Increasing restriction of the Egyptian shelf during the Early Eocene? - New insights from a southern Tethyan carbonate platform
The evolution of the isolated Galala carbonate platform has been studied intensively with respect to the Paleocene-Eocene Thermal Maximum (PETM) and the strong climatic variability from the Late Paleocene to the Early Eocene. In this study, we compare the results of different approaches which deal with the Early Palaeogene evolution of the Egyptian shelf, including new data from the Galala platform. Microfacies analyses along a platform to basin transect reveal a sedimentological response to a massive tectonic uplift along the Syrian Arc-Fold Belt in the Early Eocene. This uplift triggered the restriction of the Egyptian shelf by modulating and weakening Tethyan onshore currents from the North. The increasing deposition of quartz and proliferating gastropods, green algae and radiolaria, which indicate elevated nutrient levels, reflect an intensified eutrophication of shallow-marine platforms and deeper-marine shelf environments. Strongly depleted carbon isotope ratios in the sediments of the Galala succession strongly suggest the presence of restricted conditions throughout the Early Eocene. We assume that a strong climatic divergence with arid conditions on the shelf and humid conditions at the African hinterland triggered intensified chemical weathering at the Nubian-Arabian Craton. The enhanced riverine transport of terrestrial organic material to the North African shelf caused the increased availability of trophic resources and a strong negative shift of carbon isotope ratios between NP10 and NP14a. The recovery to open ocean conditions is linked to the termination of tectonic uplift along the Syrian Arc-Fold Belt in the latest Early Eocene and to stronger ocean currents, caused by increasing latitudinal temperature gradients. Additionally, the post-PETM carbon isotope evolution at the Galala platform indicates at least two further negative carbon isotope excursions, which reflect hyperthermal events on a global scale. The associated reorganization of shallow-marine assemblages as described for example for the Larger Foraminifera Turnover at the PETM boundary event is, however, missing. We assume that the absence of a foraminiferal reorganization in this region can be linked to an increasing robustness of the major Early Eocene platform organisms (larger benthic foraminifera) and their adaption to unfavorable conditions and repeated environmental shifts. © 2011 Elsevier B.V.