Journal articles: 'Continental denudation'

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HOWELL, D. G., and R. W. MURRAY. "A Budget for Continental Growth and Denudation." Science 233, no. 4762 (July 25, 1986): 446–49. http://dx.doi.org/10.1126/science.233.4762.446.

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Willenbring, J. K., A. T. Codilean, K. L. Ferrier, B. McElroy, and J. W. Kirchner. "Short Communication: Earth is (mostly) flat, but mountains dominate global denudation: apportionment of the continental mass flux over millennial time scales, revisited." Earth Surface Dynamics Discussions 2, no. 1 (January 29, 2014): 1–17. http://dx.doi.org/10.5194/esurfd-2-1-2014.

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Abstract. Carbon dioxide consumption by silicate mineral weathering and the subsequent precipitation of carbonate sediments sequesters CO2 over geologic timescales. The rate of this carbon sequestration is coupled to rates of continental erosion, which exposes fresh minerals to weathering. Steep mountain landscapes represent a small fraction of continental surfaces but contribute disproportionately to global erosion rates. However, the relative contributions of Earth's much vaster, but more slowly eroding, plains and hills remain the subject of debate. Recently, Willenbring et al. (2013) analyzed a compilation of denudation rates and topographic gradients and concluded that low-gradient regions dominate global denudation fluxes and silicate weathering rates. Here, we show that Willenbring et al. (2003) topographic and statistical analyses were subject to methodological errors that affected their conclusions. We correct these errors, and reanalyze their denudation rate and topographic data. In contrast to the results of Willenbring et al. (2013), we find that the denudation flux from the steepest 10% of continental topography nearly equals the flux from the other 90% of the continental surface combined. This new analysis implies global denudation fluxes of ∼23 Gt yr−1, roughly five times the value reported in Willenbring et al. (2013) and closer to previous estimates found elsewhere in the literature. Although low-gradient landscapes make up a small proportion of the global fluxes, they remain important because of the human reliance, and impact, on these vast areas.

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Jelinek, Andrea Ritter. "Evolução Paleotopográfica da Margem Continental Brasileira durante o Fanerozoico: Evidências a partir da Termocronologia por Traços de Fissão em Apatitas (Paleotopographic Evolution of the Brazilian Continental Margin during the Phanerozoic: Evidence from Apatite Fission Track Thermochronology)." Revista Brasileira de Geografia Física 12, no. 4 (November 22, 2019): 1670. http://dx.doi.org/10.26848/rbgf.v12.4.p1670-1686.

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Este trabalho explora banco de dados traços de fissão em apatitas com o objetivo de desenvolver uma visão sinóptica de padrões de denudação através do espaço-tempo na margem continental brasileira. A resposta geomorfológica aos processos de rifteamento e ruptura continental variou ao longo da margem continental brasileira. No processo de construção do relevo desta margem foram registrados três episódios de resfriamento acelerado, que são vinculados a processos denudacionais: Cretáceo Inferior, Cretáceo Superior e Paleógeno-Neógeno. As margens continentais sudeste e leste apresentam uma morfologia de margem continental passiva característica, com as bacias sedimentares offshore separadas da região continental elevada, composta pelas Serra do Mar e da Serra da Mantiqueira, por uma planície costeira relativamente estreita. As idades de soerguimento são mais jovens do que a idade do rifteamento. O resfriamento do Paleógeno-Neógeno é resultado do aumento nas taxas de denudação, que são relacionados à formação e reativação de blocos de falha de alto ângulo que se moveram em resposta às tensões intraplaca. A região do Arco de Ponta Grossa apresenta o relevo mais jovem de toda a margem, sendo um alto topográfico associado ao magmatismo Paraná-Etendeka e limitado por zonas de cisalhamento. Duas porções da margem apresentam relevo diferenciado, com episódios de denudação pré-rifte. A Depressão Sertaneja, na margem nordeste, típica região semi-árida do nordeste caracterizada como um pediplano, com vales estreitos e vertentes dissecadas, com resfriamento do Permiano-Jurássico Inferior; e a margem sul, local com topografia baixa, e soerguimento lento e contínuo do Paleozoico.A B S T R A C TThis study explores apatite fission track database with the objective of developing a synoptic view of denudation patterns across space and time in the Brazilian continental margin. The geomorphological response to the continental rift and rupture processes varied along the Brazilian continental margin. In the construction of the relief of this margin were recorded three episodes of accelerated cooling, which are linked to denudational processes: Lower Cretaceous, Upper Cretaceous and Paleogene-Neogene episodes. The southeast and eastern continental margin presents a characteristic passive continental margin morphology, with the offshore sedimentary basins separated from the elevated continental region, Serra do Mar and Serra da Mantiqueira, for a relatively narrow coastal plain. The uplifting ages are younger than the rift age. Accelerated cooling during Paleogene-Neogene is a result of increased denudation rates, which are related to the formation and reactivation of high angle fault blocks that have moved in response to intraplate stresses. The region of the Ponta Grossa Arch presents the youngest relief of the entire continental margin. It is a high topographic associated with Paraná-Etendeka magmatism and limited by shear zones. There are two parts of the continental margin with differentiated relief, which present episodes of pre-rift denudation. The Sertaneja Depression, in the northeast margin, a typical semi-arid northeast region characterized as a pediplane, with narrow valleys and dissected slopes, where occurs a Permian-Lower Jurassic cooling episode; and the south continental margin, where the topography is relatively, registering a slow and continuous uplift during the Paleozoic. Keywords: Paleotopography, rift continental margin, apatite fission tracks

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Lisker, Frank, Christopher J. L. Wilson, and Helen J. Gibson. "Thermal history of the Vestfold Hills (East Antarctica) between Lambert rifting and Gondwana break-up, evidence from apatite fission track data." Antarctic Science 19, no. 1 (February 28, 2007): 97–106. http://dx.doi.org/10.1017/s0954102007000144.

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Analysis of five basement samples from the Vestfold Hills (East Antarctica) reveals pooled apatite fission track (FT) ages ranging from 188 to 264 Ma and mean lengths of 13.7 to 14.9 μm. Quantitative thermal histories derived from these data give consistent results indicating onset of cooling/denudation began sometime prior to 240 Ma, with final cooling below 105°–125°C occurring between 240 and 220 Ma (Triassic). A Cretaceous denudation phase can be inferred from the sedimentary record of the Prydz Bay offshore the Vestfold Hills. The two denudational episodes are likely associated with Palaeozoic large-scale rifting processes that led to the formation of the adjacent Lambert Graben, and to the Cretaceous Gondwana break-up between Antarctica and India. Subsequent evolution of the East Antarctic passive continental margin likely occurred throughout the Cenozoic based on the depositional record in Prydz Bay and constraints (though tentative) from FT data.

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Codilean, A. T., R. H. Fülöp, H. Munack, K. M. Wilcken, T. J. Cohen, D. H. Rood, D. Fink, R. Bartley, J. Croke, and L. K. Fifield. "Controls on denudation along the East Australian continental margin." Earth-Science Reviews 214 (March 2021): 103543. http://dx.doi.org/10.1016/j.earscirev.2021.103543.

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Bishop, Paul. "Southeast Australian late Mesozoic and Cenozoic denudation rates: A test for late Tertiary increases in continental denudation." Geology 13, no. 7 (1985): 479. http://dx.doi.org/10.1130/0091-7613(1985)13<479:salmac>2.0.co;2.

