Roles of Relief and Climate on Composition of Detrital Sediments of Bharathapuzha Basin, Kerala

Channel sediments of Bharathapuzha (BP) basin provide an unique opportunity to examine the relative roles of climate and relief on the character of first cycle detritus derived from a source area of high grade metamorphic rocks, as the major tributaries of the river are set in diverse climatic domains. For e.g., Gayathripuzha (GP) and Thuthapuzha (TP) are in a tropical setting, while Kalpathipuzha (KP) enjoys a semi-arid climate. Sediments of a tropical-, low relief stream, the Tirur river (TR) lying adjacent to Bharathapuzha (BP) in the north, have also been examined.

The average mineralogical maturity of sands expressed as Q:F:R ratio, for the mainstream of BP varies from 72:19:9 for coarse to 53:38:9 for medium sand and to 49:44:7 for fine sand, implying an arkosic composition. The Q:F:R ratios of GP and TP, the two high relief tributaries on the one hand and of KP, the low relief trib utai) on the other are similar to that of mainstream of BP basin. However, quartz arenite (Q:F:R = 93:5:2) is under transport in the tropical-low relief, Tirur river (TR).

The chemical maturity index (CMI), i.e. the ratio of SiO₂/Al₂O₃, for the sediments of main stream (7.27) and for the tributaries, amply demonstrates the immaturity of the channel sediments. Nevertheless a value 120, for Tirur river sands indicates their super maturity.