Sedimentology And Hydrogeochemistry Of The Tista River, Rangpur Division, Bangladeshsedimentology And Hydrogeochemistry Of The Tista River, Rangpur Division, Bangladesh

Abstract

The present research work is dealt with the study of sedimentology and hydrogeochemistry of the Tista River and its adjoining area, Rangpur division, Bangladesh. Sediments of the Tista River are composed of the sand particles that are laden with cobbles and pebbles. Percentage of sand towards downstream direction is decreased with respect to increasing fraction of mud. The unimodal distribution of the sediments indicates of single source for the studied sediment samples. About sixty percent of the studied sands are very fine sand. The well sorted nature of the sand is suggestive of effective transporting capacity of the sand particles. The skewness values vary from -0.41 to 0.35 indicating the mixture of both coarse fraction and fine fraction within the sediments. Most of thð€€– samples are leptokurtic and 11 % are mesokurtic. Plots of mean size and sorting suggest that the sands are hydraulically controlled. Lithofacies matrix supported coBglomerate (Gms), massive sand (Sm), trough cross stratified sand (St), planar cross stratified sand (Sp), ripple laminated sand (Sr), parallel laminated sand (Sh), clay with silt (Fl) and massive clay (Fm) were recognized in the exposed lithosuccession of the Tista River. The channel deposits are formed under high energy conditions. The overbank fine sediments are constituted by the facies of Sr, Sh, Fl and Fm covering the uppermost pai1 of the lithosuccession. The finer sediments are the suspension products of floodplains or back swamps The minerals of illite group are the major clay sized minerals in Tista River deposits with quartz, feldspar, chlorite and kaolinite. The minerals that are found in trace quantities include lavendulan, lepidolite, enstatite, sekaninaite and ferrierite. The low illite crystallinity indices indicate that the mechanically formed illites are well crystallized. The present study shows that the sediments are acidic in nature which reflects that they are derived from acid rocks. The mean EC value of the sediments was 1.16 ds/m that indicates very low or negligible effects of salinity of the sediments. The Recent deposits of the Tista River contain low amounts of total organic carbon. The average concentration of N is 0.0268%. The concentrations of iron vary from 24367.4 mg/kg to 2789l mg/kg with the mean concentrations of 26310. 77 mg/kg. Sulphur is significantly positively correlated with copper and zinc (p<0.05) and insignificantly positively correlated with arsenic content of the sediments that indicates that the copper and zinc occur as sulphide minerals.