Structure and evolution of a passive margin in a compressive environment: Example of the south-western Alps-Ligurian basin junction during the Cenozoic     

F. Sage  M.-O. BeslierI. Thinon  C. LarroqueJ.-X. Dessa  S. MigeonJ. Angelier  P. GuennocD. Schreiber  F. MichaudJ.-F. Stephan  L. Sonnette 《Marine and Petroleum Geology》2011,28(7):1263-1282

We focus on the northern Ligurian margin, at the geological junction of the subalpine domain and the Ligurian oceanic basin, in order (1) to identify the location of the southern limit of the Alpine compressive domain during the Cenozoic, and (2) to study the influence of a compressive environment on the tectonic and sedimentary evolution of a passive margin.Based on published onshore and offshore data, we first propose a chronology of the main extensional and compressional regional tectonic events.High-resolution seismic data image the margin structure down to ∼3 km below seafloor. These data support that past rifting processes control the present-day margin structure, and that 2800-4000 m of synrift sediment was deposited on this segment of the margin in two steps. First, sub-parallel reflectors indicate sediment deposition within a subsident basin showing a low amount of extension. Then, a fan-shaped sequence indicates block tilting and a higher amount of extension. We do not show any influence of the Miocene Alpine compression on the present-day margin structure at our scale of investigation, despite the southern subalpine relief formed in the close hinterland at that time. The southern front of the Miocene Alps was thus located upslope from the continental margin.Finally, a comparison with the Gulf of Lions margin suggests that the tectonic influence of the Alpine compression on the rifting processes is restrited to an increase of the subsidence related to flexure ahead of the Alpine front, explaining abnormally high synrift thicknesses in the study area. The Alpine environment, however, has probably controlled the sedimentary evolution of the margin since the rifting. Indeed, sediment supply and distribution would be mainly controlled by the permanent building of relief in the hinterland and by the steep basin morphology, rather than by sea-level fluctuations, even during the Messinian sea-level low-stand.  相似文献   

Sedimentation styles and depositional processes in a Middle to Late Jurassic slope environment, Bowser Basin, northwestern British Columbia, Canada     

Jean-François Gagnon  John W.F. Waldron 《Marine and Petroleum Geology》2011,28(3):698-715

The Middle to Upper Jurassic Todagin assemblage in northwestern British Columbia, Canada, was deposited in the Bowser Basin above arc-related rocks of the Stikine terrane. Sedimentary structures indicate that a variety of gravity flow processes were involved in transport and deposition in deep-water slope environments. At Mount Dilworth, laterally continuous and channelized turbidites are interbedded with and overlain by mass-transport deposits in which sedimentary clasts are supported in a mudstone matrix. More than 50% of the succession consists of mass-transport deposits, indicating significant slope instability. A 300 m thick mass-transport complex exposed near the top of the succession is interpreted to result from tectonic activity, which triggered a major change in sediment supply from a local source area. At Todagin Mountain, a channel complex displays three successive channel-fills with associated overbank sedimentation units. Mass-transport deposits are rare, and confined to channel axes. Channels 1 and 2 are characterized by 40-50 m thick, ungraded pebble clast-supported conglomerate while the uppermost Channel 3 contains graded beds and occasional traction structures. The gradual change from erosive and amalgamated channel deposits at the base, to more aggradational channels at the top, is related to elevation of the equilibrium profile. Creation of accommodation favored aggradation on the mud-dominated slope succession and construction of well-developed channel-levee systems. The vertical succession exposed at Todagin Mountain is consistent with normal progradation of the slope under high sedimentation rates. In the Mount Dilworth area, extensional faulting associated with development of the restricted Eskay rift in the early Middle Jurassic produced a dissected basement above which the Todagin assemblage was deposited. These structures were inverted during collision of the Stikine and Cache Creek terranes, and likely played a major role in the stratigraphic evolution of the deep-water architectures.  相似文献   

Spatial patterns in fish herbivory in a temperate Australian seagrass meadow     

K.S. White  M.B. Westera  G.A. Kendrick 《Estuarine, Coastal and Shelf Science》2011

