Early and Middle Pleistocene river systems in eastern England: evidence from Leet Hill,southern Norfolk,England

Pleistocene sediments at Leet Hill, southern Norfolk are examined in terms of their sedimentary structures, palaeocurrent indicators, clast and heavy mineral lithology and litho- and morphostratigraphic position. Colour of the quartzite and vein-quartz clasts is used to differentiate the Bytham and the Kesgrave sands and gravels, with the Bytham sands and gravels having a significantly higher proportion of coloured material. The Kirby Cane sands and gravels are the lower sedimentary unit and were deposited by the Bytham river, which drained a catchment extending into central England. At Leet Hill, erosion of the Kesgrave Sands and Gravels by the Bytham river has given the Kirby Cane sands and gravels a distinctive lithological assemblage. Trace clast lithologies suggest that the Kesgrave Sands and Gravels in the region of Leet Hill were deposited in a coastal location with an input from northern sources as well as southern and Welsh sources diagnostic of the Thames catchment. The glaciofluvial Leet Hill Sands and Gravels were deposited by outwash from the Anglian Scandinavian ice sheet. Initially the flow direction of the outwash was determined by the Bytham river valley, but this changed to a southerly direction once the valley had been infilled. This paper provides the first indication of the location of the boundary (Early Pleistocene coastline) between the fluvial Kesgrave Sands and Gravels and the marine equivalent reworked by coastal processes, and demonstrates the way the pre-glacial relief initially controlled patterns of glaciofluvial sedimentation during the early part of the Anglian glaciation. Copyright © 1999 John Wiley & Sons, Ltd.     

Preliminary assessment of crustacean distribution patterns in New Zealand groundwater aquifers

Crustaceans were sampled in 17 groundwater wells at five locations in North and South Islands of New Zealand. Three sampling locations were associated with unconfined aquifers adjacent to gravel‐bed rivers, whereas the other two locations were distant from rivers, but associated with land‐based sewage effluent disposal sites. Crustaceans and basic physico‐chemical parameters were sampled in summer and winter. Total abundance varied from 1 to 1064 individuals/250 litre sample. Copepods dominated the fauna at four of the five locations, and were most abundant immediately downstream of a sewage effluent disposal area. Paraleptamphopus spp. (Amphipoda) was found at all five locations, and abundance was also greatest downstream of sewage effluent disposal areas. Several crustacean taxa were rare or limited in distribution, including the gammarid Paracrangonyx sp. and the anthurid isopod Cruregens sp. Syncarids were widely distributed, but found in low numbers, and no specimens were found immediately below sewage effluent disposal areas. We suggest that groundwater ecology in New Zealand is restricted by lack of knowledge of taxonomy and ecology of key groups, particularly the Copepoda.     

The Quaternary rivers of the Jurassic Coast region: From the Neogene to the Anthropocene

The Jurassic Coast World Heritage Sites (JCWHS) is not only a 95 km long coastline and remarkable Mesozoic geological section, but also a slice through a Quaternary landscape. For the majority of the last two million years this landscape lay in the periglacial zone, just south of a waxing and waning ice margin and just north of an Atlantic inlet which eventually became the English Channel. This paper reviews how the previous landscape inherited from the Cenozoic, was modified through uplift, climatically driven fluvial activity and periglaciation. Much evidence of this Quaternary history can be seen today in sections along the JCWHS coast which cuts through a number of headwater valleys the largest of which are the Exe and Axe. Recent studies, largely funded from the Aggregate Levy Tax, have produced the first independent chronologies for the Exe and Axe valleys and a model of how periglaciation interacted with the layer-cake stratigraphy of the Mesozoic bedrocks of the JCWHS. The Quaternary history of the JCWHS is also preserved in raised beaches on the Isle of Portland, coastal landforms, and in Holocene alluvial sediments associated with human activity and which may constitute part of the putative Anthropocene. An appreciation of the Quaternary history of the JCWHS is also important in understanding modern geological hazards from landslides to flooding.     

