes (Li and Keller, 1998c). In the Micula murus Zone, W. barnesae does not exceed more than 12% of the total nannofossil assemblage, except for sample Q-38, where this species reaches 20% in an interval marked by poor preservation, which could explain the high abundance of this very dissolution-resistant species. Several species are commonly recognized as cool-water indicators. The cool-water species Arkhangelskiella cymbiformis is relatively abundant in the Micula murus Zone in both sections (Figs. 8 and 9) and re£ects a major Late Maastrichtian global cooling event (Barrera, 1994; Li and Keller, 1998c). There is a signi¢cant decrease in the size of A. cymbiformis specimens towards the top of the Maastrichtian in the Micula prinsii Zone, in agreement with previous ¢ndings of Girgis (1989) and Faris (1995b) in Egypt and of Gardin (2002) in Tunisia. The decrease in size of this species coincides with warming as indicated by stable isotopes data (Barrera, 1994; Li and Keller, 1998c). Another cool-water taxon, Nephrolithus frequens, is sporadically present in low abundance ( 6 1%). This species was previously recorded from other Late Maastrichtian sections in Egypt by Sha¢k and Stradner (1971), Perch-Nielsen et al. (1978) and Faris (1997). Prediscosphaera stoveri, another cool-water species, increases in abundance in high latitudes (ODP Sites 690, 738, and 752) during the Late Maastrichtian (e.g. Pospichal and Wise,

MARMIC 905 27-1-03

346

Species Richness

8

P1 a

CF1

7

6

Calcareous Nannofossils selected species

δ13 C

δ18 O

A. cymbif ormis

Terttiary + Survivor

M. decussata

P1 c( 1 )

9

P1 b

68 64 60 56 52 48 44 40 36 32 28 24 20 -1 -3 -5 -7 -9 -1 1

W. barnesae

P1 c( 1 )

NP1c M. prinsii NP1a NP1b

10

K/ T

-1 4 -1 6 -1 8 -2 0 -2 2 -2 4 -2 6 -2 8 -3 0

Braarudosphaera bigelowii

5 -3 3

Cretaceous

-3 4

Thoracosphaera spp.

4

-3 5

3

CF3

M. murus

MARMIC 905 27-1-03

Late Maastricht ian

11

Calcareous Nannofossils select ed species

-3 6 -3 7

2

-3 8 -3 9

1

-4 0

m

-4 1 -4 2

5

10

15

20

25

Number of Species

0

30

0

40

Percent

0

30 -1

-0 .5

0

Permil ( PDB)

0

30

50

Percent

-8

-7

-6

-5

-4

-3

-2

Permil ( PDB) Hiat us Rugoglobigerina rugosa ( planktic)

Cibicidoides pseudoacutus

Fig. 10. Carbon and oxygen stable isotope data of benthic and planktonic foraminifera after Keller et al. (in press), calcareous nannofossil species richness, and selected species abundance in the Gebel Qreiya section.

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Early Danian

Qreiya, Egypt

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1990; Pospichal, 1991; Wei and Pospichal, 1991; Pospichal and Bralower, 1992) and reaches nearly 70% below the K/T boundary at ODP Sites 690 and 738. In low-latitude continental shelf sections, this species is common (V15%) near the top of the Maastrichtian as observed at Brazos River, Texas, and El Kef, Tunisia (Jiang and Gartner, 1986). Peak abundance of P. stoveri in the Qreiya section is only about 7% in sample Q20, about 85 cm below the K/T boundary (Fig. 8). Other cold-water species present in central Egypt include Ahmuellerella octoradiata, Biscutum constans, Ei¡ellithus turrisei¡elii, and Kamptnerius magni¢cus. The presence, though low abundance, of this cool-water or high-latitude assemblage (Thierstein, 1981; Pospichal, 1991) in the Micula prinsii Zone suggests cooler conditions near the end of the Maastrichtian. Thus the Upper Maastrichtian relative abundances of preserved cool and warm-water species suggest alternating cool/warm £uctuations during the latest Maastrichtian (Fig. 10). 7.2. Cretaceous/Tertiary and Early Danian The K^P and Lower Danian intervals at Qreiya and Wadi Hamama show a succession of blooms of Thoracosphaera spp., Braarudosphaera bigelowii, Neobiscutum parvulum, Cruciplacolithus primus, Zygodiscus sigmoides, and Coccolithus pelagicus. Blooms of Thoracosphaera are known from several middle to lower-latitude sites (Percival and Fischer, 1977; Perch-Nielsen et al., 1982; Jiang and Gartner, 1986; Gardin and Monechi, 1998). In the Eastern Desert of Egypt, this species shows a sudden increase in relative abundance to 57% that parallels a decrease in Cretaceous species richness in the 120 cm above the K/T boundary (Tables 1 and 2 ; Figs. 8 and 9). Thoracospahera is considered an opportunistic species that tolerates unusual marine conditions, including major changes in primary productivity (Eshet et al., 1992). Recent representatives of Thoracosphaera in the Gulf of Mexico were commonly observed in surface waters with high salinity values (Gaarder and Hasle (1971). During Danian Zone NP1/NP2 transition, Thoracosphaera also dominates, reaching about

