『Abstract
Petrographic and geochemical data on the sandstones of the Proterozoic
intracratonic Kaladgi-Badami basin, southern India are presented
to elucidate the palaeoweathering pattern, and composition and
tectonics of their provenance. The Kaladgi-Badami basin, hosting
the Kaladgi Supergroup, occupies an E-W trending area. The supergroup
unconformably overlies Archean basement TTG gneisses, granites
and greenstones, comprises a cyclic arenite-pelite-carbonate association
and is divided into the Bagalkot and Badami Groups. The immature
arkosic character of the basal Saundatti Quartzite Member (Bagalkot
Group) containing fresh and angular feldspars, along the northern
margin of the basin, suggests that during the initial stage of
deposition, this part of the basin received sediments from a restricted,
uplifted and less weathered source dominated by K-rich granites
occurring to the north. In contrast, the Saundatti Quartzite along
the southern margin displays a mostly mature, quartz-rich character
with less abundant but severely weathered feldspars, and higher
SiO2 and CIA but lower Al2O3, TiO2, Rb, Sr, Ba, K2O, K2O/Na2O,
Zr/Ni and Zr/Cr. This is interpreted in terms of a tectonically
stable, considerably weathered mixed source (Archean gneisses,
granites and greenstones) along the southern fringe of the basin.
The highly mature (quartz arenite) Muchkundi Quartzite Member
(also of the Bagalkot Group), occurring higher up in the succession,
exhibits minor but severely altered feldspars, and higher SiO2, Na2O, CIA, Cr and Ni with
lower K2O, Al2O3, TiO2 and K2O/Na2O. This reflects that with the passage of time
the source evolved to a uniform, extensively weathered, tectonically
stable peneplained provenance which consisted of less evolved
TTG gneisses and greenstones. This was followed by closure, deformation
and upliftment of the basin hosting the Bagalkot Group and subsequent
deposition of the Badami Group. Sandstone Members of this younger
Group (Cave-Temple Arenite and Belikhindi Arenite) range widely
in mineralogy (quartz arenite to arkose) band chemistry (including
CIA), and point to a source that varied from uplifted, less weathered
K-rich granites to less evolved, peneplained TTG gneisses and
greenstones or even Bagalkot sediments. Variable alteration of
feldspars in the Kaladgi sandstones and severe depletion of Ca,
Na and Sr in the associated shales indicate a humid tropical (tropical
and subtropical) climate facilitating chemical weathering.
Keywords: Kaladgo-Badami basin; Petrography; Geochemistry; Sandstone;
Palaeoweathering; Provenance; Tectonics』
1. Introduction
2. Geology of the Kaladgi-Badami basin
3. Methodology
4. Petrography
4.1. Saundatti Quartzite
4.2. Muchkundi Quartz
4.3. Cave-Temple Arenite
4.4. Belikhindi Arenite
5. Geochemistry
6. Discussion
6.1. Source
6.2. Palaeoweathering and palaeoclimate
6.3. Provenance tectonics and basin evolution
7. Conclusions
Acknowledgements
References