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Changxing Shi - One of the best experts on this subject based on the ideXlab platform.
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Ages and magnitudes of base level fall and valley Downcutting in ten tributaries (the Ten Kongduis) of the upper Yellow River, China
Geomorphology, 2019Co-Authors: Changxing ShiAbstract:Abstract Using a morphometric dating method and the S-A (channel slope vs. drainage area) power law relation, the history of tectonic uplift and valley Downcutting was investigated in the catchments of the Ten Kongduis (ten ephemeral streams) in Inner Mongolia, China, for the past ca. 5 Ma. These streams drain an area of the northern Ordos Plateau and flow northward into the Hetao Basin where they eventually debouch into the Yellow River. To derive reasonable ages of tectonic perturbation in catchments with obviously different widths between their lower and upper sections, an index was constructed for removing the effect of geometric irregularity on the morphometric ages. The morphometric analysis discloses an episode of tectonic uplift in the study area as early as 2.2–5.8 Ma, an episode or episodes of tectonic uplift after 1.15–0.50 Ma, and an episode of base level fall starting from 0.025–0.036 Ma. In the period of 1.15–0.50 Ma, the eastern stream catchments were uplifted from 0.99–1.15 Ma, a middle stream catchment was uplifted after 0.74 Ma, and a western stream catchment was uplifted after 0.50 Ma. The episode of base level fall after 0.025–0.036 Ma was detected only in some western streams, presumably indicating a recent subsidence episode of the western part of the Hetao Basin. After the episode of tectonic uplift dated to 2.2–5.9 Ma, equilibrium longitudinal profiles were formed in the streams and preserved in the sources of some streams. By comparing the elevations of the projected equilibrium profiles based on their S-A power law relations with the current ones, and considering the valley Downcutting of the equilibrium profiles in the past 0.5–1.15 Ma, the largest valley Downcutting magnitude upstream of the southernmost fault between the Ordos Plateau and the Hetao Basin in two western and three eastern streams was found to be in the ranges of 142–194 m and 52–145 m, respectively, and the base level fall at the northernmost fault between the plateau and the basin was estimated to be 317 m and 138 m on average for the two western and three eastern streams, respectively.
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Knickpoints within the Suoshui watershed and the implication for the age of sandstone pillars in Zhangjiajie, China
Geomorphology, 2014Co-Authors: Changxing Shi, Wenwei ShaoAbstract:Using DEM and topographic and geological maps alongside field surveys, this study investigated the characteristics and retreat processes of the knickpoints along the mainstream and major tributaries of the Suoshui watershed. Seven disequilibrium transient knickpoints are found along the mainstream, and 0-6 are on the trunk of each of the major tributaries. The knickpoints are labeled from KP0 to KP7 from the lowest to the highest according to their spatial position. The average drop across each knickpoint is in the range of 9-19 m, and the cumulative fall from KP7 to KP0 is about 107 m. Using a brute force two-parameter search, the coefficient m in the stream power incision model for the Suoshui watershed is found to be 0.525, and the coefficient K is variable with an inverse relationship with channel steepness. Using the stream power incision model with these parameters, the time for the highest knickpoint (KP7) to retreat from the mouth of the Suoshui River to its present location is found to be ca. 0.454 Ma. Based on the relationship between the cumulative fall and migration time of knickpoints, the average Downcutting rate of the Suoshui River is estimated to be 0.224 mm/a in the past 0.454 Ma. By comparing the Downcutting rates with the height of typical sandstone pillars in the Suoshui watershed, the formation of these pillars might commence in the early Pleistocene. (C) 2014 Elsevier B.V. All rights reserved.
Chunyen Chou - One of the best experts on this subject based on the ideXlab platform.
