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Detrital dolomite : characterization and characteristics

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

Geological Quarterly

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2018

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Vol. 62, No. 1

81--89

EN

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.

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Geochemical signatures of pervasive meteoric diagenesis of Early Miocene syn-rift carbonate platform, Red Sea, NW Saudi Arabia

Al-Ramadan K.

Geological Quarterly

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2017

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Vol. 61, No. 1

239--250

EN

Different diagenetic environments have been recognized in the Early Miocene carbonate platform of Musayr Formation in the Red Sea rift area. Early marine diagenesis includes micritisation that occurs as thin envelope around skeletal and non-skeletal grains in low-energy mud dominated facies and isopachous fibrous calcite in high-energy grain-dominated facies. Pervasive meteoric water diagenesis resulted in cementation of the carbonates by coarse-crystalline blocky-drusy calcite and meniscus cements. Depletion of oxygen (avg. –9.08‰), carbon (avg. –1.6‰) isotopes and trace elements concentrations (avg. values of Fe: 1387 ppm; Mn: 1444 ppm; Sr: 419 ppm; Na: 1194 ppm) in conjunction with negative correlation between Mn2+ and oxygen isotope data suggest variable degrees of fluid-rock interactions and pervasive meteoric diagenesis. The formation of meteoric diagenesis in the Musayr Formation can be explained by two subsequent mechanisms: (1) the presence of meteoric lenses during the time of deposition might have been associated with active freshwater input from the hinterland (NE) due to fall in the relative sea level; (2) later uplift episode during Plio-Pleistocene may have also contributed to the pervasive meteoric diagenetic alterations of the carbonates of the Musayr Formation. The first mechanism is supported by the cement stratigraphy where the blocky-drusy cements postdate the meniscus cement. The latter mechanism seems to have more pronounced effect on the alteration of Musayr carbonate sequence by observing the occurence of late cements such as blocky calcite in most of the samples. The impact of meteoric diagenesis on the studied samples suggest that dissolution is less severe than cementation, hence the visible porosity is very low. Understanding the timing of meteoric diagenesis provides useful information about the reservoir quality distribution in syn-rift carbonate sequences.

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Formation conditions and diagenetic evolution of Sand Roses in clastic sabkhas along the Arabian Gulf Coastal Region, Eastern Saudi Arabia

Al-Hussaini A., Koeshidayatullah A., Al-Ramadan K.

Geological Quarterly

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2015

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Vol. 59, No. 1

71--78

EN

This field, petrographic and geochemical study aims at constraining the formation and diagenetic evolution of sand roses (desert roses) in interdune sabkhas in Eastern Saudi Arabia. These “roses”, which are mainly cemented by gypsum, carbonate, and clay minerals, occur as disc-shaped and spherical flower-like crystals. Sands, within the sand roses, are moderately-sorted, medium-grained, and sub-arkosic. Gypsum typically exceeds 20% of the volume of the roses, and locally gypsum is partly transformed to anhydrite. In addition to gypsum and anhydrite, early diagenetic modifications include precipitation of grain coating clay, dissolution of unstable grains (e.g., feldspar grains), and weak mechanical compaction. Iron oxide cement was formed when the sand roses exposed to the surface. The XRD and petrographic data indicate an increase in amounts of gypsum cement from the water table upward towards the sabkha surface. The sand roses also are larger and lighter in colour away from the water table. This study is expected to provide a better understanding of the mode of sand roses formation in the interdunes areas, as well as the diagenetic alterations in both phreatic and vadose zones.

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Unraveling cementation environment and patterns of Holocene beachrocks in the Arabian Gulf and the Gulf of Aqaba : stable isotope approach

Koeshidayatullah A., Al-Ramadan K.

Geological Quarterly

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2014

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Vol. 58, No. 2

207--216

EN

This paper analyses Holocene beachrocks from the Arabian Gulf and the Gulf of Aqaba to explain the mechanisms that influence the cementation process in these areas. Holocene beachrocks in the Gulf of Aqaba are composed of predominantly terrigenous material derived from erosion of adjacent uplifted Precambrian basement, while the beachrocks in the Arabian Gulf are composed mainly of marine bioclasts and wind-blown siliciclastic sands. The cements of beachrocks in both areas show three textural varieties: (1) isopachous phreatic acicular aragonite; (2) a micritic envelope of high-Mg calcite (HMC); (3) meniscus and gravitational vadose HMC. Radiocarbon dating of beachrock samples from the Arabian Gulf yielded ages from ca. 2300 to 660 yr cal BP whereas samples from the Gulf of Aqaba range in age between 5500 and 2800 yr cal BP. Oxygen isotope values range from 2.6 to 4.4‰ respectively for the Arabian Gulf whereas the Gulf of Aqaba values range from 1.2 to 1.5‰. Carbon isotope values range from 3.2 to 5.9‰ for the Arabian Gulf whereas those from the Gulf of Aqaba range from 3.8 to 4.6‰. The values of δ18OVPDB and δ13CVPDB in the beachrocks of both areas suggest a marine origin. The beachrocks of the Arabian Gulf were precipitated under high evaporation conditions, while beachrocks from the Gulf of Aqaba were precipitated in normal shallow-marine conditions. The mineralogy and textural habits suggest that cementation of these beachrocks started within the shallow-marine phreatic zone.

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

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

Geological Quarterly

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2013

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Vol. 57, No. 1

165–-174

EN

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.