On the Occurrence and Origin of Concretions in Upper Tertiary Sediments of North Tripura

Concretions of varying composition and nature occur in large numbers in the upper Tertiary rocks of North Tripura. The different types of concretions can be broadly grouped into three classes. The iron oxide concretions in the ferruginous Tipam sandstones, calcareous concretions in the Boka Bil shales and siltstones and the sand coated calcareous concretionary boulders of the Bhuban sandstones. Field observations indicate both syngenetic and epigenetic origin for calcareous concretions but the ovoidal iron oxide concretions appear to have originated by oxidation.