Soil and landscape studies in Western Australia     

M. J. Mulcahy  E. Bettenay 《Australian Journal of Earth Sciences》2013,60(4):349-357

The main features of climate and geology relevant to a discussion of the soils and landscapes of Western Australia are briefly reviewed. The pattern of drainage is described in terms of six drainage divisions, each with characteristic physiography and soils. In the interior, this involves a reconstruction of an ancient drainage system, based on the maps of the Atlas of Australian Soils. It is shown, on a continental scale, that the major divides are characterised not only by deep, chemically weathered, often lateritic profiles, but also by extensive sandy deposits derived from these preweathered materials.  相似文献   

Strong seasonality in sand loading and resulting feedbacks on sediment transport,bed texture,and channel planform at Mount Pinatubo,Philippines     

Karen B. Gran 《地球表面变化过程与地形》2012,37(9):1012-1022

Declining sand inputs to a channel with bimodal bed sediment can lead to degradation, armoring, and reduced bedload transport rates. Where sand loading is episodic, channels may alternate between high‐sand and low‐sand conditions, with ensuing responses in bed texture and bedload transport rates. The effects of episodic sand loading are explored through flow, grain size, and bedload transport measurements on the Pasig‐Potrero River, a sediment‐rich channel draining Mount Pinatubo, Philippines. Sand loading on the Pasig‐Potrero River is highly seasonal, and channel adjustments between seasons are dramatic. In the rainy season, inputs from sand‐rich 1991 eruption deposits lead to active, sand‐bedded, braided channels. In the dry season, many precipitation‐driven sand sources are cut off, leading to incision, armoring, and significantly lower bedload transport rates. This seasonal transition offers an excellent opportunity to examine models of degradation, incision, and armoring as well as the effectiveness of sediment transport models that explicitly encapsulate the importance of sand on transport rates. During the fall 2009 seasonal transition, 7·6 km of channel incised and armored, carving a 2–3 m deep channel on the upper alluvial fan. Bedload transport rates measured in the August 2009 rainy season were over four orders of magnitude greater than gravel‐bedded dry‐season channels surveyed in January 2010, despite having similar shear stress and unit discharge conditions. Within dry‐season incised channels, bed armoring is rapid, leading to an abrupt gravel‐sand transition. Bedload transport rates adjust more slowly, creating a lag between armoring and commensurate reductions in transport. Seasonal channel incision occurred in steps, aided by lateral migration into sand‐rich banks. These lateral sand inputs may increase armor layer mobility, renewing incision, and forming terraces within the incised seasonal channel. The seasonal incised channel is currently being reset by precipitation‐driven sand loading during the next rainy season, and the cycle begins again. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

泰山南坡沉积物特征及第四纪冰缘环境探讨          下载免费PDF全文

郭慧玲  张建伟  郭秀岩  高擎  申卫星  袁西龙  陈岩  王锡魁 《山东国土资源》2012,28(6):6-9

针对泰山第四纪冰川有无的争议,在泰山南坡采集沉积物样品进行分析研究。孢粉分析结果显示优势植物种群为"松属+中华卷柏+蒿属+藜科",指示的沉积环境为湿冷环境。扫描电镜观察石英颗粒表面,显示出边缘棱角清晰、具贝壳状断口和解理片的冰川环境特征。通过热释光测试得样品年龄为(30.54±2.59)kaB.P.,相当于末次冰期主冰期中的Paudorf-Stillfried间冰阶。根据泰山现代气候环境推演泰山古气候温度和降水量,得出泰山地区在末次冰期时具备了形成冰川的基本气候条件。鉴于Paudorf-Stillfried间冰阶持续的时间较短,因此初步推断该沉积物指示的古气候环境为冰缘环境。  相似文献   

Fracture patterns at lava–ice contacts on Kokostick Butte, OR, and Mazama Ridge, Mount Rainier, WA: Implications for flow emplacement and cooling histories   总被引：1，自引：1，他引：0  

Robert W.D. Lodge  David T. Lescinsky   《Journal of Volcanology and Geothermal Research》2009,185(4):298-310

