River Incision Rates Research Articles

Insights into the synergistic effects of tectonics and climate from the formation and evolution of the Hongwen allochthonous deposit, southwestern China

Abstract The formation and evolution of large-scale deposits generated by mass movement are often closely related to tectonic and climatic conditions. Investigating deposits under the influence of complex geological conditions can aid in reconstructing paleoenvironmental characteristics and fluvial geomorphic evolution. The First Bend of the Yangtze River (FBYR), located in the Jinsha River basin in southwest China, represents a significant section characterized by abundant allochthonous deposits. We conducted a detailed investigation of the Hongwen allochthonous deposit (HAD) and the river sediments in the First Bend. Through terrain interpretation, dating, and paleoenvironmental analysis, the HAD was determined to be a complex deposit with multiple sources and stages (46.4–33.5 ka), formed under the combined influence of tectonic activity and climate. Three mass-movement events occurred during the interglacial stage of the last glacial period or its transitional period, coinciding with the rapid uplift stage of the Tibetan Plateau since the late Pleistocene. Prominent features of this period include significant rainfall and tectonic activities. By dating fluvial sediments and examining the evolution of the HAD, we revealed a river incision rate of 2.30 mm/yr for the Jinsha River, providing a basis for analyzing periodic river cutting and the development pattern of surface processes.

Modeling Climate and Tectonic Controls on Bias in Measured River Incision Rates

AbstractRates of land surface processes provide insights into climatic and tectonic influences on topography. Bedrock incision rates are estimated by dating perched landforms such as strath terraces, assuming a constant bedrock incision rate from terrace abandonment to the next terrace level or present river level. These estimates express biases from the stochastic nature of sediment and water discharge in controlling river incision as well as from using a mobile channel elevation as a reference frame, leading to different incision rates when calculated over different timeframes. We introduce a 1‐D model incorporating fluvial mechanics, tectonics, sediment, and climate variability to predict these biases and assess their sensitivity to climate and tectonics. Findings suggest biases intensify under highly variable climates and slow rock uplift, with climate periodicity being a primary control for our modeled scenarios. Our model provides a mechanism to improve river incision measurement uncertainty, impacting paleoclimate and tectonic geomorphology reconstructions.

Climatically-driven development of late Quaternary fluvial geomorphology in the arid inland of Asia

The forcing mechanism behind river incision and terrace formation is one of hot topics in the study of fluvial geomorphology. This work focused on the late Quaternary alluvial sequence in the south piedmont of the Chinese Altay Shan in the arid inland of Asia. In order to reveal the mechanism controlling the development of late Quaternary fluvial features along the mountain front, we conducted detailed fluvial geomorphological investigations on eight rivers, including geomorphic mapping, optically stimulated luminescence (OSL) dating, and differential global position system (dGPS) surveying. By utilizing the Monte Carlo simulation with terrace data, the late Quaternary rates of river incision along the south piedmont of the Chinese Altay Shan were determined. The results show that (1) the terraces developed by the piedmont rivers are not more than four levels and the depth of river incision in the piedmont is only dozens of meters, with deeper valleys displayed by the western piedmont rivers; (2) terrace alluviums along the mountain front were accumulated during glacial stages, and the subsequent incision occurred during interglacial stages; (3) the rate of river incision was accelerated during the Holocene, when the regional climate was characterized by progressively increasing wetness. When combining with the regional tectonic setting, we propose that the climate could have played the key role in driving the alluvial accumulation and the subsequent incision in the south piedmont of the Chinese Altay Shan during the late Quaternary. Together with the similar observations from the northeastern margin of the Tibetan Plateau and the Tian Shan, we further propose that climatically-driven fluvial geomorphological development could be a common phenomenon during the late Quaternary in the arid interior of Asia.