347

V51% of the total assemblage in the Wadi Hamama section (samples 10^12) and 28% in the Qreiya section (sample Q90) (see Tables 1 and 2, and Figs. 8 and 9). A similar Thoracosphaera bloom was observed by Eshet et al. (1992) at the same stratigraphic level. Eshet et al. (1992) assumed that the presence of both Thoracosphaera and re-deposited material indicates a second marine regression in the Early Tertiary. The taxon Braarudosphaera bigelowii reaches a peak abundance of about 25% at 120 cm and 180 cm above the boundary at Qreiya and Wadi Hamama, respectively (Figs. 8 and 9). Although Braarudosphaera bigelowii blooms just after the bloom of Thoracosphaera in several mid^low-latitude sections (e.g. Brazos, Texas, Jiang and Gartner, 1986; Agost, Pospichal, 1995 ; Zumaya, Spain, Lamolda and Gorostidi, 1992 ; Biarritz, France, Perch-Nielsen, 1979c; El Kef, Tunisia, Gardin and Monechi, 1998), this taxon is absent from other low-latitude K/T sections, including all sections in Israel (Magaritz et al., 1985; Eshet et al., 1992), DSDP Site 577A (Gardin and Monechi, 1998), and Elles, Tunisia (Gardin, 2002). Braarudosphaera bigelowii thus seems to respond to di¡erent and, as yet unknown, paleoenvironmental conditions in middle and low-latitude locations. It has been variously suggested that B. bigelowii blooms indicate nearshore depositional environments characterized by relatively shallow water (Roth and Thierstein, 1972; Mu«ller, 1985), low salinity (Bukry, 1974), increased fresh-water in£ux and lowered salinities after the K/T boundary (Thierstein and Berger, 1979; Askin, 1992; Barrera and Keller, 1994), or eutrophication (Cunha and Shimabukuro, 1996). Cyclagelosphaera reinhardtii is very rare in the Qreiya and Hamama sections, as was also observed at El Kef, Tunisia, and Agost, Spain, by Pospichal (1995). In sections of northern Spain and southern France (Seyve, 1990; Lamolda and Gorostidi, 1992), where blooms of C. reinhardtii are observed, this species is restricted to a very short interval between the initial peaks of Thoracosphaera and Braarudosphaera. The Zygodiscus sigmoides bloom or acme is most pronounced in high-latitude sites (e g. Den-

