Palynostratigraphy of the sedimentary formations of Assam, India:4. Age of the laitryngew-mawkma coal-bearing sandstones and their relationship with the Charra formation

Abstract

The present paper deals with the age of the coal-bearing sandstones of the Laitryngew-Mawkma area and their relationship with the Cherra Formation. Climatic condition and depositional environment at the time of deposition have been summarized. Since Medlicott first distinguished the coal-bearing sandstones of Laitryngew-Mawkma area, the age of these rock units have tacitly been accepted as the “Lakadong Sandstone Stage" (Lower-Middle Eocene). On the basis of stratigraphical similarity, they have been equated with the coal-bearing sandstone of Mawmluh (Lower Cherrapunji; Longitude 91°42'30" E: Latitude 25°15'15"N). Recent palynological and palaeontological studies of the sedimentary formations of the South Shillong Plateau have shown that these coal-bearing sandstones may be slightly older than what they were previously regarded. The results of the heavy mineral studies also seem to conform to palynological dating.

Since these sandstones apparently seem to be older than the Lakadong Sandstone, they may be a continuation of the sedimentary succession developed at Cherrapunji, and hence Palaeocene in age. The fossils suggest the prevalence of subtropical climate and a shallow, fresh-water or lagoonal environment of deposition.