Cosmogenic nuclide-derived downcutting rates of canyons within large limestone plateaus of southern Massif Central (France) reveal a different regional speleogenesis of karst networks

Abstract. We present 35 new burial ages (27 sites) based on 26Al / 10Be ratios of terrestrial cosmogenic radionuclides measured in clasts and sediments deep within 12 caves in the southern Massif Central, France. Our results, together with previously published burial ages, verify that cave morphogenesis has been continuously active in this region for at least the past ∼ 6 Myr. Combining sample burial ages with their associated cave elevation above the modern stream bed gives a mean regional incision rate of 88 ± 5 m Ma−1 for the Grands Causses area. South of the Cevennes Fault Zone bordering the Grands Causses, the incision rate is 43 ± 5 m Ma−1, suggesting that this difference might be accommodated by the fault zone. Sediment burial ages from caves which are not located on river valley flanks or cliff walls are surprisingly too young compared to their expected ages when calculated using this regional average river incision rate. This suggests that the classical epigenic speleogenesis model that presumes a direct correlation between cave level development and regional base level lowering does not apply for the study area. Therefore, we propose that regional speleogenesis is mainly controlled by the removal of ghost rocks by headward erosion from river canyons to central parts of the plateaus, emptying incipient primokarst passages to create cave systems. Our results suggest a continuum process from hypogene primokarst composed of passages filled with ghost rock to one of epigene karst dynamics emptying these passages and creating cave networks. We propose that these processes are the major mechanism in the southern Massif Central that initiates speleogenesis and controls the geometry of the networks. In this region, tiered karst cannot be associated with the pace of incision of the major rivers but must be explained by former ghost rock (or hypogene) processes.

Lithological controls on the timing of strath terrace staircase formation in a collisional mountain belt

AbstractIn mountain belts, strath terrace staircases serve as markers for deriving river incision rates and erosional patterns. Distinguishing between terrace patterns influenced by external perturbations like changes in climate and tectonics and those driven by internal dynamics including feedbacks between topography, erosion and sediment transport remains challenging. We demonstrate that in a collisional mountain belt, lithology can act as a first‐order control on the spatial and temporal scales of strath terrace formation. Here, we investigate the role of lithology in modulating internal dynamics and the formation of strath terraces in the Mgoun River catchment of the High Atlas in Morocco, a region characterised by constant low‐rate rock uplift, a cyclical cool‐warm/arid‐humid Quaternary climate history and contrasting bedrock lithologies. By collecting (1) modern river and terrace clast data, (2) bedrock strath and strath‐top sediment elevations of four terrace levels, (3) terrace sedimentology and (4) integration with published terrace chronology, we found a dominance of local sediment input from hillslopes, mostly from recycled bedrock conglomerates. Additionally, we found valley width, controlled by the stratigraphic and structural configuration of lithological erodibility, significantly impacts sediment connectivity. The isolation between valleys with varying widths results in varied timescales of river channel response to hillslope coupling, with hillslope‐derived stochastic sediment gravity flows preserved in fluvial terraces in some river reaches and not in others. Furthermore, asynchronous terrace formation and abandonment ages result from the low longitudinal river connectivity between multiple valleys formed in erodible rock separated by gorges in high‐strength rock. These gorges limit knickpoint migration rates, inhibiting the ability of terraces formed in one valley to spread through the catchment. These findings can inform future research distinguishing between autogenic and external signals in erosional landscapes and help carefully derive river incision rates and climate insights from terraces.

Study of a Steady-State Landscape Using Remote Sensing and Topographic Analysis

The current limited approaches to calculating hillslope erosion rate hamper the study of the relationships among the rates of hillslope erosion, river incision, and tectonic uplift and hence the discussion of steady-state landscape evolution. In this paper, we use remote sensing and geochronological methods to calculate the upper and lower bounding hillslope erosion rates in the Qilian Shan range, Tibet. Our analysis focuses on five convex landslide sediment units derived from the weathered hillslopes at Qingyang Mountain on the tectonically active northeastern Tibetan Plateau. These sediment units range in thickness from 5.5 to 12.8 m and in volume from 119 × 103 to 260 × 103 m3. Based on field observations, measurements extracted from high-resolution DEMs, and optical stimulated luminescence (OSL) ages on fluvial terraces, we obtain lower and upper bounding rates of 0.13 ± 0.03 and 0.21 ± 0.04 mm/yr, respectively. Finally, we calculate incision rates, ranging from 0.21 ± 0.02 to 0.39 ± 0.01 mm/yr, from heights of a dated fluvial terrace above the present river and the time of abandonment of the associated bedrock strath estimated from OSL ages. The rates of hillslope erosion and river incision at Qingyang Mountain and the tectonic uplift of the Qilian Mountains are estimated to be within a factor of two over the past 117 ka, suggesting that a state of dynamic equilibrium has likely existed on this timescale.