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Kerr, Andrew, and Alan Gilchrist. "Glaciation, erosion and the evolution of the Transantarctic Mountains, Antarctica." Annals of Glaciology 23 (1996): 303–8. http://dx.doi.org/10.1017/s0260305500013574.

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Modelling studies of the tectonic evolution of the Transantarctic Mountains in Antarctica have drawn differing conclusions as to the primary mechanisms involved. None has considered the role of the East Antarctic ice sheet in detail. We use a denudation—flexural model to examine the isostatic response of the continental margin to glacial erosion to determine whether glacial processes have played a role in forcing mountain uplift. The conclusion is that, although there are insufficient data formally to delimit the role of glacial erosion, available geophysical and geomorphological data are not inconsistent with the results of the differential denudation model, providing certain conditions are met. These results indicate that the current topography of the Transantarctic Mountains can be simulated, in part, from the isostatic response of the lithosphere to glacial erosion. The short wavelength and high amplitude of the Transantarctic Mountains do not require a low flexural rigidity in the unrated lithosphere, provided there is a fast escarpment retreat from the rift hinge, high escarpment denudation rates and a large differential in denudation between the coastal zone and the interior.

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Kerr, Andrew, and Alan Gilchrist. "Glaciation, erosion and the evolution of the Transantarctic Mountains, Antarctica." Annals of Glaciology 23 (1996): 303–8. http://dx.doi.org/10.3189/s0260305500013574.

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Modelling studies of the tectonic evolution of the Transantarctic Mountains in Antarctica have drawn differing conclusions as to the primary mechanisms involved. None has considered the role of the East Antarctic ice sheet in detail. We use a denudation—flexural model to examine the isostatic response of the continental margin to glacial erosion to determine whether glacial processes have played a role in forcing mountain uplift.The conclusion is that, although there are insufficient data formally to delimit the role of glacial erosion, available geophysical and geomorphological data are not inconsistent with the results of the differential denudation model, providing certain conditions are met. These results indicate that the current topography of the Transantarctic Mountains can be simulated, in part, from the isostatic response of the lithosphere to glacial erosion. The short wavelength and high amplitude of the Transantarctic Mountains do not require a low flexural rigidity in the unrated lithosphere, provided there is a fast escarpment retreat from the rift hinge, high escarpment denudation rates and a large differential in denudation between the coastal zone and the interior.

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Kravchuk, Yaroslav, and Vasyl Chalyk. "PRECARPATHIAN AND TRANSCARPATHIAN LANDFORM EVOLUTION IN THE PLIOCENE-PLEOSTOCENE AND AT EARLY STAGES." PROBLEMS OF GEOMORPHOLOGY AND PALEOGEOGRAPHY OF THE UKRANIAN CARPATHIANS AND ADJACENT AREAS, no. 09 (01) (September 25, 2019): 154–65. http://dx.doi.org/10.30970/gpc.2019.1.2808.

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The Sarmatian-Pannonian and Pontian-Pliocene stages are most important in the landform evolution of the Inner Precarpathians and Solotvyn basin. Due to the intense elevations in the upper Miocene, the Precarpathian Sea was pushed to the east and northeast. On the land freed from the sea, a hydrographic network was created, and rivers moved along the retreating sea in Northeast and Southeast directions. Original river valleys were of diagonal and inline outflow directions unlike modern transverse valleys. The Pontian-Pliocene is associated with the final phase of Carpathian and Precarpathian tectogenesis, and the proof is the undisturbed Pliocene denudation surface (Hofstein, 1985) or the upper denudation level (Teisseyre, 1933). The Solotvyno basin had continental regime before the Mukachevo basin had, so the Solotvyno basin got denudation and denudation-accumulative surfaces formed. These include the oldest denudation “Kichersky Level” researched by H. Alferyev (1948), which is believed to date to the early Pannonian. Younger denudation and denudation-accumulative surfaces are consistent with the Precarpathian and Transcarpathian regions. In the Precarpathian region, most authors distinguished two denudation-accumulative surfaces (terraces) – Krasna and Loyeva, and in the Transcarpathian, three – Dilotska, Boronyavska and Shardynska. In the Precarpathian region, they first identified pediments (Kravchuk, 1971), dating back to the Pliocene – early Pleistocene. Subsequently, I. Hofstein suggested that they should be dated the late Pliocene by analogy with the Transcarpathian pediments of Ye. Mazur (1963), but he did not deny that their formation continued in the Pleistocene. The prolonged weakening of the elevation in the early Pleistocene led to the predominance of lateral erosion, expansion of valley bottoms, and intense erosion of ancient terraces (denudation-accumulating surfaces). The analysis of terrace complexes in the Precarpathians and Transcarpathians makes it possible to determine the average heights of the Pliocene-Pleistocene elevations, which confirms the synchronicity of the landform evolution in these regions. Key words: denudation and denudation-accumulative surfaces; terraces; pediments; Pliocene-Pleistocene elevation; Precarpathians; Transcarpathians.

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Dokka, RoyK, and MichaelJ Mahaffie. "Tectonic denudation: The forgotten mechanism for rapid cooling of continental interiors." Nuclear Tracks and Radiation Measurements (1982) 10, no. 3 (January 1985): 407. http://dx.doi.org/10.1016/0735-245x(85)90136-x.

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MAROTTA, ANNA MARIA, MANUEL RODA, KATYA CONTE, and MARIA IOLE SPALLA. "Thermo-mechanical numerical model of the transition from continental rifting to oceanic spreading: the case study of the Alpine Tethys." Geological Magazine 155, no. 2 (October 3, 2016): 250–79. http://dx.doi.org/10.1017/s0016756816000856.

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AbstractWe develop a two-dimensional thermo-mechanical numerical model in which the formation of oceanic crust and serpentinite due to the hydration of the uprising mantle peridotite has been implemented, with the aim of discussing the behaviour of the lithosphere of the Alps and Northern Apennines during the transition from continental rifting to ocean spreading of the Alpine Tethys. The predictions of the model are compared with natural data related to the Permian–Triassic high-temperature – low-pressure (HT-LP) metamorphism affecting the continental lithosphere and data from the JurassicP–Tevolution of the oceanic lithosphere from the Alps and the Northern Apennines. Our analysis indicates that a thinned continental crust, an ocean–continent transition zone and an oceanic lithosphere characterize the final structure of the system in a poor magma rift pre-Alpine configuration. We also find that mantle serpentinization starts before crustal break-up and that denudation occurs before ocean spreading. The mantle denudation starts several million years before the gabbros/basalt formation, generating an ocean–continent transition zone from the passive continental margin to the oceanic lithosphere of size 160–280 km. The comparative analysis shows that the extension of a hot and weak lithosphere, which promotes the development of hyperextended Alpine margins, better agrees with the natural data. Finally, our comparative analysis supports the hypothesis that the lithospheric extension preceding the opening of the Alpine Tethys did not start in a stable continental lithosphere, but developed by recycling part of the old Variscan collisional suture.

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Stewart, A. D. "The ratio of mechanical to chemical denudation in alluvial systems, derived from geochemical mass balance." Transactions of the Royal Society of Edinburgh: Earth Sciences 84, no. 1 (1993): 73–78. http://dx.doi.org/10.1017/s0263593300005939.

