The Earliest Marine Transgression in Western India:New Insights from Calcareous Nannofossils from Lathi Formation, Jaisalmer Basin

We report the first record of an age-diagnostic, but depauperate assemblage of calcareous nannofossils, an exclusively marine phytoplankton group, from the Lathi Formation of Jaisalmer Basin, western India. The nannofossil evidence, precisely constrains the age of the Lathi Formation, traditionally considered to be a Bajocian (Middle Jurassic) continental deposit. Furthermore, the presence of several reworked nannofossil taxa of Pliensbachian, Toarcian and Aalenian ages suggests that the earliest epeiric sea transgressed western India during the Early Jurassic. Thick and luxuriant gymnosperm forests proliferated in the Jaisalmer Basin during this time. The presence of calcareous nannofossils in both the lower and upper members of the Lathi Formation (Odania and Thaiat members) points to intermittent coastal marine depositional environment.