Correlation of the tertiary geosynclinal sediments of the Surma Valley,Assam, and Tripura State (India)

The Tertiary geosynclinal sediments of the Surma Valley and Tripura State range in age from Eocene to Mio-Pliocene. They are classified into those of the Disang, Barail, Surma and Tipam groups which respectively represent sediments belonging to geosynclinal, flysch, early molasse and late molasse stages. These sediments are devoid of diagnostic and persistent faunal and palynological assemblages. Frequent lithofacial variations render lithologic criteria unsuitable for regional correlation. Heavy-mineral suites, however, appear diagnostic and they, along with lithologic criteria, can be utilised for local and regional correlations.The mode of evolution of the heavy-mineral suites is discussed. Appearance of marker heavy minerals in successively younger sequences is concluded to be a reflection of successive cycles of positive tectonism in the provenance. The study brings out that the bulk of the sediments were derived from the Shillong Plateau. Contributions from older sedimentaries are also concluded.