GRAVITY AND COMPOSITIONAL STUDY FOR RECONSTRUCTION OF LATE PALEOZOIC INTRA-CRATONIC GONDWANAN BASINS OF NORTHWEST BENGAL BASIN, BANGLADESH

Permo-Carboniferous Gondwanan sequences have been reported from several isolated basins of the Peninsular India. These siliciclastic sequences were preserved in several intracratonic basins in the northwest Bangladesh, which were encountered in wells, drilled in northwestern Bangladesh, adjacent to the Indian craton. In this study, we have used the gravity data to understand the distribution of these intracratonic basins along with the sedimentary records from few selected wells located at Barapukuria and Khalashpir area.

The land gravity data used in this study were downloaded from Bureau of Gravimetrique International (BGI). This data is based on the World Gravity Map (WGM2012) project. The data were located between 87.5° to 93° E longitude and 20° to 27° N latitude. For this study, we have analyzed Bouguer and Free Air gravity maps that show an increased value in the northwestern part of Bangladesh. Overall, the entire map within Bangladesh varies between ~20 – 100 MGal and -40 – 20 MGal for the Bouguer and Free Air anomaly maps, respectively. In contrast, a sharp increase in these values were observed in the northwestern part where the Gondwanan rocks and Precambrian basement were reported at shallower depths in the wells drilled for various purposes such as coal or hard rock mining. This gravity high is disconnected from the rest of country by a gravity low towards southeast. Cross-sectional profiles suggest a sharp variation in density from east to west and/or from northwest to southeast, which suggests a shallower basement in the northwestern platform area. This is also characterized by the sharp decrease of the Bouguer and Free Air anomaly, which may reflect the increase in depth due to normal fault bounded half-graben structures.

Sandstone petrography and detrital geochronology from drill well samples at selected depths suggest an immature arkosic sandstones sourced primarily from Ordovician to Cambrian rocks. Current study will help to better understand the distribution of normal fault bounded graben structures in northwest Bangladesh, which could farther be applied to explore the economic resources associated with these structures.