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1.
The contribution of bioturbation to downslope soil transport is significant in many situations, particularly in the context of soil formation, erosion and creep. This study explored the direct flux of soil caused by Aphaenogaster ant mounding, vertebrate scraping and tree‐throw on a wildfire‐affected hillslope in south‐east Australia. This included the development of methods previously applied to Californian gopher bioturbation, and an evaluation of methods for estimating the volume of soil displaced by tree‐throw events. All three bioturbation types resulted in a net downslope flux, but any influence of hillslope angle on flux rates appeared to be overshadowed by environmental controls over the spatial extent of bioturbation. As a result, the highest flux rates occurred on the footslope and lower slope. The overall contribution of vertebrate scraping (57.0 ± 89.4 g m?1 yr?1) exceeded that of ant mounding (36.4 ± 66.0 g m?1 yr?1), although mean rates were subject to considerable uncertainty. Tree‐throw events, which individually cause major disturbance, were limited in their importance by their scarcity relative to faunalturbation. However, tree‐throw might be the dominant mechanism of biotic soil flux on the mid‐slope provided that it occurs at a frequency of at least 2–3 events ha?1 yr?1. Although direct biotic soil flux appears to be geomorphologically significant on this hillslope, such transport processes are probably subordinate to other impacts of bioturbation at this site such as the enhancement of infiltration following wildfire. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
2.
In 1983, inhabitants of the City of Morelia, Michoacán, Mexico, began to observe a series of differential settlements causing damages to constructions along linear trends parallel to a system of regional faults. The same phenomenon occurs in others cities of the Mexican Volcanic Belt (MVB), such as Celaya, Aguascalientes, and Querétaro, and is linked to a structurally controlled subsidence, caused by groundwater withdrawal, and the presence of geological faults. We define this subsidence type as Subsidence-Creep-Fault Processes (SCFP), based on the necessary elements for their generation, and we studied them through geophysical and geotechnical techniques. In Morelia, the geophysical investigations have been carried out using ground-penetrating radar (GPR). GPR profiles, perpendicular to the axis of the surface fault generated by the SCFP were carried out. The common-offset single-fold profiling was used, with a central frequency of 50 MHz. In all cases it has been possible to visualize a fault plane dividing two blocks, the presence of synthetic and antithetic faults, influence zones from 20 m to 40 m, and a maximum “net throw” of 4 m. Exploration trenches followed the same direction of the profiles obtained with GPR (perpendicular to the axis of the surface fault). These trenches exposed a fault plane dividing two blocks with different lithology, generating a maximum “net throw” of 4.40 m; as well they help in the determination of influence zones that varied from 14 m to 40 m. 相似文献
3.
水稻旱育抛秧生长发育的动态模拟模型 总被引：9，自引：1，他引：8
通过分期播种田间试验资料,建立水稻旱育抛秧生长发育的动态模拟模型,包括叶面积发展,光合作用,呼吸作用,干物质积累与分配等。重点探讨叶面积发展与温度的关系,光合作用简化算法,净光含量的求算,分配系数随发育期的变化等。 相似文献
4.
采用断层落差法和生长指数法计算冀中坳陷廊固凹陷活动断层的古落差和生长指数,绘制了凹陷各地质历史时期的古落差和生长指数平面分布图,并详细分析了各时期断层活动特征。分析研究可知,一级控凹断层大兴断层的活动存在分段性,整体上表现为自南西到北东逐渐减弱;孔店—沙四期,三级活动性断层主要集中在凹陷的东南部,但活动都比较弱;沙三—沙二期,活动性断层的分布整体向凹陷北东方向扩展,三级以上断层活动比较强。研究结果表明,古近纪廊固凹陷断层活动主要受控于构造演化背景,大兴断层对次级断层活动具有重要的影响。 相似文献
5.
