豫西宜阳上二叠统孙家沟组孢粉组合及其地质意义*

豫西宜阳上二叠统孙家沟组为一套陆相碎屑岩,在该组中部土门段砂泥互层中发现大量的植物化石碎片和孢粉化石。文中依据孙家沟组沉积特征及孢粉组合区域对比,厘定了土门段的地质时代,并依据孢粉化石的亲缘植物关系和信息函数,结合微量元素Sr/Cu值指标,定性和半定量分析了宜阳地区的古气候特征。结果显示: 土门段共发现52属孢粉化石,以裸子植物花粉占优势,与华北地区晚二叠世孢粉组合特征有很大的相似性,推测其地质时代相当于晚二叠世长兴期。孢粉化石属种的植物亲缘关系与欧美镁灰岩统植物成分类似,表明整体上为较炎热的半干旱古气候。该成果可为华北地区晚二叠世晚期的陆相沉积环境、古植物背景以及古气候演化研究提供参考依据。     

Numerical simulation of direct shear test of rockfill based on particle breaking

Acta Geotechnica - In the traditional Mohr–Coulomb criterion, the shear strength is determined by cohesion and friction angle. However, the particle breakage that occurs on the shear failure...     

Effect of inherent anisotropy on the strength of natural granite residual soil under generalized stress paths

It is universally known that residual soils behave very differently from sedimentary soils. While the latter is widely known as cross-anisotropic, little is known regarding the strength anisotropy of residual soils. This study presents how the inherent anisotropy affects the strength of natural granite residual soils under generalized conditions, where intact specimens were carefully prepared and sheared under triaxial compression, extension, simple shear, and hollow cylinder torsional shear tests. The strength of natural residual soil, in terms of ultimate stress ratio M and undrained shear strength S_u, is found to be significantly anisotropic in a different way from normally consolidated clays with the maximum strength obtained under triaxial compression and the minimum under simple shear or at intermediate principal stress direction. As a result, the existing method failed to measure the anisotropy degree of the studied soil. Two parameters were proposed accordingly to quantify the anisotropic strength under general conditions, taking the special strength anisotropy pattern and cohesive-frictional nature of GRS into account. The proposed parameters enable the direct comparison of strength anisotropy among soils. This study serves as a data set to better understand residual soils regarding their anisotropic behaviors under generalized conditions. Although specific to granite residual soils in China, this study is expected to be more widely applicable to other weathered geomaterials.

     

贵州新元古代大塘坡期巨量锰矿成矿物质来源分析

新元古代大塘坡期,贵州松桃等地形成锰矿集聚区,并发育4个世界级锰矿床,累计探明锰资源量达7亿t。但是什么地质条件下,能导致如此巨量的锰质富集成矿,其成矿物质来源问题一直没有得到满意的解释。本文通过对含锰岩系大塘坡组基底板溪群及海底火山岩中锰含量特征、江南造山带演化以及Rodinia超大陆解体与锰矿成矿关系分析,认为基底板溪群中锰含量高,MnO含量达到0. 16%,板溪群风化壳中锰含量更高,MnO达0. 88%。板溪群中的同期岛弧玄武岩含MnO更高,达到0. 25%,它们可能是锰矿成矿的物源层,是形成巨量锰矿的基础;江南造山带造山挤压变质作用,引起板溪群和岛弧玄武岩中锰质活化、迁移富集;Rodinia超大陆解体,在650 Ma发生拉张裂谷作用,使活化富锰变质流体沿着断裂喷流出海底,形成大量锰矿。     

环境同位素在北京平谷盆地山前侧向补给研究中的应用

利用地下水水化学和同位素测试分析成果,结合区域地质、水文地质条件研究了平谷北山山区侧向补给情况和中桥水源地地区第四系松散孔隙水和下伏岩溶水关系。结果表明：研究区第四系松散孔隙水和基岩岩溶地下水均来源于大气降水,地下水化学类型均为HCO-3-Ca2+?Mg2+ 型;平谷北山山前基岩岩溶水侧向补给平原区第四系松散孔隙水和下伏岩溶地下水;通过D值估算得到中桥水源地第四系浅层地下水的山区岩溶水侧向补给和垂向降水入渗补给比例为57：43;中桥水源地基岩岩溶水接受山区岩溶水侧向补给和第四系孔隙水垂向越流补给比例为87：13。研究成果为平谷地区地下水资源量评价和地下水动力场数值模型的建设提供了关键参数,为区域地下水的合理开采和有序回补涵养提供了科学依据。     

Effect of Overpressure on Rock Frame and Its Implications for Overpressure Evolution