River incision, 10Be production and transport in a source-to-sink sediment system (Var catchment, SW Alps)

Abstract. Detrital 10Be from continental river sands or submarine sediments has been extensively used to determine the average long-term denudation rates of terrestrial catchments, based on the assumption that the rate of cosmogenic nuclide production by the interaction of source rocks with cosmic radiation balances out the loss of these nuclides by surface denudation. However, the 10Be signal recorded in sediments may be affected at the source by the response time of mountainous catchments to high-frequency forcings. In addition, transient sediment storage in piedmonts, alluvial plains and lakes or near the coast may also induce a difference between the erosive signal and its record in the sedimentary sink. Consequently, a significant part of the signal recorded in shallow-water sediments can be lost, as deep marine sediments may simultaneously record a signal coming from newly eroded source rocks along with one coming from the destabilization of previously deposited sediments. In this paper, we use the landscape evolution model Badlands to simulate erosion, deposition and detrital 10Be transfer from a source-to-sink sedimentary system (the Var River catchment, southern French Alps) over the last 100 kyr. We first compare model-based denudation rates with the ones that would be extracted from the 10Be record of local continental sediments (equivalent to river sands) and from sediments deposited offshore over time in order to examine if this record provides an accurate estimate of continental denudation rates. Then, we examine which conditions (precipitation rate, flexure, ice cover) satisfy published measured river incision rates and 10Be concentration in submarine sediments. Our results, based on the Var catchment cosmic ray exposure dating and modelling indicate that, while river sands do accurately estimate the average denudation rate of continental catchments, this is much less the case for deep submarine sediments. We find that deep-sea sediments have a different and often much smoother 10Be signature than continental ones and record a significant time lag with respect to imposed precipitation rate changes, representing the geomorphological response of the margin. A model which allows us to fit both measured 10Be concentration in marine sediments and river incision rates on land involves an increase in precipitation rates from 0.3 to 0.7 m yr−1 after 20 ka, suggesting more intense precipitation starting at the end of the Last Glacial Maximum.

Reconstruction of a Holocene landslide-dammed lake in the Yalong basin, eastern Tibetan Plateau

The failures of natural dams formed by landslides and glaciers in mountain areas have triggered the most destructive flood events on Earth. Outburst floods are effective agents in modifying landscapes, such as carving bedrock gorges and transporting surface masses. Reconstructing the ages and magnitudes of prehistoric landslide damming events allows us to capture the full range of frequencies and magnitudes of similar events and deepen our understanding of the interaction between large landslides and trunk rivers in tectonically active high-relief mountains. Previous studies have revealed many paleo-landslide-dammed lakes in the Yarlung Tsangpo River and its tributaries, the Jinsha River and the Min River. However, most studies associated with paleo-event reconstruction lack an estimation of the extent and volume of paleo-landslide-dammed lakes. The paleo-level of a landslide-dammed lake can be recorded in the variation in the sedimentary sequence and the geometry of the breach channel of a landslide dam. This information has not been fully exploited. In this study, we identified sedimentary evidence formed by an ancient landslide-dammed lake in the Liqiu River, a left-bank tributary of the Yalong River. The 12 exposures that we investigated mainly consist of typical clay or silt varves deposited in deep water and the Bouma sequence deposited by subaqueous turbidity flows, as well as climbing ripples that formed in a near-shore environment. Based on sedimentary analysis, we inferred that the minimal lake volume of this ancient lake was approximately 2.4 × 108 m3, corresponding to a lake level at 3,187 m a.s.l. The maximal lake extent derived from relict dam morphology reveals a lake volume of 3.2 × 108 m3 at the level of 3,200 m a.s.l. An initial drainage that occurred as the lake water overtopped the landslide dam was suggested to explain the small discrepancy in the lake level. The relict lake has remained stable over a long period of time and has accommodated continuous clay varve deposits. Furthermore, the optically stimulated luminescence dating results illustrate that the dammed lake initiated before 7.9 ka BP and persisted until at least 3.9 ka BP. The long-term cumulative coupled effect of tectonic movement and the rapid river incision rate provided favorable conditions for the failure of the Yuting landslide.

