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

J. Madhavaraju ¹, S. M. Hussain ², M. Guruvappan ², S. Ramaswamy ², S. P. Mohan ²

Affiliations
1 Estacion Regional del Noroeste, Institute de Geologia, Universidad Nacional Autonoma de Mexrco, Hermosillo, Sonora - 83000, MX
2 Department of Geology, School of Earth and Atmospheric Sciences, University of Madras, Guindy Campus, Chennai - 600 025, IN

Abstract

The lower Niriyur Formation of Cauvery Basin is well exposed in the Periyakurichi area. The lower Niriyur Formation exhibits three carbonate petrographic types viz wackestone, packstone and boundstone whereas clastic rocks are represented by arenite and wacke types. The clastic rocks of Niriyur Formation exhibit microgranular calcite cement and fossils namely algae, bryozoa and molluses which suggest that these sediments were deposited under shallow marine environment. The carbonate rocks of Niriyur Formation contain the rich fossil assemblages composing algae, forarmnifera, ostracodes and mollusks. An attempt has been made to study the carapace-valve ratio of ostracod fauna which suggests the slow rate of sedimentation in the basin. The occurrence of Sporolithon-Rich flora together with forarmnifera has been found to be characteristic of depth range 20-40 m. The outcrop sequence stratigraphic study of the lower Niriyur Formation shows two sequence boundaries, Transgressive Systems Tract (eight shallowing upward parasequences), Maximum Flooding Surface and Highstand Systems Tract. The lower Niriyur Formation of Ariyalur area is represented by mixed clastic and carbonate rocks showing shallowing upward metre scale parasequences, which represent the subtidal cycles.

Keywords

Petrography, Sequence Stratigraphy, Parasequences, Depositional Environments, Niriyur Formation, Cauvery Basin, Tamil Nadu.

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