Longitudinal profile evolution of valleys on coastal terraces under the compound influence of eustasy, tectonism and marine erosion

On the coast of Tosa Bay, Southwestern Japan, there is a wide coastal terrace which was formed in the Last Interglacial and has been uplifted to altitudes of 150–200 m above the present sea level by crustal movement. Many valleys dissect the terrace surface with upwardly convex profiles in downstream reaches. Numerical simulations were conducted to investigate the development of longitudinal profiles of the valleys under the influence of baselevel change and marine erosion. The basic equation used for the calculation had been derived theoretically from the hydraulic mechanism of river erosion. The independent variables are the gradient and curvature of the valley floor and the distance from the divide (drainage area per unit basin width). The parameter in the sediment transport equation is determined based on the results of laboratory experiments. A time sequence of seashore migration which has been caused by marine erosion and relative sea level change due to crustal uplift and glacial eustasy since the Last Interglacial was given as a boundary condition. Numerical calculations were conducted using a finite difference method, starting from 125000 years ago when the shoreline was located at the upper end of the terrace surface, and progressive changes in the valley profiles over time were simulated. The present profiles obtained from the calculation fit quite closely to actual valley profiles, which demonstrates the validity of the equation, and at the same time suggests a formation process for wide coastal terraces.     

Interaction of tectonics, eustasy, climate and carbonate production on the sedimentary evolution of an early/middle Jurassic extensional basin (Southern Provence Sub-basin, SE France)

This paper describes the evolution of an extensional basin in regard to the nature and sequence stratigraphic arrangement of its carbonate deposits. The purpose of this study is to evaluate the respective effects of tectonism, eustasy, climate and oceanography on a carbonate sedimentary record. The case study is the early to mid‐Jurassic age carbonate succession of the Southern Provence Sub‐basin (SE France), located within the southern part of the extensional Western European Tethyan Margin. This work is based on sedimentologic, biostratigraphic (using ammonites and brachiopods) and sequence stratigraphic analysis of the carbonate facies of the Cherty Reddish Limestone Formation (late Sinemurian to earliest Bajocian). These strata were deposited in shoreface to lower offshore depositional environments. The succession of the various environments together with the recognition of key stratigraphic surfaces allow us to define four second‐order depositional sequences; of late Sinemurian to earliest Pliensbachian, early Pliensbachian to late Pliensbachian, earliest Toarcian to middle Aalenian and late Aalenian to early Bathonian ages. The architecture of the depositional sequences (thickness and facies variations within the systems tracts, wedge‐shaped geometries) reflects a strong tectonic control. The sub‐basin was structured by extensional faults (oriented approximately 070–090/250–270). Sea‐level variations, fluctuations in carbonate production and preservation, and environmental changes were also significant controlling factors of the carbonate deposition. The interplay of the tectonic control with the other factors resulted in five main phases in the sedimentary evolution of the sub‐basin: (1) dominant tectonic control during the initial rifting stage (late Sinemurian to early Pliensbachian); (2) increasing extensional tectonics (mid‐Pliensbachian); (3) global climato‐eustatic sea‐level fall (latest Pliensbachian) and global climato‐eustatic sea‐level rise plus hypoxia/anoxia (early Toarcian); (4) relative sea‐level fall linked to tectonic uplift related to the ‘Mid‐Cimmerian phase’ (mid‐Aalenian) and (5) oceanographic events (upwelling) and reduction in carbonate production (hypoxia/anoxia) plus tectonic downwarping (late Aalenian/earliest Bajocian).     

The recent history of erosion and sedimentation on the Southern Tablelands of southeastern Australia: sediment flux dominated by channel incision

As in other regions colonised from Europe within the last few centuries, Australia's vegetation and soils have been dramatically changed by clearing, cropping and grazing. In southeastern Australia, particularly on the Southern Tablelands, the impacts of European settlement are clearly manifested by channel incision. By using stratigraphic and documentary evidence, in conjunction with aerial photographs, sediment budgets for the post-settlement period have been constructed to define the fluxes and stores of sediment for each of the major geomorphic components of the 136 km² catchment of Jerrabomberra Creek near Canberra. Using these budgets, and some plausible assumptions, it has been possible to approximate the history of both the sediment delivery ratio and sediment yield for this catchment. While the quantities estimated in this analysis are approximations, the trends through time are credible. Sediment yield increased rapidly to a peak after European settlement, and has returned to a level between the peak and the pre-European value. The delivery ratio has followed a similar trend. The most general conclusion to emerge is that in this landscape both the total sediment flux and the sediment yield of the catchment have been dominated by channel erosion. This result is contrary to the findings in many parts of the world where sheet and rill erosion dominates the fluxes. The soil conservation implication of these results is clear: to control off-site effects of erosion, the focus must be on the channels.     

