naa a22 4500 51075564X CHVBK 20180411083121.0 cr unu---uuuuu 180411e20130501xx s 000 0 eng 10.1007/s12594-013-0089-4 doi (NATIONALLICENCE)springer-10.1007/s12594-013-0089-4 Clay mineralogy of the pleistocene soil horizon in Barind Tract, Bangladesh [Elektronische Daten] [Md. Aftabuzzaman, Sohail Kabir, Md. Islam, M. Alam] Pleistocene red soil horizons were exposed in different areas of the Barind Tract in north-west Bangladesh. X-ray diffractions of twenty seven samples from different depths of these soil horizons revealed that the soil horizons consisted of kaolinite, illite and chrysotile with significant amount of opal-CT. Samples from Maddhapara, Bogra, and Nachole contain kaolinite, illite, quartz and opal-CT, and the samples from Kantabari contain chrysotile instead of kaolinite. Clay mineral compositions of different soil horizons indicated two different types of clay assemblages, viz. (a) illitekaolinite and (b) illite-chrysotile. In the village of Kantabari, illite-chrysotile clay mineral assemblage indicate that soil horizons were formed under low temperatures with alkaline and reducing conditions. However, other soil horizons of illite-kaolinite clay mineral assemblage indicate that soils were possibly formed under humid, temperate and welldrained conditions. These two soil horizons were formed under different geochemical, geomorphological and climatic conditions from different parent materials. Scanning Electron Microscopy photographs showing the presence of glass shards and no opal-A were found using XRD, suggesting that the opal-A might not be a precursor to opal-CT in the red soil horizon of the study area. This opal-CT along with the general lack of fossils and presence of glass shards was indicative of a volcanogenic rather than biogenic origin for the Opal-CT in the study area, and X-ray fluorescence data reveals higher percentages of silica which is comparable to the Toba Ash of Toba Caldera, Indonesia of about 75,000 B.P. Geological Society of India, 2013 Kaolinite nationallicence Chrysotile nationallicence Opal-CT nationallicence Barind Tract nationallicence Bangladesh nationallicence Aftabuzzaman Md University of Rajshahi, Rajshahi, Bangladesh aut Kabir Sohail Geological Survey of Bangladesh, Dhaka, Bangladesh aut Islam Md University of Rajshahi, Rajshahi, Bangladesh aut Alam M. University of Rajshahi, Rajshahi, Bangladesh aut Journal of the Geological Society of India Springer-Verlag 81/5(2013-05-01), 677-684 0016-7622 81:5<677 2013 81 12594 https://doi.org/10.1007/s12594-013-0089-4 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s12594-013-0089-4 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Aftabuzzaman Md University of Rajshahi, Rajshahi, Bangladesh aut NATIONALLICENCE 700 1- Kabir Sohail Geological Survey of Bangladesh, Dhaka, Bangladesh aut NATIONALLICENCE 700 1- Islam Md University of Rajshahi, Rajshahi, Bangladesh aut NATIONALLICENCE 700 1- Alam M. University of Rajshahi, Rajshahi, Bangladesh aut NATIONALLICENCE 773 0- Journal of the Geological Society of India Springer-Verlag 81/5(2013-05-01), 677-684 0016-7622 81:5<677 2013 81 12594 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer