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Significance of the clay mineral distribution in fluvial sediments of the Neogene to Recent Himalayan Foreland Basin (west-central Nepal)

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  • Pascale Huyghe
  • Romain Guilbaud
  • Matthias Bernet
  • Albert Galy
  • Ananta Prasad Gajurel
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<mark>Journal publication date</mark>06/2011
<mark>Journal</mark>Basin Research
Issue number3
Volume23
Number of pages14
Pages (from-to)332-345
Publication StatusPublished
Early online date23/06/10
<mark>Original language</mark>English

Abstract

Clay mineral assemblages of the Neogene Himalayan foreland basin are studied to decipher their significance with respect to tectonic and climate processes. Fluvial deposits of the Siwalik Group (west-central Nepal), and sediment of the Ganga River drainage system were analysed for clay mineralogy. The observed clay mineral assemblages are mainly composed of illite (dominant), chlorite, smectite and kaolinite. Illite and chlorite are chiefly of detrital origin, derived from Himalayan sources. Kaolinite and smectite are authigenic, and mainly developed within pore space and as coating of detrital particles. With increasing burial, diagenetic processes affected the original clay mineral signature. Illitisation of smectite and kaolinite occurred below 2500 and 3500m depth, respectively. Therefore, illite in the lower parts of the Siwalik Group consists of a mixture of inherited illite and illitised smectite and kaolinite, as suggested by illite crystallinity. Detrital grains that make up the framework of the Siwalik Group sandstones mainly consist of quartz, feldspar and lithic fragments, which are principally of sedimentary and metamorphic origin. Lithoclast content increases over time at the expense of quartz and K-feldspar in response to uplift and erosion of the Lesser Himalaya Series since about 11-10Ma. Despite mainly felsic source rocks, dominantly physical erosion processes in the Himalayan belt, and high-energy fluvial depositional systems, smectite is abundant in the