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Authors
Affiliations
1 KDM Project, Department of Applied Geology, Dibrugarh University, Assam, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 57, No 2 (2001), Pagination: 157-169
Abstract
The Therria - Lakadong unit forms a part of the Upper Assam basin explored by the Oil India Limited. Petrographic study on 47 subsurface samples drawn from 3548.5m to 4377m in five well sections has revealed that the sandstone type is dominantly wacke, minor arenite and calcareous sandstone with quartz content varying from 31.4 to 82.7%. The other constituents are feldspar, rock fragments, cement, matrix, mica, opaques, glauconite and fossils. The limestone comprises sparry calcite, micrite, bioclasts, peloids, quartz, opaques and glauconite. The heavy minerals recorded are zircon, rutile, titanite, epidote, garnet, hornblende, enstatite, hypersthene, augite and kyanite with traces of diopside, sillimanite, brookite and monazite. The heavy mineral assemblage suggests that the sediments were derived from igneous, metamorphic and sedimentary rocks. Based on IR and XRD studies, the clay minerals were identified as kaolinite, illite, montmorillonite and chlorite, which together with glauconite, suggest a nearshore depositional environment. Biosparite indicates high-energy conditions in the environment. Although some of the original porosity is lost at depth due to pressure effects, the sandstone in general has good porosity.
Keywords
Petrography, Sandstone, Limestone, Clay Minerals, Heavy Minerals, Therria - Lakadong Unit, Upper Assam Basin.
