Relationship of channel steepness to channel incision rate from a tilted and progressively exposed unconformity surface

Abstract

Key Points:• Channel incision relation to steepness calibrated from tilted bedrock surface • Chlorine-36 exposure age dating shows bedrock surface exhumed at 1 to 2 m/kyr• Low n values, consistent with shear stress (n = 2∕3) satisfy field data Supporting Information:• Table S1 • Table S2 • Readme Abstract We examine the relationship of channel steepness to incision rate from channels eroding into a previously tilted, planar, and progressively exhumed unconformity surface. Channel and unconformity slopes are measured from a suite of channels developed on erosionally resistant Paleozoic limestone exhumed by the removal of Cenozoic sediments from the Baybeiche Range bordering the Naryn basin in the western Tian Shan. The compiled data set, sampling 5 orders of magnitude of upstream drainage area (0.03 to 227 km 2 ), is used to derive the exponent, n, relating channel steepness to channel incision rate and the ratio, K∕V, of the rate constant for channel incision of the resistant substrate, K, to the erosion rate, V, of the cover strata. We show that for a typical value of intrinsic concavity (slope-area exponent, = 0.5), erosion rates that are proportional to specific stream power (n = 1) satisfy the data set. However, valley width data suggest that the intrinsic concavity is higher ( = 0.8) and that the channel incision data can also be fit if erosion is proportional to basal shear stress (n = 2∕3). Our results do not support values of n significantly greater than one. Using 36 Cl exposure age dating of the unconformity surface, we independently demonstrate that the Cenozoic cover strata have been progressively stripped downward from the unconformity surface at a vertical rate of 1 to 2 m/kyr. Using V = 1 m/kyr, we constrain the rate constant, K, to between 6 ± 1 and 9 ± 2 ×10 −4 kyr −1 for incision of resistant limestone bedrock in this field setting.

Pliocene‐Pleistocene initiation, style, and sequencing of deformation in the central Tien Shan

“…Because no suitable material for age determination was found in the deposits of either terrace level, we estimate the age of the Terek terraces based on correlation to nearby geochronologic control. Other work in the region suggests a vertical exhumation rate of the northern flank of the Baybeiche Range of ~0.7–2 mm/yr [ Oskin et al ., ]. Additionally, we make a speculative temporal correlation of the high and low Terek terraces with the middle and lowest Jaman‐davan river terraces.…”

Bedrock channels response to differential rock uplift in eastern Qilian Mountain along the northeastern margin of the Tibetan Plateau

“…(1)) base on detail model derivation (Howard, 1994;Howard and Kerby, 1983;Tucker, 2004;Whipple, 2004;Whipple andTucker, 1999, 2002;Willgoose, 1994). The slope-area analysis of channel profiles is widely applied to landscape where underlying deformation patterns are not known, in particular, coupling with additional measures of erosion rates (e.g., cosmogenic isotopes and/or thermochronologic methods) to provide some constrains on the rate and patterns of rock uplift across a landscape (e.g., Hodges et al, 2004;Kirby et al, 2007Kirby et al, , 2003Oskin et al, 2014;Wobus et al, 2003Wobus et al, , 2006aYanites et al, 2010).…”

“…Stock and Montgomery (1999) suggest that K may scale over $4 orders of magnitude owing to variability in lithologic resistance and/or climate among field sites. It is so difficult to isolate myriad influences subsumed in the erosion coefficient (K) that only a few studies have documented K values (e.g., Duvall et al, 2004;Oskin et al, 2014;Snyder et al, 2003a;Stock and Montgomery, 1999;Whipple et al, 2000b).…”

“…Therefore, bedrock channel longitudinal profiles have been regarded as more sensitive indicators of uplift rates than other morphological properties in active orogen (Whipple, 2004). The spatial distribution of rock uplift and substrate active faults can be determined directly by analyzing the systematic behavior of stream profiles in tectonically active region (e.g., Allen et al, 2013;Hack, 1957Hack, , 1973Kirby et al, 2007Kirby et al, , 2003; Kirby and Ouimet, 2011;Kirby and Whipple, 2001;Lavé and Avouac, 2001;Oskin et al, 2014;Pritchard et al, 2009;Wobus et al, 2003;Yanites et al, 2010).…”

“…Although these parameters can be estimated to a certain extent base on field survey, the available data is relatively sparse (e.g., Duvall et al, 2004;Oskin et al, 2014;Snyder et al, 2003a;Stock and Montgomery, 1999;Whipple et al, 2000b), because of the complexity of various influencing factors such as hydraulic http://dx.doi.org/10.1016/j.jseaes.2014.12.009 1367-9120/Ó 2015 Elsevier Ltd. All rights reserved. geometry characteristics, substrate erodibility, sediment supply, and transient conditions of channel morphology (Lague, 2014;Pritchard et al, 2009;Whipple, 2004).…”