The floodplain sediments of the Kaveri River, southern India, derived from Archean gneissic and charnockitic source regions, show interbedding of silty (4-4.7 Φ) and sandy units (1.4-3.7 Φ). The geochemistry of silty beds is remarkably uniform at a given location and over a lateral distance of nearly 250 km; the sandy beds have more variable chemical compositions, yet are comparable to those of silty beds except for the diluting effect of quartz. Silty sediments retain the geochemical signature of prominently exposed source rocks for almost all elements and provide evidence of tectonic instability in the source region. The floodplain sediments contain all size grades (sand, silt, and clay), which may have resulted in minimizing the biases imposed on suspended and bedload sediments due to sorting. The low Chemical Index of Alteration (CIA), the dominance of unweathered primary minerals, and the minor proportion of smectitic clay all suggest that the region has been subjected to little chemical weathering. This is possible if the region has undergone recent uplift, exposing fresh Archean rock to surface denudation. The formation of fertile farmland along the Kaveri River course and its delta is related to these recent geological processes.

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