Palaeo-environmental study in Bhuban formation, Aizawl, Mizoram, India

Abstract:

The aim of the study is to determine depositional environment in Bhuban formation of Surma group in Aizawl, Mizoram, India by using microfossils. Mizoram is situated within the Indo-Burmese ranges and located in the norteastern part of India. This report includes results of a study of the fossiliferous carbonate band of a thick siliciclastic succession of nearshore deposits selected as the Upper Bhuban unit of the Bhuban Formation - the Surma Group (early-middle Miocene age) in Mizoram. Ammonia beccari, Operculina aff. O. complata, Elphidium sp. and Miogypsina sp. are benthic in nature and the planktic forms are Globigerinoides sp., Globigerinoides trilobus (Reuss), Globigerinoides subquadratus Bronnimann, Globigerinoides sp., recrystallized Globigerina spp. and Globigerina bulloides d’Orbigny. Among the benthic forms, the stratigraphically important species is Miogypsina sp., represented by an axial section which does not allow identification up to species level. Presence of this genus is indicative of early Miocene age of the upper bhuban formation in Mizoram. Planktic foraminifers indicated an influence of an open sea. These occur in near shore environments and can tolerate influx of clastic material. Benthic form of Miogypsina prefers relatively deeper environment and can live in waters associated with clastic material. Several shell fragments show micro borings are also observed in Bhuban rocks. These features indicate mechanical reworking of shells by waves and currents, slow rate of deposition and some hard ground-like characteristics. Micropalaeontological studies suggest that the Upper Bhuban rocks were deposited in the near shore environment with high energy conditions under the influence of open sea conditions.