Gondwana Type of formation with Phosphatic Rocks in S.E. Nepal

A new Formation called the Barahakshetra Formation is recognised in Southeastern Nepal. It is separated from the Siwaliks (Tertiary) to the south by the MBT and has a tectonic contact with the Sanguri Formation (Lower Palaeozoic ?) and the Metamorphic Series (Precambrian ?) to the north.

The basal part of the Formation is marine with radiolaria, glauconite and with a penecontemporaneous trachyte-keratophyre volcanism. A glacio-marine episode is represented by the pebbly shales in the eastern part of the basin. The continental character and the regressive nature of the upper part of the Formation is indicated by the detrital materials with coal and plant fossils. The sediments were deposited in a epicontinental basin of paralic type. Littoral zones (intertidal-supratidal) are indicated by many sedimentary features.

The volcanic sandstones and the conglomerates of the region are feebly phosphatic. The Barahakshetra Formation is compared with corresponding units of the Gondwana Formations of the Himalaya. It is noticed that lithostratigraphically the Barahakshetra Formation is similar to that of Darjeeling-Sikkim area. The Gondwana affinity is confirmed by the presence of plant fossils. The geological significance of this Formation is discussed.