Interactions between semi-natural vegetation and hydrogeomorphological processes

Within Britain lowland heaths and floodplain forests are rapidly disappearing from the landscape. This paper considers the hydrogeomorphological significance of these two types of semi-natural vegetation cover using research results gathered from a drainage basin in the New Forest, southern England. Whilst heathland vegetation communities are closely adjusted to the soil water hydrological regime, floodplain forests have a distinctive and significant influence on the geomorphology of river channels. Both of these types of interaction are not only of hydrogeomorphological interest, but provide an essential foundation for the effective management and restoration of catchments and rivers containing these types of vegetation cover.     

Interactions between aeolian and fluvial systems in dryland environments

Historically, fluvial and aeolian processes in dryland environments have been viewed as mutually exclusive. However, recent research indicates that in many regions dryland aeolian and fluvial systems do not operate independently. There are interactions between the two systems that have important implications for the geomorphology of the landscape. This paper reviews the factors controlling the transfer of sediments between aeolian and fluvial systems, focusing on moisture availability, sediment supply and the magnitude/frequency characteristics of fluvial and aeolian events. We conclude by highlighting areas of future research that will contribute greatly to our understanding of aeolian–fluvial relationships in dryland areas.     

黑土侵蚀速率及其对土壤质量的影响

利用¹³⁷Cs示踪法,研究了东北黑土耕作土壤的流失厚度和速率,探讨了水土流失对土壤机械组成、有机质、土壤水分、容重及其N、P含量的影响。结果表明:研究区侵蚀坡面¹³⁷Cs的分布深度在0～25cm,¹³⁷Cs的活度在1246.05±85.90～1499.45±101.73Bq/m²,侵蚀厚度可达0.316～0.433mm/a,侵蚀强度3033.6～3940.3t/km²·a,已属于中度侵蚀水平。水土流失造成土壤质地粗化,从坡顶向坡底,耕层土壤有机质增加、容重变化不大,含水量增加,土壤养分的“贫化”现象明显。     

Numerical modelling of Cretaceous Pyrenean Rifting: The interaction between mantle exhumation and syn-rift salt tectonics

The preshortening Cretaceous Pyrenean Rift is an outstanding geological laboratory to investigate the effects of a pre-rift salt layer at the sedimentary base on lithospheric rifting. The occurrence of a pre-rift km-scale layer of evaporites and shales promoted the activation of syn-rift salt tectonics from the onset of rifting. The pre- and syn-rift sediments are locally affected by high-temperature metamorphism related to mantle ascent up to shallow depths during rifting. The thermo-mechanical interaction between décollement along the pre-existing salt layer and mantle ascent makes the Cretaceous Pyrenean Rifting drastically different from the type of rifting that shaped most Atlantic-type passive margins where salt deposition is syn-rift and gravity-driven salt tectonics has been postrift. To unravel the dynamic evolution of the Cretaceous Pyrenean Rift, we carried out a set of numerical models of lithosphere-scale extension, calibrated using the available geological constraints. Models are used to investigate the effects of a km-scale pre-rift salt layer, located at the sedimentary cover base, on the dynamics of rifting. Our results highlight the key role of the décollement layer at cover base that can alone explain both salt tectonics deformation style and high-temperature metamorphism of the pre-rift and syn-rift sedimentary cover. On the other hand, in the absence of décollement, our model predicts symmetric necking of the lithosphere devoid of any structure and related thermal regime geologically relevant to the Pyrenean case.     

Salt tectonics driven by differential sediment loading: stability analysis and finite-element experiments

At many continental margins, differential sediment loading on an underlying salt layer drives salt deformation and has a significant impact on the structural evolution of the basin. We use 2‐D finite‐element modelling to investigate systems in which a linear viscous salt layer underlies a frictional‐plastic overburden of laterally varying thickness. In these systems, differential pressure induces the flow of viscous salt, and the overburden experiences updip deviatoric tension and downdip compression. A thin‐sheet analytical stability criterion for the system is derived and is used to predict conditions under which the sedimentary overburden will be unstable and fail, and to estimate the initial velocities of the system. The analytical predictions are in acceptable agreement with initial velocity patterns of the numerical models. In addition to initial stability analyses, the numerical model is used to investigate the subsequent finite deformation. As the systems evolve, overburden extension and salt diapirism occur in the landward section and contractional structures develop in the seaward section. The system evolution depends on the relative widths of the salt basin and the length scale of the overburden thickness variation. In narrow salt basins, overburden deformation is localised and characterised by high strain rates, which cause the system to reach a gravitational equilibrium and salt movement to cease earlier than for wide salt basins. Sedimentation enhances salt evacuation by maintaining a differential pressure in the salt. Continued sedimentary filling of landward extensional basins suppresses landward salt diapirism. Sediment progradation leads to seaward propagation of the landward extensional structures and depocentres. At slow sediment progradation rates, the viscous flow can be faster than the sediment progradation, leading to efficient salt evacuation and salt weld formation beneath the landward section. Fast sediment progradation suppresses the viscous flow, leaving salt pillows beneath the prograding wedge.     

