A Long-Term Perspective on Glacial Erosion

A rough estimate of glacial erosion in the Precambrian basement is related to the total denudation of bedrock since its formation in the Proterozoic. The basis for the calculations is reference to surfaces of different age. Glacial erosion is responsible for merely polishing the northern shields. Major denudation occurred during the Proterozoic and amounted to tens of kilometres. During long periods the basement was protected by Palaeozoic cover rocks. It was re-exposed successively during the Mesozoic and Tertiary with denudation amounting to 600 m at the most. Glacial erosion can generally be counted in tens of metres though with great variations. © 1997 by John Wiley & Sons, Ltd.     

Planation surfaces on the Tibet Plateau, China

A planation hypothesis is proposed to explain landform evolution of the Tibet Plateau. A denudation threshold （T）, the maximum potential denudation rate for a certain type of rock, is introduced to explain the combined effects of lithology and tectonics on landform evolution. If the tectonic uplifting rate （U） is equal to or less than the threshold rate （U ≤ T）, the tectonic uplifting and terrain denudation are in dynamic equilibrium, and landforms are in a steady state. The end product should be planation surfaces whether the original landforms are flat plains or deeply dissected mountains. If U 〉 T, uplift and denudation are not able to reach a dynamic equilibrium state. The plateau surface is mostly underlain by soft rocks, such as the Mesozoic epimetamorphic argillites and Tertiary sedimentary rocks, while the mountain ranges comprise hard rocks, such as granite, gneiss and limestone. In soft rock regions, hills are low with a relative relief of mostly less than 100 m and the slopes are gentle at a gradient of 〈200. In contrast, hills can maintain steep slopes in hard rock regions. The Tibet Plateau has been under an equilibrium condition between tectonic uplifting and denudation except for the mountain ranges. The plateau might have reached the present altitudes before the Quaternary.     

阿克库勒凸起上奥陶统地层多期剥蚀的剖分与古构造复原

阿克库勒凸起下古生界地层遭受多期构造运动的剥蚀,其中对油气有重大作用的主要有加里东中期和海西早期构造运动.运用地层厚度趋势法原理,首先计算出上奥陶统在海西早期的剥蚀量,反映出剥蚀发生在阿克库勒凸起中部塔河主体部位,向南北方向减薄.并恢复出海西早期前的构造特征为北西高南东低且在北西地区为剥蚀暴露区的特征,在此基础上按厚度...     

Quantitative evaluation of soil processes using in situ-produced cosmogenic nuclides

In situ-produced cosmogenic nuclides provide a means for quantitative evaluation of a wide range of weathering and sediment transport processes. Although these nuclides have received attention for their power as geochronometers of surface exposure, it may be argued that they are more broadly suited for study of surface processes. In many environments, they may be used to evaluate collapse, erosion, burial, bioturbation, and creep, as well as providing a qualitative basis for distinguishing allochthonous from autochthonous materials. In addition, these nuclides can provide quantitative information on rates of erosion on scales of landforms and drainage basins. Here, we review the systematics of cosmogenic nuclide production within the Earth's surface, and present field examples demonstrating the utilization of in situ-produced cosmogenic nuclides distributions for evaluation of a range of soil evolution processes. To cite this article: E.T. Brown et al., C. R. Geoscience 335 (2003).     

四川盆地加里东期剥蚀量恢复

四川盆地是一个多旋回叠合盆地,加里东期剥蚀量是下古生界烃源岩热演化、早期油气藏的形成与演化以及下组合资源量计算等研究中不可缺少的基础参数。考虑到剥蚀量恢复方法固有的局限性和适用条件以及四川盆地早古生代时期的沉积构造演化特征,本文在分析了四川盆地志留系的原始沉积范围和下古生界残留地层分布格局的基础上,提出了"沉积速率比值+古热流反演+古地质图"法恢复四川盆地加里东期的剥蚀量。志留系原始范围广,覆盖了整个四川盆地,现今川中和川西地区志留系缺失是加里东期剥蚀所致,而不是当时没有沉积。利用钻至下古生界的29口探井的分层数据和130口虚拟井的地震数据,恢复了四川盆地加里东期的剥蚀量,并与古地质图结合,约束了剥蚀量的平面变化趋势。四川盆地加里东期剥蚀量主要受川中古隆起控制,古隆起区剥蚀量为700~1 200 m,川东和川南地区的剥蚀量一般为100~200 m,川北地区的剥蚀量为200~500 m。     

