Interaction of geodynamic and biosedimentary processes during the late Cenomanian - Coniacian on the calcareous shelf of the southern Tethyan margin (Sinai, Egypt)
Jan Bauer, Jochen Kuss and Thomas Steuber
This research project, funded by the Deutsche Forschungsgemeinschaft (DFG), aims at reconstructing the depositional history of Mid-Cretaceous, chiefly shallow marine sediments of Sinai, with special emphasis on the biosedimentary response to sea-level changes and geodynamic processes („Syrian Arc deformation“). For this purpose, an integrated approach of sedimentological, sequence stratigraphic and palaeontologic (benthic foraminifers, calcareous algae and rudists) methods is applied. We study the sedimentologic, cyclostratigraphic and paleogeographic evolution of 21 Cenomanian and Turonian sections in the Sinai. The evaluation of laterally and vertically changing stacking patterns is based on the analysis of sedimentary structures, microfacies, petrography and biostratigraphy.
Paleogeography and geodynamics
During early Late Cretaceous times, the Sinai peninsula was part of the passive continental margin of the southern Tethys, forming a wide calcareous shelf system with siliciclastic intercalations. In north central Sinai and southern Israel, the transgression coincides with a flooding of the late Cenomanian platform, reflected by deposits of an intrashelf basin (Eshet-Zenifim basin). Only the marginal facies of the basin is exposed in Sinai. A hiatus across the Cenomanian-Turonian transition occurs, which is partly related to syndepositional uplift probably reflecting first pulses of "Syrian Arc" movements. Sedimentation started again in the Eshet-Zenifim basin during the late early Turonian with deposition of partly condensed intervals. Further basin morphologies are mirrored by increasing bed-thicknesses within individual sedimentary sequences in west central Sinai. Subsequently, compression in the Coniacian resulted in an increase in detritic input from the uplifted hinterland. During the following highstand, an extended calcareous shelf system re-established in the middle and late Turonian, which was more or less stable until the Coniacian, although prominent 3rd order sea-level changes clearly affected the depositional settings.
Biosedimentary response: distribution of shallow-water benthics
The interplay between environmental and geodynamic features had a major influence on the temporal and spatial facies evolution, especially on the benthic community. Diversities and frequencies of benthic foraminifers, calcareous algae and rudists differ distinctively in the late Cenomanian-Turonian southern Tethyan inner platform deposits of the Sinai peninsula: Rudists and benthic foraminifers are common in the upper Cenomanian successions but occurrences decline drastically in the lower Turonian and recover again in the middle-upper Turonian. In contrast, calcareous algae of upper Cenomanian deposits are poor in species-and flourish in the lower and upper Turonian. In addition, the occurrence of the studied benthics is closely related to regional facies belts, which prevail in individual systems tracts. Rudists occur mainly in HSTs, benthic foraminifers and calcareous algae mainly in TSTs and HSTs. The correlation of facies, systems tracts and biota distribution suggests a link between repeated reorganisation processes of the depositional system due to relative sea-level changes and the distribution of individual benthic groups.