Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

D. Bakkiaraj ¹, R. Nagendra ¹, R. Nagarajan ², John S. Armstrong-Altrin ³

Affiliations
1 Department of Geology, Anna University, Chennai - 600 025, IN
2 Department of Applied Geology, School of Engineering and Science, Curtin University, CDT 250, 98009, Miri, Sarawak, MY
3 Unidad Academica de Geologia Marina y Ambiental, Instituto de Ciencias del Mar y Limnologia, Universidad Nacional Autonoma de Mexico, Mexico D.F., C.P. 04510, MX

Abstract

Major, trace and rare earth elements (REE) composition of sandstones from the Upper Cretaceous Sillakkudi Formation, Ariyalur Group, Cauvery Basin were studied to decipher their weathering and provenance history. Texturally, these sandstones are immature, poorly sorted and grain supported. Abundance of feldspars especially, plagioclase indicates rapid deposition of sediments from a nearby source rocks. Using the geochemical classification diagram the Sillakkudi sandstones are classified as fe-sand, quartz arenite, litharenite, sub-litharenite, sub-arkose, arkose, and wacke types, which is also supported by the petrography study. The transition trace elements like Co, Ni, and V are higher in the Sillakkudi sandstones than upper continental crust (UCC) values. However, the Sillakkudi sandstones are lower in Cr (mean ∼21) content than average UCC value (∼35). The poor correlation between Cr and Ni (r = 0.08, number of samples n = 20) imply that these sandstones were derived from felsic source rocks. Similarly, the Eu/Eu* (0.35-1.73), La/Sc (1.93-9.36), Th/Sc (0.41-6.57), Th/Co (0.14-5.01), Th/Cr (0.23-2.94), and Cr/Th (0.34-4.28) ratios support a felsic source for the Sillakkudi sandstones. The significant enrichment of Zr, Hf, and Th in fe-sand, sub-arkose and litharenite could be related to the presence of heavy minerals, especially zircon. However, the zircon geochemistry did not affect the REE distribution and its patterns in the Sillakkudi sandstones. The Chondrite normalized REE patterns of Sillakkudi sandstones are characterized by relatively flat HREE (Gd/Yb_CN = ∼0.73-2.41; subscript _CN refers to chondrite normalized value), enriched LREE (La/Sm_CN = ∼3.39-5.82) and negative Eu anomaly (mean value Eu/Eu* = 0.80). The Gd/Yb_CN ratios (∼0.73-2.50) are less than 2.5, which suggest that these Sillakkudi sandstones were derived from the less HREE depleted source rocks. The comparison of REE patterns and its Eu anomalies to the source rocks reveals that the Sillakkudi sandstones received a major contribution of sediments from Dharwar craton.

Keywords

Geochemistry, Zircon, Sandstones, Upper Cretaceous, Sillakkudi, Cauvery Basin.

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