Cooling lava commonly develop polygonal joints that form equant hexagonal columns. Such fractures are formed by thermal contraction resulting in an isotropic tensional stress regime. However, certain linear cooling fracture patterns observed at some lava–ice contacts do not appear to fit the model for formation of cooling fractures and columns because of their preferred orientations. These fracture types include sheet-like (ladder-like rectangular fracture pattern), intermediate (pseudo-aligned individual column-bounding fractures), and pseudopillow (straight to arcuate fractures with perpendicular secondary fractures caused by water infiltration) fractures that form the edges of multiple columns along a single linear fracture. Despite the relatively common occurrence of these types of fractures at lava–ice contacts, their significance and mode of formation have not been fully explored. This study investigates the stress regimes responsible for producing these unique fractures and their significance for interpreting cooling histories at lava–ice contacts.Data was collected at Kokostick Butte dacite flow at South Sister, OR, and Mazama Ridge andesite flow at Mount Rainier, WA. Both of these lava flows have been interpreted as being emplaced into contact with ice and linear fracture types have been observed on their ice-contacted margins. Two different mechanisms are proposed for the formation of linear fracture networks. One possible mechanism for the formation of linear fracture patterns is marginal bulging. Melting of confining ice walls will create voids into which flowing lava can deform resulting in margin-parallel tension causing margin-perpendicular fractures. If viewed from the ice-wall, these fractures would be steeply dipping, linear fractures. Another possible mechanism for the formation of linear fracture types is gravitational settling. Pure shear during compression and settling can result in a tensional environment with similar consequences as marginal inflation. In addition to this, horizontally propagating cooling fractures will be directly influenced by viscous strain caused by the settling of the flow. This would cause preferential opening of fractures horizontally, resulting in vertically oriented fractures.It is important to note that the proposed model for the formation of linear fractures is dependent on contact with and confinement by glacial ice. The influence of flow or movement on cooling fracture patterns has not been extensively discussed in previous modeling of cooling fractures. Rapid cooling of lava by the interaction with water and ice will increase the ability to the capture and preserve perturbations in the stress regime.  相似文献   

Coupled Process Models as a Tool for Analysing Hydrothermal Systems     

K. Gessner  M. Kühn  V. Rath  C. Kosack  M. Blumenthal  C. Clauser 《Surveys in Geophysics》2009,30(3):133-162

Hydrothermal systems are characterised by complex interactions between heat transfer, fluid flow, deformation, species transport and chemical reactions. Numerical models can provide quantitatively constrained information in regions where acquisition of new data is difficult or expensive thus providing a means for reducing risks, costs, and effort during targeting, production, and management of resources linked to hydrothermal systems. Here we show how numerical simulations of hydrothermal processes can be used to better understand coupled reactive transport in modern geothermal systems and in ancient hydrothermal ore deposits. We give examples based on the Enhanced Geothermal System at Soultz-sous-Forêts in France, hydrothermal mineralisation at Mount Isa in Australia, and the geothermal resource at Hamburg-Allermöhe in Germany.  相似文献   

Taxonomy and biogenicity of Archaean spheroidal microfossils (ca. 3.0 Ga) from the Mount Goldsworthy–Mount Grant area in the northeastern Pilbara Craton, Western Australia     

Kenichiro Sugitani  Kathleen Grey  Tsutomu Nagaoka  Koichi Mimura  Malcolm R. Walter 《Precambrian Research》2009,173(1-4):50

Microstructures recently reported from an Archaean sedimentary succession (ca. 3.0 Ga) in the Mount Goldsworthy–Mount Grant area in the northeastern Pilbara Craton meet the criteria for compelling evidence of biogenicity [Sugitani, K., Grey, K., Allwood, A., Nagaoka, T., Mimura, K., Minami, M., Marshall, C.P., Van Kranendonk, M.J., Walter, M.R., 2007. Diverse microstructures from Archaean chert from the Mount Goldsworthy–Mount Grant area, Pilbara Craton, Western Australia: microfossils, dubiofossil, or pseudofossils. Precambrian Res. 158, 228–262]. The structures are morphologically diverse. Although they were tentatively classified into five major morphological types (thread-like, film-like, small (<15 μm) and large (>15 μm) spheroidal, and spindle-like), the possible taxonomic significance of these groups was not discussed. Building on our earlier analysis, we focus on the morphology of the larger spheroids, as well as presenting further evidence relating spindles and several bizarre forms, and attempt to group them taxonomically and adduce additional evidence for their biogenicity.Taphonomic features were identified in each of the various morphological groups, but the range of morphological diversity of the spheroids cannot be attributed solely to taphonomic alteration. Four subdivisions of spheroids are proposed: (1) simple single-walled spheroids, (2) thin-walled spheroids having a diffuse envelope, (3) thick-walled spheroids, and (4) spheroids having an extensively folded wall. Simple single-walled spheroids, 15–60 μm in diameter, with various wall textures but commonly lacking envelopes or appendages form the dominant subgroup. Other complex morphologies are present and include aligned or associated bodies of thin-walled spheroids with diffuse envelopes, and spindle-like structures containing inner spheroidal bodies. The degree of morphological complexity and associations between structures suggest the presence of reproductive phases. If correct, this implies that the early Earth (ca. 3.0 Ga) showed a higher level of biodiversity than is currently postulated.  相似文献   

