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Sedimentology and Diagenesis of the Miocene Nutaysh Member of the Burqan Formation in the Midyan Area, Northwestern Saudi Arabia

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Al-Ramadan K. , Dogan A. , Senalp M.

tom Vol. 57, No. 1

165–-174

Turbidite sandstones deposited in rift settings are currently among the main targets of hydrocarbon exploration. However, the impact of style of sedimentation, cyclicity and diagenesis on reservoir quality of such sandstones is relatively poorly explored in the literature. The sedimentology, stratigraphic architecture, and diagenetic alterations of deep marine sandstones of the Mocene Nutaysh member of the Burqan Formation in the Midyan area (Saudi Arabia) are described based on number of measured sedimentologic sections, lithofacies identification in the field and laboratory studies. Three lithofacies types are here identified in the measured sections. These are from bottom to top: (1) “Lithofacies A” consisting of massive to thickly-bedded, coarse-to-very coarse-grained sandstone and conglomerates; (2) “Lithofacies B” consisting of well-bedded, coarse-to-medium-grained, well-sorted sandstone, and (3) “Lithofacies C” consisting of thin-bedded, fine to very fine-grained, current-rippled sandstone, bioturbated shaley siltstone and marl. The main diagenetic processes in the sandstones include the formation of grain-coating smectite and rhombic dolomite. Small amounts of cements include the formation of authigenic kaolinite and calcite. The reservoir quality is anticipated to have been preserved under the transformation of smectite to deep burial illite, which is believed to prevent formation of quartz cements.

Detrital dolomite : characterization and characteristics

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Radwan O. , Bu-Khamsin A. , Al-Ramadan K.

tom Vol. 62, No. 1

81--89

Investigating dolomite fragments derived from pre-existing dolomite-containing sediments or rocks, that is detrital dolomites, constitutes a challenge in carbonate sedimentology. Detrital dolomites are generally difficult to recognize and their presence can have profound consequences, even in small quantities, on the interpretation of the tectonosedimentary evolution and palaeoenvironmental conditions of the enclosing basin. In addition, identification and quantification of detrital dolomites may provide insight into provenance and sediment transportation, quality of hydrocarbon reservoirs, and some aspects of the dolomite problem. Typically, detrital dolomites are recognized by their clastic behaviour, such as 1) their wide range of grain sizes and shapes, 2) evidence for transportation and weathering, and 3) their association with other detrital grains. Detrital dolomite can be derived from dolomite-containing sediments (by reworking) or dolomite-containing rocks (by disintegration) and can be transported by various means including wind, water, glaciers and sediment gravity flows. Detrital dolomite can be found in a variety of lithofacies confirming that they are controlled by availability of dolomite detritus and not by depositional environment. The role of detrital dolomite in promoting diagenetic dolomitisation is examined whereby they have provided nucleation sites, for syntaxial overgrowth, or a source of Mg, through dissolution.