Geochemistry of the floodplain sediments of the Kaveri River, southern India

The floodplain sediments of the Kaveri River, southern India, derived from Archean gneissic and charnockitic source regions, show interbedding of silt y (4-4.7 Phi) and sandy units (1.4-3.7 Phi). The geochemistry of silty beds is remarkably uniform at a given location and over a lateral distance of n early 250 km; the sandy beds have more variable chemical compositions, yet are comparable to those of silty beds except for the diluting effect of qua rtz, Silty sediments retain the geochemical signature of prominently expose d source rocks for almost all elements and provide evidence of tectonic ins tability in the source region. The floodplain sediments contain all size gr ades (sand, silt, and clay), which may have resulted in minimizing the bias es imposed on suspended and bedload sediments due to sorting. The low Chemi cal Index of Alteration (CIA), the dominance of unweathered primary mineral s, and the minor proportion of smectitic clay all suggest that the region h as been subjected to little chemical weathering. This is possible if the re gion has undergone recent uplift, exposing fresh Archean rock to surface de nudation, The formation of fertile farmland along the Kaveri River course a nd its delta is related to these recent geological processes.