Holocene valley aggradation and gully erosion in headwater catchments,south-eastern highlands of Australia

Late Quaternary stratigraphy of a 50 km² catchment on the south-eastern highlands of Australia reveals processes and history of denudation, and helps resolve a long-standing debate about factors controlling episodic valley aggradation and degradation during Holocene times. Valley sedimentation occurred when swampy vegetation fully colonized valley floors and obliterated all channels, promoting aggradation for periods of several thousand years, with most incoming sediment being trapped in swampy meadows. Much of the sediment was reworked from late Pleistocene alluvial fan and valley fill deposits, and primary hillslope erosion was minor during the Holocene. Differing sedimentation patterns between the Late Pleistocene, Holocene and Post-European settlement periods reflect regional changes in sediment supply and transport capacity as a result of major environmental change. Within the Holocene, however, valley fill stratigraphy is controlled by massive, episodic gully erosion terminating aggradation. Gully initiation appears to be controlled more by thresholds of incision into vegetated valley floors than by changes to sediment supply. Whether the thresholds are exceeded because of climatic change, autonomous change or extreme events cannot yet be determined. Overall, the Holocene history represents continuing complex response to events of the Late Pleistocene, and does not support the K-cycle concept, which has strongly influenced late Quaternary geomorphology in Australia.     

基于MODIS的大田县均溪谷地NPP与NDVI相关性的时空变化特征

本研究应用MODIS卫星遥感资料,分析2000—2010年大田县均溪谷地植被净初级生产NPP与NDVI相关性的时空变化特征,运用Arc GIS软件对大田县均溪河做不同距离的缓冲区分析,结合土地利用状况,研究年植被净初级生产力a NPP与年均归一化植被指数ANDVI的相关性,并建立线性回归分析模型进一步分析NPP随NDVI的变化情况。可以看出,ANDVI与a NPP的空间分布特征与距河流的距离远近有着密切关系,河流不同缓冲区ANDVI与a NPP的相关性系值为0.80~0.96。研究区域3年回归模型均通过α=0.01的显著性F值相关检测,表明利用NDVI可以有效地对NPP进行实时监测。     

陆良彩色沙林旅游地学与保护

陆良彩色沙林为晚第三纪砂砾岩层中的溯源侵蚀冲沟地貌景观,世界罕见的自然奇观之一,具有较高的旅游和地理、地质研究价值。彩色沙林承继了陆良上亿年的地质发展史,淀积了10亿年来的砂、砾、矿物等物质,而形成、发育在近2Ma间,现仍处于缓慢发展阶段的溯源侵蚀冲沟中。彩色沙林景观应坚持“经营、建设、保护”并重的方针。     

Surface glaciochemistry of Taylor Valley,southern Victoria Land,Antarctica and its relationship to stream chemistry

We have analysed a series of surface samples from the alpine glaciers of Taylor Valley, Southern Victoria Land, Antarctica for their geochemical composition. This was done to better establish the role of glaciochemical variation on the chemical composition of meltwater streams emanating from the glaciers. The chemistry of the snow and ice changes with proximity to the ocean and with elevation of the glacier surface. The aeolian transport of dry valley dust, as indicated by both chemical and particulate matter variations, is a major process affecting the overall glacier chemistry and the chemistry of the meltwaters. Streams originating on the western edges of the glaciers are more impacted by the aeolian input as they are in the direct path of the major regional wind direction. Our data strongly suggest that the variation in stream geochemistry in Taylor Valley is a result in part of the differences in chemical composition of glacier melt. Copyright © 2003 John Wiley & Sons, Ltd.     

Using fossil spring deposits in the Death Valley region,USA to evaluate palaeoflowpaths

Spring deposits reveal the timing and environment of past groundwater discharge. Herein, however, the potential for fossil spring deposits to infer water sources and palaeoflowpaths through trace elements and stable and radiogenic isotopes is examined. Past discharge (70 to 285 ka) in the Tecopa Basin in the Death Valley region of southeastern California is represented by tufa deposits, including mounds, pools, cemented ledges and rare calcite feeder veins. δ¹⁸O values indicate that spring discharge was a mixture of far‐travelled (regional) water with a significant, and perhaps dominant contribution of local recharge on a nearby range front and alluvial pediment, rather than simply representing an elevated regional water table. δ¹³C values indicate regional water had a high TDS, whereas solute data imply low overall solute contents, consistent with dilution by a large component of local recharge. Radiogenic isotope data (U‐series, ⁸⁷Sr/⁸⁶Sr) for tufa indicate that siliciclastic rocks (a regional aquitard) interacted with discharging water. To access this aquitard, regional flow was probably partitioned into a permeable north–south damage zone of a north–south range‐bounding fault along the foot of the Resting Spring Range, which ultimately controlled the location of groundwater discharge. Existing models for modern discharge in the Tecopa Basin, by contrast, call upon westward interbasin flow in carbonate rocks from the Spring Mountains through the intervening (and nearly perpendicular) Nopah and Resting Spring Ranges. Understanding the controls on regional groundwater flow is critical in this and other arid regions where water is, by definition, a scarce resource. Thus, although it is a case study, this report highlights a fruitful approach to palaeohydrology that can be widely applied. Copyright © 2007 John Wiley & Sons, Ltd.     

