Petrography and Mineralogy of Oxbow Lake Sediments in the Ganga Alluvial Plain, India: A Case Study with Implications for Provenance and Tectonic Setting

Abstract

Detailed petrographic, heavy mineral, petrofacies, and XRD investigations were conducted on nineteen sediment sample from an oxbow lake in the Ganga plain. The grains are angular to sub-rounded in shape, with some sub-rounded quartz grains. The dominant constituents of the framework grains are primarily quartz, followed by rock fragments, feldspar, mica, and heavy minerals. The majority of the quartz grains are monocrystalline, exhibiting undulatory extinctions, while the remaining are polycrystalline, displaying both distinct and suture intercrystallite boundaries. The feldspar category comprises both fresh and altered varieties, including plagioclase and microcline. Additionally, biotite, as well as large flakes of muscovite and mica, have been observed. The rock fragments include various types such as quartzite, schist, gneiss, phyllite, chert, sandstone, limestone, and siltstone. The heavy minerals encompass a range of minerals such as tourmaline, garnet, opaque minerals, zircon, andalusite, kyanite, sillimanite, staurolite, actinolite/tremolite, hornblende, biotite, rutile, muscovite, chlorite and apatite. Petrographic investigations reveal that the sediments of the ox-bow lake are sublitharenites. Heavy mineral analyses confirm the possibility of mixed provenance for the ox-bow lake sediments. The ox-bow lake petrofacies indicate their derivation from cratonic interiors, recycled orogenic, and quartzose recycled provenances, under semi-humid to humid climatic conditions. The abundance of clay minerals supports the interpretations derived from petrofacies plots regarding the provenance and tectonic setting of the oxbow lake sediments. Based on the analysis of lighter and heavy minerals, it is concluded that the sediments of the oxbow lake originated from a variety of low-grade to high-grade metamorphic rocks, as well as acid and basic igneous rocks. This case study provides comprehensive insights into the sedimentological characteristics, provenance, and tectonic setting of oxbow lake sediments in the Ganga alluvial plain, contributing to the broader understanding of sedimentary processes and geological history in this region.