黄河内蒙古河段河道冲淤演变与凌情响应机制

黄河上游内蒙古冲积性河道凌汛问题突出,研究河道冲淤演变与凌情响应机制可为该河段防凌减灾提供技术支持。根据内蒙古河段凌情、河道冲淤演变资料,分析凌情变化表征指标及与之密切相关的河道冲淤演变特征指标,研究河道冲淤演变特征指标与凌情变化表征指标的响应关系。结果表明:河道冲淤演变的特征指标平滩流量与凌情表征指标冰下过流能力、槽蓄水增量关系密切,冰下过流能力为平滩流量的1/5左右,随着平滩流量减小而减小,而槽蓄水增量随着平滩流量的减小而增大,有利内蒙古河段防凌的平滩流量宜不小于2 000 m3/s,槽蓄水增量宜不超过14亿m3。本研究成果可为内蒙古河段冰凌灾害防治提供参考。     

泥石流扇形地危险性评价研究

本文应用数学统计方法探讨了泥石流扇形地危险性评价方法，根据专家综合调查，确定了泥石流堆积厚度，最大石块粒径，扇面沟道位置，扇面纵比降和扇面糙率五个主导因子参与泥石流危险度评价。应用德菲尔分析方法计算了和因子的权重，由此建立了泥石流扇形地危险度分区的简易模型。     

论贵州中部九架炉组铝矿系冲洪积扇沉积特征

通过对贵州中部石炭系九架炉组铝矿系的较系统研究,认为该套沉积物是由冲洪积作用及湖泊作用在负地形堆积而成的陆相岩系,冲洪积扇是最常见的一种冲洪积相沉积物,贵州中部大部分大型铝土矿床都是由此种沉积作用形成的扇群席状砂体经铝土矿化改造而成。     

Fluvial architecture and diagenesis of the Mt Eclipse Sandstone,northern Ngalia Basin,Australia

The Upper Devonian to Carboniferous Mt Eclipse Sandstone is a basin-wide host to uranium mineralisation in the Ngalia Basin, NT. The fluvial depositional architecture and diagenesis of the Mt Eclipse Sandstone at the Bigrlyi uranium deposit on the northern margin of the basin are deduced from hyperspectral mineral results captured from 200 drill holes, combined with core and outcrop observations across a ~10 km strike length. The succession hosting the uranium mineralisation is interpreted to be deposited in the lower parts of a mature alluvial fan system with low slope angle and dominated by immature, kaolinised, medium-grained subarkosic sandstones and patchy calcite cement. This study reveals the fluvial channel sequence is estimated to be 3 km wide, 100–200 m thick and sourced from the north. This multidisciplinary study also uncovers the complex interaction and codependencies between fluvial/groundwater activity, evaporation, oxidation, fluctuating pH and detrital mineralogy controlling early diagenetic processes in the alluvial fan sediments. Carbon isotope data identify calcite cements as groundwater calcrete, while strontium isotope data suggest limited prolonged water–rock interaction prior and during calcite cementation. The petrographic data reveal the importance of early calcite cement occluding all pore space and preserving detrital minerals from later diagenetic processes. The hyperspectral results highlight the intermittent distribution of the calcite cement and the commonly repetitive mineralogical zonation throughout the 200 drill holes, including the inverse spatial correlation between kaolinite ± goethite ± gypsum vs white mica ± hematite dominated zones. X-ray diffraction and the hyperspectral data reveal the scarcity of early diagenetic clay minerals such as montmorillonite. This paper is the first to report on a systematic mineralogical and sedimentological study for the Mt Eclipse Sandstone. By focusing on the diagenesis and fluvial architecture of this stratigraphic unit, a framework to support exploration for sediment-hosted uranium deposits is established.     

Could alluvial knickpoint retreat rather than fire drive the loss of alluvial wet monsoon forest,tropical northern Australia?

