Mesoproterozoic surface process, weathering condition and climate: an insight from siliciclastic sedimentary rocks of the Badami group, Karnataka India

• Published in: Journal of Sedimentary Environments 2022-09, Vol.7 (3), p.579-602
• Main Authors: Hegde, Venkatraman S, Sreenivas, Bulusu, Havannavar, Girish, Hanamgond, Pramod T., Pratihari, Asim Ranjan, Hulaji, Shivani, Shalini, G.
• Format: Article
• Language: English
• Subjects: cities; Earth and Environmental Science; Earth Sciences; Environment; Evolutionary Biology; Geography; Original Article; Sedimentology; towns; Urban Geography; Urbanism (inc. megacities
• ISSN: 2662-5571; 2447-9462
• DOI: 10.1007/s43217-022-00109-3

Both, glaciations and deep chemical weathering implying cold and warm climate, respectively, were reported from Mesoproterozoic sedimentary cover, hence Mesoproterozoic climate is enigma. Mesoproterozoic subarkosic siliciclastic sedimentary rocks from the western margin of the Kaladgi–Badami basin in Karnataka, covering parts of Deshnur, Gokak, Ramdurg and Sogal are studied in this paper to understand their provenance, palaeoweathering condition and Mesoproterozoic surface process. The rocks are medium to coarse grained, moderately well rounded, consisting of dominantly quartz and subordinate amounts of feldspar. Rock fragments in them include quartzite, chert, banded-iron formation and granite. Heavy mineral assemblage consisting of zircon, monazite, sphene and tourmaline suggests granitic source. Geochemically, they are subarkosic in composition, matured (Al 2 O 3 /Na 2 O–17–49). They are characterized by negative Eu/Eu* (0.17–0.3), moderately to less fractionated REE pattern (La N /Yb N , 1–9); fractionated Cr/Ni (2–12); Cu/Zn (06–60) and low abundance of Rb, Sr and Ba (average 4, 7 and 20 mg kg −1 , respectively). Their chemical indices of weathering (CIW) and plagioclase index of weathering (PIA) range between 74–91 and 57–83, respectively. The rocks show on an average 19–30% increase in K 2 O due to K metasomatism. Integration of petrographic and geochemical composition followed by mixing calculation indicated a source consisting of 65% granite, 20% tonalite–trondhjemite–granodiorite (TTG), 5% each mafic, banded-iron formation (BIF) and quartzite. Sediments were derived from locally uplifted, moderately weathered source terrain and deposited in a passive margin coastal environment. The study indicated that Mesoproterozoic surface condition in South India was dominated by CO 2 rich, anoxic, humid climate, and land surface free from vegetation.