Geomorphic fluvial markers reveal transient landscape evolution in tectonically quiescent southern Peninsular India

Abstract

The morphology of 19 adjacent westward‐flowing and four eastward‐flowing major catchments draining across the Western Ghat escarpment in southern Peninsular India was studied to examine how the channel patterns and their longitudinal profiles reflect the landscape evolution. Field surveys were complemented with the quantitative morphometric analysis of fluvial channel profiles using digital topographic data. Results show distinctive differences between eastward‐ and westward‐flowing drainage systems. The channel profiles of eight westward‐flowing drainage basins show an apparent morphological equilibrium characterized by concave upward shape, whereas most channels from the other westward‐flowing basins display knickpoint(s). All studied eastward‐flowing drainage basins display the morphological signature of disequilibrium in the form of knickpoints. The eastern and western margins of southern Peninsular India have experienced major tectonic events ~120 and ~65 Ma ago, respectively, and are since then tectonically quiescent. All studied westward‐flowing basins share the same Arabian Sea base level, flow over comparable lithologies and developed under similar climatic conditions. The studied eastward‐flowing basins have the Bay of Bengal as base level and similar climatic conditions. Therefore, the spatial variations in catchment morphometry is interpreted as a dynamic response to complex interactions and feedbacks between (i) pre‐existing topography along and across the escarpment margins, and (ii) vigorous drainage piracy in more recent times. We hypothesize that the studied drainage basins have experienced different forcing magnitudes that can be quantified to a first order using the present day topography. Copyright © 2016 John Wiley & Sons, Ltd.

Cenozoic epeirogeny of the Indian peninsula

“…It also disagrees with thermochronologic evidence for significant post‐40 Ma denudation at rates of m Ma −1 across the Kerala‐Konkan lowlands since Late Miocene times [ Kalaswad et al ., ; Gunnell et al ., ; Campanile et al ., ; Mandal et al ., ]. These rates are consistent with cosmogenic nuclide studies and with evidence for ongoing escarpment retreat [ Mandal et al ., , ]. Differential uplift could have occurred as a result of a combination of offshore sedimentary loading and onshore denudational unloading that is manifest in seaward downwarping of the lowland pediment.…”

“…These knickzones have wavelengths of up to 300 km with amplitudes that consistently exceed 150 m. These wavelengths and amplitudes exceed changes in base level that are attributable to glacioeustatic sea‐level fluctuations [ Siddall et al ., ; Miller et al ., ]. There is poor correlation between major changes in lithology and knickzone development, indeed the majority of knickzones occur within the relatively homogeneous Precambrian basement or Deccan basalt of the cratonic interior [ Ambili and Narayana , ; Mandal et al ., ]. Furthermore, major knickzones do not coincide with the location of Archaean and Proterozoic fault systems, pointing to limited Cenozoic tectonic reactivation of these ancient structures [ Gunnell and Harbor , ; Kale et al ., ].…”

“…This systematic sweep reveals that there is a weak global minimum at where the quoted uncertainty reflects values of m that yield misfit values of that at the global minimum. This range of values broadly agrees with published estimates [ Stock and Montgomery , ; van der Beek and Bishop , ; Mandal et al ., ]. The shape of the misfit function emphasises that m is unlikely to have a fractional value significantly greater than 0.5.…”

“…Geochemistry, Geophysics, Geosystems 10.1002/2016GC006545 fluctuations [Siddall et al, 2003;Miller et al, 2005]. There is poor correlation between major changes in lithology and knickzone development, indeed the majority of knickzones occur within the relatively homogeneous Precambrian basement or Deccan basalt of the cratonic interior [Ambili and Narayana, 2014;Mandal et al, 2016]. Furthermore, major knickzones do not coincide with the location of Archaean and Proterozoic fault systems, pointing to limited Cenozoic tectonic reactivation of these ancient structures [Gunnell and Geochemistry, Geophysics, Geosystems…”

Weathering history and landscape evolution of Western Ghats (India) from 40 Ar/ 39 Ar dating of supergene K–Mn oxides

“…Indeed, negligible Neogene denudation rates documented on either side of the WGE (Beauvais et al, 2016;Bonnet et al, 2016;present work) imply that the escarpment is at least 50 Ma old and challenge the popular model of uplift and/or rejuvenation of the escarpment in the Neogene advocated by most authors (e.g., Radhakrishna, 1993;Widdowson and Gunnell, 1999;Mandal et al, 2017). Furthermore, combined geomorphology and Ar-Ar geochronology of the western coastal lateritic lowland of the Peninsula infers negligible uplift since c. 50 Ma (Beauvais et al, 2016;Bonnet et al, 2016).…”