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mark, Perch-Nielsen, 1979b ; ODP Site 690, Pospichal and Wise, 1990; Site 752, Pospichal, 1991). This species, however, is rare in Lower Paleocene assemblages from middle to low-latitude regions (e.g. Biarritz, France, Perch-Nielsen, 1979c ; Gubbio, Monechi, 1979 ; Zumaya, Percival and Fischer, 1977). In the Qreiya and Hamama sections, an increase in the abundance of Z. sigmoides is observed in Zone NP2, where it ranges from 4% to 13% of the total nannofossil assemblage. Neobiscutum romeinii and Neobiscutum parvulum, two very small forms, are usually present in very low abundances in Subzones NP1a and NP1b. The latter species is more dominant in the middle part of Subzone NP1c, where it reaches 40% of the assemblage at Wadi Hamama (sample 16) about 2 m above the K/T boundary (Fig. 9). Perch-Nielsen (1985) observed that N. romeinii and N. parvulum are present in the Tethys region but not in higher northern or southern latitudes. Cruciplacolithus primus ( 6 5 Wm) is very rare in the basal part of Subzone NP1c of the Qreiya and Hamama sections and very abundant just above the dissolution interval, reaching a maximum of 30% of the total nannofossil assemblage at 16 m above the base of both sections. At Wadi Hamama, both small ( 6 5 Wm) and larger ( 6 9 Wm) morphotypes are present in Zone NP2 (Fig. 9), where they reach a combined abundance of 5% to 13%. The C. primus bloom has been recorded in many low and middle-latitude sections by various workers (e.g. Pospichal, 1991, 1995; Gardin and Monechi, 1998). Gardin and Monechi (1998) and Gardin (2002) suggested that the appearance of C. primus marks the onset of the return to more stable environmental conditions after the perturbations at the K/T boundary. Coccolithus pelagicus is relatively abundant at the top of the Wadi Hamama section, where it reaches more than 40% of the total nannofossil assemblage (Fig. 9). Wei and Pospichal (1991) observed that C. pelagicus decreased in abundance towards higher latitudes. In the modern ocean, C. pelagicus is most abundant in the cool waters of the northern high latitudes (McIntyre and Be¤, 1967). This was interpreted by Haq and Lohmann

(1976) as indicating that C. pelagicus has undergone an evolutionary shift in its ecological response.

8. Discussion 8.1. Productivity Eshet et al. (1992) and Eshet and Almogi Labin (1996) used calcareous nannofossil species abundances as indicators of productivity based on the comparison of their distribution with independent data from other sources, such as planktonic foraminifera (Almogi Labin et al., 1993) and organicwalled dino£agellate cysts (Eshet et al., 1994). They concluded that nannoplankton reach their highest species diversity and abundance in intervals of lowered productivity and that relative species abundances are suppressed by high productivity conditions. Similarly, Thunell and Sautter (1992) suggested an inverse relationship between nannofossils and foraminiferal populations with planktonic foraminiferal populations increasing and nannofossils declining during peaks of productivity. On the other hand, Young (1994) suggested that the number of nannofossils increased with productivity, but is suppressed in extreme eutrophic environments. Further clues to the environmental signi¢cance of calcareous nannofossil abundance and species diversity can be obtained from the Qreiya section of Egypt (Fig. 11), where planktonic foraminifera have been analyzed quantitatively along with carbon isotope studies of the benthic species Cibicidoides pseudoacutus and the planktonic foraminifera Rugoglobigerina rugosa (Keller et al., in press). These studies show a positive correlation between calcareous nannofossil species richness and planktonic foraminifera, and a positive correlation of both with primary productivity as indicated by carbon isotopes (Fig. 10). In the Upper Maastrichtian Micula murus Zone, the calcareous nannofossil species richness increased in the basal part of the section, corresponding to a signi¢cant increase in surface productivity as might be indicated by higher N13 C values (Fig. 10; Keller et al., in press). However, in the

MARMIC 905 27-1-03

Wadi Hamama

low

10

Increased abundance of Z. sigmiodes

P1C(2)

19

18

30

b

Q 30

8

40

Q -5 Q -1 0

7

Q -1 5

6

Q -2 5

Q -2 0

P1a

c

P1C(1)

(NP1)

Hiatus

10

Hiatus

50 60 9

75

CF1

30 5

M. prinsii

70 8

Q -

80

Hiatus

3

4 Q -4 0

(m ) 0

Max. species richness

Maximum abundance

85

3 Q-4 2

2

1 (m )

Cool-water taxa influx

5 2

1

1st Thoracosphaera bloom Species richness & Abundance decrease

6

M. murus

M. murus

CF3

Q -3 5

CF3

Dakhla

7 4

Braarudosphaera bigelowii bloom

35

Warm-water taxa influx

11

a

9

A. cymbiformis bloom

Major sea-level lowstand.

