Mahasthangarh, Physical Setup

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Mahasthangarh, Physical Setup so far the oldest archaeological site of Bangladesh, lies on the western bank of river karatoya, about 12 km north of Bogra town, and is connected by a good metalled road. The site includes partly shibganj and partly bogra sadar upazilas of bogra district and lies between latitudes 24'50'N and 25'0'N and longitudes 89'15'E and 89'30'E. The spectacular site is an imposing landmark in the area, having a fortified, oblong enclosure measuring 1524m by 1370m with an average height of 5m from the surrounding paddyfields.

Climate characterised by tropical monsoon climate, with the bulk of rainfall occurring between May and October. Considering the variations in temperature, pressure and precipitation, the site can be included within the climatic sub-zone of hot summer and moderate rainfall. The annual precipitation in the area decreases from east to west. The maximum temperature ranges from 37'C to 39'C whereas the minimum temperature varies from 7'C to 10'C.

Soil about 60% of the soil is composed of semi-consolidated older Madhupur Clay, which forms the Barind and Lalmai terraces. The remainder of the soil is developed in unconsolidated recent and subrecent alluvial deposits laid down by the rivers bangali and Karatoya.

Agriculture most of the area is under cultivation, but natural vegetation remains in several small areas. Mixed forest, scrub and replanted Gajari and Shal (Shorea robusta) occupy patchy areas of the higher ridges of Barind and Lalmai terraces. Floodplain soils were probably covered with grassland. crops are grown almost everywhere and farming practices have strongly influenced the present vegetation. Approximately 10% of the area are triple cropped, 38% double cropped and 40% single cropped. Grassland and barren lands together occupy about 2 percent whereas settlements, water bodies and rivers constitute about 10%. The present landuse is mainly determined by elevation of the land in relation to the duration and depth of seasonal flooding and by the availability of soil moisture in the dry season. rice, mainly aus' [aush] and transplanted aman' [aman], is by far the most extensive crop. In the floodplains, where the land is only shallowly flooded or water can be kept on the land by artificial field bunds, farmers grow aus followed by transplanted aman. Man-made platforms and homestead areas are used for vegetables, bananas, fruit trees, Pan (Betel leaf) and seedbed for aman rice.

Topography and relief it stands on the red bed barind tract that comprises slightly elevated landform terraces within the alluvium. These areas are higher in elevation than the surrounding flat plains and form a distinct, relatively flood free physiographic unit. The elevation of the Mahasthangarh ranges from 15m to 25m. The ridge tops in between the valleys are almost level and the valley sides and floors have been closely terraced for cultivation.

Drainage the Pleistocene (2 to 0.1 million years ago) the archaeological sites of Mahasthangarh and paharpur stand on Barind Tract, is well drained by numerous small, entrenched, meandering streams and rivers. The western Barind is drained by mahananda and punarbhaba rivers and their numerous tributaries that discharge into the padma towards the south. The middle and eastern Barind is drained by two major rivers, atrai and Karatoya discharging into the mighty jamuna river to the southeast. The Punarbhaba, Atrai and Old Jamuna rivers have cut across the Pleistocene Barind Terrace. Most of the small streams of the Barind areas are seasonal and are fed by monsoon season. The major rivers are perennial, shallow and narrow during the dry season and overflooded with water during the monsoon season.

In the Mahasthangarh, Karatoya is the major river that passes near the eastern margin and flows towards the south. Three small rivers (ichamati, bangali and nagar) are around the Mahasthangarh. East of the Mahasthangarh, the Bangali and Ichamati rivers flow southeast. The Nagar located in the west flows southwest. Many swampy areas, locally known as beels, are also found around the area.

Landform units broadly speaking, the Mahasthangarh of Bogra district can be conveniently subdivided into two landform units: (1) Barind terrace and (2) Karatoya-Bangali meander floodplain.

Barind terrace situated west of the Karatoya river. This unit represents a series of uplifted blocks of Madhupur Clay, believed to be equivalent in age to the Pleistocene. The greater part of the Barind Tract is undissected and has poorly drained grey soils overlying clay at a shallow depth. Only a few minor rivers cross this almost level area. Two sub-units of the Barind Tracts are: (i) Nearly level Barind Tract, and (ii) Broad dissected Barind Tract.

The nearly level Barind Tract occupies the western part of Bogra district and comprises a low, nearly level, uplifted terrace. Fault scarps mark the edges of the outcrop. The Karatoya and the little jamuna channels run at the foot of these scarps. The level Barind tract includes grey, variably mottled, less permeable soils overlying the little weathered Madhupur Clay at a shallow depth.

The broad dissected Barind Tract is relatively higher than the remainder of the tract and occurs mostly in the eastern and northeastern part of the Barind Tract. The area has been uplifted, tilted and broadly dissected by valleys, most of which are streamless. It is relatively deeply weathered, and has well to moderately well drained red or brown soils.

Karatoya-Bangali meander floodplain 'a complex landscape containing sediments of diverse ages and origins. Sediments from both the rivers appear to have partially buried an older landscape, which extended up to the lower Tista floodplain. The greater part of this floodplain comprises broad ridges and basins. Silts predominate on the ridges and clays in the basins. Sands occur only patchily on ridges and along river channels.

Geology The archaeological site of Mahasthangarh is situated on the shelf area of Bangladesh. Tectonically, it includes the active Bogra Slope nearest to the hinge zone. Aeromagnetic survey has revealed that the basement is criss-crossed by numerous fault traces. Faults have vertical displacement trending N-S, E-W and NNE-SSW. Only a few of the faults form outcrops, such as Karatoya river fault.

The seismic zoning adopted by the committee of experts on earthquake hazard subdivides the country into three zones. Mahasthangarh lies within zone II where shocks of maximum intensity of VIII and basic seismic coefficient (the number part in front of an algebraic term, signifying multiplication) of 0.05 are suggested. The structural activity of this region is mainly differential vertical movement. The relative displacements along the basement faults have resulted in horst and graben features and the inducement of contrasted relief.

No sediments older than the Pleistocene Madhupur Clay Formation are exposed in Mahasthangarh. However, in the subsurface of the Stable Shelf region including the Bogra slope sedimentary rocks ranging in age from Permian (286 million years to 245 million years ago) to Recent (0.1 million years ago till today) are laid down on the Precambrian basement. [Sifatul Quader Chowdhury]