Response of a landscape to tectonics using channel steepness indices (ksn) and OSL: A case of study from the Jalisco Block, Western Mexico

Rapid tectonic uplift is known to increase river incision rates and to trigger the propagation of knickpoints along a river profile, augmenting local relief. Thus, the topography of mountainous landscapes records long-term interactions between tectonics and climate. We evaluate the geomorphic response to differential rock uplift with topographic analysis of 16 river basins including the normalized channel steepness index (ksn). Our study focuses on rivers incising the northern and western sectors of the Jalisco Block (Western Mexico), a crustal unit bounded by Plio-Quaternary extensional faulting. We use OSL signals from 17 riverbed samples to assess erosion rates. The results indicate that basins in the northern sector have higher rates of rock uplift and erosion (mean ksn = 111 ± 18 m0.9) than those in the southwest (mean ksn = 77 ± 23 m0.9), in spite of the Plio-Quaternary lavas that cap large areas of the northern sector. The development of Plio-Quaternary grabens and half-grabens along the northern boundary of the Jalisco Block has increased the erosion rates augmenting the local relief. By contrast, the topography of the basins in the southwestern sector has resulted from a long erosional history controlled by the migration of old tectonic signals farther upstream. In this region the landscape seems to have reached the steady-state, and is currently experiencing the propagation of knickpoints due to the increase in the rate of rock uplift in the coast of Jalisco during the Holocene.