Return of normal marine conditions.

Appearance of . C. primus

b

12

Q 40

dissol.

25

P1C(1)

13

Q 50

P1b

Q 70 Q 60

M. prinsii

CF1

20

M. inversus

Lithology

Thickness

Calcareous Nannofossils c

11

a

Stage

Sample No.

14

Relatively cool climate.

High productivity, poor water mass stratification.

N. parvulum bloom

Q 80

M. inversus (NP1)

P1C(1) P1C(1)

Danian Formatio n

Q 90

10

2nd Thoracosphaera bloom, re-entry of some Cretaceous taxa

15

Q 20 Q -1

P1b

Hiatus

16

12

P1a

Maastrichtian

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Formation Planktic P1C(2) Foraminifera

17

15

Warm climate, High productivty.

C. pelagicus bloom

a

5

high

Nearshore, shallow water, increased fresh water influx, lower salinity Productivity minimum, High salinity, low sea level Warm climate, ? High productivity

Cool climate, ? Low productivity, Highly stressed environment

A.A.A.M. Tantawy / Marine Micropaleontology 47 (2003) 323^356

C. tenuis (NP2)

20

Paleoenvironmental Interpretation

Nannofossil Events

b

Pld

1 21

Sea Level (Li et al., 2000: Keller & Stinnesbeck, 1996; this study)

Increased abundance of Micula decussata

Gebel Qreiya

90

0

Fig. 11. Sea-level changes, important nannofossil events and summary of the paleoenvironmental interpretation of the Upper Cretaceous^Lower Tertiary sequence in the Central Eastern Desert of Egypt (Keller and Stinnesbeck, 1996; Li et al., 2000; this study).

349

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middle part of the M. murus Zone, calcareous nannofossils exhibit lower species richness associated with the breakdown in ocean primary productivity, as might be suggested by lower N13 C values. In the Micula prinsii Zone, primary productivity increased signi¢cantly and calcareous nannofossils attain highest species richness values (Fig. 10; Keller et al., in press). A decrease in surface productivity near the top of the Maastrichtian is associated with the apparent decrease in nannofossil species richness and abundance (Figs. 6 and 10). The decrease in surface productivity at the top of the Maastrichtian is consistent with this pattern elsewhere in the Tethys Ocean (e.g. Keller and Lindinger, 1989; Zachos et al., 1989; Barrera, 1994; Barrera and Keller, 1994; Li and Keller, 1998a; Keller et al., in press). At Wadi Hamama, the Cretaceous calcareous nannofossil species richness shows trends similar to the nearby Qreiya section, except for the lower part of the section in the lower Micula murus Zone, where species richness decreased (Fig. 7). This decrease may be due to the poor preservation at Wadi Hamama and the shallower depositional environment. At the K/T boundary, species richness and relative abundances of Cretaceous species decrease, whereas Cretaceous survivor species and Tertiary species increase. In the Lower Danian (Subzones NP1a and NP1b), both calcareous nannofossil groups show low abundances and marked £uctuations in species richness. Carbon isotope data indicate low, but £uctuating productivity during this interval. In Subzone NP1c and Zone NP2, the species richness and relative abundances increase along with surface productivity, as indicated by increased N13 C values (Fig. 10) and the return to normal marine condition in the upper part of the Danian. These observations parallel the post-K/T recovery of planktonic foraminifera, the return to normal marine productivity, and re-establishment of the normal surface-to-deep gradient in low to middle latitudes in the upper part of Subzone P1c(1), nearly 2 Myr after the K/T boundary event (Keller, 1988; 1996; Zachos et al., 1989; Barrera and Keller, 1994; Keller et al., in press).

