Geochemical Characterization of Rasulpur - Subarnarekha River Mouths Estuarine Complex, EC of India: Provenance, Palaeo Weathering and Depositional Environment

Major and trace element geochemistry of sediments is a very useful tool for understanding the provenance, intensity of weathering, tectonic settings, and depositional environment of the sediments. Sediments collected from different geomorphic domains (onshore and nearshore) of Rasulpur to Subarnarekha River mouths estuarine complex, East coast of India, were analyzed for their geochemical (major, trace contents) and mineralogical characteristics to determine their provenance, compositional maturity, paleo-weathering condition, and depositional environment. From geochemical studies, it is evident that the samples from the nearshore area suffered more weathering than the onshore samples. Geochemistry of the sediments suggests the protolith of the area to be of intermediate to felsic source rocks. A relative increase in the Alsub2/subOsub3/sub/TiOsub2/sub ratio in sediments also suggests that they are derived mainly from intermediate to felsic source rocks. A strong positive correlation between Fesub2/subOsub3/sub, MnO, Ksub2/subO, MgO, CaO, Psub2/subOsub5/sub, and major oxides with respect to Alsub2/subOsub3/sub indicates that they are associated with micaceous/clay minerals. The Index of Compositional Variability (ICV) indicating low compositional and mineralogical maturity of the sediments. The Chemical Index of Alteration (CIA) value clearly pointing towards intense to intermediate weathering in the source area sediments. Similarly, Chemical Index of Weathering (CIW) results also supporting the same trend of weathering. The results of Plagioclase Index of Alteration (PIA) suggesting moderate destruction of feldspars during source weathering, transport, sedimentation, and diagenesis. The Ternary plot of A-CN-K and the binary plot of CIA/ICV also suggest that both geomorphological domains are immature in nature and suffered intense to moderate weathering. Trace-element concentrations in sediments result from the competing influence of provenance, weathering, diagenesis, and sediment sorting. The felsic province is also corroborated by elevated values of Ba, K, and Sr. EPMA analysis reveals the presence of heavy minerals comprising Ilmenite, garnet as major constituents followed by sphene and rutile. Other minerals include sphene, epidote, amphibole, pyroxene, biotite, apatite, chlorite, tourmaline, muscovite, and alumino-silicate. The concentration of TiOsub2/sub in Ilmenitedepicting a metamorphic signature with an igneous source. Micro-textural studies reveal different types of surface features of the grains, the various micro features have been produced by different transportational processes under different environmental conditions. Based on all geochemical and mineralogical data and different plots, it is evident that the sediments from both geomorphological domains are immature in nature and suffered intense to moderate weathering derived from mixed igneous and metamorphic sources.