A Study on Lithology and Petrography of the  Tipam Sandstones Exposed along the Tipong  Pani River Section of Upper Assam Basin

Dr. Pradip Borgohain

Volume : I, Issue : VII, April - 2012

A Study on Lithology and Petrography of the Tipam Sandstones Exposed along the Tipong Pani River Section of Upper Assam Basin

Dr. Pradip Borgohain

Abstract :

The Tipong–Pani river section is on the southern limb of the Namdang Syncline and it exposes most of the Tertiary rock strata. The area of present investigation is situated in the northeastern part of the Tinsukia district of Assam near Tipong Colliery within 27°13N–27020N latitude and 95°30 E–95°55 E longitude. It falls within the Naga Hills ranges, which is a part of the Assam Arakan geological province. The Tipam Sandstone Formation in the study area comprises of sandstones of massive nature with alternation of shale and gritty sandstone at places. They sandstones are medium to fine grained and characterized by typical salt and pepper texture. The bottommost unit shows current bedding and contains carbonized wood. Clay balls are also present in the base of certain sandstone bed. In the lower part of the section, a sandstone unit with gritty nature exhibiting graded bedding and an arenite band containing red coloured jasper are recorded. This band is overlain by about 5.5ft thick conglomerate bed. Graded bedding and arenites are usually not developed in fluvial environment. These facts indicate that this part of the section was not deposited in fluvial environment. Therefore, conglomeratic band in this section may be the base of Tipam Sandstone Formation and the part below the conglomerate band belong to the Surma Group. However, to establish this fact further extensive work need to be done. The presence of prominent current bedding in the Tipam Sandstone Formation indicates that the sediments were deposited under fluviatile environment. The petrographic analysis reveals that the sandstones are mainly quartz dominating followed by feldspar, rock fragments, chert and mica. They are sublithic arenites and lithic–greywacke type and moderate to ill sorted. Various triangular plots indicates that the sediments were derived mainly from recycled orogen sources, tectonically uplifted subduction complexes and crustal collision orogen sources comprising of sedimentary and metasedimentary thrust sheets. Diamond diagram plot also supports this view.