Tipam Group in the Subsurface of Upper Assam Valley, South of Brahmaputra

The Tipam group in the subsurface of Upper Assam valley is discussed in this paper. The group is divisible into four formations in'ascending order: the Geleki sandstone, the Lakwa clay, the Nazira sandstone, and the Girujan clay. Within the Geleki sandstone a basal member, the Safrai, and Teok sandstone member within the Girujan clay are mappable. These rock-stratigraphic units are systematically described. The group unconformably overlies the Barail group, and is overlain unconformably by the Namsang formation. The problem of the Surma group in the area is discussed and it is concluded that this group is not developed here. Its age equivalents form a part of the Geleki sandstone. The age of the Tipam group ranges from Middle Miocene to Pliocene. The present subcrop Tipam rocks were formed by fluvial processes in an intermountain continental basin. Commercial accumulation of oil in these rocks and older formations has fed to extensive deep drilling which provided data for the present study.