Timing of mid-Cretaceous carbonate platform depositional cycles, northern Sinai, Egypt

Abstract

The northern Sinai Upper Aptian to Middle Cenomanian succession represents an example of a carbonate platform, where stratigraphic interpretations are mainly based on benthic foraminifera, ostracods and rudists. This paper presents a concept combining the stratigraphic study of benthic organisms with graphic correlation and sequence stratigraphy, at a scale that determines the timing of sequence boundaries and quantification of sediment-accumulation rates. Biostratigraphic analyses result in multibiostratigraphic zonations and contribute to a northern Sinai fossil range chart for benthic larger and smaller foraminifera, ostracods and rudists. The age interpretation results from the careful comparison of the ages given in the literature and the distribution patterns in the northern Sinai sections. The northern Sinai chart for many fossil ranges matches with other studies, but also indicates some exceptions. Ostracods were grouped into assemblages characterised by short local ranges, which enables the exact correlation of different sections. The use of graphic correlation techniques within this framework improves the stratigraphic resolution and results in timing of the sequence boundaries. These chronostratigraphic assignments allow comparison of the Sinai sequence boundaries with those described from other regions. Furthermore, graphic correlation measures long-term sediment-accumulation rates of the northern Sinai. Based on their variations, we calculate the relative sea-level changes, resulting in a detailed second-order sea-level curve. In the Upper Aptian to Middle Cenomanian succession, important changes in the long-term sediment-accumulation rate were measured. They reflect three second-order sea-level cycles, which subdivide a general relative sea-level rise. 18 sequences superimpose the second-order sea-level change: 3 sequences in the Upper Aptian, 11 sequences in the Albian, and 4 sequences in the Lower–Middle Cenomanian. Both sequence-stratigraphic patterns and long-term sea-level changes were compared with those from the Tethyan domain, the African/Arabian Plate and the western Pacific. Abundance and distribution of the Sinai sequence boundaries were similar to the patterns described from other regions. We distinguish between sequence boundaries with regional extent correlating with examples from the North African/Arabian Plate or the western Pacific, sequence boundaries of possibly global or Tethyan extent and the few sequence boundaries of local extent. The influence of the regional and global signals on the studied successions reflect the Sinai location between the southeastern and southwestern Tethyan realms. Local tectonics or changes in subsidence are only of subordinate importance for the creation of sequence boundaries. The comparison of the chronostratigraphic assignments of the second-order sea-level curve with other descriptions indicates a second-order relative sea-level history of its own for Sinai triggered by the interaction of subsidence, sediment supply and eustasy.