oa Integrated Diagenesis and Sequence Stratigraphic Study of Tidal Sandstones: the Adedia Formation (Cambro-Ordovician), Sinai, Egypt

This work examines the effects meteoric vs. marine diagenesis on Cambro-Ordovician tidal sandstones<br>owing to fluctuation of relative sea level (RSL). The distribution of diagenetic alterations is thus<br>constrained within the sequence stratigraphic framework of the succession. Initially, a rise in RSL<br>resulted in the deposition of transgressive systems tract (TST) sands directly onto crystalline<br>basement. These sandstones display evidence of limited cementation by marine, grain-fringing<br>dogtooth-like and fibrous calcite. A fall in RSL resulted in the progradation of a tidal flat complex and<br>deposition of highstand systems tract (HST) and lowstand systems tract (braided fluvial) sandstones.<br>Contemporaneous meteoric-water flux into sands of all the systems tracts resulted in the dissolution<br>and kaolinitization of feldspars, micas and mud intraclasts in all systems tracts. Sequence boundaries<br>(SB) are marked by fluvial incision of tidal sands and by the development of palaeosols. Mesogenetic<br>alterations include partial transformation of kaolinite into dickite, intergranular pressure dissolution,<br>and formation of variable amounts of syntaxial quartz overgrowths in all systems tracts. Telogenetic<br>alteration (i.e. weathering) in the sandstones includes the formation of goethite and calcite. Thus, the<br>integration of diagenesis with sequence stratigraphy provides a useful tool with which to understand<br>reservoir quality distribution in sand-dominated, tidal sediments.