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ABSTRACTMass balance equations are derived which link the ratios Ts/ (suspended load/dissolved load from chemical weathering) and Tb/Ts (bed load/suspended load), with any two geochemical components present in the source rock and the alluvial system. If the dissolved load is unknown the ratios can be estimated from the relatively insoluble silica and alumina. The ratio Ts/, which for large river basins depends on climate and relief, can thus potentially be determined from ancient alluvial sequences.The equations help define the source composition of a group of 13 modern rivers for which Ts, and alluvial geochemistry are known. These rivers together drain 27% of the continental surface. For a source area with the average continental sandstone to shale ratio of 0·6 the observed average value of Ts/ is obtained when limestone, sandstone and shale are present in the proportions 6·7:21·6:35·7. The figure of 64% sediment in the source area is very similar to the 66% determined by Blatt and Jones (1975) from geological maps of the continents. The equations also show that average bed load transport rate into these 13 basins is about 27% of total transport, and into the Amazon basin about 37%. Bed load transport rates out of the basins, into the sea, are relatively very small.

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Souza, Daniel H., Peter C. Hackspacher, Bruno V. Silva, Marli C. Siqueira-Ribeiro, and Silvio T. Hiruma. "Temporal and spatial denudation trends in the continental margin of southeastern Brazil." Journal of South American Earth Sciences 105 (January 2021): 102931. http://dx.doi.org/10.1016/j.jsames.2020.102931.

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Green, Paul F., Karna Lidmar-Bergström, Peter Japsen, Johan M. Bonow, and James A. Chalmers. "Stratigraphic landscape analysis, thermochronology and the episodic development of elevated, passive continental margins." Geological Survey of Denmark and Greenland (GEUS) Bulletin 30 (December 30, 2013): 1–150. http://dx.doi.org/10.34194/geusb.v30.4673.

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The continental margin of West Greenland is similar in many respects to other elevated, passive continental margins (EPCMs) around the world. These margins are characterised by extensive regions of low relief at elevations of 1–2 kilometres above sea level sloping gently inland, with a much steeper, oceanward decline, often termed a 'Great Escarpment', terminating at a coastal plain. Recent studies, based on integration of geological, geomorphological and thermochronological evidence, have shown that the high topography of West Greenland was formed by differential uplift and dissection of an Oligo-Miocene peneplain since the late Miocene, many millions of years after continental break-up between Greenland and North America. In contrast, many studies of other EPCMs have proposed a different style of development in which the high plateaux and the steep, oceanward decline are regarded as a direct result of rifting and continental separation. Some studies assume that the elevated regions have remained high since break-up, with the high topography continuously renewed by isostasy. Others identify the elevated plains as remnants of pre-rift landscapes. Key to understanding the development of the West Greenland margin is a new approach to the study of landforms, stratigraphic landscape analysis, in which the low-relief, high-elevation plateaux at EPCMs are interpreted as uplifted peneplains: low-relief surfaces of large extent, cutting across bedrock of different age and resistance, and originally graded to sea level. Identification of different generations of peneplain (re-exposed and epigene) from regional mapping, combined with geological constraints and thermochronology, allows definition of the evolution leading to the formation of the modern-day topography. This approach is founded particularly on results from the South Swedish Dome, which document former sea levels as base levels for the formation of peneplains. These results support the view that peneplains grade towards base level, and that in the absence of other options (e.g. widespread resistant lithologies), the most likely base level is sea level. This is particularly so at continental margins due to their proximity to the adjacent ocean. Studies in which EPCMs are interpreted as related to rifting or break-up commonly favour histories involving continuous denudation of margins following rifting, and interpretation of thermochronology data in terms of monotonic cooling histories. However, in several regions, including southern Africa, south-east Australia and eastern Brazil, geological constraints demonstrate that such scenarios are inappropriate, and an episodic development involving post-breakup subsidence and burial followed later by uplift and denudation is more realistic. Such development is also indicated by the presence in sedimentary basins adjacent to many EPCMs of major erosional unconformities within the post-breakup sedimentary section which correlate with onshore denudation episodes. The nature of the processes responsible is not yet understood, but it seems likely that plate-scale forces are required in order to explain the regional extent of the effects involved. New geodynamic models are required to explain the episodic development of EPCMs, accommodating post-breakup subsidence and burial as well as subsequent uplift and denudation, long after break-up which created the characteristic, modern-day EPCM landscapes.

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Bigot-Cormier, Florence, Christophe Basile, Gérard Poupeau, Jean-Pierre Bouillin, and Erika Labrin. "Denudation of the Côte d'Ivoire-Ghana transform continental margin from apatite fission tracks." Terra Nova 17, no. 2 (April 8, 2005): 189–95. http://dx.doi.org/10.1111/j.1365-3121.2005.00605.x.

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Campforts, Benjamin, Veerle Vanacker, Frédéric Herman, Matthias Vanmaercke, Wolfgang Schwanghart, Gustavo E. Tenorio, Patrick Willems, and Gerard Govers. "Parameterization of river incision models requires accounting for environmental heterogeneity: insights from the tropical Andes." Earth Surface Dynamics 8, no. 2 (June 3, 2020): 447–70. http://dx.doi.org/10.5194/esurf-8-447-2020.

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Abstract. Landscape evolution models can be used to assess the impact of rainfall variability on bedrock river incision over millennial timescales. However, isolating the role of rainfall variability remains difficult in natural environments, in part because environmental controls on river incision such as lithological heterogeneity are poorly constrained. In this study, we explore spatial differences in the rate of bedrock river incision in the Ecuadorian Andes using three different stream power models. A pronounced rainfall gradient due to orographic precipitation and high lithological heterogeneity enable us to explore the relative roles of these controls. First, we use an area-based stream power model to scrutinize the role of lithological heterogeneity in river incision rates. We show that lithological heterogeneity is key to predicting the spatial patterns of incision rates. Accounting for lithological heterogeneity reveals a nonlinear relationship between river steepness, a proxy for river incision, and denudation rates derived from cosmogenic radionuclide (CRNs). Second, we explore this nonlinearity using runoff-based and stochastic-threshold stream power models, combined with a hydrological dataset, to calculate spatial and temporal runoff variability. Statistical modeling suggests that the nonlinear relationship between river steepness and denudation rates can be attributed to a spatial runoff gradient and incision thresholds. Our findings have two main implications for the overall interpretation of CRN-derived denudation rates and the use of river incision models: (i) applying sophisticated stream power models to explain denudation rates at the landscape scale is only relevant when accounting for the confounding role of environmental factors such as lithology, and (ii) spatial patterns in runoff due to orographic precipitation in combination with incision thresholds explain part of the nonlinearity between river steepness and CRN-derived denudation rates. Our methodology can be used as a framework to study the coupling between river incision, lithological heterogeneity and climate at regional to continental scales.

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Andersen, T., G. A. Botha, and M. A. Elburg. "A late Mesozoic – early Cenozoic sedimentary recycling system on the Gondwana rifted margin of southeast Africa." South African Journal of Geology 123, no. 3 (September 1, 2020): 343–56. http://dx.doi.org/10.25131/sajg.123.0023.

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Abstract Detrital zircons in late Cretaceous – Palaeogene, calcareous sandstone and conglomerate deposited in continental basins on the southeastern African margin after the breakup of Gondwana have characteristic combinations of age and epsilon-Hf that indicate an origin by recycling of Palaeoproterozoic (Waterberg, Soutpansberg and Pretoria groups) and Phanerozoic (Karoo Supergroup) cover successions. The latter is dominant in the south and east (Boane, Mahosi, Chilojo Cliffs), and the Palaeoproterozoic sources in the northwest (Pafuri, Wright’s Tower, Masisi). This recycling and mixing regime was restricted to late Mesozoic and Palaeogene time in northeastern South Africa and adjoining parts of Mozambique and Zimbabwe. Detrital zircon distribution patterns in these deposits reflect the denudation history of the southern African continental surface after breakup of the Gondwana supercontinent.

