Katihar Fm

Holo: Karandighi-1, Latitude 24o 40' 53" N, Longitude 87o 55' 15" E, Drilled depth: 3143 m. The top of the formation is at 1635 m and bottom at 2425 m (Shukla et al., 1993).

Sandstone, claystone and Coal. This unit is composed of alternation of sandstone, shale and coal in the type area while towards north siltstone is also present. In the upper part of the section, the coals are usually less than 1 m thick whereas in the lower part thicker sandstone and coal appears. Sandstone is white to buff colored, mostly medium to coarse grained and poorly sorted. These sandstones are relatively more feldspathic than the Dinajpur Formation sandstones and composed 65% quartz, 30% feldspar and 5% monocrystalline. Feldspars (both microcline and orthoclase) are much altered with frequent replacement of kaolinite by calcite grains. The rock fragments are mostly granitic with quartzite and claystone fragments. Matrix is usually silty and clayey. Cementing material is often calcareous and cherty. Carbonaceous shale is black, hard, compact, fissile and micaceous. The siltstone (north of the type area) is dark colored, hard, compact, micaceous and non-calcareous. Coal is dull black, sub-bituminous to bituminous and moderately hard with vitrinite bands. The coals range in thick from .5 to 2.5 m with an average thick of .8 m. A total number of 35 coal seams were identified which are mostly concentrated in the lower part. Cummulative thickness of the coal is 27.5 m and coal to non-coal ration is 1:27. Thickness of the Katihar Fm ranges between 400 m to 790 m with a decrease in thick towards north.

The palynoflora comprises of Leiotrilletes sp., Ver ticipollenites sp., Scheuringipollenites sp., Sahnites sp. and Faunipollenites sp.