The Rise and Fall of the Davisian Cycle of Erosion: Prelude,Fugue, Coda,and Sequel

The Cycle of Erosion formulated by the American geographer William Morris Davis in the 1880s remained the dominant paradigm in geomorphology well into the 20th century, before it waned in response to improved understanding of Earth's crustal and surface behavior. The Davisian model sought to explain landforms in terms of structure, process, and stage. Following initial rapid tectonic uplift, landforms were presumed to evolve on a quiescent crust through stages of youth, maturity, and old age, to culminate in a peneplain. A new cycle would be initiated by landform rejuvenation in response to a changing base level of erosion. This model was a reflection of its time, of the cycle mania of the 19th century, which in turn was founded on Hutton's limitless "succession of worlds" and dissatisfaction with earlier notions of landscape origins constrained by limited Earth time. Davis's model was derived from ideas regarding orogenic cycles favored by Dana and Le Conte, and of prolonged subaerial denudation toward base-level observed by Powell and Dutton. The model's supremacy was challenged from time to time, notably by the Pencks (father and son) and by alternative cyclic denudation models that invoked pediplanation and etchplanation rather than peneplanation. The relevance of the Davisian model declined after 1940 in response to a growing awareness of Earth's crustal mobility, changing climates and geomorphic processes, and refined dating of geologic time. The subsequent quantitative revolution in geomorphology, with its emphasis on measurement of form and process aided by rapidly improving technologies, and based in part on lingering antecedents, sounded the death knell for the Davisian model but also triggered something of a theoretical hiatus. In recent years, resurrection of the concept of isostasy, defined by Dutton but ignored by Davis, has led to the formulation of a more realistic but more complex model, briefly introduced here, in which landforms may be viewed as responses to more-or-less continuous interaction between tectonic activity, subaerial denudation, and isostatic adjustment.     

Linking source and sink: Evaluating the balance between onshore erosion and offshore sediment accumulation since Gondwana break-up, South Africa

The geomorphic origin and evolution of the tectonically unique interior highland of southern Africa, the Kalahari Plateau, and its flanking low-lying coastal planes, remain largely unresolved because of a lack of regional quantitative analyses of its uplift and erosion history. Here we focus on the southern Cape, South Africa and link onshore denudation, based on new apatite fission track thermochronology results, to offshore sediment accumulation, using abundant well data and a seismic reflection profile. We attempt to relate source and sink in order to resolve some first order issues concerning timing of the exhumation and development of the topographic features of southern Africa. The volume of sediment accumulated off South Africa's south coast is calculated using 173 wells and a seismic reflection profile. A total, uncompacted, sediment volume of 268,500 km³ accumulated off South Africa's south coasts since  136 Ma, in the Outeniqua and Southern Outeniqua Basins. Accumulation volumes and rates were highest in the early Cretaceous (48,800 × 10⁴ km³ at  8150 km³/Ma from  136 to 130 Ma, and 57,500 × 10⁴ km³ at 5750 km³/Ma from  130 to 120 Ma) and mid–late Cretaceous (83,700 × 10⁴ km³ at 3200 km³/Ma from  93 to 67 Ma). Volumes and accumulation rates were lowest for the early–mid-Cretaceous (47,400 × 10⁴ km³ at 1750 km³/Ma from  120 to 93 Ma) and the Cenozoic (31,200 × 10⁴ km³ at 450 km³/Ma from  67 to 0 Ma). Although our analysis shows that the accumulated volume of offshore sediments does not match the calculated volume of onshore erosion, as quantified through apatite fission track thermochronology (e.g. Tinker, J.H., de Wit, M.J., Brown, R., 2008. Mesozoic exhumation of the 439 southern Cape, South Africa, quantified using apatite fission track thermochronology. Tectonophysics, doi: 10.1016/j.tecto.2007.10.009), the timing of increased sediment accumulation closely matches the timing of increased onshore denudation. This suggests that the greatest volumes of material were transported from source to sink during two distinct Cretaceous episodes, and that the processes driving onshore denudation decreased by an order of magnitude during the Cenozoic.     