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Zhang, Lili, Muhong Chen, Rong Xiang, Lanlan Zhang, and Jun Lu. "Productivity and continental denudation history from the South China Sea since the late Miocene." Marine Micropaleontology 72, no. 1-2 (June 2009): 76–85. http://dx.doi.org/10.1016/j.marmicro.2009.03.006.

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Mellett, Claire L., David M. Hodgson, Andrew J. Plater, Barbara Mauz, Ian Selby, and Andreas Lang. "Denudation of the continental shelf between Britain and France at the glacial–interglacial timescale." Geomorphology 203 (December 2013): 79–96. http://dx.doi.org/10.1016/j.geomorph.2013.03.030.

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Hiscott, Richard N., and Ali E. Aksu. "Quaternary Sedimentary Processes and Budgets in Orphan Basin, Southwestern Labrador Sea." Quaternary Research 45, no. 2 (March 1996): 160–75. http://dx.doi.org/10.1006/qres.1996.0017.

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AbstractThe continental slope in Orphan Basin, northeast of Newfoundland, is underlain by several seaward-thinning debris-flow wedges alternating with acoustically stratified, regionally extensive, mainly hemipelagic sediments. δ18O stratigraphy and volcanic ash layers in a 11.67-m core indicate that the uppermost debris-flow wedge formed during the last of several sea-level lowstands in isotopic stages 2–4. Similarly, seismic reflection correlation of dated levels at DSDP Site 111 with the Orphan Basin succession suggests that two deeper debris-flow wedges were deposited during oxygen isotopic stages 6 and 8. The oldest of the debris-flow deposits in at least three of the wedges formed well into the corresponding glacial cycle, after ice sheets had reached the edge of the continental shelf. Slower deposition by hemipelagic processes and ice rafting formed the acoustically stratified units, including Heinrich layers. The youngest three debris-flow wedges each have volumes of 1300–1650 km3. Approximately two-thirds of this material is attributed to glacial erosion of Mesozoic and Tertiary strata beneath the Northeast Newfoundland Shelf. The remainder is believed to have been derived by glacial erosion of older bedrock that now forms the island of Newfoundland. The observed sediment volumes and the inferred basal and upper ages of the debris-flow wedges imply an average glacial denudation rate of about 0.13 mm/yr for this older bedrock, and an average of about 60 m of glacial bedrock erosion since oxygen isotope stage 22. This denudation rate is similar to estimates from the Barents Sea region off Norway.

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Bell, M., and E. P. Laine. "Erosion of the Laurentide Region of North America by Glacial and Glaciofluvial Processes." Quaternary Research 23, no. 2 (March 1985): 154–74. http://dx.doi.org/10.1016/0033-5894(85)90026-2.

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Collection of seismic reflection data from continental margins and ocean basins surrounding North America makes it possible to estimate the amount of material eroded from the area formerly covered by Laurentide ice sheets since major glaciation began in North America. A minimum estimate is made of 1.62 × 106 km3, or an average 120 m of rock physically eroded from the Laurentide region. This figure is an order of magnitude higher than earlier estimates based on the volume of glacial drift, Cenozoic marine sediments, and modern sediment loads of rivers. Most of the sediment produced during Laurentide glaciation has already been transported to the oceans. The importance of continental glaciation as a geomorphic agency in North America may have to be reevaluated. Evidence from sedimentation rates in ocean basins surrounding Greenland and Antarctica suggests that sediment production, sediment transport, and possibly denudation by permanent ice caps may be substantially lower than by periodic ice caps, such as the Laurentide. Low rates of sediment survival from the time of the Permo-Carboniferous and Precambrian glaciations suggest that predominance of marine deposition during some glacial epochs results in shorter lived sediment because of preferential tectonism and cycling of oceanic crust versus continental crust.

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Ring, U., K. Gessner, S. Thomson, and V. Markwitz. "Along-strike variations in the Hellenide Anatolide orogen: A tale of different lithospheres and consequences." Bulletin of the Geological Society of Greece 47, no. 2 (January 24, 2017): 625. http://dx.doi.org/10.12681/bgsg.11096.

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Structure and exhumation history of the Hellenide-Anatolide Orogen in the Aegean Sea region and the adjacent Anatolian peninsula is controlled by along-strike variations of pre-Alpine palaeogeography. In the Hellenides, Mesozoic extension created ribbon-like continental fragments of thinned and dense lithosphere that pinch out eastwards. In the east, the relatively large Anatolide microcontinent mostly escaped Mesozoic extension and lithospheric thinning, presumably because it had a distinctly different, thicker and more depleted lithosphere. In the Aegean transect these alongstrike differences in lithosphere structure ultimately resulted in sustained highpressure metamorphism followed by progressive slab retreat since about 60 Ma. Further east, collision of the Anatolide microcontinent at about 42 Ma formed a south verging greenschist-facies thrust-and-fold belt. Pronounced slab retreat in the Aegean forced differential extension resulting in a broad sinistral wrench corridor that started to from at 24-23 Ma. Since then, extension in both regions mainly controlled denudation. This review highlights how differences in pre-orogenic architecture control lithospheric thickening and the subsequent exhumation of high-pressure rocks, and how large-scale continental extension evolves

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Jelinek, A. R., F. Chemale, P. A. van der Beek, F. Guadagnin, J. A. Cupertino, and A. Viana. "Denudation history and landscape evolution of the northern East-Brazilian continental margin from apatite fission-track thermochronology." Journal of South American Earth Sciences 54 (October 2014): 158–81. http://dx.doi.org/10.1016/j.jsames.2014.06.001.

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Gallagher, K., C. J. Hawkesworth, and M. S. M. Mantovani. "The denudation history of the onshore continental margin of SE Brazil inferred from apatite fission track data." Journal of Geophysical Research: Solid Earth 99, B9 (September 10, 1994): 18117–45. http://dx.doi.org/10.1029/94jb00661.

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ANGELOVA, D. "Quaternary geology, geomorphology and tectonics in the Ogosta river valley system, the Danubian plain (Bulgaria)." Bulletin of the Geological Society of Greece 34, no. 1 (January 1, 2001): 55. http://dx.doi.org/10.12681/bgsg.16943.

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The Quaternary in the Ogosta River valley system (the Danubian plain) is represented by various genetic types of continental Quaternary sediments (eolian, alluvial, deluvial, proluvial). They lie on a diverse pre-Quaternary base. It is uneven and with various denudation. The accepted correlation schemes are based on local data in which the tectonic factor and duration of deformation have not been accounted for. The present work considers the complex results obtained during the investigation of the Quaternary sediments and formations. The filling consists of clayey-sandy or calcareous-sandy materials, coloured in rusty nuances by iron hydroxides. Their age has been determined on the basis of the found fauna: Elephas meridionalis Nesti,Anancus arvernensis Cr. et Gob (Bakalov, Nikolov, 1962).

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Sloan, L. Cirbus, Gregg J. S. Bluth, and G. M. Filippelli. "A comparison of spatially resolved and global mean reconstructions of continental denudation under ice-free and present conditions." Paleoceanography 12, no. 1 (February 1997): 147–60. http://dx.doi.org/10.1029/96pa03070.

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ANDREWS, JOHN T. "Holocene denudation of the northwest sector of Iceland as determined from accumulation of sediments on the continental margin." Boreas 36, no. 3 (August 2007): 240–52. http://dx.doi.org/10.1111/j.1502-3885.2007.tb01248.x.

