Christian Scheibner

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.

Recalibration of the Tethyan shallow-benthic zonation across the Paleocene-Eocene boundary: the Egyptian record

The Galala Mountains in Egypt provide an excellent platform-basin transect with deposits spanning the Paleocene/ Eocene (P/E) boundary. These interfingering deposits enable a recalibration between platform and open marine biostratigraphic schemes. We investigated 18 sections from a shallow-water carbonate platform margin, dominated by larger benthic foraminifera, to basinal marls with pelagic and deep marine biota. The Late Paleocene to Early Eocene development of larger foraminifera is well recorded in the Galala transect, in particular the Tethyan evolutionary event known as the larger foraminifera turnover (LFT). This turnover distinguishes Paleocene assemblages dominated by glomalveolinids, miscellanids and ranikothalids typical for shallow benthic Zone 4 (SBZ4) from those of SBZ5, dominated by alveolinids, nummulitids, and orbitolitids. Our data agree with previous studies that suggested that the larger foraminifera turnover (LFT) coincides with the Paleocene/ Eocene boundary, delineated by the carbon isotopic excursion (CIE) and that it correlates with the boundary between calcareous nannofossils subzones NP9a/b, the benthic extinction event in smaller benthic foraminifera and the boundary between planktic foraminifera Biozones P5/E1.

Facies patterns within a Lower Jurassic upper slope to inner platform transect (Jbel Bou Dahar, Morocco)

SummaryThis study concentrates on the description of a plat-from edge of a Lower Jurassic carbonate platform in the High Atlas of Morocco. The Jbel Bou Dahar displays a well-preserved platform to basin morphology with no major tectonic disturbance.A clear separation in facies belts could be made for the upper slope to platform interior environment. At the transition from the upper slope to the inner platform no prominent reef can be observed. Only a small zone exists withLithiotis mud-mounds and some corals, probably associated with sponges. It separates the ooid shoals of the platform interior from the upper-slope environment with its characteristic boulder beds. The angle of repose within the upper slope ranges from 23° to 35°, at the platform edge between 6° to 10° (Lithiotis mud-mounds zone), and within the platform interior from 1° to 4°. Nine microfacies types could be distinguished. These microfacies types include i.e. laminated pelmicrites, biopelsparites, and boundstones. Facies analysis showed that the sediments were deposited in facies belts 4 (slope of the platform) to 7 (open platform areas) afterWilson (1975).

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.

Circum-Tethyan carbonate platform evolution during the Palaeogene: the Prebetic platform as a test for climatically controlled facies shifts

* Correspondence: scheibne@uni-bremen.de

Stratigraphic modelling of carbonate platform-to-basin sediments (Maastrichtian to Paleocene) in the Eastern Desert, Egypt

Abstract In the Galala Mountains of the Eastern Desert, Egypt, carbonate platform and basin deposits have excellent exposure. These exposures show a late Campanian–early Paleocene rimmed platform evolving into a late Paleocene distally steepened ramp. We modelled the evolution of the platform–basin transition from the Maastrichtian to Selandian (68.7–59 Ma) with the 2-D stratigraphic simulation program PHIL and compared the modelled results with outcrop sections. Stratigraphic, facies, and environmental data are summarized and operate as input and control parameters for the computer simulation. The most important parameters that control the depositional geometries of the late Cretaceous mixed carbonate siliciclastic platform and the Paleogene carbonate platform are changes in relative sea level, sediment flux and initial topography. The simulation provides an understanding of platform growth and slope to basin deposition, particularly in areas of the platform that are poorly exposed or have been eroded. Moreover, the simulated geologic parameters like lithology, overall thickness and palaeowater depth closely resemble field and laboratory measurements of the individual sections. In an earlier study, the Maastrichtian slope angle was calculated to be 5–8° and this was confirmed in this study. In this earlier study also the timing of the transition from a rimmed platform to a distally steepened ramp was established to be during latest Maastrichtian–early Paleocene. The present study shows that the rimmed platform persisted at least until the late Paleocene (59 Ma), as indicated by the relatively high slope angle of 6°.

New Paleocene large cassiduline foraminifera (Cassidinidae fam. nov., Miscellanacea) from Egypt and its phylogeny

Larger foraminifera of the Late Paleocene–Early Eocene lower slope to toe-of-slope deposits of the southern Galala, Egypt, are described. Sulcocassidina nakkadyi n. gen. et sp. (base) and Vacuolicassidella dakhlensis n. gen. et sp. (top) represent a phylogenetic line related to the family Cassidinidae (new family), superfamily Miscellanacea (new superfamily) in the latest Paleocene (shallow benthic zone 4) of the southern Galala, Egypt. In addition, Oscucassidella cassis n. gen. et sp., Pellatispiroides youssefi n. gen. et sp. and Chordcassidella ainshamsiana n. gen. et sp. are described and illustrated. Genus: Pomerolina n. gen. (Type species: Alveolina meandrina Carter, 1861, is newly erected and it belongs to Cassidinidae. In this family, the chambers are initially arranged streptospirally, whereas in later stages they are planispirally enrolled. Lateral chamberlets (retral process) are separated from the laminae by a passage and a marginal crest is added during growth.