Holocene tectono-geomorphic evolution of parts of the Upper and Middle Gangetic plains, India

Terminal fans and the Ganga plain tectonism: A study of neotectonism and segmentation episodes of the Indo-Gangetic foreland basin, India

“…In particular, sheet flow processes are more commonly observed on the down thrown blocks of the faults. Srivastava et al (2003) observed the sheet flow process to be common in filling the abandoned pond along the paleochannels and the same processes are too observed in the low lying swampy regions in the middle Gangetic plains by Pati (2008). Sheets flow processes are more prominent in the tectonically active periods in the region.…”

“…This vast stretch of alluvium chiefly consists of coarse to fine grained sand and mud deposited by the Ganga River and its tributaries. Alternate gravel and sand sequences are reported in the northern part of the region i.e., in the piedmont zone (Pati et al, 2011b) and at places gravel progradation by thrusting is also observed in the GandakKosi interfan region (Pati et al, 2011a). Due to unconsolidated nature of the sediments, fluvial reworking is frequent which promotes frequent fan building events on the down thrown blocks of faults during or soon after the faulting activities.…”

“…Acharya et al (2012) confirmed the subsurface presence of the Markanda fault by ground penetrating radar (GPR) and observed that instead of the whole Markanda River, a splay off the main river diverted at the Markanda fault, was responsible for the formation of the terminal fan. In the mean time, many terminal fans associated with normal faults have also been reported from the upper Gangetic plain Bhosle et al, 2008;Pati et al, 2011b) and in the middle Gangetic plain between the Gandak-Kosi interfan region associated with reverse faults (Pati et al, 2011a). So it is not necessary to have arid or semiarid climate and ephemeral channels to form terminal fans in fact it is the relief difference across the stream course which is vital for it.…”

“…Due to unconsolidated nature of sediments, these depositional features form during or soon after faulting activities in the accommodation space created on the down-thrown blocks of normal as well as reverse faults (Fig. 5), and hence have successfully been used in dating the faulting events in the Gangetic plains Bhosle et al, 2008;Pati et al, 2011aPati et al, ,b, 2012Acharya et al, 2012).…”

“…Along the fault, due to erosion of the fault scarps, variable relief differences have been observed. The frequency of the faulting episodes among the different segments of the plain is not uniform throughout space and time because of their differential convergence and upliftment rates (Avouac et al, 1998;Wesnousky et al, 1999;Lave and Avouac, 2000), variation in directional movement (Sridevi, 2004) and change in compression directions (Parkash et al, 2000;Pati et al, 2011a). Pati et al (2012) studied the neotectonic deformations between the Ghaghara and Kosi rivers and observed that the segments exhibiting relatively high rate of convergence and upliftment along the Himalayan Frontal Thrust (HFT) are prone to observe more frequent faulting episodes in the plain and vice versa.…”