Middle and Late Pleistocene evolution of the Ardèche Valley archaeological landscapes (France)

Most archaeological and palaeo-environmental archives are preserved in specific environments (buried sediments, rock shelters, cave environments). Hence, the information we can obtain is usually incomplete, and lacking spatial and morphological significance. Studying landscape evolution can help us to understand the location and distribution of past societies and their relation to Quaternary environments. In the Ardèche Valley, most Middle and Late Palaeolithic sites are preserved in caves and rock-shelters and in rare cases in fluvial sediments. Here we apply an integrated geomorphological approach to the study of the evolution of the Ardèche Valley combining multi-method dating, geomorphological mapping and surveys of cave and fluvial formations. We review chronological results obtained through multi-method dating (electron spin resonance (ESR), infrared stimulated luminescence (IRSL), uranium-series (U-series), combined electron spin resonance/uranium-series (ESR/U-series)) on cave and riverine objects and combine them with topographic and stratigraphic observations in an integrated Bayesian hierarchical model. The results are in agreement with those obtained from other rivers in mountainous environment around the Mediterranean Sea and show sedimentation/incision phases that match the 100 ka glacial/interglacial cycles. The mean rate of river incision deduced from the established chronology for the Middle and Late Pleistocene period, 76 ± 7 m.Ma−1, shows adjustments to a moderate uplifting dynamic that shaped the main topographical features seen today in the landscape of the Ardèche Gorge. The spatially reconstructed alluvial features provide a palaeogeographic framework that can be used directly as a chronological and topographical constraint for archaeological research in the Ardèche catchment.

Three-dimensional control of alluvial fans by rock uplift in an extensional regime: Aydın Range, Aegean extensional province

Tectonics imparts a first-order control on the overall morphology of alluvial fan systems in extensional settings by influencing sediment flux and accommodation space, while other factors such as climate, catchment lithology, and fault footwall characteristics are secondary. Previous alluvial fan modeling studies have focused on the link between the three-dimensional development of alluvial fans and rock uplift, however, despite the potential influence of tectonics on the overall three-dimensional morphology of alluvial fans, the controlling mechanisms, as well as their relative importance, remain largely unquantified in a natural setting with a targeted source-to-sink approach. Here, we examine 45 alluvial fans and their catchments along the southern mountain front of the Aydın Range, delimited by segmented normal faults in the western Anatolia Extensional Province, to quantify the role of rock uplift. We quantify river incision rates and catchment-wide erosion rates together with a series of topographic analyses across the southern flank of the Aydın Range as a proxy for rock uplift. Our results indicate that the spatial distribution of thicker and steeper alluvial fans fit well with higher rock uplift rates along the strike of the mountain front. In contrast, a lower uplift rate is responsible for prograding alluvial fans with decreasing thickness and gradients. Also, our data shows that alluvial fan thickness compared to other alluvial fan metrics strongly associated with the pattern of the rock uplift. This study demonstrates a field-based, quantitative linkage between three-dimensional alluvial fan morphology and rock uplift which has significant implications for improving alluvial fan models and understanding how alluvial fans respond to tectonics in extensional regions.

