Evidence for short-scale stress field variations within intraplate central-western France     

Yves Mazabraud  Nicole Béthoux  Jocelyn Guilbert  Olivier Bellier 《Geophysical Journal International》2005,160(1):161-178

  相似文献   

Normal faulting as a control on the stratigraphic development of shallow marine syn-rift sequences: the Nukhul and Lower Rudeis Formations, Hammam Faraun fault block, Suez Rift, Egypt   总被引：2，自引：0，他引：2  

C. A. L. JACKSON  R. L. GAWTHORPE  I. D. CARR  I. R. SHARP 《Sedimentology》2005,52(2):313-338

Tectono-stratigraphic analysis of the East Tanka fault zone (ETFZ), Suez Rift, indicates that the evolution of normal fault segments was an important control on syn-rift depositional patterns and sequence stratigraphy. Sedimentological and stratigraphic analysis of the Nukhul Formation indicates that it was deposited in a narrow (ca 1–2 km), elongate (ca 5 km), fault-bounded, tidally influenced embayment during the low subsidence rift-initiation phase. The Nukhul Formation is composed of transgressive (TST) and highstand (HST) systems tract couplets interpreted as reflecting fault-driven subsidence and the continuous creation of accommodation in the hangingwall to the ETFZ. The overlying Lower Rudeis Formation was deposited during the high subsidence rift-climax phase, and is composed of forced regressive systems tract (FRST) shallow marine sandbodies, and TST to HST offshore mudstones. Activity on the ETFZ led to marked spatial variability in stratal stacking patterns, systems tracts and key stratal surfaces, as footwall uplift, coupled with regressive marine erosion during deposition of FRST sandbodies, led to the removal of intervening TST–HST mudstone-dominated units, and the amalgamation of FRST sandbodies and the stratal surfaces bounding these units in the footwall. This study indicates that the evolution of normal fault segments over relatively short (i.e. <1 km) length-scales has the potential to enhance or suppress a eustatic sea-level signal, leading to marked spatial variations in stratal stacking patterns, systems tracts and key stratal surfaces. Crucially, these variations in sequence stratigraphic evolution may occur within time-equivalent stratal units, thus caution must be exercised when attempting to correlate syn-rift depositional units based solely on stratal stacking patterns. Furthermore, local, tectonically controlled variations in relative sea level can give rise to syn-rift stacking patterns which are counterintuitive in the context of the structural setting and perceived regional subsidence rates.  相似文献   

Effects of calculation procedure and sampling site on trap method estimates of sediment resuspension in a shallow lake   总被引：1，自引：0，他引：1  

JUKKA HORPPILA  LEENA NURMINEN 《Sedimentology》2005,52(4):903-913

Resuspension estimates given by two different trap methods in a shallow lake were compared. The sensitivity of the methods to errors in estimates of gross sedimentation and organic fraction of trapped material was explored. The methods were label method, in which resuspension is estimated by determining the organic fraction of surface sediment, suspended seston and trapped material, and SPIM/SPM method, where the relationship between settling particulate inorganic matter (SPIM) and total settling particulate matter (SPM) is used. During the whole 111 day study period, according to the label method, at a sheltered station 1949 g m⁻² dry weight of sediment was resuspended, whereas SPIM/SPM gave an estimate of 1815 g m⁻². The difference in the estimates was probably due to mineralization loss of organic material in the traps during the two week exposure periods. Sensitivity analysis showed that of the two methods, the label method was more sensitive to variations in the organic content of trapped material. At a wind-exposed station, the total amounts of resuspended matter given by the label method and by the SPIM/SPM method were 4966 g m⁻² and 4971 g m⁻², respectively. Due to wind effects, escape of trapped material took place, which caused underestimation of gross sedimentation and compensated the effects of mineralization loss to diminish the difference between the methods. Of the two methods, the SPIM/SPM method seems thus more suitable for lakes, where bacterial activity is high. If cyanobacterial blooms take place, the label method is probably more reliable, providing that the exposure time of sediment traps is kept adequately short.  相似文献   

浅埋暗挖技术在南平市天台隧道工程施工中的应用          下载免费PDF全文

李耀卿 《探矿工程》2005,32(12):56-58

主要介绍了在Ⅱ、Ⅲ类围岩中施工城市浅埋隧道的施工技术，以“短开挖、快封闭、强支护、勤量测”为指导，将隧道分成上、下两个台阶进行开挖，及时进行初期支护，保证施工始终处于安全状态。  相似文献   