Plant community patterns in a gypsum area of NE Spain. I. Interactions with topographic factors and soil erosion

The aim of this paper is to explain how topographical factors and soil erosion affect plant community patterns in the gypsum hills of the Middle Ebro Basin (NE Spain).Both the altitudinal location on the hill and, secondarily, the aspect determine a regular distribution pattern of the plant communities, which is closely related to soil and erosion features, as well as to some plant attributes. Tall perennial grasses dominate the valley bottoms, and scrub vegetation the hillsides and hilltops. Water availability, soil depth and particle movement down the slope are the main factors that could explain this segregation.     

环嵩山地区9000-3000aBP聚落分布与区域构造的关系

利用GIS叠置分析与统计分析,按照裴李岗、仰韶、龙山、夏商四个时期对环嵩山地区9000-3000 aBP 聚落分布特征与区域构造及地貌的之间关系进行分析。结果显示,早期聚落分布与区域构造存在密切的关系,构造活动深刻影响着区域地形的高低起伏与地势的陡峭和缓,而早期聚落选址对于平坦地形的偏好使得聚落分布时空特征形成过程中与区域构造密切相关。由于主要受正断层控制,环嵩山地区东部华北坳陷与嵩箕台隆地带呈整体抬升与下降特征,区域发育有大量断块山地丘陵、断陷盆地、平原等地势平坦的地貌单元,大量早期聚落分布于这一区域,甚至一些海拔较高、顶部平坦的山地、丘陵顶部也有早期聚落分布。而边缘地带的熊耳山、外方山、伏牛山等区域,由于多为褶皱控制的褶皱构造山地,区域平坦地形较少,早期聚落则分布较少。环嵩山地区9000-3000 aBP聚落分布与区域构造关系研究表明,早期人类与自然环境的交互作用中,环境起到基础性作用,其为人类活动提供了不同自然条件的多种舞台。而人类活动在这一过程中具有主观能动性,其通常依据自身的文化特征,选择适合自身发展的自然环境栖息、生活。     

Exploring some relationships between biological soil crusts, soil aggregation and wind erosion

A portable wind tunnel was used to test the contribution of biological and physical elements to overall soil aggregation on a soil dominated by biological soil crusts in south-eastern Australia. After moderate disturbance and simulated wind erosion, 90% of surface aggregates on the loamy soil and 76% on the sandy soil were dominated by biological elements (cryptogams). Lower levels of biological bonding were observed on the severely disturbed treatment. Linear regression indicated a significant positive relationship (r²=0·72) between biological soil crust cover and dry aggregation levels greater than 0·85mm. To maintain sediment transport below an erosion control target of 5gm⁻¹s⁻¹ for a 65kmh⁻¹ wind at 10m height, a crust cover of approximately 20% is required. When a multiple regression model which sequentially fitted biological crust cover and dry aggregation greater than 0·85mm was applied to the data, dry aggregation accounted for more of the variation in sediment transport rate than biological crust cover. These data were used to develop a conceptual model which integrates crust cover and dry aggregation, and provides a useful framework within which to predict the likely impacts of changes in soil crust cover and aggregation.     

Relationship between erosion and sediment yield in drainage basins of loess gully-hilly areas

From a long-term point of view, the balance between erosion and sediment yield in a drainage system can basically realize, i.e., the delivery ratio can be close to 1. However, substantial variations among individual rainfall events or between annual delivery ratio exist, causing frequent sediment retaining or re-erosion and re-delivery of the retained sediments in a short period of time. Thus the delivery ratio will be < 1 or > 1. The sediment delivery ratio is closely related to the spatial distribution of rainfall and magnitude of rise and fall of peak flood and that of runoff depth in the drainage system. Delivery ratio of single event in a drainage system and changes of delivery capacity of silt-laden runoff in various classes of gullies can be expressed by transformation mechanism of shear force of a single rainstorm event with flood resulting from increase and decrease of peak flood per unit area.     

