Akmal M. Marzouk

Turnover of larger foraminifera during the Paleocene-Eocene Thermal Maximum and paleoclimatic control on the evolution of platform ecosystems

The larger-foraminifera turnover (LFT) during the Paleocene-Eocene transition constitutes an important step in Paleogene larger-foraminifera evolution, involving a rapid increase in species diversity, shell size, and adult dimorphism. A platform-to-basin transect in Egypt provides new data on timing and causal mechanisms through correlation with planktic biozonations and through integration with regional paleoenvironmental data. The LFT coincides with the boundary between shallow benthic biozones SBZ4 and SBZ5 and closely correlates with the Paleocene-Eocene Thermal Maximum (PETM). Enhanced oligotrophy from the late Paleocene onward favored the diversification of K-strategist larger foraminifera. We suggest that a short-term eutrophication during the PETM led to a temporary decline of extreme K-strategist larger-foraminifera species, providing opportunities for new taxa with different ecological strategies to develop. During post-PETM oligotrophic conditions, these new taxa were able to evolve rapidly and soon dominated early Eocene larger-foraminifera assemblages, whereas many Paleocene taxa gradually disappeared. The success of larger foraminifera during the early Paleogene appears climatically controlled. Because of the vulnerability of corals to high surface-water temperatures, the late Paleocene to early Eocene global warming may have favored larger foraminifera at the expense of corals as the main carbonate-producing component on carbonate platforms at lower latitudes.

Maastrichtian-Early Eocene litho-biostratigraphy and palægeography of the northern Gulf of Suez region, Egypt

Abstract The Maastrichtian-Lower Eocene sediments on both sides of the northern Gulf of Suez can be subdivided into eight formal formations (including one group) and one informal formation that are described in detail. These lithostratigraphic units reflect three different environmental regimes of deposition or non-deposition. The first regime is characterised by uplift and erosion or non-deposition resulting mostly from the uplift of the Northern Galala/Wadi Araba structure, a branch of the Syrian Arc Foldbelt. The shallow water carbonate platform and slope deposits of the Late Campanian-Maastrichtian St Anthony Formation and the Paleocene-Lower Eocene Southern Galala and Garra Formations represent the second regime and are found north and south of the Northern Galala/Wadi Araba High. The third regime is represented by basinal chalks, marls and shales of the Maastrichtian Sudr Formation and of the Paleocene-Eocene Dakhla, Tarawan and Esna Formations, the Dakhla/Tarawan/Esna informal formation and the Thebes Group. The distribution and lateral interfingering of the above mentioned environmental regimes reflect different vertical movements, changing basin morphology, sea level changes and progradation of shallow water sediments and is illustrated on 11 palaeogeographic maps.

Shelf architectures of an isolated Late Cretaceous carbonate platform margin, Galala Mountains (Eastern Desert, Egypt)

Abstract An asymmetrical carbonate platform margin to basin transect has been investigated in the Upper Campanian–Maastrichtian succession of the Galala Mountains, northern Egypt. Identification of systems tracts and their lateral correlation was possible in slope sections only, whereas the monotonous chalk-marl alternations of the basinal sections could not be subdivided with respect to sequence stratigraphic terminology. The platform asymmetry is expressed by varying large-scale depositional architectures exhibiting a rimmed platform with a sigmoidal slope curvature in south-easterly dip-sections and a ramp with a linear slope curvature in south-westerly dip-sections. The rimmed platform is subdivided into a gentle upper slope and a steep lower slope. The platform formed as a result of the initial topography that was controlled by the tectonic uplift of the Northern Galala/Wadi Araba Syrian Arc structure. The calculated angles of the steep lower slope of the rimmed part range from 5 to 8°, whereas the ramp part has an angle of less than 0.1°.

Cretaceous — Paleogene Sequence Stratigraphy of the Levant Platform (Egypt, Sinai, Jordan)

This contribution represents a summary of our interdisciplinary studies of the Cretaceous-Paleogene Levant Platform (LP) to reconstruct the factors controlling its growth and geometry. We define six platform units (PU1, PU2a, b, PU3 and PU4a, b) based on facies characteristics. Four key surfaces are defined that occur elsewhere in the LP and are of North African or Tethyan importance. They are due to prominent changes of the tectonic or paleoceanographic regimes. Stacking patterns of Aptian to Paleogene platform units and important surfaces are defined within a biostratigraphic frame and allow to interprete a total number of 35 third-order depositional sequences, some of which have been amalgamated locally. Comparisons of our sea level charts with those from neighbouring platforms indicate several mismatches that may be due to local uplift, subsidence, or increasing clastic input.

