Mineralogical changes during intense chemical weathering of sedimentary rocks in Bangladesh |
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| Authors: | Md R Islam Rojstaczer Stuart Aario Risto Peuraniemi Vesa |
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| Institution: | a Division of Earth and Ocean Sciences, Duke University, Box 90227, Durham, NC 27708-0227, USA;b Department of Geology, Institute of Geosciences, University of Oulu, FIN-90570, Oulu, Finland |
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| Abstract: | Bangladesh is situated in a subtropical to tropical climatic zone. A recently weathered crust has developed on sedimentary bedrock (sandstone, siltstone, shale and claystones) of Tertiary–Quaternary age. Weathered samples were collected from 16 sections totaling 68 samples and were analyzed mineralogically. The main primary minerals identified in the weathered crust of sedimentary rocks are quartz, plagioclase, K-feldspar, biotite, muscovite, sparse carbonate and epidote. The secondary minerals are kaolinite, illite, chlorite, gibbsite and goethite. Weathering initiated along the grain boundaries and cleavage planes of the minerals, forming small cloudy materials which were very difficult to identify. In the advanced stage of weathering, these cloudy materials have turned into secondary minerals. In region 1, high rain fall (7100 mm/yr) and monsoonic climate resulted in a kaolinite–gibbsite–goethite suite through the weathering of feldspars and biotite. The occurrence of gibbsite in the relatively elevated lands of Sylhet and Fe-kaolinite throughout the study areas is indicative of a humid–tropical climate during formation of the weathered crust. |
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| Keywords: | Chemical weathering Sedimentary rocks Kaolinite Gibbsite Bangladesh |
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