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the preservation of last glacial 50 to 40 ka colluvium on low relief surfaces in alishan an actively uplifting mountain in southwestern taiwan
Geomorphology, 2018Co-Authors: Menglong Hsieh, Alan Hogg, Suchen Kang, Chunyen ChouAbstract:Abstract Geomorphic studies on the Taiwan orogen have long focused on the rapid erosion and efficient sediment transport in response to active tectonic uplift and frequent earthquakes/heavy rains. Little attention has been paid to the common low-relief surfaces in high mountains that appear to have been geomorphically stable for a long period of time. We undertook a study on a group of such gentle surfaces in Alishan, which consist of poorly drained hummocky slopes averaging 15° and as wide as 2 km. These gentle slopes are underlain by mass-wasting gravels 60–100 m thick, from which 22 radiocarbon dates >50 to 40 ka BP in age were obtained. Below these thick colluvial deposits are ~20° bedrock bedding planes apparently exposed by dip-slope failures. Combining these data reveals alternating hillslope erosion and deposition, along with episodic river Downcutting, at a time scale of several 104 yr. We relate this temporal change in geomorphic processes to glacial-interglacial climate change. During the wet inter-/post-glacial periods characterized by frequent heavy rains, landslides/debris flows prevailed and rivers were capable of conveying most sediment eroded from hillslopes. Frequent debris flows combined with sufficient bedload sediments serving as tools for fluvial erosion caused rapid river Downcutting. In contrast, the low river erosion/transport capacity during the dry last-glacial period allowed progressive deposition of thick colluvium on the preexisting, gentle bedding surfaces probably eroded during the last interglacial period. This study shows how glacial-interglacial climate change influenced the river/hillslope processes and landscape evolution of the Taiwan orogen.
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The preservation of last-glacial (>50 to 40 ka) colluvium on low-relief surfaces in Alishan, an actively uplifting mountain in southwestern Taiwan
Geomorphology, 2018Co-Authors: Menglong Hsieh, Suchen Kang, Alan G. Hogg, Chunyen ChouAbstract:Abstract Geomorphic studies on the Taiwan orogen have long focused on the rapid erosion and efficient sediment transport in response to active tectonic uplift and frequent earthquakes/heavy rains. Little attention has been paid to the common low-relief surfaces in high mountains that appear to have been geomorphically stable for a long period of time. We undertook a study on a group of such gentle surfaces in Alishan, which consist of poorly drained hummocky slopes averaging 15° and as wide as 2 km. These gentle slopes are underlain by mass-wasting gravels 60–100 m thick, from which 22 radiocarbon dates >50 to 40 ka BP in age were obtained. Below these thick colluvial deposits are ~20° bedrock bedding planes apparently exposed by dip-slope failures. Combining these data reveals alternating hillslope erosion and deposition, along with episodic river Downcutting, at a time scale of several 104 yr. We relate this temporal change in geomorphic processes to glacial-interglacial climate change. During the wet inter-/post-glacial periods characterized by frequent heavy rains, landslides/debris flows prevailed and rivers were capable of conveying most sediment eroded from hillslopes. Frequent debris flows combined with sufficient bedload sediments serving as tools for fluvial erosion caused rapid river Downcutting. In contrast, the low river erosion/transport capacity during the dry last-glacial period allowed progressive deposition of thick colluvium on the preexisting, gentle bedding surfaces probably eroded during the last interglacial period. This study shows how glacial-interglacial climate change influenced the river/hillslope processes and landscape evolution of the Taiwan orogen.
Frederik M. Van Der Wateren - One of the best experts on this subject based on the ideXlab platform.