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Poag, C. Wylie, and William D. Sevon. "A record of Appalachian denudation in postrift Mesozoic and Cenozoic sedimentary deposits of the U.S. Middle Atlantic continental margin." Geomorphology 2, no. 1-3 (September 1989): 119–57. http://dx.doi.org/10.1016/0169-555x(89)90009-3.

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CUNNINGHAM, M. J. M., A. L. DENSMORE, P. A. ALLEN, W. E. A. PHILLIPS, S. D. BENNETT, K. GALLAGHER, and A. CARTER. "Evidence for post-early Eocene tectonic activity in southeastern Ireland." Geological Magazine 140, no. 2 (March 2003): 101–18. http://dx.doi.org/10.1017/s0016756802007240.

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The role played by Cenozoic deformation in denudation and landscape development in Ireland has historically been difficult to assess because of the lack of widespread pre-glacial Cenozoic deposits onshore. Here we combine analysis of apatite fission-track data and geomorphic observations to place constraints on the timing, kinematics and magnitude of onshore deformation in southeastern Ireland. Relationships between apatite fission-track central age and elevation for samples from the Wicklow and Blackstairs Mountains and Tullow Lowland suggest that these rocks record an exhumed apatite partial annealing zone, which after cooling was dismembered by differential vertical displacements of up to several hundred metres. We use inverted models of sample thermal history to show that samples across the region experienced very similar thermal histories up to and including a cooling event in late Paleocene or early Eocene time. This effectively rules out strongly spatially heterogeneous denudation, and implies that differential rock uplift occurred in post-early Eocene time. The central age–elevation relationships define at least three spatial domains with internally consistent apatite fission-track data, separated by known faults or topographic escarpments. Geomorphic analysis of these structures shows that patterns of catchment incision and sinuosity, as well as the presence of antecedent drainage, are best explained by differential vertical displacements at or near the domain boundaries. The kinematics and magnitudes of these displacements are consistent with those implied by the apatite fission-track results, and are compatible with other examples of known Cenozoic deformation from Ireland and the adjacent continental margin.

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Maltsev, K. A., O. P. Yermolaev, and V. V. Mozzherin. "Suspended sediment yield mapping of Northern Eurasia." Proceedings of the International Association of Hydrological Sciences 367 (March 3, 2015): 326–32. http://dx.doi.org/10.5194/piahs-367-326-2015.

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Abstract. The mapping of river sediment yields at continental or global scale involves a number of technical difficulties that have largely been ignored. The maps need to show the large zonal peculiarities of river sediment yields, as well as the level (smoothed) local anomalies. This study was carried out to create a map of river sediment yields for Northern Eurasia (within the boundaries of the former Soviet Union, 22 × 106 km2) at a scale of 1:1 500 000. The data for preparing the map were taken from the long-term observations recorded at more than 1000 hydrological stations. The data have mostly been collected during the 20th century by applying a single method. The creation of this map from the study of river sediment yield is a major step towards enhancing international research on understanding the mechanical denudation of land due mainly to erosion.

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Peulvast, Jean-Pierre, Vanda Claudino Sales, François Bétard, and Yanni Gunnell. "Low post-Cenomanian denudation depths across the Brazilian Northeast: Implications for long-term landscape evolution at a transform continental margin." Global and Planetary Change 62, no. 1-2 (May 2008): 39–60. http://dx.doi.org/10.1016/j.gloplacha.2007.11.005.

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Silva, Rafael M., and Victor Sacek. "Shallow necking depth and differential denudation linked to post‐rift continental reactivation: The origin of the Cenozoic basins in southeastern Brazil." Terra Nova 31, no. 6 (September 4, 2019): 527–33. http://dx.doi.org/10.1111/ter.12423.

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33

Gunnell, Y., K. Gallagher, A. Carter, M. Widdowson, and A. J. Hurford. "Denudation history of the continental margin of western peninsular India since the early Mesozoic – reconciling apatite fission-track data with geomorphology." Earth and Planetary Science Letters 215, no. 1-2 (October 2003): 187–201. http://dx.doi.org/10.1016/s0012-821x(03)00380-7.

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34

Jacobs, Joachim, Norbert Kaul, and Klaus Weber. "The history of denudation and resedimentation at the continental margin of western Dronning Maud Land, Antarctica, during break-up of Gondwana." Geological Society, London, Special Publications 108, no. 1 (1996): 191–99. http://dx.doi.org/10.1144/gsl.sp.1996.108.01.14.

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Parphenuk, O. "Postcollisional evolution features of the intracontinental structures formed by overthrusting." Georesursy 20, no. 4 (November 30, 2018): 377–85. http://dx.doi.org/10.18599/grs.2018.4.377-385.

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The investigation of intracontinental collision structures is conducted based on the complex model of the thermal and mechanical evolution of overthrusting process for the rheologically layered lithosphere, which includes brittle upper crust, the lower crust and lithospheric upper mantle with different effective viscosity values. Finite element models with Lagrangian approach were used for the problem simulation. It was shown that thermal evolution of continental orogens essentially results from the geometry and topography due to thrusting and postcollision stage. This work concentrates on the thermal parameters influence on the evolution of collision zones aimed to the study of possibility of granite melt formation. Calculations for mean continental initial temperature distribution lead to the conclusion of possibility of granite melt formation for the case of “wet” granite solidus. The horizon of temperatures higher than “wet” granite solidus appears at the level of 30-40 km, moving upward to the depth 15-20 km at postcollision stage. The early postcollision evolution shows some heat flow increase due to the thickening of the upper crust with maximum heat generation rate. Further history leads to the stable heat flow values because additional loading redistribution resulting from the denudation of surface uplift and corresponding sedimentation is small due to the local erosion in our model. It was shown that surface heat losses after the termination of horizontal shortening depend to a greater extent on radiogenic heat generation rather than thermal conductivity value in the upper crust.

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Friedmann, S. Julio, and John P. Grotzinger. "Sedimentology, stratigraphy, and tectonic implications of a paleo-Proterozoic continental extensional basin: the El Sherana – Edith River groups, Northern Territory, Australia." Canadian Journal of Earth Sciences 31, no. 4 (April 1, 1994): 748–64. http://dx.doi.org/10.1139/e94-068.

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The ca. 1.83 Ga El Sherana – Edith River basin of Northern Territory, Australia, contains terrestrial sedimentary and volcanic rocks deposited during continental extension or transtension. Braid-plain sandstones and conglomerates, turbiditic sediments, and interbedded mafic and felsic volcanics, including ignimbrites, filled the basin. Alluvial fans and rock avalanche breccias are locally developed. Prebasinal structure controlled antecedent topography and influenced drainage patterns, thickness changes, and facies distribution.Unconformities bound all formations of the El Sherana and Edith River groups, revealed by beveled and incised strata, reversals in paleocurrent trends, sharp discordance in juxtaposed facies, and paleovalleys filled with unique sediments. Scarp-derived sediments are preserved only in a small, transfer-related strike-slip basin within the larger basin environment. Unconformities are regional and are interpreted as time lines throughout the basin. These unconformities developed during regrading of slopes forced by active tectonism, accompanied by syntectonic sedimentation and basin depocenter migration.The El Sherana – Edith River strata overlie older sediments (~2.1–1.88 Ga) of the Pine Creek orogen, which formed during a period of global orogeny related to continental assembly. Development of the El Sherana – Edith River basin began substantially (40–50 Ma) after denudation of the Pine Creek orogen belt, and is related to regional postcollisional extension. This extension is recorded by basin formation, bimodal tholeiitic and alkalic magmatism, and elevated geotherms. Other paleo-Proterozoic basins of northern Australia show a similar history of rift deposition above a fossil compressional belt.

