Geochemistry and petrographic analysis of sandstones of the Lower Permian Barakar Formation (Lower Gondwana) Mand valley basin, Chhattisgarh, India have been undertaken to interpret their provenance, tectonic setting, paleoweathering and climatic conditions. The petrology of these Barakar sandstones reveal that they are mainly composed of variable amounts of monocrystalline and polycrystalline quartz, potash and plagioclase feldspars with minor amount of micas and chert as well as metamorphic and sedimentary rock fragments in addition to heavy accessories. Based on the modal analysis, the Barakar sandstones are classified as subarkose and sublitharenite types. Plots of sandstone composition in tectonic setting discrimination diagrams suggest derivation of these detritus from craton interior and recycled orogenic provenance. Tectonic setting discrimination diagrams based on major elements composition suggest a quartzose sedimentary provenance in a passive continental margin. Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Plagioclase Index of Alteration (PIA) indices and A-CN-K plot suggest moderate to intense weathering of source rocks under humid climatic condition.
The present study deals with the petrographic interpretation of Talchir Formation sandstone, in and around Chirimiri area, Koriya district, Chhattisgarh state India located in Son-Mahanadi basin. This basin is an elongate graben showing northwest-southeast trend and considered to be one of the largest intra-cratonic rift basins of Indian peninsula. Talchir Formation is the lowermost unit of thick classical Gondwana sedimentary succession and rests unconformably on Precambrian basement. The petrographic studies consisting of point count show the presence of quartz as a dominant framework mineral with subordinate amounts of feldspars and rock fragments. The data plot in the fields of cratonic interior and transitional margin of continental block provenance. In the Qt (quartz)-F (feldspar)-L (lithic fragments) triangular diagram, indicating the source of these sediments was located in transitional margin and continental block provenance. The petrographic classification suggests that this formation in the study area dominantly contains compositionally immature to submature arkosic, sub-arkosic and lithic-arkosic sandstones. The bivariate plot between Qp/(F+R) vs. Qt/(F+R) indicates changes in climatic conditions from semi-arid to semi-humid during Permo-Carboniferous period.
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