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|Title:||Genesis and Diagenesis of Chert within the exposed Upper Dammam Formation in Al Ahmadi Quarry, Kuwait||Authors:||Rehab Ahmad Taher Naqi||Supervisor:||Prof. Fikry Ibrahim Khalaf||Keywords:||Genesis and Diagenesis of Chert , Upper Dammam Formation in Al Ahmadi Quarry, Kuwait||Issue Date:||2018||Publisher:||Kuwait university - college of graduate studies||Abstract:||This study is focused on the genesis and diagenesis of chert hosted in Eocene dolostone of Dammam Formation which is approximately 20 meters thick sequence exposed within a rock quarry in the southeast of Kuwait. It is divided into two lithological units. The lower part of this sequence is mostly porous chalky dolostone where chert commonly occurs as elongated nodules and thin bands along the bedding planes. The upper part is mostly formed of extensively karstified chertified hard dolostone. Two exposures were selected for the study, one represents the chalky dolostone part and the other represents the upper karstified dolostone. Chert samples were collected from these two sites and have been prepared for petrographic, mineralogical and geochemical investigations. Detailed SEM examinations and EDS analysis were also carried out. The results indicated that the chert was developed as a result of silica precipitation within voids and replacement of dolomite within the host dolostone. Several silica mineral phases were recognized including: opal-A nanoglobules, opal-CT lepispheres, fibrous quartz (as segregated fibers, feathery quartz and chalcedony) and equant quartz crystals of various sizes. Such mineralogical variations may be attributed to the nature of the host rock, fluctuation in the pH and in the concentration of silica within the interstitial water, and availability of Mg ions. The acidic environment required for the dissolution of carbonates and precipitation of silica, where the reduction in pH may have been promoted by the near surface oxidation of the seeped hydrocarbon gases and the associated H2S from the deep seated oil bearing formations. The textures and fabrics of these minerals indicate that chertification postdates the dolomitization of the host rock. It is suggested that silica was mainly derived from meteoric water recharged to the fractured and porous Dammam dolostone upon its emergence. The stratal nature of nodular chert bands may suggest that chertification may have took place at former water table stands within a subsurface meteoric phreatic zone.||URI:||http://hdl.handle.net/123456789/948|
|Appears in Programs:||2095 Applied Geosciences & GIS|
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