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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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J. Madhavaraju ¹, S. Ramasamy ¹, S. P. Mohan ¹, S. M. Hussain ¹, N. Gladwin Gnana Asir ¹, V. Stephen Pitchaimani ¹

Affiliations
1 Department of Geology, School of Earth and Atmospheric Sciences, University of Madras, Guindy Campus, Chennai- 600 025, IN

Abstract

Petrography, fluid inclusions and surface texture studies have been carried out on the Nimar Sandstone, which have provided fruittful results on pravenance and depositional environment The detrital omposition of sandstones plotted in the Q-F-L diagram suggests cratonic orrgin The modal percentages of different types of quartz plotted in the diamond diagram Indicate that these sediments were derived from the low-grade metamorphic rocks Quartz grains show randomly distributed primary inclusions, small trails of pseudosecondary inclusions and needle-shaped solid phases also support that the source rocks are mainly low-grade metamorphc rocks The surface textures on quartz grains reveal the presence of twenty-two distinct surface textures Based on their origin, these textures are grouped into three types viz I) thirteen features that show mechanical origin, II) five features that exhibit mechanical and/or chemical origin and III) four features that reveal chemical (precipitational)origin The quartz grans exhibit conchoidal fractures, arcuate steps, and fractured plates/planes, which resulted during the liberation of these grains from the crystalline formations They also exhibipt petransportational features such as pedological overgrowths, silica globules, flower and pellicles, which are indicative of short transportation and rapid deposition of these sediments Vs, straight and curved scratches are more common on the quartz grains from the upper Nimar Sandstone (whtch are characteristic features of marine environment), whereas the lower frequency of these features on the quartz grains from the lower Nimar Sandstone suggest fluvia depositional environments.

Keywords

Petrography, Quartz grains, Fluid inclusion, Surface textures, Nimar Sandstone, Provenance, Depositional environment, Bagh Beds, Madhya Pradesh.

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J. Madhavaraju ¹, H. J. Hansen ², S. Ramasamy ¹, S. P. Mohan ¹

Affiliations
1 Department of Geology, School of Earth and Atmospheric sciences, University of Madras. Gundy Campus, Chennai 600025, IN
2 Geological lnstitute, University of Copenhagen, Oster Volgade 10, Copenhagen, DK

Abstract

The present study reports the magnetic susceptibility study of Late Maastrichtian sediments (Kallamedu Formation) of Anyalur Group The Nimyur section exhibits two types of susceptIbility pattern Ie C-zero and C4 The susceptibility pattern of this sectIon fits well with the patterns observed In the mterval of Upper Cretaceous part of the reversed interval (29R) The K/T boundary has been fixed above the C-zero peak 10 most of the studied sections around the world We suggest that the K/T boundary should be placed above the Nimyur section, based on the characteristicc magnetic susceptibility pattern.

Keywords

Magnetic susceptibility, Late Maastrichtian, Kallamedu Formation, Anyalur Group, Tamil Nadu.

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J. Madhavaraju ¹, S. Ramasamy ¹, S. P. Mohan ¹, N. Gladwin Gnana Asir ¹

Affiliations
1 Department of Geology, School of Earth and Atmospheric Sciences, University of Madras, Guindy Campus, Chennai 600 025, IN

Abstract

An ooid-rich limestone band of Sillakkudi Formation is encountered in a well section near Ariyalur. The ooids are believed to be deposited in a marine regime. They contain berthierine as the major mineral and haematite, siderite and quartz as minor minerals. They exhibit alternate rings of berthierine and haematite which shows that these minerals were developed under changing physico-chemical conditions. In the present paper, the petrographical characters, mineralogy, origin and depositional environment of the ooids are discussed.

Keywords

Ooids, Berthierine, Sillakkudi Formation, Depositional Environment, Ariyalur, Tamil Nadu.

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P. Chowdappa ¹, V. Sridhar ², P. V. R. Reddy ², S. Sriram ², S. P. Mohan ²

Affiliations
1 ICAR-Central Plantation Crops Research Institute, Kasaragod 571 124, IN
2 ICAR-Indian Institute of Horticultural Research, Bengaluru 560 089, IN

Abstract

Stramenopile pathogens of the genus Phytophthora cause devastating diseases on a wide range of agricultural and horticultural crops, natural vegetation and forestry worldwide. There are over 140 species in the genus and many have wide host range.

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