Extensional tectonic activity in the cratonward parts (peripheral bulge)
of the Ganga Plain foreland basin, India
Abstract. Flexural subsidence of the
Indian lithosphere created the foreland basin in front of the emerging
Himalayan mountain belt. The continued northward push of the Indian plate and
thrust sheet loading in the Himalayan orogen caused an up-warping along its
cratonward margin, in the form of a regional gentle bulge. In the cratonward
peripheral bulge small-scale to moderate size deformation features, e.g.,
gentle folds (up-arching of the sediment layers), extensional normal faults and
uplifted tilted blocks, and incised river channels with 20–60-m-high
cliffs, developed. Cliff sections of many rivers in this cratonward part of the
foreland basin expose deposits of latest Pleistocene–Holocene age and
show evidences of active tectonics in the last few thousand years: vertical
uplift leading to deep incision of the river system, development of prominent
fractures cutting through the sedimentary succession, bending and tilting of
the strata, and tilted blocks. In the Late Quaternary relaxation phase of the
Himalayan orogen-foreland, there is increased vertical tectonic activity in the
region of the peripheral bulge. The vertical uplift in this part of the Ganga
Plain foreland basin caused the rivers (including the axial rivers) to make
further deep incision without shifting from their courses. During periods of
increased tectonic activity in the Himalayan region, i.e., the addition of
thrust slices more rapidly, probably caused the maximum down-bending in the
proximal part of the Ganga plain foreland basin. The high amplitude and
asymmetric nature of this foreland basin is partly controlled by extensional
tectonism.