Neyveli lignites and associated sediments-their palynology, palaeoecology, correlation and age

Abstract

The Neyveli Formation is a subsurface stratigraphic unit, containing thick workable lignite deposits at its top, and is unconformably overlain by the Cuddalore Formation. The age of the lignite has remained a subject of controversy and therefore effort has been made here to date it by means of palynological evidence. Rich palynofloras have been recorded from the Neyveli Formation encountered in the Neyveli Mines-I and II in South Arcot District and Jayamkondacholapuram well-12 in Tiruchirapalli District, Tamil Nadu. These assemblages contain pteridophytic spores, angiospermous pollen and algal and fungal remains with angiospermous pollen being predominant. Based on the present day distribution and habitat of the families represented, a tropical climate with plenty of rainfall has been inferred during the sedimentation of the Neyveli Formation. The environment of deposition for these sediments has been deduced as coastal, ranging from back mangrove to mangrove, with a short transgressive phase before the deposition of lignite. The Neyveli Formation is divisible into three biozones, viz., Neocouperipollis spp. Cenozone, Triangulorites bellus Cenozone, and Trilatiporites sellingii Cenozone. These are identifiable by their characteristic significant and restricted palynotaxa and correlatable with the Late Palaeocene to Middle Eocene biozones of Kutch, Rajasthan, Bengal Basin, Garo, Khasi and Jaintia Hills of Meghalaya and Cauvery Basin. A Late Palaeocene to Middle Eocene age has therefore been assigned to the Neyveli Formation.