Constraining a model of punctuated river incision for Quaternary strath terrace formation

In the small fraction of Earth's surface with the highest erosion rates such as the Alps and Himalayas quantifying rates of incision, rock uplift and inferring climatic controls on the landscape can be relatively straightforward once the ages of river terraces cut in bedrock (strath terraces) are constrained. However, in many mid to lower relief settings that are more typical of mountain belts worldwide, periods of net river incision and riverbed lowering are relatively short (punctuated), interrupted by long periods of sediment aggradation or stasis. We define a conceptual model of punctuated river incision and strath terrace formation for the calculation of incision and rock uplift rates, and recommend strategies for geochronological sampling and interpretation. An approach using OSL dating of terrace gravels allows us to constrain a detailed ~150 kyr history of punctuated river incision and strath terrace formation spanning two stratigraphic landform levels in the High Atlas Mountains (NW Africa). Extensive preservation and exposure of strath-top gravels, within a post-orogenic setting unaffected by eustatic influences, enables the derivation of rates of base-level fall, integrated over periods of strath-top aggradation and incision, that are consistent with independently constrained regional rock uplift rates. Combining a punctuated river incision model with our well-constrained terrace formation history allows us to demonstrate how assumptions concerning Quaternary river incision and aggradation can lead to the problematic Sadler Effect, an apparent dependence of incision rates on measured time interval. Subsequently, we demonstrate that an approach to reinterpreting previously published data using the punctuated incision model, even when combined with limited terrace age data, results in more consistent conclusions about rates of river incision, rock uplift and base-level lowering across the mountain belt. Our recommendations for sampling strategies to constrain rock uplift rates require samples to be taken just above the strath surface, and in addition towards the top of the deposit for river incision rates. In a setting with punctuated river incision and strath terrace formation, both rock uplift and incision rates require burial dates, as exclusive use of abandonment ages will not yield constraints on accurate rates of rock uplift or incision. Furthermore, we find that only with multiple along-stream locations and multiple burial dates in each terrace deposit, could a reliable climatic signal be extracted: this signal would not have shown up in terrace abandonment ages such as those derived from cosmogenic exposure dates. The demonstrated effects of assumptions about strath terrace formation, and the recommended approaches for sampling and interpretation, have implications for those attempting to constrain palaeoclimatic, tectonic, and geomorphic histories from strath terrace records in regions exhibiting punctuated river incision.

Spatiotemporal Variation of Late Quaternary River Incision Along the Heihe River in the Northeastern Tibetan Plateau, Constrained by Dating Fluvial Terraces

Rates of river incision are widely used to track changes in rock uplift rate and climate over time and space. However, the relationship between the spatiotemporal variation of river incision and past tectonic or climatic processes is still unclear. Here, we focus on the spatial patterns of river incision in the interior and front of the Qilian Shan in the northeastern Tibetan Plateau. A sequence of late Quaternary terraces is well preserved along the Heihe River across the central Qilian Shan. We complement existing chronologic data with five new optically stimulated luminescence ages and one cosmogenic radionuclide 10Be exposure age of terrace abandonment. At the mountain front, the river incision rate was ∼1 mm/yr over the past 100 kyr, while the range was from 2 to 7 mm/yr during the Holocene. We attribute the fast incision rates during the Holocene to the progressive decrease of the river gradient induced by the warm and wet Holocene climate. In the interior of the mountains (the Qilian basin site), the river incision rates were close to 1 mm/yr since ∼53 ka, suggesting that the upstream incision rate remained stable from the late Pleistocene to the Holocene. This observation further suggests that the adjustment of the climate-induced longitudinal river profile is limited to the downstream reach, especially along the front of the mountain range. We conclude that the long-term incision rate (during the late Pleistocene) is explained by ongoing uplift driven by fault activity, which determines the background rate of fluvial incision (∼1 mm/yr). On the other hand, denudation rates on the millennial timescale estimated by previous studies in this region are < 1 mm/yr, suggesting that landscape-scale erosion lags behind trunk river incision.

