Sitakunda Upazila - Geology

Geology

The geological structure of Sitakunda, 70 kilometres (43 mi) long and 10 kilometres (6 mi) wide, is one of the westernmost structures of Chittagong and Chittagong Hill Tracts, delimited by the Feni River in the north, the Karnaphuli River in the south, the Halda River in the east and the Sandwip Channel in the west. The Sitakunda Range acts as a water divide between the Halda Valley and the Sandwip Channel. The 88 kilometres (55 mi) -long Halda flows from Khagrachari to the Bay of Bangal, and is one of the six tributaries of Karnafuli, the major river in the area. Sandwip Channel represents the northern end of the western part of the Chittagong-Tripura Folded Belt.

The structure contains a thick sedimentary sequence of sandstone, shale and siltstone. The exposed sedimentary rock sequences except limestone, 6,500 metres (21,325 ft) thick in an average, provide no difference in overall lithology of Chittagong and Chittagong Hill Tracts. The Sitakunda fold is an elongated, asymmetrical, box-type double plunging anticline. Both the gently dipping eastern and steeper western flanks of the anticline are truncated abruptly by the alluvial plain of the Feni River. For a lack of infrastructure in Bangladesh, this anticline is one of the few regularly surveyed structures in the country. The syncline from Sitakunda separates the eastern end of the Feni Structure located in the folded flank of the Bengal Foredeep.

Local experts consider the Sitakunda–Teknaf fault to be one of the two most active seismic faults in Bangladesh. After the earthquake of 2 April 1762, which caused a permanent submergence of 155.4 square kilometres (60.0 sq mi) of land near Chittagong and the death of 500 people in Dhaka, two volcanoes are said to have opened in the Sitakunda hills. During a seismic tremor on 7 November 2007, fire broke out at the Bakharabad Gas Systems Limited in the Faujderhat area of the upazila when a pipeline was fractured. The Girujan Clay Formation runs through Sitakunda at a thickness of 168 metres (551 ft). In the Sitakunda hills, the Boka Bil Shale Formation contains Ostrea digitalina, Ostrea gryphoides and numerous plates of Balanus (a type of Barnacles), fragments of Arca, Pecten, Trochus, Oliva and corals. Both formations were identified and named by early 20th-century British petroleum geologist P. Evans.