Drainage rejuvenation through headward migration of alluvial knickpoints is common in ephemeral semi‐arid streams, but has not yet been described for tropical rivers. In the Australian monsoon tropics (AMT), wet monsoon forests have an important ecological function, and are present along many alluvial valleys and springs within a eucalypt‐savanna dominated landscape. Using a combination of LiDAR, remote sensing and field evidence, we observe the ongoing destruction of wet monsoon forest through hydro‐geomorphic feedbacks, along with the headward retreat of an alluvial knickpoint at Wangi Creek in Litchfield National Park, Northern Territory. Due to the highly transmissive shallow aquifer along the lower Wangi Creek, this knickpoint retreat leads to a downstream drop in in‐channel water level, which in turn drives a decrease in the local groundwater table. The lowered groundwater level causes the shallow anabranches and formerly water saturated peaty floodplain soil to desiccate, which results in a reduction of vegetation density. The resulting dry surface conditions allow annual to bi‐annual high frequency low‐intensity fires to affect the monsoon forest, while wet rainforest upstream of the knickpoint remains intact. In this paper, we argue that such hydro‐geomorphic feedbacks may cause the initial destabilization of the forest, which then provides the necessary conditions for the impact of fire. This scenario thus challenges the prevalent view that fire is a first‐order control on the spatial extent of wet monsoonal rainforest in the study area, and provides a new and testable hypothesis for further studies in the AMT. Copyright © 2016 John Wiley & Sons, Ltd.     

REGIME MORPHOLOGY OF EQUILIBRIUM ALLUVIAL CHANNELS

IINTRODUCTIONThequestfordeterminingthedesigncharacteristicsofregimechannelshasbeengoingonforalongtime.Peoplehavebeenexcavatingnewormodifyingexistingchannelstousethemforirrigation,watersupply,navigation,floodcontrolandotherpurposes.Recently,archeologistsdiscoveredwhatiscurrentlybelievedtobetheoldestman(madecanalsystem.ItwasfoundintheareawhereMesopotamiausedtoexistanditisdatedbacktoabollt4,000BC.Ifachanne]isnotproperlydesigned,erosionofitsbanksordepositionofsedimentwithinitscross-sectionw…     

A precipiton‐based approach to model hydro‐sedimentary hazards induced by large sediment supplies in alluvial fans

Mountain ranges are frequently subjected to mass wasting events triggered by storms or earthquakes and supply large volumes of sediment into river networks. Besides altering river dynamics, large sediment deliveries to alluvial fans are known to cause hydro‐sedimentary hazards such as flooding and river avulsion. Here we explore how the sediment supply history affects hydro‐sedimentary river and fan hazards, and how well can it be predicted given the uncertainties on boundary conditions. We use the 2D morphodynamic model Eros with a new 2D hydrodynamic model driven by a sequence of flood, a sediment entrainment/transport/deposition model and a bank erosion law. We first evaluate the model against a natural case: the 1999 Mount Adams rock avalanche and subsequent avulsion on the Poerua river fan (West Coast, New Zealand). By adjusting for the unknown sediment supply history, Eros predicts the evolution of the alluvial riverbed during the first post‐landslide stages within 30 cm. The model is subsequently used to infer how the sediment supply volume and rate control the fan aggradation patterns and associated hazards. Our results show that the total injected volume controls the overall levels of aggradation, but supply rates have a major control on the location of preferential deposition, avulsion and increased flooding risk. Fan re‐incision following exhaustion of the landslide‐derived sediment supply leads to sediment transfer and deposition downstream and poses similar, but delayed, hydro‐sedimentary hazards. Our results demonstrate that 2D morphodynamics models are able to capture the full range of hazards occurring in alluvial fans including river avulsion aggradation and floods. However, only ensemble simulations accounting for uncertainties in boundary conditions (e.g., discharge history, initial topography, grain size) as well as model realization (e.g., non‐linearities in hydro‐sedimentary processes) can be used to produce probabilistic hazards maps relevant for decision making. Copyright © 2017 John Wiley & Sons, Ltd.