Geochemical signatures of recent bar deposits in the Tista river, Bangladesh: Implications to provenance, paleoweathering and tectonics

Abstract

Petrography and geochemical composition of sediments is a sensitive indicator which archives the signature of a previous record of a source rock and depositional environments in a basin. This study deals with the elemental geochemistry of recent bar deposits of the Tista river in the north western part of Bangladesh to evaluate their provenance, paleoweathering and tectonic setting. Petrographically, the sediments are rich in quartz (70%), whereas feldspar and lithic fragments are found about 8% and 3%, respectively. The geochemical composition of the samples exhibits dominantly quartzose litharenites with low grade sedimentary and metasedimentary lithics, low feldspar indicates tectonic provenance field of recycled orogeny. Discrimination functions revels that the sediments of the Tista river are the derivation of active continental margin. The analyses also reflect that the sediments are dominantly a mixture of felsic (e.g., granitic/Gneiss, quartzite, amphibolite, granulite facies rock types) and some of mafic source (e.g., alkali-basalt/greenschist facies). It may occur, since 60% of the sedimentary flux carried out by the river from low-grade metamorphic rock and the rest from high-grade rock (in the west and north Sikkim Himalaya respectively). The weathering indices highlight that the source rocks have not undergone significant chemical weathering. The immature sorting status and petrographic evidences indicate that the sediments deposited in the Tista river basin are simply the product of mechanically weathered rocks.

Modern River-Sand Geochemical Mapping in the Manufahi Municipality and its Surroundings, Timor-Leste: Implications for Provenance

“…The ICV values in the study area ranged from 0.93 to 1.55, with an average of 1.26, which was much higher than those of PAAS and UCC (Table 1). The high concentrations of TiO 2 , Fe 2 O 3 , MnO, MgO, and P 2 O 5 compared with UCC and PAAS, as well as the positive association between these elements in most drainage basins, corroborate the presence of mafic sources containing heavy and accessory minerals (such as amphibole, pyroxene, biotite, ilmenite, hematite, sphene, rutile, and garnet) [84,99]. These results revealed the abundance of chlorite minerals along with mafic, heavy, and accessory minerals in the river sand.…”

“…In this study, several ratios of selected major elements, the Pearson correlation coefficient matrix, and the index of compositional variability (ICV) were used to analyze and interpret provenance [32,35,40,[84][85][86][87][88][89].…”

“…The SiO 2 /Al 2 O 3 and K 2 O/Na 2 O ratios, as well as the geochemical index of ICV, are also frequently used to evaluate the abundance of quartz, clay, K-feldspar, plagioclase, and other less resistant minerals to identify provenance [32,35,40,[84][85][86][87][88][89][90][93][94][95]. The SiO 2 /Al 2 O 3 ratio has different average values for determining source rock compositions and sediment maturities in clastic sediments; in basic igneous rocks, the ratio is approximately 3 and the ratio is approximately 5 in acidic igneous rocks.…”

“…The K 2 O/Na 2 O ratio also has variational values in defining the abundance of K-feldspar relative to plagioclase; with high values (> 1) suggesting potential contributions from alkali feldspar or mica and/or possibly from secondary K-bearing minerals, whereas for the abundance of sodium-bearing minerals or plagioclase, the ratios were < 1 [84,[87][88][89].…”

“…Cox et al (1995) also determined ICV values greater than 1 for the sediments rich in non-clay minerals (chlorites, feldspars, amphiboles, and pyroxenes), whereas values less than 1 were found for sediments with significant concentrations of clay minerals (kaolinite, illite and montmorillonite) [32,84,86,88,89].…”