First discovery of Holocene Alaskan and Icelandic tephra in Polish peatlands     

《第四纪科学杂志》2017,32(4):457-462

Despite the discovery of cryptotephra layers in over 100 peatlands across northern Europe, Holocene cryptotephra layers have not previously been reported from Polish peatlands. Here we present the first Holocene tephra findings from two peatlands in northern Poland. At Bagno Kusowo peatland we identify the most easterly occurrence of the AD 860 B tephra, recently correlated to the White River Ash (WRAe) derived from Mount Churchill, Alaska. A shorter core from Linje peatland contains tephra from the Askja 1875 eruption, extending the spatial distribution and regional importance of this Icelandic tephra in Eastern Europe. Our research indicates the potential of cryptotephra layers to date and correlate the growing number of palaeoenvironmental studies being conducted on Polish peatlands and contributes towards the development of a regional Holocene tephrostratigraphy for Poland. Copyright © 2017 The Authors. Journal of Quaternary Science Published by John Wiley & Sons, Ltd.

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第四纪冰川遗迹的判别标准与方法问题——兼论蒙山巨砾堆积堤之成因   总被引：2，自引：1，他引：1  

王乃昂  戴霜  张律吕  余莺潇  于昕冉  田璐  尹丽颖 《冰川冻土》2017,39(6):1289-1297

判断中国东部中低山地冰川作用遗迹的真伪,只能通过科学实践检验和学术争鸣加以解决。利用实地考察所测数据资料,证明山东蒙山确无第四纪冰川遗迹。包括蒙山在内的山东中低山丘陵,迄今为止没有发现符合判别标准的末次冰期冰川地貌三要素组合。蒙山兰溪峡谷的谷形指数（0.07~0.24）与世界各地真正的冰川槽谷不符,被当作冰川证据的蒙山兰溪峡谷谷壁擦痕和拦马墙巨砾堆积堤砾石擦痕,不具有作为冰川地貌证据的唯一性或专属性,而是砾石沿河谷滚动、拖拽摩擦和撞击的结果。不连续、不对称分布于兰溪下游凹岸的拦马墙巨砾堆积堤,沿流向延伸或呈流线构造,具有平行主流的平顶、陡坡砾石堆和立石等景观,砾石的圆度、分选和砾组构造均指向泥石流堆积堤或特大洪水巨石边滩。它可能是1668年7月25日郯城大地震保存下来的群发性灾害遗迹。  相似文献   

A parametric and comparative study of different tephra fallout models     

S. Scollo  A. Folch  A. Costa 《Journal of Volcanology and Geothermal Research》2008

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Pyroclastic density currents resulting from the interaction of basaltic magma with hydrothermally altered rock: an example from the 2006 summit eruptions of Mount Etna,Italy   总被引：2，自引：1，他引：1  

B. Behncke  S. Calvari  S. Giammanco  M. Neri  H. Pinkerton 《Bulletin of Volcanology》2008,70(10):1249-1268

After 16 months of quiescence, Mount Etna began to erupt again in mid-July 2006. The activity was concentrated at and around the Southeast Crater (SEC), one of the four craters on the summit of Etna, and eruptive activity continued intermittently for 5 months. During this period, numerous vents displayed a wide range of eruptive styles at different times. Virtually all explosive activities took place at vents at the summit of the SEC and on its flanks. Eruptive episodes, which lasted from 1 day to 2 weeks, became shorter and more violent with time. Volcanic activity at these vents was often accompanied by dramatic mass-wasting processes such as collapse of parts of the cone, highly unusual flowage processes involving both old rocks and fresh magmatic material, and magma–water interaction. The most dramatic events took place on 16 November, when numerous rockfalls and pyroclastic density currents (PDCs) were generated during the opening of a large fracture on the SE flank of the SEC cone. The largest PDCs were clearly triggered explosively, and there is evidence that much of the energy was generated during the interaction of intruding magma with wet rocks on the cone’s flanks. The most mobile PDCs traveled up to 1 km from their source. This previously unknown process on Etna may not be unique on this volcano and is likely to have taken place on other volcanoes. It represents a newly recognized hazard to those who visit and work in the vicinity of the summit of Etna.  相似文献