Tectonics Of Madhupur Tract and Lalmai Hill Ranges

English Abstract:

Natural disasters such as floods, landslides, earthquakes etc. are common phenomena in Bangladesh. Each year 6188 peoples die and about $5.5×108 in economic damage occurs due to natural disasters. Thus it is very important to know about the tectonic and geologic settings to understand the causes of the calamities in order to design mitigation strategies.

The north-south elongated Madhupur Tract, exposed at the central part of the country, is an uplifted interfluve of Pleistocene deposits in Bangladesh. Its upper part is the Madhupur Clay with the top silty fine sand layer underlain by Dupi Tila sandstone in the lower part. The en echelonlinear segments on its western margin are known as Madhupur fault. The Bengal earthquake of magnitude M7 is interpreted to have occurred on this fault (see figure). The 1787 earthquake north of the Madhupur tract induced an avulsion of the Brahmaputra River from its Old Brahmaputra course east of the Mudhupur to its present Jamuna River course flowing parallel to the western edge of the tract.

The Lalmai Hill is north­south elongated anticline, 17 km long and 1­2.4 km wide hill. The hill is the westernmost exposed anticline of the Indo-Burma foldbelt, the subaerial accretionary prism of the subduction of India beneath the Burma microplate. In the exposed hill, the capping are reddish­brown deposits, also called the Madhupur Clay of Pleistocene age, underlain by the Dupi Tila Formation of Plio­Pleistocene age. The boundary between Madhupur Clay and Dupi Tila Formation is characterized by a gravel bed, called Quartz Chalcedony Gravel Bed.

Madhupur Tract and Lalamai Hill Ranges both expose the same Pleistocene deposits. Most parts of Holocene strata are contaminated with arsenic, while the Pleistocene is low arsenic. The LGMP (Last Glacial Maximum Palaeosol) clay often acts as a barrier to flow arsenic in aquifers. We will present additional data from buried sections Lalmai Hill to establish whether the LGMP clay is continuous of breached across the truncated parts of the anticline. Already collected data from the Madhupur Tract shows an abrupt edge of the Holocene strata against the Madhupur Tract at the linear features. This research will search the best correlation between the two upland areas in lithology, tectonics, structural settings and relative age difference of their uplift.