Growing mountain ranges and quenched river networks     

Sbastien Castelltort  Guy Simpson 《Comptes Rendus Geoscience》2006,338(16):1184-1193

River networks in mountain ranges owe their existence to the competing effects of tectonic uplift and climate-controlled erosion. However, paradoxically, the universal geometric properties of river networks are independent of both tectonics and climate. Currently, this paradox has still not been resolved. Here we propose a solution that consists in considering that the geometry of river networks is established on the lowland margins of incipient uplifts, and is quenched into the erosion zone as the mountain belts widen with time. In our model, the geometry of river networks simply reflects the downward coalescence of alluvial rivers on un-dissected surfaces outside of mountain belts, and is therefore independent of erosion processes. To cite this article: S. Castelltort, G. Simpson, C. R. Geoscience 338 (2006).  相似文献   

Analysis of split operator methods applied to reactive transport with Monod kinetics     

Matthew J. Simpson  Kerry A. Landman 《Advances in water resources》2007

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Early Mesoproterozoic evolution of midcontinental Laurentia: Defining the geon 14 Baraboo orogeny     

L. Gordon Medaris  Brad S. Singer  Brian R. Jicha  David H. Malone  Joshua J. Schwartz  Esther K. Stewart  Amanda Van Lankvelt  Michael L. Williams  Peter W. Reiners 《地学前缘(英文版)》2021,12(5):101174

New geochronologic data from midcontinental Laurentia demonstrate that emplacement of the 1476-1470 Ma Wolf River granitic batholith was not an isolated igneous event,but was accompanied by regional metamorphism,deformation,and sedimentation.Evidence for such metamorphism and deformation is best seen in siliciclastic sedimentary rocks of the Baraboo Interval,which were deposited closely following the1.65-1.63 Ga Mazatzal orogeny.In Baraboo Interval strata,muscovite parallel to slatey cleavage,in hydrothermal veins,in quartzite breccia,and in metamorphosed paleosol yielded ~(40)Ar/~(39)Ar plateau age s of 1493-1465 Ma.In addition,U-Th-total Pb dating of neoblastic overgrowths on detrital monazite gave an age of 1488±20 Ma,and recrystallized hematite in folded metapelite gave a mean U/Th-He age of 1411± 39 Ma.Post-Baraboo,arkosic polymictic conglomerate,which contains detrital zircon with a minimum peak age of 1493 Ma,was intruded by a 1470 Ma granite porphyry at the northeastern margin of the Wolf River batholith.This episode of magmatism,regional deformation and metamorphism,and sedimentation,which is designated herein as the Baraboo orogeny,provides a midcontinental link between the Picuris orogeny to the southwe st and the Pinware orogeny to the northeast,completing the extent of early Mesoproterozoic(Calymmian) orogenesis for 5000 km along the southern margin of Laurentia.This transcontinental orogen is unique among Precambrian orogenies for its great width(～1600 km),the predominance of ferroan granites derived from partial melting of lower continental crust,and the prevalence of re gional high T-P metamorphism related to advective heating by granitic magmas emplaced in the middle to upper crust.  相似文献   

The complexity of sediment recycling as revealed by common Pb isotopes in K-feldspar   总被引：1，自引：0，他引：1  

Simon P.Johnson  Christopher L.Kirkland  Noreen J.Evans  Brad J.Mc Donald  Huntly N.Cutten 《地学前缘(英文版)》2018,9(5):1515-1527

Detrital zircon U-Pb geochronology has become the gold standard in evaluating source to sink relationships in sedimentary basins. However, the physical and chemical robustness of zircon, which make it such a useful mineral for provenance studies, is also a hindrance as zircon can be recycled through numerous sedimentary basins, thus obscuring the first cycle source to sink relationship. An elegant approach to addressing this potential issue is to compare the Pb isotope composition of detrital K-feldspar, a mineral which is unlikely to survive more than one erosion-transport-deposition cycle, with that of magmatic K-feldspar from potential basement source terranes. Here we present new in situ Pb isotope data on detrital K-feldspar from two Proterozoic arkosic sandstones from Western Australia, and magmatic K-feldspar grains from potential igneous source rocks, as inferred by the age and Hf isotope composition of detrital zircon grains. The data indicate that the detrital zircon and K-feldspar grains could not have been liberated from the same source rocks, and that the zircon has most likely been recycled through older sedimentary basins. These results provide a more complete understanding of apparently simple source to sink relationships in this part of Proterozoic Western Australia.  相似文献   

Norse–Inuit interaction and landscape change in southern Greenland? A geochronological,Pedological, and Palynological investigation     

Kirsty A. Golding  Ian A. Simpson  J. Edward Schofield  Kevin J. Edwards 《Geoarchaeology》2011,26(3):315-345