长江中下游地区深部地球物理调查成果及对地质构造与成矿预测的新认识

在长江中下游地区先后做了八条大地电磁测深剖面,取得了较系统的深部地质结构的实际资料,对一些重要断裂及构造分区提出了新的认识,并用板块观点对板块的拼合、缝合线、洋壳俯冲等问题进行了探讨,提出了区域成矿预测意见,指出了一些新的成矿远景区。     

浅析文山州清水沟地区地质条件及找矿前景

文山州清水沟地区具一定的铜、金、铁找矿前景。该区有较好的成矿地质条件及物化探异常。成矿作用主要受构造与岩浆岩活动的控制。矿产分布与北东向构造裂隙及基性岩浆岩活动定位关系密切。找矿靶区选定于成矿远景区内断裂发育的独角村背斜核部、成矿元素富集区及基性岩浆岩活动地带。     

Depositional features and transportation mechanism of valley-filling Iwasegawa and Kaida debris avalanches, Japan

 The depositional features of two valley-filling debris avalanche deposits were studied to reveal their transportation and depositional mechanisms. The valley-filling Iwasegawa debris avalanche deposit (ca. 0.1 km³) is distributed along the valleys at the southeastern foot of Tashirodake Volcano, northern Honshu, Japan. Debris-avalanche blocks range in size from <35 m proximally to <10 m in the distal zone and consist dominantly of fragile materials. Debris-avalanche matrix percentages increase from 35–60% in the proximal zone to 95% in the distal zone. The debris-avalanche matrix is greater in volume (80–90%) at the bottom and margins of the deposit. Normal grading of large clasts and reverse grading of wood logs and branches occur within the debris-avalanche matrix. Preferred orientation of 311 wood logs and branches within the deposit coincide with the interpreted local flow direction. The basal part of the deposit is characterized by (1) erosional features and incorporated clasts of underlying material; (2) a higher proportion (30–50%) of incorporated clasts than the upper part; and (3) reverse grading of clasts. The valley-filling Kaida debris avalanche deposit (50 000 y B.P., >0.3 km³) is distributed along the valleys at the eastern-southeastern foot of Ontake Volcano, central Japan. Debris-avalanche blocks range in size from <25 m proximally to <7 m in the medial zone. Debris-avalanche matrix percentages increase from 50–70% in the proximal zone to 80% in the distal zone. The debris-avalanche matrix is more abundant (80–90%) at the bottom part of the deposit. Deformation structures observed in the debris-avalanche blocks include elongation, folding, conjugate reverse faults, and numerous minor faults in unconsolidated materials. Lithic components within the debris-avalanche matrix tend to have a higher percentage of plucked clasts from the adjacent underlying formations. A Bingham "plug flow" model is consistent with the transportation and depositional mechanisms of the valley-filling debris avalanches. In the plug of the debris avalanche, fragile blocks were transported without major rupturing due to relatively small shear stresses in regions of small strain rate. The debris-avalanche matrix was mainly produced by shearing at the bottom and margins of the avalanche. Valley-filling debris avalanches tend to have smaller debris-avalanche blocks and larger amounts of debris-avalanche matrix than do unconfined debris avalanches. These differences may be due to disaggregation of debris-avalanche blocks by shearing against valley walls and interaction between debris-avalanche blocks and valley walls. Oriented wood logs and branches, reverse grading of clasts at the base, and a higher proportion of incorporated clasts at the base are interpreted to result from shearing along the bottom and valley walls. Received: 25 March 1998 / Accepted: 10 October 1998     

Measuring alluvial fan sensitivity to past climate changes using a self‐similarity approach to grain‐size fining,Death Valley,California

The effects of climate change on eroding landscapes and the terrestrial sedimentary record are poorly understood. Using mountain catchment–alluvial fan systems as simple analogues for larger landscapes, a wide range of theoretical studies, numerical models and physical experiments have hypothesized that a change in precipitation rate could leave a characteristic signal in alluvial fan sediment flux, grain size and down‐system fining rate. However, this hypothesis remains largely untested in real landscapes. This study measures grain‐size fining rates from apex to toe on two alluvial fan systems in northern Death Valley, California, USA, which each have well‐exposed modern and ca 70 ka surfaces, and where the long‐term tectonic boundary conditions can be constrained. Between them, these surfaces capture a well‐constrained temporal gradient in climate. A grain‐size fining model is adapted, based on self‐similarity and selective deposition, for application to these alluvial fans. This model is then integrated with cosmogenic nuclide constraints on catchment erosion rates, and observed grain‐size fining data from two catchment‐fan systems, to estimate the change in sediment flux from canyon to alluvial fan that occurred between mid‐glacial and modern interglacial conditions. In a fan system with negligible sediment recycling, a ca 30% decrease in precipitation rate led to a 20% decrease in sediment flux and a clear increase in the down‐fan rate of fining, supporting existing landscape evolution models. Consequently, this study shows that small mountain catchments and their alluvial fan stratigraphy can be highly sensitive to orbital climate changes over <10⁵ year timescales. However, in the second fan system it is observed that this sensitivity is completely lost when sediment is remobilized and recycled over a time period longer than the duration of the climatic perturbation. These analyses offer a new approach to quantitatively reconstructing the effects of past climate changes on sedimentation, using simple grain‐size data measured in the field.     

Retrogression characteristics of landslides in fine-grained permafrost soils, Mackenzie Valley, Canada

Thirteen landslides (retrogressive thaw flows) were investigated to study the behavior of thaw retrogression in permafrost in the Mackenzie Valley, Northwest Territories (NWT), Canada. Those landslides are all in fine-grained ice-rich permafrost soils. Such landslides usually start from small-scale slope failures followed by retrogressive thaw flows when ice-rich permafrost soils are exposed to the atmosphere. The landslides were marked with survey stakes to measure their retreat rates for the thawing season of 2007. Two correlations are presented: one is between scarp wall height and retreat rate; another is between overall slope angle and retreat rate. It was found that thaw flow retrogression rate increases with increase in scarp wall height and slope angle up to a certain limit. It was also confirmed that thaw flow retrogression is not influenced by slope orientation.