PALAEOENVIRONMENTAL CHANGES DURING EARLY EOCENE: A CASE STUDY FROM BHAVNAGAR LIGNITE MINE, GUJARAT

Abstract

Early Paleogene (55.5-50Ma) consists of several long and short duration global warm events. The geological records of these events are spread all over the globe. India during its northward journey towards Asia, was situated at the equatorial zone during the late Paleocene-early Eocene time span. Western Indian margin encompasses extensive lignite bearing successions of early Paleogene in age. The present study of open cast lignite mine near Bhavnagar, Gujarat helps to understand the palaeoenvironmental and facies architecture during Early Eocene at low latitude. The succession is 28.0 m thick with 5 in thick lignite followed by fossiliferous shale and overlying grey shale. The palynological study reveals abundant organic matter, mangrove pollen, pterodophytic spores, fungat spores and fruiting bodies, foraminiferal test linings and dinoflageltate cysts at specific levels. Combining the palynofacies and lithofacies data, environment of deposition, have been deciphered for Bhavnagar lignite succession. The Bhavnagar lignite sediments were deposited in a low energy coastal marsh- bay complex. Incursion of fresh and marine water along with the sediments derived from weathering and erosion of Deccan traps, controls the facies architecture of Bhavnagar lignite succession. The study reveals following subenvironment in an ascending order ( restricted bay, fresh water marshes, mangrove marshes,tidal creek, open bay etc). The presence of Homotryblium tenuispinosum and few MuratodiniumfImbriatum in the fossiliferous shale horizon suggest Early Ypresian age for the Bhavnagar succession