Lithological control on the geomorphic evolution of the Shillong Plateau in Northeast India

Abstract

The Shillong Plateau in Northeast India is a block of raised topography in the Himalayan foreland which consists of crystalline basement rocks partially covered by a Cretaceous to Miocene sedimentary succession. It is dominated by a mature, low relief landscape surrounded by high relief, fluvially dissected margins, particularly along its southern flank which is bounded by the Dauki thrust Fault. We use river profiles and geological relationships to show that the low relief plateau is a topographic expression of a re-exposed basement palaeosurface following the stripping of sedimentary cover by scarp retreat. We show that initiation of the wave of incision does not require surface rupture on the Dauki Fault or an increase in fault slip rate at the end of the Miocene, as suggested by previous studies. We propose that incision has been spatially controlled by the slope of the basement palaeosurface, likely moderated by an incision threshold. River profiles in the Shillong Plateau cannot be interpreted as simple records of surface uplift. The observed heterogeneous spatial pattern of steepness is a function of a dynamic landscape response to the erosion of layered lithology with contrasting erodibility. Such dynamics have *Revised manuscript with no changes marked Click here to view linked References implications for fluvial geomorphology, highlighting that near-horizontal lithological contacts can strongly influence river profiles and topography, even when no longer physically preserved. The topography of the northern Shillong Plateau is controlled by the structure of basement rocks and is reminiscent of stable cratonic interior landscapes, consistent with its surface exposure during late Cretaceous times.

Process inference from topographic fractal characteristics in the tectonically active Northwest Himalaya, India

“…Topographic variations in response to the different landscape governing processes or events are generally characterized, among other indices, in terms of RR (Tucker and Whipple, 2002; Ellis and Barnes, 2015; Black et al ., 2017; O'Hara et al ., 2019; Strong et al ., 2019). RR is usually calculated for a specific window size.…”

“…The landscape evolution studies in the Himalayan terrain have primarily focused on the relative role of tectonic uplift and (or) climate (e.g. Gabet et al ., 2004; Hilley and Strecker, 2004; Bookhagen et al ., 2005; Whipple, 2009; Korup and Weidinger, 2011; Anoop et al ., 2012; Godard et al ., 2014; Olen et al ., 2016; Dey et al ., 2016a,b; Nennewitz et al ., 2018; Jaiswara et al ., 2019), whereas the role of lithology has not received major emphasis except for a few limited studies (Attal and Lavé, 2006; Barnes et al ., 2011; Allen et al ., 2013; Ellis and Barnes, 2015; Strong et al ., 2019). However, lithology has been advocated as an important control of landscape evolution in the tectonically passive landscapes (Gallagher and Brown, 1997; Weissel and Seidl, 1997; Gunnell et al ., 2003; Gunnell and Harbor, 2010; Scharf et al ., 2013; Mandal et al ., 2017; Guha and Jain, 2020).…”

Isolating Lithologic Versus Tectonic Signals of River Profiles to Test Orogenic Models for the Eastern and Southeastern Carpathians

“…Bernard et al, 2019; in the river network, resulting in ambiguity in interpreting the main forcing controlling the steepening (e.g. Strong et al, 2019).…”

Rock strength and structural controls on fluvial erodibility: implications for drainage divide mobility in a collisional mountain belt

“…Any movement of the drainage divide can result in the rearrangement of catchments, rejuvenation of topography, and changes in erosion rates and sediment flux (Bonnet, 2009;Giachetta et al, 2014). Bedrock erodibility is expected to play a significant role in drainage divide reorganisation since heterogeneous exhumation of weak and strong substrates can enhance and suppress erosion respectively (Giachetta et al, 2014;Gallen, 2018) and cause topographic rejuvenation, for example through the exhumation of a basement palaeosurface (Strong et al, 2019). This is especially the case in postorogenic settings where erosion is dominant over crustal thickening (Gallen, 2018;Bernard et al, 2019).…”