Spatiotemporal variability in hydrochemistry of shallow groundwater in a small pre‐alpine catchment: The importance of landscape elements     

Leonie Kiewiet  Jana von Freyberg  H.J. van Meerveld 《水文研究》2019,33(19):2502-2522

Topography and landscape characteristics affect the storage and release of water and, thus, groundwater dynamics and chemistry. Quantification of catchment scale variability in groundwater chemistry and groundwater dynamics may therefore help to delineate different groundwater types and improve our understanding of which parts of the catchment contribute to streamflow. We sampled shallow groundwater from 34 to 47 wells and streamflow at seven locations in a 20‐ha steep mountainous catchment in the Swiss pre‐Alps, during nine baseflow snapshot campaigns. The spatial variability in electrical conductivity, stable water isotopic composition, and major and trace ion concentrations was large and for almost all parameters larger than the temporal variability. Concentrations of copper, zinc, and lead were highest at sites that were relatively dry, whereas concentrations of manganese and iron were highest at sites that had persistent shallow groundwater levels. The major cation and anion concentrations were only weakly correlated to individual topographic or hydrodynamic characteristics. However, we could distinguish four shallow groundwater types based on differences from the catchment average concentrations: riparian zone‐like groundwater, hillslopes and areas with small upslope contributing areas, deeper groundwater, and sites characterized by high magnesium and sulfate concentrations that likely reflect different bedrock material. Baseflow was not an equal mixture of the different groundwater types. For the majority of the campaigns, baseflow chemistry most strongly resembled riparian‐like groundwater for all but one subcatchment. However, the similarity to the hillslope‐type groundwater was larger shortly after snowmelt, reflecting differences in hydrologic connectivity. We expect that similar groundwater types can be found in other catchments with steep hillslopes and wet areas with shallow groundwater levels and recommend sampling of groundwater from all landscape elements to understand groundwater chemistry and groundwater contributions to streamflow.  相似文献   

Significance of shallow core transects for reef models and sea‐level curves,Heron Reef,Great Barrier Reef          下载免费PDF全文

Gregory E. Webb  Luke D. Nothdurft  Jian‐Xin Zhao  Bradley Opdyke  Gilbert Price 《Sedimentology》2016,63(6):1396-1424

A sequence of shallow reef cores from Heron Reef, Great Barrier Reef, provides new insights into Holocene reef growth models. Isochron analysis of a leeward core transect suggests that the north‐western end of Heron Reef reached current sea‐level by ca 6·5 kyr bp and then prograded leeward at a rate of ca 19·6 m/kyr between 5·1 kyr and 4·1 kyr bp (pre‐1950) to the present reef margin. A single short core on the opposing margin of the reef is consistent with greater and more recent progradation there. Further to the east, one windward core reached modern sea‐level by ca 6·3 kyr bp , suggesting near ‘keep‐up’ behaviour at that location, but the opposing leeward margin behind the lagoon reached sea‐level much more recently. Hence, Heron Reef exhibited significantly different reef growth behaviour on different parts of the same margin. Mean reef accretion rates calculated from within 20 m of one another in the leeward core transect varied between ca 2·9 m and 4·7 m/kyr depending on relative position in the prograding wedge. These cores serve as a warning regarding the use of isolated cores to inform reef growth rates because apparent aggradation at any given location on a reef varies depending on its location relative to a prograding margin. Only transects of closely spaced cores can document reef behaviour adequately so as to inform reef growth models and sea‐level curves. The cores also emphasize potential problems in U‐series dates for corals within a shallow (ca 1·5 m) zone beneath the reef flat. Apparent age inversions restricted to that active diagenetic zone may reflect remobilization and concentration of Th in irregularly distributed microbialites or biofilms that were missed during sample vetting. Importantly, the Th‐containing contaminant causes ages to appear too old, rather than too young, as would be expected from younger cement.  相似文献   

Progradational and backstepping shoreface deposits in the Ladinian to Early Norian Snadd Formation of the Barents Sea          下载免费PDF全文

Tore G. Klausen  Alf Ryseth  William Helland‐Hansen  Helge K. Gjelberg 《Sedimentology》2016,63(4):893-916

