H. Hoseini; N. Kohansal Ghadimvad; M. Zamani Pedram; M. R. Majidifard; A. R. Shahidi
Abstract
Accumulation of Shemshak group lithofacies have been started during Early-Cimmerian orogeny from middle of Late-Triassic and ended with Middle- Cimmerian discontinuity dating Millde-Jurrasic. So the mostly Siliciclastic and occasionally Marin lithostratigraphic unite has evidences of two major tectonic ...
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Accumulation of Shemshak group lithofacies have been started during Early-Cimmerian orogeny from middle of Late-Triassic and ended with Middle- Cimmerian discontinuity dating Millde-Jurrasic. So the mostly Siliciclastic and occasionally Marin lithostratigraphic unite has evidences of two major tectonic events as orogenic activity at lower and upper border of sequence. Therefor the lower contact of Shemshak group is composed of Middle-Triassic platform carbonates known as Elika formation which distinguished with Plaeokarsts including bauxit and laterit horizons and the upper contact with parallel unconformity with Delichay formation fossiliferous marls and carbonates of Bajocian stage (Middle Jurrasic). Results of deposition environment and facies studies have shown that the mentioned siliciclastic group (Shemshak) composed of three major facies, 22 subfacies and have been deposited in three different environments including Fluvial (Terrestrial), mid-tidal and shallow marine environments. The vertical changes of facies have declared that the sequence has formed due to erosion of Early-Cimmerian uplands and have experienced progess of shallow marine. The existing shallow marine sediments in the end of Shemshak group states that, in comparison with surrounding area , clastic sediments of end of Shemshak cycle, because of erosional cycles of Middle-Cimmerian orogeny, befor deposition of Delichay marine formation, have been eroded.
T Rabani; N Taghipour; R Aharipour
Abstract
Gheshlagh district contains coal deposits in a large syncline in Shemshak group sediments in East Alborz. To determine the palaeoenvironmental setting of the coal deposits based on organic and mineral components, eleven samples from coal seams from four active mines are collected. Minerals such as quartz, ...
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Gheshlagh district contains coal deposits in a large syncline in Shemshak group sediments in East Alborz. To determine the palaeoenvironmental setting of the coal deposits based on organic and mineral components, eleven samples from coal seams from four active mines are collected. Minerals such as quartz, kaolinite, pyrite, siderite, biotite, montmorillonite and dolomite are identified in Gheshlagh coal mines. The Ground Water Index (GWI) suggests ombrotrophic hydrological conditions for coal layers in Gheshlagh coal region. K13 and k11 layers have much higher GWI among others due to its higher mineral content than other layers. Vegetation index (VI) of the Gheshlagh coals is less than 3, which could indicative of the dominance of aquatic/herbaceous plants in the formation of coal seams. Petrographic data on organic and inorganic matter with facies diagram suggest evidences of anaerobic to low oxygen, alkaline conditions and variations in water level with relative proximity to the marine environment.