Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

A. S. M. Woobaidullah ¹, K. M. Ahmed ¹, M. A. Hasan ¹, M. K. Hasan ²

Affiliations
1 Department of Geology, University of Dhaka, Dhaka 1000, BD
2 Dept. of Geological Sciences, University College, London, Gower Street London, WCIE 6BT, GB

Abstract

The study area is dependent on ground water for irrigation during the dry months of the year as sufficient surface water resources are not available. Occurrence of saline ground water in some parts of the area, particularly at Kashopara and Kasab unions. restricts the use of ground water for irrigation purposes. Ground water electrolytic conductivity (EC) monitoring and resistivity sounding show a distinct vertical ground water zoning with varying salinity, viz .. an upper zone (0-30 m) of relatively fresh Na/CaHCO₃-type ground water with EC values <1000 μS/cm and a lower zone (below 30 m) of NaCI-type (brackish) ground water with EC values >2000 μS/cm. It is suggested that salinity prohlems in the affected area can be managed through minimum abstraction of saline ground water, proper selection of crops, land development and by changing methods of irrigation.

Keywords

Hydrogeology, Ground Water, Salinity, Ground Water Management, Bangladesh.

Full Text

     

A. S. M. Woobaidullah ¹, Shahid Hossain Chowdhury ¹, K. Matin Ahmed ¹, Mohammad Wahidur Rahman ¹, Khandker Sadia Arafin ¹, Obaidullah Al-Ejaz ²

Affiliations
1 Department of Geology, Dhaka University, Dhaka 1000, BD
2 Cairn Energy Companies in Bangladesh (CEEiB), BD

Abstract

The study area, located in the middle part of Chandpur district, Bangladesh, belongs to Meghna floodplain region. The shallow aquifer in the area is highly contaminated. Eight vertical electrical soundings using Schlumberger configuration with spreading of 800 m (AB/2 = 400 m) were conducted. The geophysical model exhibits three distinct ranges of resistivity zones: low (4.0 to 11.90 Ωm), moderate (13.0 to 58.0 Ωm) and variable (10.3 to 75.0 Ωm). Geological interpretation reflects anomalous resistivity for topsoil horizon, moderate resistivity for the fresh water bearing sandy materials and low resistivity for the saline water bearing sands or clay. Physico-chemical analysis of groundwater samples shows pH in the range of 6 to 9, EC values 1169 to 4330 μs/cm for the shallow aquifer (20 to 77 m), and 367 to 3820 μs/cm for deep aquifer (198 to 260 m); changing of water quality with depth and higher concentration of sodium and chloride in the shallow aquifer than in the deep aquifer. Hydrochemical facies analysis shows the water of shallow aquifer is NaCl type and that of deep aquifer Ca-Mg-HCO₃ type.

Keywords

Geo-Electric, Resistivity Survey, Hydrogeology, Groundwater, Bangladesh.

Full Text

     

Bidhan Chandra Mandal ¹, A. S. M. Woobaidullah ²

Affiliations
1 Geological Survey of Bangladesh, 153 Pioneer Road, Shegunbagicha, Dhaka 1000, BD
2 Department of Geology, University of Dhaka, Dhaka 1000, BD

Abstract

Depositional history and tectonic evolution of the Bengal Basin commenced with the collision between Asia and Greater India in Late Paleocene (55 Ma). Sedimentation within the basin was activated during the Eocene in response to the simultaneous collision of the Indian and Burmese plates in the east and the Indian and Tibetan plate in the north. The dominant compressional force for development of the eastern fold belt resulted from subduction of the Indian plate beneath the Burmese plate in eastern part of the basin. From Miocene onward, the Indian plate has been subducting beneath the Burmese plate with a counter clockwise rotational movement, while the Burmese plate was overriding the ' Indian plate with a clockwise rotation. Consequently, the overall trend of folded structures varies from NNW in the southern part to NNE in the northern part of the eastern fold belt. This variation in structural style along with the presence of longitudinal thrust faults and transverse faults suggests that the Indian plate initially pushed towards east and then turned northeastward during the Cenozoic. Structural style of the eastern fold belt is characterized by the presence of a series of elongated en-Echelon folds, which are tight and steep in the east, while towards the west they tend to be gentler and box shaped. Presence of longitudinal and cross faults along most of the folds suggests their hybrid origin. In seismic sections these faults appear to be heterogeneous in nature; and are believed to represent different time domain of their formation. Analysis of the stratigraphic succession in seismic profiles of selected structures suggests a close relationship between sedimentation style and tectonic framework within the eastern fold belt. Occurrence of overpressure zones in the lower Surma Group is believed to be primarily due to undercompaction caused by rapid accumulation of fine-Grained clastics and not tectonic deformation. Interpretation of seismic data and comparison of subsurface structural depth contour maps of different horizons reveals heterogeneous flexuring rates. The westward shift of the culminations and closures of different horizons from bottom to top reflects the imprints of time variant evolution of the folded structures. Hence it is thought that intensity and direction of the tectonic force responsible for development of compressional deformations within eastern fold belt of the Bengal Basin was time variant and contemporaneous with sedimentation.

Keywords

Sedimentary Tectonics, Subduction, Eastern Fold Belt, Surma Group, Bengal Basin, Bangladesh.

Full Text