Abdel Aziz Tantawy

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

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.

High-stress paleoenvironment during the late Maastrichtian to early Paleocene in Central Egypt

Biostratigraphic, mineralogical, geochemical and isotopic analyses of the Gebel Qreiya section in the Asyut Basin of central Egypt indicate a depositional environment interrupted by periods of erosion due to local tectonic activity exacerbated by eustatic sea-level fluctuations, and by high-stress environmental conditions akin to those normally experienced during the Cretaceous–Tertiary boundary transition. During the late Maastrichtian (66.8–65.4 Ma) this region experienced a breakdown of the biologically mediated surface to bottom gradient of the 13C/12C ratio with planktic δ13C values 0.2–0.8‰ lighter than benthic values. Planktic foraminiferal species diversity was reduced by more than 50%, with faunal assemblages dominated (75–90%) by the opportunistic disaster species Guembelitria cretacea, which alternate with abundance of small, low oxygen-tolerant heterohelicids (Heterohelix navarroensis, H. dentata, H. globulosa). This prolonged breakdown in ocean primary productivity occurred during a time of global climate cooling and sea-level regressions (at 66.8 and 65.5 Ma), though clay mineralogy suggests that locally low seasonality warm, wet, tropical and subtropical conditions prevailed. The high detrital influx suggests that the biologically high-stress environment was primarily linked to the existing shallow shelf conditions in southern Egypt, and possibly to local tectonic activity and restricted circulation. A normal carbon isotope gradient was briefly re-established during the short climate warming and rising sea level between 65.4 and 65.2 Ma, a time of increased species diversity, peak abundance of rugoglobigerinids and common heterohelicids. During the last 200 000 years of the Maastrichtian, increased precipitation and terrestrial runoff (increased phyllosilicates and kaolinite) and increasing total organic carbon values are associated with Heterohelix-dominated planktic foraminiferal assemblages. The K/T boundary is marked by a red clay layer and Ir anomaly of 5.4 ppb. During the early Danian, planktic foraminiferal populations and stable isotope data indicate that similarly fluctuating high-stress conditions prevailed in central Egypt as elsewhere in the marginal eastern Tethys.

Palaeoenvironmental and climatic changes during the Palaeocene–Eocene Thermal Maximum (PETM) at the Wadi Nukhul Section, Sinai, Egypt

The Palaeocene–Eocene Thermal Maximum (PETM) interval at the Wadi Nukhul section (Sinai, Egypt) is represented by a 10 cm thick condensed clay-rich layer corresponding to the NP9a–NP9b nannofossil subzone boundary. The Wadi Nukhul Palaeocene–Eocene boundary (PEB) is characterized by (1) an abrupt negative excursion in carbonate and organic carbon isotope ratios (−6‰ in δ13Ccarb and −2‰ δ13Corg), (2) an abrupt persistent negative shift in organic nitrogen isotope values (δ15Norg), (3) a significant increase in phosphorus concentrations just above the carbon isotope excursion, (4) a decrease in carbonate content and significant increase in kaolinite and (5) high vanadium and low manganese contents coincident with the occurrence of framboidal pyrite. The abrupt correlative isotopic excursions of δ13Ccarb, δ13Corg and δ15N suggest that the lowermost part of the PETM is missing. The decrease in carbonate content indicates dilution by high detrital input triggered by acid weathering and carbonate dissolution in response to increased atmospheric CO2 resulting from the oxidation of methane. The sudden increase in kaolinite content reflects a short-lived change to humid conditions. The δ15N values close to 0‰ above the PEB suggest a bloom of N2-fixing cyanobacteria. Increased bacterial activity may be either the cause or the result of the anoxia locally associated with the PETM.

Biostratigraphy of Paleocene sections in Egypt

Six Egyptian Paleocene–early Eocene sections (Figs. 1, 2) have been analysed for stratigraphic completeness and faunal/floral turnover across the Cretaceous/Paleogene, Danian/Selandian, Selandian/Thanetian, and Paleocene/Eocene boundaries. They are located along the southern Nile Valley (Gebel Owaina), the mid Nile Valley (G. Abu Had), the Quseir region (G. Duwi), the Western Desert (G. Um Elghanayem, Kharga Oasis and Bir Abu Nusf, Farafra Oasis) and the northern Eastern Desert (Wadi Tarfa). The three best expanded Paleocene sections of G. Owaina, G. Duwi and G. Abu Had were critically analysed at high resolution with different stratigraphic tools. The determination of different marker events including planktonic foraminifera, calcareous nannofossils, calcareous benthic foraminifera, and stable isotopes allows for precision correlation and dating of the rocks at the widely distant localities and for global correlations. At G. Abu Had, a complete bioand chemostratigraphic record has been determined across the Maastrichtian/Danian boundary. The uppermost Maastrichtian is indicated by the planktonic foraminifera (P. hantkeninoides) and calcareous nannofossil (M. prinsii) Zones, while the lowermost Paleocene strata are indicated by the P. eugubina and the M. inversus (NP1) Zones. The faunal turnover coincides with a major negative shift in the carbon isotope composition, on the order of 3.5‰ (Fig. 3). At Gebel Duwi, Quseir region, only the basal part of the Danian is missing (or just lacking in CaCO3), while no significant strata are missing at the top of the Maastrichtian. This is indicated by both calcareous plankton stratigraphy and chemostratigraphy (Fig. 4). A hiatus of varying magnitude is recorded across the K/P boundary at Gebel Owaina (Fig. 5), G. Um Elghanayem, Bir Abu Nusf, and Wadi Tarfa. The Danian/Selandian boundary lies within the upper, shaly part of the Dakhla Formation. It is best placed within the basal part of Zone NP4 of Martini (1971) at a level which is nearly coincident with the P2/P3a zonal boundary at both G. Abu Had and G. Duwi. It coincides with the top of a sharp and major negative shift in the carbon isotope curve of the G. Abu Had section, on the order of 3.5‰. This major δC excursion is immediately folFig. 1. Location map of the sections studied. 1, Wadi Tarfa; 2, G. Abu Had; 3, G. Duwi; 4, G. Owaina; 5, G. Um Elghanayem; 6, Bir Abu Nusf.

