Integrated diagenesis and sequence stratigraphic study of tidal sandstones: the Adedia Formation (Cambro-Ordovician), Sinai, Egypt

Abstract

This work examines the different effects meteoric versus marine diagenesis had on Cambro-Ordovician tidal sandstones during episodes of fluctuating sea level. The distribution of diagenetic fabrics was compared to a sequence stratigraphic framework. Initially, a rise in relative sea level (RSL) resulted in deposition of transgressive systems tract sands directly onto crystalline basement. These sandstones display evidence of limited cementation by marine, grain-fringing dogtooth-like and fibrous calcite. A fall in RSL resulted in the progradation of a tidal flat complex and deposition of highstand systems tract (HST) and lowstand systems tract (braided fluvial) sandstones. Contemporaneous meteoric-water flux into sands of all the systems tracts occurred. Sequence boundaries (SB) are marked by fluvial incision of tidal sands and by the development of palaeosols. Meteoric incursion during sea-level lowstands resulted in the dissolution and kaolinitization of feldspars, micas and mud intraclasts in all systems tracts, but is most extensive in HST sandstones below the SB. The effect of meteoric-water flux on the dissolution of marine calcite cements is poorly known. Mesogenetic alterations include intergranular pressure dissolution and formation of variable amounts of syntaxial quartz overgrowths in all systems tracts. Telogenetic alteration (i.e. weathering) in the sandstones includes the formation of goethite and calcite. Thus, the integration of diagenesis with sequence stratigraphy provides a useful tool with which to understand reservoir-quality distribution in sand-dominated, tidal sediments.