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Dubyna, D. V., T. P. Dziuba, S. M. Iemelianova, and L. М. Makhynia. "Syntaxonomy and ecological differentiation of the pioneer vegetation of Ukraine. 1. Classes: Cakiletea maritimae, Ammophiletea, Crithmo-Staticetea, Crypsietea aculeatae, Therosalicornietea." Biosystems Diversity 28, no. 1 (February 12, 2020): 68–80. http://dx.doi.org/10.15421/012011.

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Pioneer plant communities grow on newly-formed ecotopes of coastal and partially continental areas, on patches that have dried after the surface water flooding. They are affected by sea tides, wind-induced effect, salinity, denudation, accumulation and sharp changes in soil humidity. To these factors are added chemical and biological pollution, as well as anthropogenic pressure. Due to these reasons, such plant communities have a specific floristic composition, structure, functional regime and resilience mechanisms, which are different from coenoses of more stable habitats. On the basis of the analysis of more than 600 phytosociological relevés using TWINSPAN modified algorithm the current state of littoral and halophytic classes of pioneer vegetation in Ukraine has been established and their syntaxonomic structure identified. It has been determined that the level of pioneer phytocoenoses diversity in Ukraine is similar to that of Central Europe. The Cakiletea maritimae class is presented by 1 order, 1 alliance, and 4 associations; Ammophiletea – by 1 order, 1 alliance, and 8 associations; Crithmo-Staticetea – by 1 order, 2 alliances, and 3 associations; Crypsietea aculeatae – by 1 order, 3 alliances, and 4 associations, Therosalicornietea – by 1 order, 2 alliances, and 10 associations. Synoptic tables of vegetation classes are given and nine alliances are briefly characterized. Using DCA-ordination analysis of syntaxa in the association-rank level we identified that the main factors of ecological differentiation are soil humidity and aeration as well as the nitrogen content. For the pioneer plant communities, other significant impact factors are the extremality of environmental conditions, their unevenness and non-equilibrium, in particular, the mechanical action of the sea waves, the dynamic processes of denudation and accumulation, salinity, as well as the variability of damping during the year. This research contributes to the identification of the place of the distinguished syntaxa of Ukrainian pioneer vegetation in the European system.

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Zgorzelski, Marek. "Ladakh and Zanskar." Miscellanea Geographica 12, no. 1 (December 1, 2006): 13–24. http://dx.doi.org/10.2478/mgrsd-2006-0002.

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Abstract The Himalayan mountain chain is orographically fragmented, both in the east-west and in the north-south directions. The latter area is characterised by a greater landscape diversity, owing to its zonality and the vertical zonation of both climate and vegetation. In terms of tectonics and orography, and taking into account the prevalent influence of the monsoon and continental climates, the Himalayan mountain system can be divided into two parts – the external arc (southern), that is the Higher (or Great) Himalayas and the internal arc (northern), that is the so-called Trans-Himalayas. Similarly to the external arc of the Himalayas, the post-glacial relief in the Trans-Himalayas is marginal only. It is an area with a prevalence of denudation (nival, frost, gravitation and eolian) processes. Slopes of tectonic valleys or basins, covered with colourful surface deposits rising as high as even two thirds of their altitude, dominate the landscape. The Zanskar ridges and the Ladakh range represent a transitional zone between the Trans-himalayas and Eastern Karakoram.

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Butler, Robert W. H. "Tectonic evolution of the Himalayan syntaxes: the view from Nanga Parbat." Geological Society, London, Special Publications 483, no. 1 (August 30, 2018): 215–54. http://dx.doi.org/10.1144/sp483.5.

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AbstractCurrent tectonic understanding of the Nanga Parbat–Haramosh massif (NPHM) is reviewed, developing new models for the structure and deformation of the Indian continental crust, its thermorheological evolution, and its relationship to surface processes. Comparisons are drawn with the Namche Barwa–Gyala Peri massif (NBGPM) that cores an equivalent syntaxis at the NE termination of the Himalayan arc. Both massifs show exceptionally rapid active denudation and riverine downcutting, identified from very young cooling ages measured from various thermochronometers. They also record relicts of high-pressure metamorphic conditions that chart early tectonic burial. Initial exhumation was probably exclusively by tectonic processes but the young, and continuing emergence of these massifs reflects combined tectonic and surface processes. The feedback mechanisms implicit in aneurysm models may have been overemphasized, especially the role of synkinematic granites as agents of rheological softening and strain localization. Patterns of distributed ductile deformation exhumed within the NPHM are consistent with models of orogen-wide gravitation flow, with the syntaxes forming the lateral edges to the flow beneath the Himalayan arc.

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40

Kounov, A., S. Niedermann, M. J. de Wit, G. Viola, M. Andreoli, and J. Erzinger. "Present denudation rates at selected sections of the South African escarpment and the elevated continental interior based on cosmogenic 3He and 21Ne." South African Journal of Geology 110, no. 2-3 (September 1, 2007): 235–48. http://dx.doi.org/10.2113/gssajg.110.2-3.235.

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41

Martignole, Jacques. "Exhumation of high-grade terranes—a review." Canadian Journal of Earth Sciences 29, no. 4 (April 1, 1992): 737–45. http://dx.doi.org/10.1139/e92-063.

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High-grade (granulite-facies) terranes are brought to the surface by a combination of uplift and erosion (exhumation). The reported mechanisms and durations of exhumation are variable and depend partly on the mode of formation of a given high-grade terrane. In this paper, we consider the case of granulite-facies conditions that are attained (i) in juvenile crust, in the roots of magmatic arcs (e.g., Kohistan, Fiordland), (ii) around deep-seated high-temperature plutonic complexes, and (iii) in the lower parts of thickened continental crust. In the case of the roots of magmatic arcs, Phanerozoic examples suggest that they are exhumed along shallow-dipping contraction faults or shear zones that developed during continental obduction in a convergent tectonic regime. This process is not fundamentally different from processes leading to the exhumation of high-pressure (blueschist, eclogite) terranes. In contrast, deep-seated high-temperature plutonic complexes are thermostructural domes, analogous to the lower levels of core complexes, which may also have contributed to the uprise of high-grade terranes. Such domes should be sought for around anorthositic or mafic plutons, where their ascent may also have been favoured by continental extension. These modes of exhumation are compatible with a monocyclic evolution. However, many high-grade terranes show evidence of a polycyclic evolution and, in such cases, the nature of the thermal perturbation responsible for granulite-facies metamorphism is still debated. Thermal modelling based on heat conduction in collision orogens shows that granulites cannot form at mid-cristal levels, namely those exposed after isostatically driven denudation. Thus, magmatic underplating and crustal extension have been suggested as causes of steepened geotherms. Underplating (or intraplating) supplies the heat and thickens the crust from below. Postcollisional extension has also been considered as a mechanism providing a heat pulse emanating from the asthenosphere, probably after the "detachment" of a relatively cold thermal boundary layer. Finally, isolated crustal-scale intracratonic thrusting may favour the rise of intermediate to lower crustal wedges (e.g., the Kapuskasing wedge, uplifted prior to the trans-Hudson collision).