Climatic evolution on the southern and northern margins of the Tethys from the Paleocene to the early Eocene

The late Paleocene corresponds to one of the more prominent climatic changes in Earth history with a warming of 6 to 8°C in deepand high-latitude surface waters (referred as late Paleocene thermal maximum, or LPTM; Kennett & Stott 1991). During the LPTM the abundance of kaolinite in oceanic sediments indicates a time of high humidity with enhanced chemical weathering in the South Atlantic and southern Ocean (Antarctica) (Robert & Chamley 1991). This period of warming and high rainfall has also been observed in lower latitude sections (central North Sea: Knox 1996; New Jersey continental margin: Gibson et al. 1993; Basque Basin, northern Spain: Gawenda et al. 1999). In the coastal basins and peri-marine environments of West Africa, from Morocco to Benin, palygorskite deposition increased during the late Paleocene and dominated the clay fraction in the early Eocene. This important palygorskite episode indicates that low latitudes, and especially their coastal areas, were submitted to intensive dryness and evaporation (Robert & Chamley 1991). Based mainly on the clay mineral variations and the carbon and oxygen isotopic records observed in some sections located in the Tethys (Tunisia, Israel, Egypt, Spain, Kazakstan, Uzbekistan), we attempt, in this study to reconstruct the climate evolution on the southern and northern Tethyan margins from the Paleocene to the Eocene, with special attention to the LPTM. During the early Paleocene, southern Tunisia, located close to the Saharan platform, and the Negev area (Israel) are characterized by the abundance of kaolinite indicating humidity and warmth during this period. The simultaneous gradual disappearance of kaolinite to the benefit of palygorskite and sepiolite in these two regions located at about the same latitude (c. 20°N), but separated by more than 2,700 km suggests a latitudinal change from a humid and warm climate to an arid one. In southern Tunisia the development of arid conditions coincides with the first occurrence of phosphate deposits. On the Arabian Platform these arid climatic conditions were already initiated in the Danian (base of planktic Zone P2) and settled largely in the Selandian (middle of Zone P3). This aridity persisted through the late Paleocene, reaching a maximum in the early Eocene coinciding with those observed in West Africa (Benin to Morocco). During this time interval, gypsum deposits were accumulated over vast areas of the Arabian Peninsula (Oberhansli 1992) as a result of enhanced evaporation. In Egypt, during this period the increase of kaolinite in direction to the shoreline to the south could reflect increased humidity toward the continental hinterland in contrast with the arid climatic conditions developed in the peri-marine environments at the same time. During the LPTM, northern Tunisia and southern Spain are characterized by a sharp but short-lived increase in kaolinite relative to smectite and mica which can be related to the humid episode affecting mainly high latitude areas and the North Atlantic. The abrupt decrease in kaolinite above the LPTM to the benefit of smectite in northern Tunisia and of palygorskite in southern Spain, indicates increased aridity in this part of the Tethys

Toward a better understanding of Paleocene-Eocene Thermal Maximum: A multidisciplinary record from Dababiya GSSP, Luxor, Egypt

The Paleocene-Eocene thermal maximum (PETM) shows an extraordinary drop in both δ 13 Ccarb and δ 13 Corg values, suggesting that a massive amount of 12 C-rich carbon dioxide was released into the atmosphere in a very short time (on the order of few hundred ky). The Dababiya GSSP (Luxor, Egypt) is thought to be the most complete known PETM section. The expanded sedimentary record of the Dababiya GSSP improves our understanding of the processes leading to the PETM events. Our multiproxy dataset, which includes geochemistry, mineralogy, micropaleontology and sedimentology, provided the following crucial clues for the PETM interval at Dababiya GSSP (Fig. 1). The Dababiya GSSP is deposited in the deepest part of an asymmetric submarine channel as indicated by the paleotopography, and absence of uppermost Paleocene and lowermost Eocene sediments from the Eastern section located 25m away from the main GSSP outcrop (Fig.1). At 50 m to the NW, the sediment beds thin out and finally disappear at about 150 m from the main GSSP outcrop. Thus, the Dababiya GSSP represents a localized expanded PETM sequence with a maximum extent of about 200m. At the GSSP, the PaleoceneEocene boundary (PEB) coincides therefore with a sequence Toward a better understanding of Paleocene-Eocene Thermal Maximum: A multidisciplinary record from Dababiya GSSP, Luxor, Egypt