Ruins representing both medieval Norse and Inuit (Thule culture) settlements can be found together on the coast at Sandhavn (59°59′ N, 44°46′ W), Greenland. The site presents a rare opportunity to investigate the character of past contact and interaction between these two peoples. Soils‐based, radiocarbon, and palynological analyses demonstrate the creation of hortic anthrosols within Norse home‐fields used between the mid‐11th and late 14th centuries A.D. Irrigation channels have been identified within the home‐fields, while rising grass pollen influx reveals intensification in hay production over the period ca. A.D. 1260–1350 despite climatic deterioration setting in around this time. Floor deposits and wall packing from an Inuit winter house returned dates of cal. A.D. 1220–1290 (2σ), yet no direct landscape‐based evidence for Inuit activity could be determined. Although the exact nature of the relationship between Norse and Thule at Sandhavn remains unclear, the role of this site as a harbor and possible trading area may have attracted Inuit settlers keen to participate in European trade networks. © 2011 Wiley Periodicals, Inc.  相似文献   

Effect of rapidly changing river stage on uranium flux through the hyporheic zone   总被引：2，自引：1，他引：1  

Fritz BG  Arntzen EV 《Ground water》2007,45(6):753-760

Measurement of ground water/surface water interaction within the hyporheic zone is increasingly recognized as an important aspect of subsurface contaminant fate and transport. Understanding the interaction between ground water and surface water is critical in developing a complete conceptual model of contaminant transport through the hyporheic zone. At the Hanford Site near Richland, Washington, ground water contaminated with uranium discharges to the Columbia River through the hyporheic zone. Ground water flux varies according to changes in hydraulic gradient caused by fluctuating river stage, which changes in response to operation of dams on the Columbia River. Piezometers and continuous water quality monitoring probes were installed in the hyporheic zone to provide long-term, high-frequency measurement of hydraulic gradient and estimated uranium concentrations. Subsequently, the flux of water and uranium was calculated for each half-hour time period over a 15-month study period. In addition, measurement of water levels in the near-shore unconfined aquifer enhanced the understanding of the relationship between river stage, aquifer elevation, and uranium flux. Changing river stage resulted in fluctuating hydraulic gradient within the hyporheic zone. Further, influx of river water caused lower uranium concentrations as a result of dilution. The methods employed in this study provide a better understanding of the interaction between surface and ground water in a situation with a dynamically varying vertical hydraulic gradient and illustrate how the combination of relatively standard methods can be used to derive an accurate estimation of water and contaminant flux through the hyporheic zone.  相似文献   

Cultural sediment analyses and transitions in early fishing activity at Langenesværet,Vesterålen,Northern Norway     

Ian A. Simpson  Sophia Perdikaris  Gordon Cook  John L. Campbell  William J. Teesdale 《Geoarchaeology》2000,15(8):743-763

The development of specialized and commercial fishing activity in the island archipelago of Lofoten and Vesterålen in northern Norway is a critical foundation from which to understand the subsequent spread of commercial fishing across the north Atlantic region during the medieval and early modern period. One little understood aspect of this development is the relationship between medieval commercial fishing stations (fiskevaer) and earlier fishing activity. In this article, cultural sediment deposits at Langenesværet, Vesterålen, Northern Norway provide an opportunity to examine this relationship and its implications for current historical models of fishing development in northern Norway and the north Atlantic region. Conventional and AMS radiocarbon dating techniques are used to establish a chronology for the deposits, while activities associated with the sediments are characterized using thin‐section micromorphology supported by proton induced X‐ray emission spectrometry (PIXE). The results suggest that the site commenced formation as early as ca. 3000 B.C. and that the site was first used for specialized fishing activity from the early centuries A.D. The medieval commercial fiskevaer settlement at Langenesværet was introduced to an area that had a longstanding tradition of specialised fishing activity. © 2000 John Wiley & Sons, Inc.  相似文献   

Local‐scale adaptations: A modeled assessment of soil,landscape, microclimatic,and management factors in Norse home‐field productivities     

W. Paul Adderley  Ian A. Simpson  Orri Vsteinsson 《Geoarchaeology》2008,23(4):500-527

Adaptation of farming practices to inherent site conditions was essential to the success of Norse colonization in pristine landscapes. A key factor in the initial success of colonization, or landnám, of Iceland was management of the area adjacent to the domestic dwelling, the home‐field, to provide fodder for over‐wintering livestock. In this paper we examine three settlement home‐fields in the Mývatn and Laxá valley area of northeast Iceland. Contemporary evidence reveals a distinct climatic toposequence together with differences in the nature of the inherent soils between sites. By considering the influence of these differences, microscale adaptations in early land management practices in the production of hay are sought within a tightly defined chronological context. Using an integrated agroecosystem modeling approach, the factors affecting long‐term sustainability of hay production in the Norse home‐field are examined. Results indicate that regional‐level climate differences will have an impact on production, especially pronounced cold periods. It is also clear that small‐scale climate factors, as well as inherent soil differences between sites influenced productivity for the Norse farmer. However, productivities overall are at subsistence level, emphasizing the need for optimized land management to sustain home‐field production. After examining different management scenarios, it is apparent that the effect of an increased rate of manuring will be most apparent during the first century of settlement; thereafter the effect is relatively diminished. © 2008 Wiley Periodicals, Inc.  相似文献