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University of Bremen, Fachbereich Geowissenschaften, P.O. Box 330 440, 28334 Bremen, Germany bachmann{at}geochron.uni-bremen.de
The Middle Cretaceous carbonate ramp of the northern Sinai developed in two stages on a passive continental margin overlying basal rift suites. The lower delta-dominated ramp (Upper Aptian-Lower Albian) in the north evolved into the upper carbonate-dominated ramp (Middle Albian-Cenomanian) which covered the central and southeastern parts of the Sinai. The transition between the two ramp settings took place during a period of a second-order sea-level rise and a major change in climatic conditions. The sedimentary patterns are superimposed upon by higher-frequency relative sea-level changes. The influence of the third-order relative sea-level changes on the ramp deposition was reconstructed on the basis of facies patterns, sedimentary geometries, and the distribution of microfacies types. As regional tectonic movements were of subordinate importance, a sequence stratigraphic interpretation allows a fine-scale estimation of the changing ramp settings and their characteristics. The combined use of semiquantitative microfacies analysis and sequence stratigraphy allows study of the factors controlling deposition during the different systems tracts, including the respective microfacies distributions. These factors indicate that third-order sea-level fluctuations result not only in simple shifts of facies belts up and down the ramp but also in changing environmental factors such as water circulation, carbonate production and siliciclastic input.
