Geology of The Sitapahar Hill Range, Chittagong, Bangladesh

Author: Syed Ashraful Ferdous

(Copyright Reserved)

A considerable thickness of clastic sediments of Miocene age is exposed on the western flank of Sitapahar Hill Range at Kaptai under the district of Rangamati in Bangladesh. So Kaptai is one of the most important places from the geological point of view. A comprehensive study was undertaken in that area in multidiscipline of geology within a short span of time. Hence, this article includes the gist of the overall geology of Kaptai region; particularly of Sitapahar anticline, where multidisciplinary approaches like geomorphology, stratigraphy, structural geology, and to some extent tectonic behavior of that area are incorporated.

Structurally the Sitapahar Hill Range is situated within the eastern sub-zone of the folded flank of the Arakan-Yoma Geanticlines. This anticline is a plunging and asymmetric one, the axis of which is in the direction NNW-SSE. Other minor structural features include joints; bedding planes, ripple marks etc.

The tectonic evolution of this region ranges from Cretaceous through Tertiary to Quaternary. Sedimentary features found in the area suggest that the deposition took place under shallow marine to continental fluviatile environment.

The study area comprises a continuous succession of sandstone, silt stone, and shale. The rock sections are divided into three lithostratigraphic units, mainly on the basis of gross lithology. These units are equivalent to upper Bhuban, Bokabil, and Alluvium Formations.

Due to the absence of paleontological records in the area, actual age determination of the rocks was not possible. However, from correlation, it is found that the rocks are of Miocene age.

Grain size analysis of the samples ascertains that the sediments were carried in and deposited by river; and transportation occurred mostly by saltation process.

Sandstone, silt stone, and shale of this area are being used for different purposes, which have got economic importance to some extent. The region is supposed to contain oil and gas as some of their traces were found. Hence detail exploration should be accomplished immediately.