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Contrasting Neogene denudation histories of different structural regions in the Transantarctic Mountains rift flank constrained by cosmogenic isotope measurements
1999Co-Authors: Frederik M. Van Der Wateren, Tibor J. Dunai, Ronald T. Van Balen, Werner Klas, A.l.l.m. Verbers, Sandra Passchier, U. HerpersAbstract:Separate regions within the Transantarctic Mountains, the uplifted flank of the West Antarctic rift system, appear to have distinct Neogene histories of glaciation and valley Downcutting. Incision of deep glacial outlet valleys occurred at different times throughout central and northern Victoria Land. This is corroborated by measurements of cosmogenic nuclides 21Ne, robe and 26Al of glacial erosion surfaces and high-elevated moraines. 21Ne ages of two summit plateaus, at elevations of 1650 m in central Victoria Land and ~ 2800 m in northern Victoria Land, range from 3.84 to 11.2 Ma, respectively. The latter date indicates that these glacial erosion surfaces are the oldest known exposure dated surfaces on Earth. Glacial erosion terraces, remnants of early phases of valley Downcutting, have 21Ne ages of 1.27 and 6.45 Ma for central and northern Victoria Land, respectively. Therefore, deglaciation of summit plateaus, valley Downcutting and topographic uplift occurred during the Mid-Miocene in northern Victoria Land and not earlier than the Mid-Pliocene in central Victoria Land. In northern Victoria Land, ice flow directions changed markedly from the time a regional ice sheet occupied the level of the highest summits to the present condition with summits rising up to 800 above the valley glaciers. In central Victoria Land, the oldest documented ice flow direction occupying the summit erosion surface prior to incision was SW-NE, draining the East Antarctic Ice Sheet along an outlet glacier at least 10 times as wide as the present E-W-flowing David Glacier. This great variation in denudation histories probably results from differential tectonic uplift of various regions within the presently active rift flank. Three tectonic processes contribute to Late Neogene uplift: (1) ongoing extension in adjacent Ross Sea rift basins; (2) regional dextral transtension following SE-trending Precambrian and Palaeozoic structural trends which offsets the ~ N-S-trending grain of the rift and reactivates earlier faults; and (3) isostatic response to valley Downcutting and related denudation. (C) 1999 Elsevier Science B.V.
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Contrasting Neogene denudation histories of different structural regions in the Transantarctic Mountains rift flank constrained by cosmogenic isotope measurements
Global and Planetary Change, 1999Co-Authors: Frederik M. Van Der WaterenAbstract:Separate regions within the Transantarctic Mountains, the uplifted flank of the West Antarctic rift system, appear to have distinct Neogene histories of glaciation and valley Downcutting. Incision of deep glacial outlet valleys occurred at different times throughout central and northern Victoria Land. This is corroborated by measurements of cosmogenic nuclide
Kelvin Berryman - One of the best experts on this subject based on the ideXlab platform.
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the post glacial Downcutting history in the waihuka tributary of waipaoa river gisborne district implications for tectonics and landscape evolution in the hikurangi subduction margin new zealand
Marine Geology, 2010Co-Authors: Kelvin Berryman, Michael Marden, A S Palmer, Kate Wilson, Colin Mazengarb, Nicola LitchfieldAbstract:Abstract Determining the spatial and temporal deliveries of sediment from the Waipaoa River catchment in the post-glacial period is a major goal of integrated source-to-sink landscape evolution studies in the region. In a 2.2 km long section of the Waihuka tributary (217 km 2 ) of the Waipaoa River (2150 km 2 ) in eastern North Island, New Zealand, a sequence of at least ten fluvial terraces and abandoned meanders up to 45 m above the present river records rates and times of post-glacial Downcutting. Dateable organic and tephra horizons in the terrace and meander infill stratigraphy indicate that Downcutting at this location on the Waihuka tributary was dominated by a short-lived event in the early Holocene from 10–8 ka BP, when as much as half of the Downcutting was accomplished in only 10–15% of post-glacial time. The large Downcutting event is interpreted to record the passing of a succession of major knickpoints or a knickzone through this tributary. The initiation of knickpoint retreat in the catchment was primarily a consequence of reduction in sediment supply at the end of MIS 2. Based on the timing of rapid Downcutting in the Waipaoa River mainstem, we estimate that the rate of knickpoint retreat along the Waihuka tributary was about 2 km/kyr. In the period before and after rapid Downcutting in the Waihuka tributary, modest incision rates, averaging 1–2 mm/yr, probably represent the regional tectonic uplift rate.
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Dating the culmination of river aggradation at the end of the last glaciation using distal tephra compositions, eastern North Island, New Zealand
Geomorphology, 2001Co-Authors: Dennis N. Eden, Michael Marden, Alan Palmer, Shane J. Cronin, Kelvin BerrymanAbstract:An extensive terrace (Waipaoa-1) that can be traced for about 29 km in the Waipaoa valley, eastern North Island, New Zealand, is underlain by at least 10 m of coarse, aggradational, river gravels. Terrace cover beds contain tephras erupted from central North Island volcanoes and these provide minimum ages for the underlying gravels. Tephra or tephric layers occurring in the lower cover beds were investigated at five sites using a combination of stratigraphy, mineralogy, and the major element composition of glass shards together with discriminant function analysis (DFA). The basal tephra is identified as the ca. 14,700 14C years old (ca. 17,700 cal. years B.P.) Rerewhakaaitu Tephra, erupted from Okataina Volcanic Centre. Using the stratigraphic relationship of Rerewhakaaitu Tephra, the end of aggradation is dated at ca. 15,000 14C years (ca. 18,000 cal. years). Correlation with aggradational terraces elsewhere in North Island and northern South Island indicates that aggradation ended at the same time over a wide area and confirms a climatic origin for the terraces. Subsequent Downcutting was apparently rapid because Rerewhakaaitu Tephra also occurs at the base of cover beds on a ca. 15 m lower terrace. The Downcutting represents a major change in river dynamics and is most likely the response to climatic change and the resultant upper catchment landscape stability.