8.2. Climate The Upper Maastrichtian Micula murus Zone is characterized by global cooling, culminating in a sea-level lowstand at 65.5 Ma that is generally associated with a hiatus at the top of planktonic foraminiferal Zone CF3 (Barrera et al., 1997; Li and Keller, 1998c). In the present study, the M. murus Zone at Gebel Qreiya exhibits a similar cooling trend, as might be indicated by more positive N18 O values (Fig. 10; Keller et al., in press). This cooling event is marked by a decrease in the warm-water species Watznaueria barnesae and the increased abundance of the cool-water species (e.g. Arkhangelskiella cymbiformis, Gartnerago obliquum and Nephrolithus frequens Figs. 8 and 9) at both Qreiya and Wadi Hamama. In the Micula prinsii Zone, a warming trend is indicated by the increase in the warm-water species W. barnesae and by the lower benthic and planktonic N18 O values (Fig. 10). This warming is consistent with the middle to high-latitude climate trends, where cooling in Zone CF3 is followed by 3^4‡C warming in Zones CF1^2 interval (Li and Keller, 1998c). A warm climate prevailed during the deposition of the Lower Danian Subzones NP1a^b, as indicated by benthic N18 O values, whereas cooler climatic conditions were re-established during the sedimentation of the upper part of Subzone P1c(1) and Subzone NP1c, as indicated by both benthic and planktonic N18 O values (Fig. 10; Keller et al., in press). At Wadi Hamama, cooler climatic conditions prevailed into planktonic foraminiferal Subzone P1c(2) and into the lower part of calcareous nannofossil Zone NP2, as indicated by a marked increase in the abundance of Zygodiscus sigmoides. This cooling trend is accompanied by the recovery of surface productivity and re-establishment of normal marine conditions. The top of the Wadi Hamama section is marked by increased abundance of Coccolithus pelagicus, which may indicate a warmer climate during the upper part of Zone NP2. 8.3. Paleoenvironment of Central Egypt The paleoenvironmental signi¢cance of various

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calcareous nannoplankton species in the Late Cretaceous and Early Tertiary is not yet well understood. The present study of the Central Eastern Desert of Egypt yields further clues to environmental a⁄nities, as summarized in Fig. 11. During the Late Maastrichtian, the Micula murus Zone is characterized by a cooler and relatively low-productivity, high-stress environment, as indicated by an in£ux of cool-water taxa, a bloom of Arkhangelskiella cymbiformis, abundance of Micula decussata and low carbon isotope value. The subsequent Micula prinsii Zone is characterized by a warmer climate and increased productivity, as indicated by an in£ux of warm-water taxa, higher nannofossil species richness and increased carbon isotope values. At the K/T boundary and in the Early Danian Subzone NP1a, the environment was characterized by very low productivity, high salinity and low sea level, as indicated by decreased nannofossil species richness and low carbon isotope values, and high-stress conditions, as indicated by a bloom of the opportunistic Thoracosphaera spp. The Early Danian Subzone NP1b is characterized by increased fresh-water in£ux and lower salinity, as indicated by the bloom of the disaster species Braarudosphaera bigelowii. The appearance of Cruciplacolithus primus in Subzone NP1c marks the gradual return to more stable environmental conditions, characterized by increased productivity and poor water mass strati¢cation, as indicated by the dwarfed Neobiscutum parvulum bloom. A major sea-level regression occurred at the top of Subzone NP1c and the base of Subzone NP2a, as inferred from the second bloom of Thoracosphaera spp. and the re-entry of some Cretaceous taxa. A relatively cool climate prevailed during the upper part of Subzone NP2a, as suggested by the increased abundance of Zygodiscus sigmoides, followed by a warmer climate, high productivity, and high sea level, as indicated by a Coccolithus pelagicus bloom and increased N13 C values within Subzone NP2b (Fig. 11).

