The Neyveli lignite deposits (Cauvery basin), India: organic composition, age and depositional pattern

Abstract

The palynological, particulate organic material (palynodebris) and biopetrological aspects of the main lignite seam encountered in NLE-27, NLE-35 and NLE-36 borehole sections in mine III of the Neyveli lignite field of the Cauvery basin were investigated. The palynoflora is rich in angiospermic pollen (79.6%) distributed in 33 genera ( and 86 species). Pteridophytic (spores) representation is only 20.4% with 5 genera (and 9 species). Quantitatively, palynofossil assemblage of the seam from mine III resembles fairly well with those from the mines I and II. Based on geological, geophysical and palynological data the lignite seam has been assigned a Miocene age. The lignite seam has a very high proportion of structured terrestrial organic matter (OM) with a subordinate amount of biodegraded terrestrial, fungal and amorphous materials, in addition to resin. Petrologically, the seam is rich in the huminite group of macerals, usually dominated by attrinite, densinite (humodetrinite) macerals. Botryococcus is common, as are framboidal pyrite and concretions. The seam in mine III is lower in rank ( R o max 0.39%) than its counterpart in mine I ( R o max. 0.47%). From a critical assessment of the palynological, palynodebris and biopetrological data, together with published geological information, it is assumed that the main lignite seam was formed from in situ mangrove-mixed moist tropical forests vegetation, probably in a lagoon on a prograding delta with freshwater inlets from the western and restricted seawater channels from the east.