In December 2008, 694 trees uprooted within a 108 ha (1·08 km2) watershed in central Massachusetts due to a severe ice storm, resulting in the displacement of ~1300 m3 of root material, unconsolidated sediment, and fractured bedrock. Overall, we find that uprooting and tree throw is often grouped in clusters and cascades; conifers displace more material than deciduous trees; areas with abundant mature hemlock and steep slopes are more susceptible to tree throw, with clusters as dense as 125 per hectare; and failure is predominantly downhill, suggesting that ice storms promote efficient downslope hillslope sediment transport in northern hardwood forests. Combining the recurrence interval of severe storms in New England (20–75 years) with the forest response presented here, we calculate a sediment transport rate of 2–5 × 10?5 m3 m?1 a?1 averaged over the entire watershed. Forest susceptibility to tree throw differed based on location in the watershed; some areas experienced up to ~30× higher than average sediment transport rates, while others experienced no tree throw. Two severe storms following the 2008 ice storm (hurricane in 2011; snow storm in October 2012) did not result in significant tree throw within the study area, highlighting that the coupling of storm severity and forest susceptibility controls the amount of tree throw during a given forest disturbance. In addition to recent tree throw from the 2008 ice storm, widespread pit and mound microtopography in the study area indicates that tree throw is a recurrent process in this landscape. Two factors emerge that will influence future ice storms related hillslope sediment transport in the steep forested hillslopes of New England: regional climate gradients and changing climate determine the size, intensity and recurrence of ice storms; forest management practices and health control the tree age and type. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
6.
Erosion of soil by water is facilitated by both diffusive and fluvial processes. Here we examine three different soil redistribution processes operating at very different spatial and temporal scales in the monsoonal tropics of northern Australia. The first process, rainsplash, operates across the entire catchment. This process, while subject to annual and seasonal variations in rainfall amount and intensity, can be considered a constant forcing and redistributes on average 9 t ha−1 year−1 (range −0.9 to 19 t ha−1 year−1). The second process, bioturbation, where in this study soil is disturbed by feral pigs (wild boar), occurs in selected areas throughout each year. Pigs exhume 3 to 36.0 t ha−1 year−1 (average ~11 t ha−1 year−1). The effect of this disturbance may last for many years afterwards. The third process is the disturbance of the soil surface by tree throw and creation of pit–mound topography (also a form of bioturbation), together with the resultant placement of the tree superstructure (above ground biomass) on the ground, which may form debris dams. Tree throw at the scale examined here is likely to occur only once every 50–100 years, with the influence of this single event lasting for at least 10 years post event. Tree throw in a single event exhumed ~5 t ha−1 (1.1–9.5 t ha−1) of soil. In contrast to rainsplash, pig disturbance and tree throw events are largely point-based phenomena. Field observation suggests that it takes many years for the disturbance from both pigs and tree throw to be removed. We find here that in terms of relative soil redistribution, rainsplash has the largest influence, with any erosional disturbance by pigs and tree throw being within the variability of rainsplash. However, the disruption of surface flow by the pig digs and tree throw disrupts sedimentological and hydrological connectivity. 相似文献
7.
断距纵剖面图 （T H图）是指以断层的垂直断距为横轴、以地层或地质年龄为纵轴所绘制的随地层或地质年龄所变化的断距分布图。断距纵剖面图为确定正断层类型、断层形成时间和断层的纵向演化史提供了一个简单迅捷的工具。概念模型表明，断距纵剖面图可以明确无误地区分出简单后沉积型正断层、后沉积拱顶拉张型正断层、同沉积生长型正断层及其复合型正断层。简单后沉积型正断层的断距不随地层年龄的变化而变化， 其断距纵剖面图为一垂直线段。后沉积拱顶拉张型正断层的断距随地层年龄的增大而减小并趋向零值，同沉积生长型正断层的断距随地层年龄的增大而增大，复合型正断层则具其组合型断距纵剖面形态。除简单后沉积型正断层外，断距纵剖面图中的最大断距点代表了该断层的起始形成年代。 相似文献
8.
