wAbstract
@Small rivers (
100 km length) are likely to drain fewer rock
types. Therefore, their solutes and sediments are good indicators
of weathering environments typical of their basins and help constraining
the nature of their source rocks. To understand this, the texture,
mineralogy, major and trace element compositions of the sediments
deposited by the River Hemavati, a northern upland tributary of
the Cauvery River in southern India, are analyzed and discussed.
@The Hemavati sediments are overall of fine sand size (mean 2-3Σ),
and the high concentrations of FeO (
7 wt.), TiO2
(
1.2 wt.), Cr (
350 ppm) and Ni (
125 ppm). Major and trace
element distribution call for a binary source for the sediments,
and particularly point to contrasting climatic conditions of their
provenances. the source areas in the upstream and downstream parts
are exposed to sub-humid high relief and sub-arid low relief conditions,
respectively, with distinct weathering characteristics. The CIA
values (85-48) decrease from near the source to downstream, suggesting
that the downstream rain-shadow part of the catchment suffered
only minor chemical weathering.
@On the other hand, the REE distribution in the Hemavati sediments
indicates contrasting lithologies in their provenance, and is
not controlled by chemical weathering. On the basis of REE patterns,
the sediments are divided into two compositional groups. The Type
1 sediments have a REE chemistry similar to the upper continental
crust, and have been derived from the 3.2 Ga composite peninsular
gneisses occurring in the low-lying, semi-arid Mysore Plateau.The
Type 2 sediments, however, have dominantly intermediate to mafic
granulite contributions from the tectonically uplifted Western
Ghats, weathered under sub-humid conditions. High concentrations
of FeO, TiO2, Cr and Ni in the sediments
suggest mafic-dominated source lithologies in the upper catchment,
a feature also confirmed by field observations and petrographic
study.
Keywords: Small rivers; Sediment; Geochemistry; Granulites; Gneisses;
Southern Indiax
1. Introduction
2. Physiography and climate
3. Geological features and catchment rock types
4. Methodology
@4.1. Sampling
@4.2. Analyses
5. Mineralogy and grain size analyses
6. Geochemistry
@6.1. Major elements
@6.2. Trace elements
@6.3. Rare Earth Elements (REE)
7. Discussion
@7.1. Weathering index and CIA pattern
@7.2. Source rock characteristics
@@7.2.1. Evidence from A-CNK-FM plots
@@7.2.2. Evidence from ferromagnesian transition metals
@@7.2.3. Evidence from Rare Earth Elements (REE)
@@7.2.4. Relative contributions of mafic and felsic sources
8. Concluding remarks
Acknowledgements
References