Seagrass grazing by fish was measured in a large seagrass-dominated temperate bay (Geographe Bay, Western Australia) to examine whether: (1) seagrass herbivory occurs; (2) the level of herbivory is influenced by nitrogen in seagrass leaves; and (3) how herbivory and herbivorous fish communities vary with water depth and seagrass species. Species and abundance of fish and herbivore bite marks on seagrass leaves were recorded from diver surveys of 23 sites of varying depth ranging from 1 m to 18 m. Posidonia sinuosa, Posidonia coriacea, Amphibolis griffithii, and Amphibolis antarctica seagrass leaves were collected, dried and analysed for total nitrogen. Evidence for low levels of seagrass grazing was found at over half the sites surveyed, though high levels of grazing were recorded at only one site. An east–west pattern was observed in the location of grazed sites and of herbivorous fish species that corresponded with the general prevalence of patch reefs, indicating that reef associated fish assemblages may be responsible for the observed grazing. Total nitrogen was elevated in seagrass leaves associated with drains, although increased nitrogen was not associated with increased grazing. While grazing was recorded in this temperate seagrass meadow, the abundance of herbivorous fish was low and the amount of biomass removed by them was small compared to the balance of the meadow remaining, and to seagrass grazing studies elsewhere.  相似文献   

The Irminger Gyre: Circulation, convection, and interannual variability   总被引：2，自引：0，他引：2  

Kjetil Våge  Robert S. PickartArtem Sarafanov  Øyvind KnutsenHerlé Mercier  Pascale LherminierHendrik M. van Aken  Jens MeinckeDetlef Quadfasel  Sheldon Bacon 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(5):590-614

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中国天山西部季节性森林积雪物理特性   总被引：2，自引：0，他引：2  

陆恒  魏文寿  刘明哲  韩茜  洪雯 《地理科学进展》2011,30(11):1403-1409

积雪特殊的物理特性对冰雪水文过程、积雪生态系统、不同尺度的气候系统有重要影响。目前对林下积雪物理特性缺乏系统性研究,因此对天山雪岭云杉林下季节性积雪深度、沉降速率、密度和含水率进行观测分析。结果表明：林下积雪深度小于开阔地;林下积雪沉降速率和新雪密实化率小于开阔地,且稳定期沉降速率小于融雪期。稳定期林下积雪密度小于开阔地,林下雪层密度最大值位于中粒雪层,开阔地则位于粗粒雪层;融雪期则全层密度趋于一致。稳定期林下雪层含水率随深度递减,开阔地雪层最大值出现粗粒雪层;融雪期雪层汗水峰值出现在细粒雪层,新雪层最小,林下雪层由细粒雪层到深霜层始终呈减小趋势,开阔地雪层由细粒雪层至中粒雪层逐渐减小,粗粒雪层至深霜层逐渐增大;稳定期雪层含水率日变化随深度的递减逐渐减小,开阔地大于林下;开阔地的新雪层和细粒雪层含水率的日变化大于林下,粗粒雪层到深霜层则小于林下。  相似文献   

基于场强模型的海西区地级及以上城市影响腹地的空间格局   总被引：4，自引：1，他引：3  

邱岳  韦素琼  陈进栋 《地理研究》2011,30(5):795-803

随着近年来建设海峡西岸经济区上升为国家战略,该区域城市的发展倍受关注.本文采用场强模型测算了2007年海西区20个地级及以上城市影响力,划分3个城市群强影响圈层.通过场强与等高线的叠加分析,发现900m以上的高大山脉对城市影响力的削减明显,并造成了3个强影响圈的割据分布.进一步依据场强取大原则划分腹地范围,从腹地与行政...  相似文献   

Impact of Land-use Patterns on Distributed Groundwater Recharge and Discharge——A Case Study of Western Jilin, China     

Moiwo Juana PAUL 《中国地理科学(英文版)》2006,16(3)

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Exhumation of the Schistes Lustrés complex: in situ laser probe ⁴⁰Ar/³⁹Ar constraints and implications for the Western Alps     