Late Maastrichtian litho- and ecocycles from hemipelagic deposits of eastern Sinai, Egypt

Abstract A biostratigraphical and palaeoecological survey employing calcareous nannofossils and planktonic and benthonic foraminifera has been carried out in four sections of hemipelagic marls and chalks of the Late Maastrichtian Abathomphalus mayaroensis Zone of eastern Sinai, in order to evaluate the mechanisms controlling the composition of the well preserved microfauna and nannoflora. The Abathomphalus mayaroensis Zone in eastern Sinai can be easily identified by the wide occurrence of the index fossil A. mayaroensis and can be further subdivided by the first occurrences of Plummerita reicheli (ex. P. hantkeninoides) and Micula prinsii. Microfossil abundances and lithologies are characterised by pronounced repetitive distribution patterns. These include low and high frequency fluctuations of the planktonic/benthonic (P/B) foraminiferal ratio, repetitive changes in the abundance of calcareous nannofossils and benthonic foraminifera, as well as the development of chalk-marl couplets and thinning upward chalk packets. both microfossil distribution patterns and the occurrence of rhythmites are attributed to changes in primary palaeoproductivity. Semiquantitative investigations of calcareous nannofossils and a few selected benthonic foraminifera yield evidence of the presence of high (HP) and low (LP) productivity assemblages. The interpreted HP assemblage is dominated by Glaukolithus diplogrammus, Manvitella pemmatoidea, Microrhabdulus decoratus and Micula murus and the benthonic foraminifera Neoflabellina jarvisi; the LP assemblage is characterised by Lithraphidites quadratus and Bolivinoides draco. However, further quantitative studies are necessary to reconstruct the exact composition of these assemblages and to explain deviatory developments. The chalk-marl couplets, thinning-upward chalk packets and the high frequency P/B patterns are interpreted to reflect productivity changes related to orbital forcing. These hemipelagites were deposited during the latest phase of the southern Tethyan upwelling system, which was active from the Santonian to the Late Maastrichtian with a peak in the Campanian. Termination of upwelling just before the K/T boundary also provides a good explanation for the change towards a palaeobathymetric control on foraminiferal distribution, as observed for the Palaeocene of central east Sinai.

Methane seepage in a Cretaceous greenhouse world recorded by an unusual carbonate deposit from the Tarfaya Basin, Morocco

During the Cretaceous major episodes of oceanic anoxic conditions triggered large scale deposition of marine black shales rich in organic carbon. Several oceanic anoxic events (OAEs) have been documented including the Cenomanian to Turonian OAE 2, which is among the best studied examples to date. This study reports on a large limestone body that occurs within a black shale succession exposed in a coastal section of the Tarfaya Basin, Morocco. The black shales were deposited in the aftermath of OAE 2 in a shallow continental sea. To decipher the mode and causes of carbonate formation in black shales, a combination of element geochemistry, palaeontology, thin section petrography, carbon and oxygen stable isotope geochemistry and lipid biomarkers are used. The 13C‐depleted biphytanic diacids reveal that the carbonate deposit resulted, at least in part, from microbially mediated anaerobic oxidation of methane in the shallow subseafloor at a hydrocarbon seep. The lowest obtained δ13Ccarbonate values of −23·5‰ are not low enough to exclude other carbon sources than methane apart from admixed marine carbonate, indicating a potential contribution from in situ remineralization of organic matter contained in the black shales. Nannofossil and trace metal inventories of the black shales and the macrofaunal assemblage of the carbonate body reveal that environmental conditions became less reducing during the deposition of the background shales that enclose the carbonate body, but the palaeoenvironment was overall mostly characterized by high productivity and episodically euxinic bottom waters. This study reconstructs the evolution of a hydrocarbon seep that was situated within a shallow continental sea in the aftermath of OAE 2, and sheds light on how these environmental factors influenced carbonate formation and the ecology at the seep site.

Integrated microfossil biostratigraphy, facies distribution, and depositional sequences of the upper Turonian to Campanian succession in northeast Egypt and Jordan

Six upper Turonian to Campanian sections in Egypt (Sinai) and Jordan were studied for their microfossil biostratigraphy (calcareous nannofossils and planktonic foraminifera), facies distribution and sequence stratigraphic frameworks. Carbonate (mostly chalk) and chert lithofacies dominate the basinward northern sections passing laterally and vertically to mixed carbonate/siliciclastic lithofacies towards the shoreline in the southeast. Twenty-six lithofacies types have been identified and grouped into six lithofacies associations: littoral siliciclastic facies belt; peritidal carbonate; intertidal carbonate platform/ramp; high-energy ooidal shoals and shelly biostromes; shallow subtidal; and pelagic facies association. The following calcareous nannofossil biozones were recognized: Luianorhabdus malefomis (CC12) (late Turonian), Micula staurophora (CC14) (early Coniacian), Reinhardtites anthophorus (CC15) (late Coniacian), Lucianorhabdus cayeuxii (CC16) (early Santonian) and Broinsonia parcaparca (CC18) (Campanian). Equivalent planktonic foraminifera zones recognized are: Dicarinella concavata (Coniacian), the lower most part of Dicarinella asymetrica (earliest Santonian) and Globotruncanita elevata (early Campanian). The integrated zonation presented here is considered to provide higher resolution than the use of either group alone. The absence of calcareous nannofossil biozones CC13 and CC17 in most of the studied sections, associated with regional vertical lithofacies changes, indicates that recognition of the Turonian/Coniacian and Santonian/Campanian stage boundary intervals in the region have been hampered by depositional hiatuses at major sequence boundaries resulting in incomplete sections. These disconformities are attributed to eustatic sea-level fluctuations and regional tectonics resulting from flexuring of the Syrian Arc fold belt. The Coniacian to Santonian succession can be divided into three third-order depositional sequences, which are bounded by four widely recognized sequence boundaries.