Spatial variability of 10 Be-derived erosion rates across the southern Peninsular Indian escarpment: A key to landscape evolution across passive margins

Mandal, Sanjay Kumar; Lupker, Maarten; Burg, Jean‐Pierre; Valla, Pierre G.; Haghipour, Negar; Christl, Marcus

doi:10.1016/j.epsl.2015.05.050

Cited by 81 publications

(123 citation statements)

References 115 publications

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“…Ouimet et al, 2009;DiBiase et al, 2010;Scherler et al, 2014;Mandal et al, 2015;Harel et al, 2016) have demonstrated that k s is positively correlated with erosion rate, mirroring the predictions of Gilbert (1877) over a century earlier. Many authors have used channel steepness to examine fluvial response to climate, lithology, and tectonics (e.g.…”

supporting

confidence: 48%

How concave are river channels?

et al. 2018

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Abstract. For over a century, geomorphologists have attempted to unravel information about landscape evolution, and processes that drive it, using river profiles. Many studies have combined new topographic datasets with theoretical models of channel incision to infer erosion rates, identify rock types with different resistance to erosion, and detect potential regions of tectonic activity. The most common metric used to analyse river profile geometry is channel steepness, or k s . However, the calculation of channel steepness requires the normalisation of channel gradient by drainage area. This normalisation requires a power law exponent that is referred to as the channel concavity index. Despite the concavity index being crucial in determining channel steepness, it is challenging to constrain. In this contribution, we compare both slope-area methods for calculating the concavity index and methods based on integrating drainage area along the length of the channel, using so-called "chi" (χ) analysis. We present a new χ-based method which directly compares χ values of tributary nodes to those on the main stem; this method allows us to constrain the concavity index in transient landscapes without assuming a linear relationship between χ and elevation. Patterns of the concavity index have been linked to the ratio of the area and slope exponents of the stream power incision model (m/n); we therefore construct simple numerical models obeying detachment-limited stream power and test the different methods against simulations with imposed m and n. We find that χ-based methods are better than slope-area methods at reproducing imposed m/n ratios when our numerical landscapes are subject to either transient uplift or spatially varying uplift and fluvial erodibility. We also test our methods on several real landscapes, including sites with both lithological and structural heterogeneity, to provide examples of the methods' performance and limitations. These methods are made available in a new software package so that other workers can explore how the concavity index varies across diverse landscapes, with the aim to improve our understanding of the physics behind bedrock channel incision.

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supporting

confidence: 48%

How concave are river channels?

et al. 2018

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“…It also disagrees with thermochronologic evidence for significant post‐40 Ma denudation at rates of

\sim 60

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.…”

Section: Calibration and Testingmentioning

confidence: 92%

Cenozoic epeirogeny of the Indian peninsula

Richards

Hoggard

White

2016

Geochem Geophys Geosyst

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Peninsular India is a cratonic region with asymmetric relief manifest by eastward tilting from the 1.5 km high Western Ghats escarpment toward the floodplains of eastward‐draining rivers. Oceanic residual depth measurements on either side of India show that this west‐east asymmetry is broader scale, occurring over distances of > 2000 km. Admittance analysis of free‐air gravity and topography shows that the elastic thickness is 10 ± 3 km, suggesting that regional uplift is not solely caused by flexural loading. To investigate how Indian physiography is generated, we have jointly inverted 530 river profiles to determine rock uplift rate as a function of space and time. Key erosional parameters are calibrated using independent geologic constraints (e.g., emergent marine deposits, elevated paleosurfaces, uplifted lignite deposits). Our results suggest that regional tilt grew at rates of up to 0.1 mm a−1 between 25 Ma and the present day. Neogene uplift initiated in the south and propagated northward along the western margin. This calculated history is corroborated by low‐temperature thermochronologic observations, by sedimentary flux of clastic deposits into the Krishna‐Godavari delta, and by sequence stratigraphic architecture along adjacent rifted margins. Onset of regional uplift predates intensification of the Indian monsoon at 8 Ma, suggesting that rock uplift rather than climatic change is responsible for modern‐day relief. A positive correlation between residual depth measurements and shear wave velocities beneath the lithosphere suggests that regional uplift is generated and maintained by temperature anomalies of ±100 °C within a 200 ± 25 km thick asthenospheric channel.

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“…It further provides a convenient framework to relate catchment‐scale erosion rates to topographic relief, which scales with the channel steepness index [ DiBiase et al , ]. The utility of this approach has been confirmed with empirical data that show robust trends between channel steepness index and detrital 10 Be‐derived erosion rates across different landscapes [e.g., Ouimet et al , ; DiBiase et al , ; Cyr et al , ; Scherler et al , ; Mandal et al , ]:

E_{10 Be} \propto {k_{s}}^{ϕ},

where E 10Be is 10 Be‐derived erosion rate and ϕ is an empirical exponent. The scaling parameters of this relationship vary widely between landscapes, as a result of differences in climate and/or rock erodibility [ Kirby and Whipple , ; Lague , ].…”

Section: Introductionmentioning

confidence: 99%

Testing monsoonal controls on bedrock river incision in the Himalaya and Eastern Tibet with a stochastic‐threshold stream power model

et al. 2017

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10Be‐derived catchment average erosion rates from the Himalaya and Eastern Tibet show different relationships with normalized channel steepness index (ksn), suggesting differences in erosional efficiency of bedrock river incision. We used a threshold stream power model (SPM) combined with a stochastic distribution of discharges to explore the extent to which this observation can be explained by differences in the mean and variability of discharge between the two regions. Based on the analysis of 199 daily discharge records (record lengths 3–45 years; average 18.5 years), we parameterized monsoonal discharge with a weighted sum of two inverse gamma distributions. During both high‐ and low‐flow conditions, annual and interannual discharge variabilities are similarly low in each region. Channel widths for 36 rivers indicate, on average, 25% wider streams in Eastern Tibet than in the Himalaya. Because most catchments with 10Be data are not gauged, we constrained mean annual discharge in these catchments using gridded precipitation data sets that we calibrated to the available discharge records. Comparing 10Be‐derived with modeled erosion rates, the stochastic‐threshold SPM explains regional differences better than a simple SPM based on drainage area or mean annual runoff. Systematic differences at small ksn values can be reconciled with ksn‐dependent erosion thresholds, whereas substantial scatter for high ksn values persists, likely due to methodological limitations. Sensitivity analysis of the stochastic‐threshold SPM calibrated to the Himalaya indicates that changes in the duration or strength of summer monsoon precipitation have the largest effect on erosional efficiency, while changes in monsoonal discharge variability have almost no effect. The modeling approach presented in this study can in principle be used to assess the impact of precipitation changes on erosion.

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Spatial variability of 10 Be-derived erosion rates across the southern Peninsular Indian escarpment: A key to landscape evolution across passive margins

Cited by 81 publications

References 115 publications

How concave are river channels?

How concave are river channels?

Cenozoic epeirogeny of the Indian peninsula

Testing monsoonal controls on bedrock river incision in the Himalaya and Eastern Tibet with a stochastic‐threshold stream power model

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