Ongoing landscape transience in the eastern Amazon Craton consistent with lithologic control of base level

Abstract

Geomorphic features such as drainage captures, knickpoints, paleochannels, and wind-gaps have long been observed in the Amazon region and typically thought to result from climate change and intraplate tectonics. The influence of rock type as a trigger of these landscape transients is largely overlooked. In the eastern Guiana Shield of the Amazon Craton, shield rivers flow over to the sedimentary rocks of the Amazon Basin across a sharp lithologic transition before their confluence with the Amazon River. This transition is marked by an expressive main escarpment (ME) formed over resistant sandstones of the basal units of the Amazon Sedimentary Basin. Here, systematic patterns of divide migration and river captures provide a natural laboratory to study the influence of rock type in landscape transience in a cratonic setting. Through quantitative geomorphologic analysis of the topography, drainage divides, and rivers, we investigate if this sharp lithologic transition contributed to the observed patterns of drainage rearrangement. The results revealed that rivers of larger drainage areas flowing across shorter lengths over the resistant rocks of the ME systematically capture neighbouring basins. We argue that, as tributaries draining the shield respond to downcutting and/or base-level fall of the Amazon River, bedrock incision and knickpoint propagation are differentially slowed down by the resistant rocks according to their incision capacity, generating a series of transients such as drainage capture and divide migration. The widespread and systematic geomorphic features suggest this mechanism could be an important autogenic control of drainage network rearrangement in the Amazon region and other postorogenic landscapes as well. The protracted exhumation of resistant rocks in cratons and intraplate settings may keep landscapes in perpetual disequilibrium depending on their lithological complexity and offer an exceptional natural laboratory to study landscape dynamics associated with rock type.

Drainage rearrangement in an intra-continental mountain belt: A case study from the central South Tian Shan, Kyrgyzstan

“…All three types of knickpoints can be either stable, i.e., anchored in space, or transient and mobile, generally migrating upstream. Stable knickpoints may occur due to lithologic change or structures accommodating differential rock uplift such as folds or faults (Crosby and Whipple, 2006;Wobus et al, 2006;Gallen and Wegmann, 2017;Giachetta and Willett, 2018;Marrucci et al, 2018;Fadul et al, 2022;Seagren et al, 2022).…”

“…River capture can divert a stream into a neighbouring stream, leaving anomalies like sharp (i.e., ≥ 90°) bends, abandoned river valleys, wind-gaps, and knickpoints near the point of the capture (Bishop, 1995;Seagren and Schoenbohm, 2019;Fadul et al, 2022). Water discharge will increase in the capturing stream, triggering incision (Bishop, 1995;Giachetta and Willett, 2018;Rohrmann et al, 2023).…”

“…To identify structural and lithologic knickpoints, we referred to geologic mapping (Mikolaichuk et al, 2008) Knickpoints related to lithologic contrasts or to differential rock uplift are usually located on the boundaries of lithologies with different erodibilities or on mapped faults, respectively (Marrucci et al, 2018;Fadul et al, 2022). We identified lithologic and structural knickpoints as those lying within 250 m horizontal distance from the boundaries of lithologic contacts or Cenozoic faults, respectively.…”

Introduction to the Women in Geomorphology special issue

“…Remote sensing ( 26) Agostini et al, 2022;Atwood & West, 2022;Davies et al, 2022;Davis et al, 2021;Fadul et al, 2022;Gervasi et al, 2021;Hendrickx et al, 2022;Hodge & Buechel, 2022;Hooke, 2022;Hovenga et al, 2021;Konlechner & Hilton, 2022;Lefebvre et al, 2022;Marchetti et al, 2022;McKenzie et al, 2022;Mol & Grenfell, 2022;Opalka et al, 2022;Rabanaque et al, 2022;Regalla et al, 2022;Reitman et al, 2022;Sampietro-Vattuone et al, 2021;Schoch-Baumann et al, 2022;Thompson et al, 2022;Vah et al, 2022;Valentine et al, 2022;Zhang et al, 2022 Physical experiments (8) Bako et al, 2022;Bywater-Reyes et al, 2022;Demiral et al, 2022;Friedrich et al, 2022;Negreiros et al, 2022;Rachelly et al, 2022;Roelofs et al, 2022;Vah et al, 2022 Numerical models ( 11) Agostini et al, 2022;Bywater-Reyes et al, 2022;Cullen et al, 2022;Glover et al, 2022;Hodge & Buechel, 2022;Kooijma...…”

“…Many of the major research directions in contemporary geomorphology are reflected in this collection of papers. With respect to fluvial environments, including alluvial fans, individual papers examine use of images to detect sediment motion during physical experiments (Vah et al, 2022); comparison of grain‐size distributions from field measurements and remotely acquired images (Marchetti et al, 2022); physical experiments on bedload saltation under differing conditions (Demiral et al, 2022); numerical modelling of critical shear stress for grain entrainment based on imagery of bed‐rock channels (Hodge & Buechel, 2022); biogeomorphology (Bywater‐Reyes et al, 2022; Gurnell et al, 2022); channel morphology and classification (Lane et al, 2022), hydromorphology of ephemeral streams (Rabanaque et al, 2022) and interpretation of geomorphic unit assemblages (Fryirs & Brierley, 2022); flood effectiveness (Gervasi et al, 2021); channel evolution, terraces and sediment sources (Guyez et al, 2022) and the influence of sediment supply on gravel‐bed river widening (Rachelly et al, 2022); hydrological variation and meander morphodynamics (Hooke, 2022); the dynamics of wood in river corridors (Guiney & Lininger, 2022; Gurnell et al, 2022; Wohl, 2022) and numerical modelling of wood‐related processes (Friedrich et al, 2022); numerical model validation (Negreiros et al, 2022) and numerical modelling of groundwater‐driven network evolution (Cullen et al, 2022); base‐level controls and landscape evolution (Fadul et al, 2022); long‐term dryland channel response to urbanization (Chin, 2022); watershed restoration and management, including human alterations of process and form (Atkins et al, 2023; Davis et al, 2021; Goodman et al, in press; Gurnell et al, 2022; Hinshaw et al, 2022; Mossa & Chen, 2022; Sampietro‐Vattuone et al, 2021; Valentine et al, 2022); and alluvial fan dynamics (Opalka et al, 2022; Quock et al, 2022; Regalla et al, 2022; Schoch‐Baumann et al, 2022). Papers addressing process and form in coastal environments include examinations of dune morphodynamics and evolution (Hovenga et al,...…”