P. Agard  P. Monié  L. Jolivet  B. Goffé 《Journal of Metamorphic Geology》2002,20(6):599-618

The Schistes Lustrés (SL) suture zone occupies a key position in the Alpine chain between the high‐pressure (HP) Brianconnais domain and the ultrahigh‐pressure (UHP) Dora Maira massif, and reached subduction depths ranging from c. 40–65 km (Cottian Alps). In order to constrain the timing of HP metamorphism and subsequent exhumation, several phengite generations were differentiated, on the basis of habit, texture, paragenesis and chemistry, as belonging to the first or second exhumation episode, respectively, D2 or D3, or to earlier stages of the tectono‐metamorphic evolution. Ten carefully selected samples showing D2, D3 (D2 + D3), or earlier (mostly peak temperature) phengite population(s) were subjected to laser probe ⁴⁰Ar/³⁹Ar analysis. The data support the results of the petrostructural study with two distinct age groups (crystallization ages) for D2 and D3 phengite, at 51–45 and 38–35 Ma, respectively. The data also reveal a coherent age cluster, at 62–55 Ma, for peak temperature phengite associated with chloritoid which were preserved in low strain domains. The age of the D3 event in the SL complex appears very similar to ages recently obtained for greenschist facies deformation on the border of most internal crystalline massifs. Exhumation rates of the order of 1–2 mm yr^?1 are obtained for the SL complex, which are compatible with velocities documented for accretionary wedge settings. Similarly, cooling velocities are only moderate (c.5 °C Myr^?1), which is at variance with recent estimates in the nearby UHP massifs.  相似文献   

Ecological changes and the tradeoff and synergy of ecosystem services in western China     

NIU Linan  SHAO Quanqin  NING Jia  HUANG Haibo 《地理学报(英文版)》2022,32(6):1059-1075

Since the implementation of the Development of Western Regions in 2000, a series of major ecological construction projects have been implemented, leading to a series of changes in the ecological conditions and ecological services of western China. This study calculated the amount of ecosystem services in total in the western region from 2000 to 2019, and analyzed ecological changes and the characteristics of spatio-temporal variations in ecological services. A relevant analysis method was applied to explore the tradeoff and synergy of service. It was found that the area of settlements and wetland ecosystems in the western region increased significantly from 2000 to 2015, whereas grassland showed a downward trend year by year. The vegetation fraction showed a decreasing belt-like distribution from south to north. It showed a fluctuating increase during 2000 to 2019, with inter-annual and large spatial differences. The water conservation service (WCS) had a slight downward trend from 2000 to 2019, and the main decreasing areas were distributed in southeastern Tibet, the western part of the Three Rivers Source region, and the karst rocky desertification area. The soil conservation service (SCS) showed an increasing but fluctuating trend, with the greatest increases observed in the Loess Plateau region, western Sichuan and Yunnan, northwest Tibet, and southeast Tibet. The windbreak and sand fixation service (SFS) showed a downward trend, and the sharp decline was mainly in the central and western parts of Inner Mongolia, Tibet and parts of northern Xinjiang. Ecosystem supply and WCS, and SCS were mainly synergistic, which were found in areas north of the Qinling Mountains-Huaihe River (QM-HR) line, especially in Ningxia and Inner Mongolia. Ecosystem supply was mainly tradeoffs with SFS, and it was found in the agriculture-pastoral transition zone. The synergistic degree of ecosystem services in areas subjected to ecological engineering policy was greater than that in non-engineering areas. Quantitative assessment of ecosystem service changes and their tradeoffs is helpful for scientific ecological management and maximizing ecological benefits.  相似文献   

西秦岭—松潘金三角地区金矿带划分及特征   总被引：3，自引：0，他引：3       下载免费PDF全文

李亚东 《甘肃地质》2003,(1):43-49

西秦岭—松潘地区是我国西部重要的卡林型金矿成矿的集中区 ,依据其成矿规律可划分为同仁—夏河—岷县金成矿带 ;青海军功—甘肃尕海—舟曲—成县南金成矿带 ;玛沁—玛曲—南坪金成矿带 ;青海德尔尼—积石山—平武金成矿带 ;青海达日—斑马—马尔康金成矿带 ;四川松潘哲波山—文县—康县金银铜成矿带等 6个重要的金矿成矿带  相似文献