Optical Dating of Quartz Grains From the Minjiang Fluvial Terraces in the Sonpan Area on the Eastern Margin of the Tibetan Plateau

The fluvial terraces along the banks of the Minjiang River are very important for understanding the tectonic activities of the eastern margin of the Tibetan Plateau and have been widely investigated. However, the reliability of the ages previously reported for the terraces needs further evaluation. In this study, the Minjiang River terraces in the Sonpan area from Hongqiaoguan to the Songpan town were investigated and dated using optically stimulated luminescence (OSL) techniques on quartz grains. Seven strath terraces (T1–T7) were recognized based on the exposures of fluvial sediment and the elevation of bedrock strath, and two of them have been reported by previous studies. The terrace deposits and overlying loess were sampled for OSL dating. The samples exhibited a large scatter in De, even for loess samples, which could be attributed to poor bleaching at deposition. However, the OSL ages obtained using the minimum age model were underestimated, and those obtained using the central age model are considered relatively reliable based on stratigraphic and geomorphological consistency and the comparison of the ages between stratigraphically parallel samples. The results show that the loess samples overlying fluvial terrace sediments were deposited later than terrace formation and their OSL ages cannot represent the terrace formation ages. The T1, T3, T4, T5, and T6 terraces were dated to 13.5 ± 0.6, 29.0 ± 1.7, 48.0 ± 3.3, 44.3 ± 5.2 and 63.8 ± 4.7 ka, respectively. The T4 and T5 terraces may be the same terrace with a weighted mean age of 46.9 ± 2.8 ka. The ages of the T2 and T7 terraces were inferred to be ∼20 and ∼80 ka, respectively, based on the relationship between strath ages and elevations of the other terraces. The mean bedrock river incision rates were calculated to be 1.2 ± 0.1 mm/a for the time period of 64 ka for the T6 terrace—14 ka for the T1 terrace, and 0.15 mm/a for the past 14 ka.

Timing of sulfuric acid speleogenesis (SAS) as an indicator of canyon incision rates of the Shoshone and Bighorn rivers, Wyoming, USA

Two sulfuric acid speleogenesis (SAS) cave sites in northern Wyoming host speleogenetic byproducts that have been dated using the uranium-series method and thus provide the timing of the SAS events. Gypsum crusts that formed as byproducts of SAS in Lower Kane Cave, exposed by Bighorn River incision into the Little Sheep Mountain anticline, yield uranium-series dates of 20.5 ± 0.2 ka to 16.2 ± 0.2 ka that represent the timing of late stage speleogenesis of that cave. A calcite mammillary engulfed by elemental sulfur that formed during SAS of Shoshone Canyon Conduit Cave, exposed by Shoshone River incision of the homonymous canyon, yielded a uranium-series age of 174 ± 5 ka and represents late stage speleogenesis of that cave, although the process continued after the cave was elevated above the water table until at least 100 ± 5 ka. In addition to the timing of speleogenesis, the U-series results provide incision rates for these two canyons. The rate of canyon incision for the last 200 kyr by the Bighorn River in Little Sheep Mountain Canyon is measured as 190 ± 50 m/Ma, and for the Shoshone River in Shoshone Canyon as 400 ± 40 m/Ma. Using the Bighorn River incision rate, Upper Kane Cave located 33 m above Lower Kane Cave has a projected age of 170 ± 60 ka. We suggest that climatically driven hydrologic mechanisms rather than magmatic ones likely produced the pulses of SAS at these two cave sites.

Sedimentary evolution of a foreland basin from the northeastern Qilian Mountains based on the integration of geomorphological and luminescence dating of alluvial conglomerates and fluvial terrace sediments

Sedimentary deposits in the foreland basin of the northeastern Qilian Mountains are crucial documents recording tectonic activity and climate changes on the Tibetan Plateau. In this study, luminescence dating was used to date alluvial conglomerates and fluvial terrace sediments collected from the Beida River in the Jiuquan Basin, a foreland basin in the Hexi Corridor, northeastern Qilian Mountains. Detailed sedimentology and luminescence ages reveal that alluvial conglomerates accumulated from before 620 ka to 12 ka and that sediment accumulation rates increased at ∼330 ka and ∼35 ka, coinciding with the dates of two tectonic events (∼350 and ∼50 ka) and followed by climate cooling (from marine isotope stage (MIS) 9 to MIS 8 and from MIS 3 to MIS 2). This reveals that variations in the sediment accumulation rates are controlled by the coupling of tectonic uplift and climate cooling. The highest terrace (T7) that developed on the alluvial conglomerate base formed at ∼ 12 ka. The incision rate in the early Holocene was ∼2.1 mm/yr and increased to ∼14.6 mm/yr during the middle and late Holocene. The variations in the river incision rate provide geomorphic evidence for Holocene climate patterns in arid and semiarid areas. Luminescence dating offers a credible temporal framework for the deposits and reveals climate and tectonic effects on the evolution of the foreland basin, northeastern Qilian Mountains.