John E Whittaker - One of the best experts on this subject based on the ideXlab platform.
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a new chronological framework for middle and upper pleistocene landscape evolution in the sussex hampshire coastal corridor uk
Proceedings of the Geologists' Association, 2010Co-Authors: Martin Bates, Rebecca M Briant, Edward J Rhodes, Jeanluc Schwenninger, John E WhittakerAbstract:The unique Middle and Late Pleistocene sedimentary record preserved along the Sussex/Hampshire Coastal Corridor between Romsey and Brighton contains a wealth of deposits including highstand marine sediments associated with a variety of different aged beaches, fluvial sediments associated with rivers crossing the coastal plain and cold stage deposits accumulating above the marine and fluvial sediments. Although quarrying activity has been extensive across much of the area it has been undertaken in flooded workings due to the high level of the watertable. Consequently little is known in detail about the sequences except where they outcrop on the foreshore around the coast. This paper examines recent work from the lower coastal plain using a multi-disciplinary approach these deposits to elucidate the age of the sequences and their associated environments of deposition. OSL dates from two of the beaches, the Aldingbourne and Brighton/Norton Beaches, place both within MIS 7. Although these OSL dates cannot differentiate between sub-stages within MIS 7, coupling these results with inferences from local geography, lithology and contained microfossils it is clear that the beaches belong to two different phases within MIS 7. These two beaches are clearly divided by a major phase of erosion and Downcutting associated with a fall in sea-level. Fluvial sediments from Solent Terrace 2 and Arun Terrace 4 also date within MIS 7 and are tentatively ascribed to the Downcutting event between the beaches. Together this information allows us to propose, for the first time, a robust independently dated framework for the lower parts of the coastal plain integrating for the first time the marine and terrestrial record.
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A new chronological framework for Middle and Upper Pleistocene landscape evolution in the Sussex/Hampshire Coastal Corridor, UK
Proceedings of the Geologists' Association, 2010Co-Authors: Martin Bates, Rebecca M Briant, Edward J Rhodes, Jeanluc Schwenninger, John E WhittakerAbstract:The unique Middle and Late Pleistocene sedimentary record preserved along the Sussex/Hampshire Coastal Corridor between Romsey and Brighton contains a wealth of deposits including highstand marine sediments associated with a variety of different aged beaches, fluvial sediments associated with rivers crossing the coastal plain and cold stage deposits accumulating above the marine and fluvial sediments. Although quarrying activity has been extensive across much of the area it has been undertaken in flooded workings due to the high level of the watertable. Consequently little is known in detail about the sequences except where they outcrop on the foreshore around the coast. This paper examines recent work from the lower coastal plain using a multi-disciplinary approach these deposits to elucidate the age of the sequences and their associated environments of deposition. OSL dates from two of the beaches, the Aldingbourne and Brighton/Norton Beaches, place both within MIS 7. Although these OSL dates cannot differentiate between sub-stages within MIS 7, coupling these results with inferences from local geography, lithology and contained microfossils it is clear that the beaches belong to two different phases within MIS 7. These two beaches are clearly divided by a major phase of erosion and Downcutting associated with a fall in sea-level. Fluvial sediments from Solent Terrace 2 and Arun Terrace 4 also date within MIS 7 and are tentatively ascribed to the Downcutting event between the beaches. Together this information allows us to propose, for the first time, a robust independently dated framework for the lower parts of the coastal plain integrating for the first time the marine and terrestrial record.