Shoreface sandstone deposits within the Early Carnian part of the Snadd Formation of the Norwegian Barents Sea can be traced for hundreds of kilometres in the depositional strike direction and for tens of kilometres in the depositional‐dip direction. This study uses three‐dimensional seismic attribute mapping and two‐dimensional regional seismic profiles to visualize the seismic facies of these shoreface deposits and to map their internal stratigraphic architecture at a regional scale. The shoreface deposits are generally elongate but show variable width from north‐east to south‐west, which corresponds to a sediment source in the northern part of the basin and a southward decrease in longshore sediment transport. The Snadd Formation presents an example of how large‐scale progradational shoreface deposits develop. The linear nature of its shoreface deposits contrasts with more irregular, cuspate wave‐dominated deltaic shorelines that contain river outlets, and instead implies longshore drift as the main sediment source. In map view, discrete sets of linear features bounded by truncation surfaces scale directly to beach ridge sets in modern counterparts. The shoreface deposits studied here are characteristic in terms of scale and basin‐wide continuity, and offer insight into the contrast between shallow marine deposition under stable Triassic Greenhouse and fluctuating Holocene Icehouse climates. Findings presented herein are also important for hydrocarbon exploration in the Barents Sea, because they describe a hitherto poorly understood reservoir play in the Triassic interval, wherein the most prominent reservoir plays have so far been considered to be found in channelized deposits in net‐progradational delta‐plain strata that form the topsets to shelf‐edge clinoforms. The documented presence of widespread wave‐dominated shoreface deposits also has implications for how the relative importance of different sedimentary processes is considered within the basin during this period.  相似文献   

叶蛇纹岩脆性-半脆性破裂研究     

邵同宾  宋茂双  李建峰  张桂男  夏莹 《岩石学报》2016,32(6):1675-1687

利用Paterson气体介质高温高压流变仪对纯叶蛇纹岩在100~400MPa围压、25~700℃温度和10-5~1.5×10-6s-1应变速率下进行了三轴压缩变形实验。实验结果表明叶蛇纹石在低压条件下表现为脆性破裂,高压或脱水条件下表现为半脆性破裂。随着温度的增加,叶蛇纹石的强度显示逐渐降低的趋势;尤其在脱水条件下,温度的增加可导致叶蛇纹石强度大幅度地降低,而且此时预热时间对强度的影响比未发生脱水时更加显著。结合前人的研究并对比发现,围压在室温下的增加导致叶蛇纹岩强度增加;但在高温下围压的增加导致试样强度整体上降低,这很可能是试样内聚力的局部损失与韧性增强引起的。围压和温度的升高,以及断层面上流体的增加很可能会增加破裂面的韧性,从而减小摩擦系数。此外,叶蛇纹石并非以往人们所认为的那样具有极低的强度,其强度要比低温蛇纹石(如利蛇纹石和纤蛇纹石)的大得多,即便在高温(大约600℃)下差应力大于约600MPa和中-低温(≤400℃)下差应力大于约1000MPa时仍没有表现出明显屈服的迹象。在脱水条件下,蛇纹岩并没有发生脱水致脆,相反脱水使得试样的断裂行为变得更加温和些。因此,俯冲带蛇纹岩脱水更可能诱发其周围更加脆性的岩石发生地震而不是脱水的蛇纹岩本身发生地震。  相似文献   

以钻代槽勘查方法研究与应用          下载免费PDF全文

赵洪波  何远信  祝强 《探矿工程》2016,43(11):6-10

为解决槽、井探等传统地表揭露手段自身局限性问题及减少对环境的破坏,提出以钻代槽勘查方法研究的技术路线,总结归纳出浅钻技术方法与钻孔布孔方案,同时初步探讨了基于钻孔数据的三维地质建模方法。最后将以钻代槽方法成果在西藏等地进行了推广应用,验证了可行性和有效性。  相似文献   

圆回线和矩形回线源瞬变电磁响应差异性计算     

薛俊杰  周楠楠  王贺元 《物探与化探》2018,(1):178-184

在回线源瞬变电磁发展的早期,往往使用圆回线产生的场来近似模拟多边形回线的场。为了对这种近似的影响进行分析,本文以矩形回线为例,对圆回线近似模拟多边形回线的误差进行计算。首先,根据给出的圆回线和矩形回线内外任一点的感生电动势新的计算方法,对两种回线装置内的感生电动势分布进行对比。研究结果表明:在扩散场早期,圆回线和矩形回线场的等值线分布形态存在较大的差别,而在扩散场中晚期,两种回线感生电动势相对误差较小。两种回线感生电动势相对误差的变化特征可以用感应电流烟圈扩散的理论进行解释。通过理论模型的分析可知,圆回线近似矩形回线会对浅层电性结构分析带来较大影响。  相似文献