New chronological constraints on the Plio-Pleistocene uplift of the Guizhou Plateau, SE margin of the Tibetan Plateau

The Guizhou Plateau represents a geomorphic transition between the Tibetan Plateau and the Yangtze River Plain. It likely formed in response to the propagation of surface uplift in southeastern Tibet during India-Eurasia continental collision. However, the uplift history of the region is unclear largely due to a lack of datable material. The bedrock geology is dominated by carbonate rocks, which contains numerous multi-level caves in the main river valleys that are linked to the river incision history. Cosmogenic 26 Al and 10 Be burial dating of sediments in caves and river terraces from the northwestern and southern plateau reveals the fluvial chronology and provides the first direct determination of long-term river incision rates. The caves and terraces on the Liuchong River in NW Guizhou yield burial ages of between 0.41 ± 0.12 Ma and 2.85 ± 0.21 Ma, indicating an average incision rate of 57 ± 3 m/Ma. Four level caves at Libo in southern Guizhou yield burial ages of between 0.56 ± 0.16 Ma and 3.54 (+0.25/-0.22) Ma, indicating slightly slower incision rate (47 ± 5 m/Ma). These new results imply that the high elevation of the Guizhou Plateau had developed before the Late Pliocene, and that surface uplift during the Late Cenozoic was largely uniform across the region.

Neogene variations in slab geometry drive topographic change and drainage reorganization in the Northern Andes of Colombia

The tropical Northern Andes of Colombia are one the world's most biodiverse places, offering an ideal location for unraveling the linkages between the geodynamic forces that build topography and the evolution of the biota that inhabit it. In this study, we utilize geomorphic analysis to characterize the topography of the Western and Central Cordilleras of the Northern Andes to identify what drives landscape evolution in the region. We supplement our topographic analysis with erosion rate estimates based on gauged suspended sediment loads and river incision rates from volcanic sequences. In the northern Central Cordillera, an elevated low-relief surface (2500 m in elevation, ~40 × 110 km in size) with quasi-uniform lithology and surrounded by knickpoints, indicates a recent increase in rock and surface uplift rate. Whereas the southern segment of the Central Cordillera shows substantially higher local relief and mostly well graded river profiles consistent with longer term uplift-rate stability. We also identify several areas of major drainage reorganization, including captures and divide migrations. These changes in the topography coincide with the proposed location of a slab tear and flat slab subduction under the northern Central Cordillera, as well as with a major transition in the channel slope of the Cauca River. We identify slab flattening as the most likely cause of strong and recent uplift in the Northern Andes leading to ~2 km of surface uplift since 8–4 Ma. Large scale drainage reorganization of major rivers is likely driven by changes in upper plate deformation in relation to development of the flat slab subduction geometry; however, south of the slab tear other factors, such as emplacement of volcanic rocks, also play an important role. Several biologic observations above the area of slab flattening suggest that surface uplift isolated former lowland species on the high elevation plateaus, and drainage reorganization may have influenced the distribution of aquatic species.

Evaluating the Vertical Accuracy of DEM Generated from ZiYuan-3 Stereo Images in Understanding the Tectonic Morphology of the Qianhe Basin, China