琼东南盆地古近纪基底断裂的活动特征分析 总被引：1，自引：0，他引：1
为优化油气盆地内断裂活动强度的研究方法,分析了断层生长指数、断层落差和断层活动速率等定量研究断裂活动强度的常用参数,提出了根据断裂两侧的构造沉降差异计算断裂的垂直断距和垂直活动速率的新方法。然后应用这种方法研究琼东南盆地古近纪基底断裂的活动特征。研究表明,琼东南盆地古近纪基底断裂的活动分为3个阶段:第一阶段(40—36MaBP),琼东南盆地东部NE向断裂发生强烈活动,垂直断距800m左右,垂直活动速率约200m.Ma 1;第二阶段(36—30MaBP),盆地东部NE向断裂活动减弱,盆地西部E-W向断裂开始活动,两者垂直断距约400—800m,垂直活动速率70—130m.Ma 1;第三阶段(30—21MaBP),盆地内部断裂活动再次增强,垂直断距700—1800m,垂直活动速率80—200m.Ma 1,而边界断裂活动较弱,垂直断距约500m,垂直活动速率不足60m.Ma 1。 相似文献
9.
Fault growth and interactions in a multiphase rift fault network: Horda Platform,Norwegian North Sea
Physical models predict that multiphase rifts that experience a change in extension direction between stretching phases will typically develop non-colinear normal fault sets. Furthermore, multiphase rifts will display a greater frequency and range of styles of fault interactions than single-phase rifts. Although these physical models have yielded useful information on the evolution of fault networks in map view, the true 3D geometry of the faults and associated interactions are poorly understood. Here, we use an integrated 3D seismic reflection and borehole dataset to examine a range of fault interactions that occur in a natural multiphase fault network in the northern Horda Platform, northern North Sea. In particular we aim to: i) determine the range of styles of fault interaction that occur between non-colinear faults; ii) examine the typical geometries and throw patterns associated with each of these different styles; and iii) highlight the differences between single-phase and multiphase rift fault networks. Our study focuses on a ca. 350 km2 region around the >60 km long, N–S-striking Tusse Fault, a normal fault system that was active in the Permian–Triassic and again in the Late Jurassic-to-Early Cretaceous. The Tusse Fault is one of a series of large (>1500 m throw) N–S-striking faults forming part of the northern Horda Platform fault network, which includes numerous smaller (2–10 km long), lower throw (<100 m), predominantly NW–SE-striking faults that were only active during the Late Jurassic to Early Cretaceous. We examine how the 2nd-stage NW–SE-striking faults grew, interacted and linked with the N–S-striking Tusse Fault, documenting a range of interaction styles including mechanical and kinematic isolation, abutment, retardation and reactivated relays. Our results demonstrate that: i) isolated, and abutting interactions are the most common fault interaction styles in the northern Horda Platform; ii) pre-existing faults can act as sites of nucleation for 2nd-stage faults or may form mechanical barriers to propagation; iii) the throw distribution on reactivated 1st-stage faults will be modified in a predictable manner if they are intersected or influenced by 2nd-stage faults; iv) sites of fault linkage and relay-breaching associated with the first phase of extension can act as preferential nucleation sites for 2nd-stage faults; and v) the development of fault intersections is a dynamic process, involving the gradual transition from one style to another. 相似文献
10.
Mark D. Schwartz 《自然地理学》2013,34(6):536-550
This study is part of a program to examine spring plant-climate interactions in the major agricultural regions of eastern North America. The project's objectives were to: (1) document the yearly onset of the spring green wave and associated phenomena from 1908 to 1987 using phenological models, and (2) analyze regional dynamics and recent changes. Examining past variations in the green wave provides a context within which present and future variations can be assessed. Spring index dates, last -2.2°C (28°F) frost dates, and the difference between these two dates (termed the damage index) were generated for selected United States Daily Historical Climatology Network (HCN) stations between 1908 and 1987. The results show considerable geographic and temporal variations over the study period, and suggest that the threat of late spring frost damage may have decreased slightly from about 1960 to 1987. In future research, an improved version of the spring index (and associated surface phenological data) will be compared with satellite-derived vegetation condition data, in order to facilitate many kinds of atmosphere-biosphere interaction studies. [Key words: phenology, spring, “green wave” climatology.] 相似文献