Modelling of hydrogeochemical potential of three lake catchments in Polesie region (Eastern Poland)

Total dissolved solids (TDS) in lake and catchment water is a result of geological structure, as well as duration of rock and water contact and human activity. In this paper, a potential dissolved solids (PtDS) in three ??czna–W?odawa Lake catchments was determined using extraction and computer software (GIS and AquaChem). Human pressure on water quality was estimated as a difference of the TDS and a catchment hydrogeochemical potential (TPtDS, total potential dissolved solids). TPtDS coefficient included hydrogeological features of the aquifer, soil cover impact on infiltrated water quality, and sediments susceptibility to denudation. The main advantage of the model is a possibility of its employment for every catchment or other areas (e.g. administrative) on both microscale and mesoscale. The highest TPtDS occurred in the catchment, favoured with underground supply, which was located in the vicinity of the Cretaceous mesoregional unit (Che?m Hills). The lowest value was observed in the catchment built with organogenic sediments and coarse material. A seasonal constancy of TPtDS values proved a stability of the lake‐catchment systems under study. Copyright © 2012 John Wiley & Sons, Ltd.     

应用天文地层学方法对山东昌潍北部新生代不整合时间和剥蚀量的计算及其意义

为进一步推动山东昌潍北部地区的新生代油气勘探,应用潍北、牛头镇和侯镇等3个凹陷9个层段的天文地层年龄分析,计算出新生代不整合时间和剥蚀量。天文地层学计算方法主要包括:地层分层,测井频谱分析,寻找40万年周期和旋回的对比。得到结果:孔三段-孔二段界线的年龄为61.819Ma,孔二段-孔一段界线的年龄为54.638Ma,孔一段-沙四下亚段界线的年龄为48.448Ma,沙四下-沙四上亚段界线的年龄为43.516Ma,沙四上亚段顶的年龄为40.362Ma,馆陶组-明化镇组界线的年龄大约为35.778—31.896Ma。通过剥蚀的时间和沉积环境的分析提出如下观点:1)大约在48.448Ma以前,昌潍坳陷北部的沉积是全盆地的、稳定的,其中包括:约长达4Myr期间孔三段断断续续出现玄武岩喷发,大约7Myr时间内孔二段出现沼泽和浅湖相的沉积,约6Myr时间内孔一段主要为干旱相的小水塘、水坑"红色"沉积;2)从沙河街组开始(48.448Ma)至东营组末(23.03Ma)期间,也即大约25Myr期间,潍北的昌参1、昌1等井的中心部位,仍然是不断下陷、沉积;3)馆陶组沉积期间(大约23.03—13Ma)盆地全区上升。因此在大约10Myr的剥蚀时间过程中,不仅没有沉积,而把原沉积的沙三亚段至东营组不断‘反剥’到沙四段下部;4)馆陶组末(大约13Ma)到明化镇组顶(2.588Ma)沉积期间,全区开始以河流泛滥平原相为主的泥岩和泥质粉细砂岩的沉积,形成盖层。根据天文地层方法的剥蚀量计算,潍北凹陷中有3个"反剥高点"。这些"反剥高点"在始新世末至渐新世的沉积和构造上升和剥蚀过程中,可能造成砂岩回弹和孔隙扩张,形成好的储集区。根据计算,最大的"反剥高点"是在昌36—央5—昌8井一带,剥蚀厚度约达1800—3000m,与多年油田勘探取得成果是一致的。     

陕西洛南洛源原生金地球化学异常特征与洛河砂金矿预测

洛源原生金地球化学异常具有浓集中心分散、规模小、几何浓度内带大面积出露、组分较复杂和水平分带不清等特征,表明洛源金矿化主要为分散矿化,而且具较大的剥蚀深度。金的原生地球化学异常源为小的含金断裂构造带。地球化学异常区的冰川活动,加速了此区的剥蚀作用。洛河砂金矿是在上淤汇水盆地中金的分散矿化被强烈剥蚀下形成的。金的分散矿化范围大,空白水系少,稀释作用受仰制,为洛河砂金矿形成创造了良好的条件。从洛河的淘金历史和现状以及对砂金的总量预测来看,洛河砂金矿是很有远景的。