Currently available high-resolution digital elevation model (DEM) is not particularly useful to geologists for understanding the long-term changes in fluvial landforms induced by tectonic uplift, although DEMs that are generated from satellite stereo images such as the ZiYuan-3 (ZY3) satellite include characteristics with significant coverage and rapid acquisition. Since an ongoing analysis of fluvial systems is lacking, the ZY3 DEM was generated from block adjustment to describe the mountainous area of the Qianhe Basin that have been induced by tectonic uplift. Moreover, we evaluated the overall elevation difference in ZY3 DEM, Shuttle Radar Topography Mission (1″ × 1″) (SRTM1), and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM) by using the Ice Cloud and Land Elevation Satellite/Geoscience Laser Altimeter (ICESat/GLAH14) point cloud and a DEM of 1:50,000 scale. The values of the root mean square error (RMSE) of the elevation difference for ZY3 DEM were 9.31 and 9.71 m, respectively, and are in good agreement with SRTM1. The river long profiles and terrace heights were also extracted to compare the differences in channel steepness and the incision rates with SRTM1 and ASTER GDEM. Our results prove that ZY3 DEM would be a good alternative to SRTM1 in achieving the 1:50,000 scale for DEM products in China, while ASTER GDEM is unsuitable for extracting river longitudinal profiles. In addition, the northern and southern river incision rates were estimated using the ages and heights of river terraces, demonstrating a range from 0.12–0.45 to 0.10–0.33 m/kyr, respectively. Collectively, these findings suggest that ZY3 DEM is capable of estimating tectonic geomorphological features and has the potential for analyzing the continuous evolutionary response of a landscape to changes in climate and tectonics.

Spatial Variations of Tectonic Uplift - Subducting Plate Effects on the Guerrero Forearc, Mexico

Uplift is the predominant factor controlling fluvial systems in tectonically deforming regions. Mountains along subduction zones force incision, aggradation, or sinuosity modifications, showing differential uplift and variations in erosion rates, in river incision, and in channel gradient produced by ongoing tectonic deformation. Thus, landscape can provide information on the tectonic activity of a defined region. Here, field studies, analysis of geomorphic indices using a digital elevation model, and dating of river terraces were undertaken to extract the following: (1) determine rates of ongoing tectonic deformation, (2) identify evidence of active faulting, and (3) explain the possible relation of ongoing differential uplift in the topography of the overriding plate with the geometry and roughness effects of subducting slab along the Mexican subduction within the Guerrero sector. Landscape analysis using geomorphic indices suggests segmentation along stream of the studied Tecpan River basin. Rates of tectonic uplift were derived from river incision rates computed with the combination of strath terrace heights and associated dating. Tectonic uplift rates vary from ∼1 ± 0.3 mm/yr up to ∼5 ± 0.6 mm/yr during the Holocene, consistent with inferred high tectonic activity in this zone. These results vary significantly spatially, i.e., increasing upstream. Possible explanations for spatial variations of tectonic uplift rates are most likely related to an effect of the geometry and the rugged seafloor of the oceanic Cocos plate subduction beneath a faulted continental lithosphere.

Luminescence Chronology of the Yellow River Terraces in the Heiyukou Area, China, and Its Implication for the Uplift Rate of the Ordos Plateau

Abstract The precise chronology of the fluvial terraces of the Yellow River in China is essential to understand its geomorphological evolution history. More terrace ages are needed for the correlation of the terraces along the river and the construction of the longitudinal profile. In this study, seven terraces (T1–T7) in the Heiyukou area of the Jinshaan Canyon of the river were identified and were sampled for optical dating. The reliability of the ages was evaluated on the bases of bleachability, comparison of optical ages on fine and coarse grains, stratigraphic consistency of OSL ages, age distribution and geomorphological setting. The results show that the paired T2 terrace was formed at 72 ± 3 ka, and the T4, T5 strath terraces were dated to 108 ± 4 and >141 ± 4 ka, respectively. The ages for the samples from T6 and T7 were significantly underestimated, and the ‘infinitely old’ pre-Quaternary Red-Clay sample on the T7 terrace was dated to 134 ± 6 ka. The long-term river incision rates were calculated to be <0.36, 0.34 and 0.18 mm/a for at least the past 141, 108 and 72 ka, respectively, which also reflect the uplift rates of the Ordos plateau. The implication for dating terrace deposits is that terraces should be systemically sampled and dated using both fine and coarse grain fractions. The reliability of the ages obtained for high terraces should be evaluated using a relative chronology of dated samples on a case-by-case basis, if no independent numerical age controls are available.