351

ma sections of the Eastern Desert of Egypt are among the very few localities where the planktonic foraminifera Plummerita hantkeninoides (Zone CF1) and Parvularugogloberina eugubina (P1a) Subzone and calcareous nannofossil Micula prinsii and Markalius inversus (NP1) Zones are present, and where the K/T boundary is marked by a red layer and Ir anomaly. 2. This is the ¢rst study that quantitatively analyzes calcareous nannofossil assemblages across the K/T boundary in Egypt, based on closely spaced samples and high-resolution age control, that provides a more accurate assessment of the £oral assemblage turnovers than is possible with standard species ¢rst and last appearance studies. 3. The Late Maastrichtian assemblages in central Egypt are typical of low to mid-latitudes with the vanishing Cretaceous nannofossil assemblage abundant and diverse (99.5% to 93.3%) in the Micula murus Zone and gradually decreasing in the Micula prinsii Zone correlative with an increase in the survivor assemblage (mainly Thoracosphaera and Braarudosphaera bigelowii). The Tertiary assemblage is a minor component (V2.5%) of the Early Danian nannofossil assemblages, but increases rapidly to 56% at the base of NP2. 4. Calcareous nannofossil abundance and species richness indicate that the Late Maastrichtian Micula murus Zone is characterized by a cooler climate, a high-stress environment and low productivity, whereas a warmer climate and higher productivity characterize the Micula prinsii Zone. 5. Minimum productivity, high salinity and a low sea-level mark the K/T boundary and Subzone NP1a. Subzone NP1b is characterized by increased fresh-water in£ux and lower salinity. 6. Normal marine environmental conditions returned in Subzone NP1c, marked by increased productivity and possibly poor water mass strati¢cation. A major sea-level regression occurred at the NP1c/NP2a transition.

Acknowledgements 9. Conclusions 1. The Gebel Qreiya and nearby Wadi Hama-

I am grateful to Prof. Gerta Keller, Department of Geosciences, Princeton Uinversity, USA for

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discussions, comments, critical review of this manuscript, and for making available her lab facilities. I also thank the reviewers, Prof. Katharina von Salis Perch-Nielsen and Prof. T. Bralower, for critical comments and helpful suggestions for improvement of this manuscript, Prof. Thierry Adatte for ¢eldwork collaboration, and Prof. W. Berggren and Prof. M.-P. Aubry for their helpful comments and suggestions. This publication was sponsored by the US^Egypt Science and Technology Joint Fund in cooperation with NSF and NRC under Project OTH2-008-001-98. References Abbas, H.L., Habib, M.M., 1969. Stratigraphy of west Mawhoob area, Southwestern Desert. Egypt. Bull. Desert Institute, Egypt 19, 48^108. Abdelmalik, W.M., Bassiouni, M.A., Kerdany, M.T., Obeid, F.L., 1978. Biostratigraphy of Upper Cretaceous^Lower Tertiary rocks from West central Sinai. 2. Calcareous nannoplankton. Ann. Mines Geol. 28, 217^241. Abdel Razik, T.M., 1969. Stratigraphical studies on the phosphate deposits between River Nile and Red Sea (south of latitude 27‡N). Fac. Sci. Bull. Cairo Univ. 42, 299^324. Abdel Razik, T.M., 1972. Comparative studies on the Upper Cretaceous^Early Paleogene sediments on the Red Sea coast, Nile Valley and Western Desert, Egypt. 6th Arab Petroleum Congr., Algeria, 71: 1^23. Alcala¤-Herrera, J.A., Grossman, E.L., Gartner, S., 1992. Nannofossil diversity and equitability and ¢ne-fraction D13 C across the Cretaceous/Tertiary at Walvis Ridge Leg 74, South Atlantic. Mar. Micropaleontol. 20, 77^88. Almogi Labin, A., Bein, A., Sass, E., 1993. Late Cretaceous upwelling system along the southern Tethys margins (Israel): interrelationship between productivity, bottom-water environments and organic matter preservation. Paleoceanography 8, 671^690. Askin, R.A., 1992. Preliminary palynology and stratigraphic interpretation from a new Cretaceous^Tertiary boundary section from Seymour Island. Antarct. J. US 25, 42^44. Barrera, E., 1994. Global environmental changes preceding the Cretaceous^Tertiary boundary: Early^Late Maastrichtian transition. Geology 22, 877^880. Barrera, E., Keller, G., 1994. Productivity across the K/T boundary in high latitudes. Geol. Soc. Am. Bull. 106, 1254^1266. Barrera, E., Savin, S.M., Thomas, E., Jones, C.E., 1997. Evidence for thermohaline circulation reversals controlled by sea-level change in the latest Cretaceous. Geology 25, 715^ 718. Barron, T., Hume, W.F., 1902. Topography and geology of the Eastern Desert of Egypt (Central Portion), Survey Dept. Cairo.

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