Relation between the erosion and sedimentation zones in the Yellow River, China

Sedimentation in the lower reaches of the Yellow River is a major problem requiring implementation of large-scale control measures in the upper and middle drainage basin. For maximum benefit, major sediment generation areas must be delimited. For this purpose, the upper and middle drainage basin of the Yellow River has been divided into four major sediment and water source areas. A series of databases of runoff and sediment yields from these source areas and for the corresponding quantities of sedimentation in the lower Yellow River channel have been established. On this basis, a set of multiple-regression equations has been established that define the relationships between sedimentation in the lower Yellow River and the yearly or event-based runoff and sediment yields from the four source areas or subsystems. Based on the regression equations obtained, the contribution of the four major source areas to the sedimentation in the lower Yellow River channel can be estimated. The results obtained indicate that, given other factors, for each ton of sediment reduced from the coarse-sediment producing area (CSA), the sediment deposited in the lower Yellow River would be reduced by 0.455 ton; for each ton of sediment reduced from the fine-sediment producing area (FSA), the sediment deposited in the lower Yellow River would be reduced by 0.154 ton only. Therefore, if limited erosion control measures are applied to the coarse-sediment producing area, the benefits for sedimentation reduction in the lower Yellow River will be much larger than if similar resources are applied to the fine-sediment producing area.     

Relationship between erosion and sediment yield in drainage basins of loess gully-hilly areas

From a long-term point of view, the balance between erosion and sediment yield in a drainage system can basically realize, i.e., the delivery ratio can be close to 1. However, substantial variations among individual rainfall events or between annual delivery ratio exist, causing frequent sediment retaining or re-erosion and re-delivery of the retained sediments in a short period of time. Thus the delivery ratio will be < 1 or > 1. The sediment delivery ratio is closely related to the spatial distribution of rainfall and magnitude of rise and fall of peak flood and that of runoff depth in the drainage system. Delivery ratio of single event in a drainage system and changes of delivery capacity of silt-laden runoff in various classes of gullies can be expressed by transformation mechanism of shear force of a single rainstorm event with flood resulting from increase and decrease of peak flood per unit area.     

Analysis of deposition and erosion of Dongting Lake by GIS

The sediments of the Dongting Lake come from four channels (one of them was closed in 1959), connected with the Yangtze River, four tributaries (Lishui, Yuanjiang, Zishui and Xiangjiang) and local area, and some of them are transported into the Yangtze River in Chenglingji, which is located at the exit of the Dongting Lake, some of them deposit into drainage system in the lake region and the rest deposit into the lake. The annual mean sediment is 166,555x104 t, of which 80% come from the four channels, 18% from the four tributaries and 2% from local area, whereas 26% of the total sediments are transported into the Yangtze River and 74% deposited into the lake and the lake drainage system. Based on topographic maps of 1974, 1988 and 1998, and the spatial analysis method with geographic information system (GIS), changes in sediment deposition and erosion are studied in this paper. By overlay analysis of 1974 and 1988, 1988 and 1998, erosion and sediments deposition areas are defined. The main conclusions are: (1) sediment rate in the lake is larger than erosion rate from 1974 to 1998. The mean deposition in the lake is 0.43 m; (2) annual sediment deposition is the same between 1974-1988 and 1988-1998, but the annual volume of deposition and erosion of 1988-1998 is bigger than that in 1974-1988; (3) before the completion of the Three Gorges Reservoir, there will be 7.82x108 m3 of sediments deposited in the lake, which would make the lake silted up by 0.33 m; (4) in the lake, the deposition area is found in the north of the east Dongting Lake, the south-west of the south Dongting Lake, and the east of the west Dongting Lake; while the eroded area is in the south of the east Dongting Lake, the middle of the south Dongting Lake, the west of the west Dongting Lake, as well as Xiangjiang and Lishui river flood channels.     

Analysis of deposition and erosion of Dongting Lake by GIS

The Dongting Lake is located in the south beach of the middle reaches of the Yangtze River. Its catchment, with an area of 262,823 km2 or about 12% of the total Yangtze River catchment, is situated between 28o43?29o32扤 and 112o54?113o8扙, and crosses Hubei and Hunan provinces in administrative division. The main tributaries include Xiangjiang, Zishui, Yuanjiang, Lishui rivers (4 Tributaries) and some local rivers, such as Miluo River, Xinqiang River and other little streams. In the nor…     

Interactions between rabbits and dung beetles influence the establishment of Erodium praecox

We examine the potential for two species – the wild rabbit Oryctolagus cuniculus and the dung beetle Thorectes valencianus – to affect the establishment of Erodium praecox, an endemic plant of the Iberian Peninsula. Rabbit latrines may be considered potential maternal parent areas of E. praecox. The spatial and temporal stability for nutrients and surface irregularities caused by the activity of rabbits increases bare soil areas. A negative relation between diameter of the basal rosettes of Erodium and the distance to the centroid of latrines was observed. Rabbit latrines were important for E. praecox distribution but their effect was higher when T. valencianus burrows exist. In laboratory conditions, a higher number of seeds buried was observed in latrines with dung beetles, while a lower number of seeds buried was observed in bare soil. T. valencianus activity plays the role of a soil fertilizer, increasing the rate of nutrient cycling and microbial activity which could raise the rate of decomposition of pellets and result in the further release of nutrients. The excavation of the dung beetles increases the soil fertilization and the surface irregularities required for the seeds of E. praecox to be easily self-buried.