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Gunnell, Yanni, Jean-Claude Thouret, Stéphanie Brichau, Andy Carter, and Kerry Gallagher. "Low-temperature thermochronology in the Peruvian Central Andes: implications for long-term continental denudation, timing of plateau uplift, canyon incision and lithosphere dynamics." Journal of the Geological Society 167, no. 4 (July 2010): 803–15. http://dx.doi.org/10.1144/0016-76492009-166.

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43

Ducassou, Céline, Christine Strullu-Derrien, Michel Ballevre, Marie-Pierre Dabard, Philippe Gerrienne, Hubert Lardeux, and Cécile Robin. "Age and depositional environment of the Sainte-Anne Formation (Armorican Massif, France): the oldest (Emsian) evidence for mountain erosion in the Variscan belt." Bulletin de la Société Géologique de France 180, no. 6 (October 1, 2009): 529–44. http://dx.doi.org/10.2113/gssgfbull.180.6.529.

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Abstract The palaeogeography of the internal zones of the Variscan belt during the early stages of the convergence remains unclear. Sedimentary sequences that recorded the denudation of an early relief have generally been removed by erosion. In the Chalonnes area (southeast of the Armorican Massif), the reefal carbonates of the Chalonnes Formation (Fm) are overlain by the immature, poorly-sorted sandstones of the Sainte-Anne Fm. This formation is characterised by the occurrence of gravity flow deposits and contains immature and poorly sorted sandstones with a large amount of plant debris and lithic fragments, suggesting a depositional environment in a delta front dominated by floods. A revision of the palaeoflora content allows to assign an Emsian age to the Sainte-Anne Fm. Lithic fragments are mainly of sedimentary and volcanic origin, suggesting moderate erosion level of the source area. Palaeocurrent data indicate a southern origin for the sediments. These features collectively demonstrate that the Sainte-Anne Fm is the record of the erosion of a continental area located farther south, and experiencing incipient tectonic uplift during the Emsian. The Sainte-Anne Fm could represent therefore the earliest record in France of the very first stages of the Variscan orogeny.

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Bragina, Tatyana М. "Soil macrofauna (invertebrates) of Kazakhstanian Stipa lessingiana dry steppe." Hacquetia 15, no. 2 (December 1, 2016): 105–12. http://dx.doi.org/10.1515/hacq-2016-0017.

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Abstract Stipa lessingiana steppes used to be prevalent on the dry Trans-Ural denudation plains, particularly, on the Sub-Ural and the Turgay Plateau. But, most of them have been lost because they were plowed up during the Virgin Land campaign in the second part of 20th century. This paper presents a detailed study of the faunistic composition and the structure of soil-dwelling invertebrate communities (macrofauna) of a temperate-dry bunch feather grass steppe in the Turgai Plateau (Northern-Turgai physical-geographical province of steppe Kazakhstan, Kostanay Oblast). The study site is located in the territory of the Naurzum State Nature Reserve, a part of the UNESCO World Heritage site “Saryarka Steppe and Lakes of Northern Kazakhstan”, where remnants of Virgin S. lessingiana steppes have been preserved to the present day. This region is the driest and most continental in climate of all the dry steppes of Kazakhstan. The total abundance and biomass of soil invertebrate communities in the investigated site were lower than in the northern and western steppe areas. Soil invertebrates are among the major components that determine the functioning of terrestrial natural ecosystems.

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45

Ribeiro, Alexandre Cunha. "Tectonic history and the biogeography of the freshwater fishes from the coastal drainages of eastern Brazil: an example of faunal evolution associated with a divergent continental margin." Neotropical Ichthyology 4, no. 2 (June 2006): 225–46. http://dx.doi.org/10.1590/s1679-62252006000200009.

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The eastern Brazilian coastal drainages are of great biogeographical significance, because of their highly endemic fish faunas. Phylogenetic patterns suggest a close biotic relationship between the rivers that flow into the Atlantic and those on the adjacent upland crystalline shield. However, little has been said on the dynamics of the geological processes causally related to the cladogenetic events between these areas. Distributional and phylogenetic patterns suggest a close association with the geological history of the passive continental margin of South America, from the Cretaceous to the present day. In this area megadome uplifts, rifting, vertical movements between rifted blocks and the erosive retreat of the South American eastern continental margin are hypothesized as the main geological forces controlling the distribution of freshwater fishes. The tectonic activity associated with the break-up of Gondwana and separation of South America and Africa formed six megadomes that control most of the current courses of the main crystalline shield river basins. Except for basins located at the edges of such megadomes, these river systems developed long, circuitous routes over the ancient Brazilian crystalline shield before emptying into the recently opened Atlantic Ocean. Initial cladogenetic events between upland crystalline drainages and Atlantic tributaries were probably associated with vicariant processes, and some ancient basal sister-groups of widespread inclusive taxa are found in these coastal hydrographic systems. Later, generalized erosive denudation resulted in an isostatic adjustment of the eastern margin of the platform. These, along with reactivations of ancient rifts led to vertical movements between rifted blocks and gave rise, in southeastern Brazil, to taphrogenic (rift related) basins. These basins, such as the Taubaté, São Paulo, Curitiba and Volta Redonda basins, among others, captured adjacent upland drainages and fauna. The fossil fishes from the Tremembé Formation (Eocene-Oligocene of Taubaté Basin) exemplify this process. Other taphrogenic systems of Tertiary age were also identified in other segments of the Atlantic continental margin, such as in Borborema province, in NE Brazil, with marked influence over drainage patterns. At the same time, erosive retreat of the eastern margin of the platform successively captured upland rivers, which became Atlantic tributaries evolving associated to main rift systems. The continued nature of these processes explains the mixed phylogenetic and distributional patterns between Atlantic tributaries and the upland crystalline shield areas, especially in the southeastern continental margin, represented by successively, less inclusive sister-groups associated with cladogenetic events from the Late Cretaceous to the present.

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46

Schaller, Morgan F., and Megan K. Fung. "The extraterrestrial impact evidence at the Palaeocene–Eocene boundary and sequence of environmental change on the continental shelf." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 376, no. 2130 (September 3, 2018): 20170081. http://dx.doi.org/10.1098/rsta.2017.0081.

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We have identified clear evidence of an extraterrestrial impact within the onset of the carbon isotope excursion (CIE) that defines the Palaeocene–Eocene (P-E) boundary hyperthermal event (approx. 56 Ma) from several sites on the eastern Atlantic Coastal Plain and offshore. We review and update the state of the evidence for an impact at the P-E boundary, including a K-Ar cooling age of the ejecta that is indistinguishable from the depositional age at the P-E, which establishes the ejecta horizon as an isochronous stratigraphic indicator at the P-E. Immediately above the ejecta peak at the base of the coastal plain Marlboro Clay unit, we identify a sharp increase in charcoal abundance coincident with the previously observed dramatic increase in magnetic nanoparticles of soil pyrogenic origin. We therefore revisit the observed sequence of events through the P-E boundary on the western Atlantic Coastal Plain, showing that an extraterrestrial impact led to wildfires, landscape denudation and deposition of the thick Marlboro Clay, whose base coincides with the spherule horizon and CIE onset. The Sr/Ca ratio of the spherules indicates that the carbon responsible for the onset may be vaporized CaCO 3 target rock mixed with isotopically light carbon from the impactor or elsewhere. Crucially, we do not argue that the impact was responsible for the full manifestation of the CIE observed globally (onset to recovery approx. 170 kyr), rather that a rapid onset was triggered by the impact and followed by additional carbon from other processes such as the eruption of the North Atlantic Igneous Province. Such a scenario agrees well with recent modelling work, though it should be revisited more explicitly. This article is part of a discussion meeting issue ‘Hyperthermals: rapid and extreme global warming in our geological past’.

