Integrated diagenesis and sequence stratigraphic study of tidal sandstones: the Adedia Formation (Cambro-Ordovician), Si
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ORIGINAL PAPER
Integrated diagenesis and sequence stratigraphic study of tidal sandstones: the Adedia Formation (Cambro-Ordovician), Sinai, Egypt Khalid Al-Ramadan & Essam El-Khoriby
Received: 4 June 2011 / Accepted: 27 October 2011 / Published online: 22 November 2011 # Saudi Society for Geosciences 2011
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 K. Al-Ramadan (*) Department of Earth Sciences, King Fahd University of Petroleum and Minerals, Dhahran 3126( P.O. Box 1400, Saudi Arabia e-mail: [email protected] E. El-Khoriby Department of Geology, Faculty of Science, Mansoura University, 355 16, El-Mansoura, Egypt
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. Keywords Diagenesis . Tidal sandstones . Sequence stratigraphy . Cambro-Ordovician . Sinai . Egypt
Introduction Sand-dominated, tidal flat deposits can form excellent hydrocarbon reservoirs owing to their high depositional porosity and permeability (Klein 1977; Yang 1989; Lambiase et al. 2002). Diagenetic fabrics may exert considerable control on reservoir quality, often in decreasing permeability, but also by creating cemented baffles and barriers to fluid flow. Accordingly, prediction of the distribution patterns of heterogeneous diagenetic fabrics can influence efficient hydrocarbon exploration and production strategies (Morad et al. 2000; Bloch et al. 2002). Recent work has demonstrated that the distribution of diagenetic alterations in sandstones can be linked to the sequence stratigraphic framework of paralic and shallow-marine deposits,
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