Overpressure is a hot topic in the study of sedimentary basins. It is important in generation,maturation migration,and accumulation of hydrocarbon,but the effects of overpressure on rock frame have not been investigated. In this study,experiments were carried out to study the effects of overpressure on rock frame structures using five core samples from the Junggar basin,Northwest China. The deformations and velocities for the samples were measured at different effective pressures related to non-equilibrium compaction and fluid expansion overpressure mechanisms. The results show that the effect of overpressure on rock frames gradually increases when the effective pressure drops down to a certain value (called critical pressure). Moreover,non-equilibrium compaction mechanism has more effects on rock frames than fluid expansion mechanism under the same effective pressure. Furthermore to study rock frame structural changes,we use Kuster and Toks?z's expressions to simulate the effective aspect ratios of inclusions α (penny shapes) for different effective pressures. The results show that the α decreases dramatically when the effective pressure decreases from the critical pressure. Changes of α can be interpreted as responses to the rock frame changes when grains conform one another by rotating and self-adjusting. However,different mechanisms of overpressure have different effects on rock frames. The rock frame can be affected more easily by overpressure in shallow regions generated by non-equilibrium compaction mechanism. Once this kind of rock frames are preserved after overpressure releases to a normal hydrostatic pressure,they can be identified by their specific rock frame characters. This method provides a new way to study overpressure release and fluid migration and accumulation.     

区域资源定量评价中面金属量法的应用

地球化学方法被普遍应用于矿产资源评价,但多数方法都只是基于地球化学数据本身而进行的,较少考虑除成矿物质来源之外的诸如构造、地层等地质环境的影响。文章运用面金属量法,在充分研究地质因素的基础上,确定了预测单元及地球化学背景值,在一定程度上屏蔽了虚假资源量,对东天山地区铜的资源量进行了定量评价。预测认为,东天山地区铜的资源潜力巨大。     

Late Pleistocene baldcypress (Taxodium distichum) forest deposit on the continental shelf of the northern Gulf of Mexico

Approximately 13 km south of Gulf Shores, Alabama (United States), divers found in situ baldcypress (Taxodium distichum) stumps 18 m below the ocean surface. These trees could have only lived when sea level fell during the Pleistocene subaerially exposing the tectonically stable continental shelf. Here we investigate the geophysical properties along with microfossil and stratigraphical analyses of sediment cores to understand the factors that lead to this wood’s preservation. The stumps are exposed in an elongated depression (~100 m long, ~1 m deep) nested in a trough of the northwest–southeast trending Holocene sand ridges and troughs with 2–5 m vertical relief and ~0.5 km wavelength. Radiocarbon ages of the wood were infinite thus optically stimulated luminescence (OSL) dating was used to constrain the site’s age. Below the Holocene sands (~0.1–4 m thick), separated by a regional erosional unconformity, are Late Pleistocene mud-peat (72±8 ka OSL), mud-sand (63±5, 73±6 ka OSL), and palaeosol (56±5 ka OSL) facies that grade laterally from west to east, respectively. Foraminiferal analysis reveals the location of the terrestrial-marine transitional layer above the Pleistocene facies in an interbedded sand and mud facies (3940±30 (1σ) ¹⁴C a BP), which is part of a lower shoreface or marine-dominated estuarine environment. The occurrence of palaeosol and swamp facies of broadly similar ages and elevation suggests the glacial landscape possessed topographic relief that allowed wood, mud and peats to be preserved for ~50 ka of subaerial exposure before transitioning to the modern marine environment. We hypothesize that rapid sea-level rise occurring ~60 or ~40 ka ago provided opportunities for local flood-plain aggradation to bury the swamp thus preserving the stumps and that other sites may exist in the northern Gulf of Mexico shelf.     

再探青藏高原十大关键地学科学问题——《地质学报》百年华诞纪念

本文重新审视了青藏高原的关键科学问题,为解决板块构造理论的"登陆"难题提供新的线索,为理解板块汇聚边界的大陆岩石圈演化及其能源资源、地质灾害和全球环境效应提供新的思路.本文探讨了青藏高原如下十大关键地学问题:①印度大陆北漂模型;②印度-亚洲初始碰撞时限;③青藏高原的古特提斯造山作用;④古近纪喜马拉雅造山带的地壳缩短;⑤...     

武夷山成矿带及邻区上地幔速度结构及其对燕山期岩浆-成矿活动的启示

武夷山成矿带燕山期岩浆-成矿活动的深部动力学机制一直是学者们研究的热点。已有的研究结果表明,武夷山成矿带及邻区的上地幔存在着显著的低速异常,可能与地表的岩浆-成矿活动存在着密切的联系。本研究利用分布在华夏地块98个固定地震台站以及59个流动地震台站所记录到的278个远震事件,采用远震层析成像方法构建了武夷山成矿带及邻区上地幔三维P波速度结构模型。成像结果表明,武夷山成矿带及其东侧的上地幔存在着显著的低速异常,代表了热物质富集的地幔楔,且上地幔的热物质在这些地幔楔间进行着横向流动。东南沿海的地幔过渡带存在着一个显著的低速异常,推测为新生代欧亚板块与菲律宾海板块碰撞俯冲的产物。南岭成矿带下方的低速异常从上地幔一直向上延伸到上地壳,可能指示了一个热物质上涌的通道。结合已有的研究结果,本研究认为武夷山成矿带燕山期岩浆-成矿活动可能与古太平洋板块的俯冲和后撤所引起的热物质上涌有关。