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47

Dingle, Elizabeth H., Hugh D. Sinclair, Jeremy G. Venditti, Mikaël Attal, Tim C. Kinnaird, Maggie Creed, Laura Quick, Jeffrey A. Nittrouer, and Dilip Gautam. "Sediment dynamics across gravel-sand transitions: Implications for river stability and floodplain recycling." Geology 48, no. 5 (February 14, 2020): 468–72. http://dx.doi.org/10.1130/g46909.1.

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Abstract The gravel-sand transition (GST) is commonly observed along rivers. It is characterized by an abrupt reduction in median grain size, from gravel- to sand-size sediment, and by a shift in sand transport mode from wash load–dominated to suspended bed material load. We documented changes in channel stability, suspended sediment concentration, flux, and grain size across the GST of the Karnali River, Nepal. Upstream of the GST, gravel-bed channels are stable over hundred- to thousand-year time scales. Downstream, floodplain sediment is reworked by lateral bank erosion, particularly during monsoon discharges. Suspended sediment concentration, grain size, and flux reveal counterintuitive increases downstream of the GST. The results demonstrate a dramatic change in channel dynamics across the GST, from relatively fixed, steep gravel-bed rivers with infrequent avulsion to lower-gradient, relatively mobile sand-bed channels. The increase in sediment concentration and near-bed suspended grain size may be caused by enhanced channel mobility, which facilitates exchange between bed and bank material. These results bring new constraints on channel stability at mountain fronts and indicate that temporally and spatially limited sediment flux measurements downstream of GSTs are more indicative of flow stage and floodplain recycling than of continental-scale sediment flux and denudation rate estimates.

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48

Sirevaag, Hallgeir, Anna Ksienzyk, Joachim Jacobs, István Dunkl, and Andreas Läufer. "Tectono-Thermal Evolution and Morphodynamics of the Central Dronning Maud Land Mountains, East Antarctica, Based on New Thermochronological Data." Geosciences 8, no. 11 (October 26, 2018): 390. http://dx.doi.org/10.3390/geosciences8110390.

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The lack of preserved Mesozoic–Cenozoic sediments and structures in central Dronning Maud Land has so far limited our understanding of the post-Pan-African evolution of this important part of East Antarctica. In order to investigate the thermal evolution of the basement rocks and place constraints on landscape evolution, we present new low-temperature thermochronological data from 34 samples. Apatite fission track ages range from 280–85 Ma, while single-grain (U-Th)/He ages from apatite and zircon range from 305–15 and 420–340 Ma, respectively. Our preferred thermal history models suggest late Paleozoic–early Mesozoic peneplanation and subsequent burial by 3–6 km of Beacon sediments. The samples experienced no additional burial in the Jurassic, thus the once voluminous continental flood basalts of western Dronning Maud Land did not reach central Dronning Maud Land. Mesozoic–early Cenozoic cooling of the samples was slow. Contrary to western Dronning Maud Land, central Dronning Maud Land lacks a mid-Cretaceous cooling phase. We therefore suggest that the mid-Cretaceous cooling of western Dronning Maud Land should be attributed to the proximity to the collapse of the orogenic plateau at the Panthalassic margin of Gondwana. Cooling rates accelerated considerably with the onset of glaciation at 34 Ma, due to climate deterioration and glacial denudation of up to 2 km.

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Sevigny, J. H., and R. J. Thériault. "Geochemistry and SrNd isotopic composition of Eocene lamphrophyre dykes, southeastern British Columbia." Canadian Journal of Earth Sciences 40, no. 6 (June 1, 2003): 853–64. http://dx.doi.org/10.1139/e03-014.

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Mineral compositions, geochemical analyses, and SrNd isotopic compositions are reported for alkaline and calc-alkaline lamprophyres collected along the southern margin of the Valhalla Complex, southeastern British Columbia. The lamprophyres were emplaced during Eocene extension and lithospheric thinning associated with tectonic denudation of the Valhalla Complex. SiO2 contents range from 44.451.6 wt.%, K2O from 1.33.7 wt.%, and volatile contents (H2O + CO2 + SO3) from 0.84.6 wt.%. MgO and Cr contents are 9.57.6 wt.% and 540130 ppm, respectively, for samples with Mg#s between 0.69 and 0.65. Chrondrite-normalized rare-earth element patterns are strongly fractionated with Cen = 120375 and Ybn = 8.412.7. Alkaline lamprophyres contain biotite ± kaersutite ± calcic plagioclase and exhibit a limited range in initial 87Sr/86Sr (0.70510.7057), initial εNd (3.7 to 4.3), and TDM (766796 Ma). Calc-alkaline lamprophyres contain F-rich phlogopite and sodic plagioclase, and exhibit a wider range in initial 87Sr/86Sr (0.70640.7090), initial εNd (6.3 to 11.9), and TDM (9171,614 Ma). Alkaline lamprophyres are interpreted as uncontaminated melts derived from a long-term, volatile, and incompatible element-enriched mantle reservoir. Mantle enrichment coincided with continental rifting of western North America (ca. 760 Ma). The enriched mantle reservoir remained isolated for ~700 Ma. Lamprophyres were generated by partial melting of the mantle reservoir in response to adiabatic decompression and lithospheric thinning during Eocene extension.

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Keppie, J. D., and R. D. Dallmeyer. "Late Paleozoic collision, delamination, short-lived magmatism, and rapid denudation in the Meguma Terrane (Nova Scotia, Canada): constraints from 40Ar/39Ar isotopic data." Canadian Journal of Earth Sciences 32, no. 5 (May 1, 1995): 644–59. http://dx.doi.org/10.1139/e95-054.

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The Meguma Terrane consists of 8–15 km of early Paleozoic stratified rocks, deposited on a continental basement, that were deformed and metamorphosed during the late Paleozoic as a result of lithospheric plate collision. The oldest cleavage (previously published, whole-rock, 40Ar/39Ar plateau ages of 415–395 Ma) dates the onset of crustal thickening, which was followed by voluminous, but short-lived, Late Devonian granitic and minor mafic magmatism (380–370 Ma). This magmatism may have been the product of delamination of the lower lithosphere and upwelling of asthenosphere, which effected melting above the new Moho and resulted in intrusion at depths of 5–12 km. 40Ar/39Ar plateau ages of hornblende, muscovite, and biotite indicate that, at the present erosion level, most of the Meguma Terrane cooled through ~300 °C by 368–360 Ma, slightly earlier than for the southwestern Meguma Terrane (ca. 345 Ma). The present erosion level was exhumed by the latest Devonian–Early Carboniferous (Visean): the age of the oldest unconformably overlying rocks. Subsequent burial beneath ~6 km of Carboniferous sediments would not have been sufficient to completely rejuvenate older intracrystalline mica systems and result in the observed 40Ar/39Ar mica plateau ages between ca. 350 and 260 Ma. Such rejuvenation may have resulted from migration of hot fluids along shear zones derived from the lower crust and mantle, and from granitoid magma intruded at ca. 316 Ma. The recurrence of deformation, magmatism and denudation in the middle Carboniferous suggests that further delamination may have occurred. The temperature of these fluids decreased from 400–500 °C during the Carboniferous to 300–400 °C during the Early Permian.

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Journal articles on the topic 'Continental denudation'

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