苏北盆地晚白垩世—新近纪原型盆地分析

苏北盆地是我国东部中新生代箕状含油气盆地群,主要由东台坳陷、盐-阜坳陷和建湖隆起三大构造单元组成;坳中有凸,隆中有凹,一系列凸、凹构造组成盆地的二级单元。运用盆地原型分析方法,对盆地的蚀源区、沉降史、沉积中心、盆地边界构造和沉积间断等进行了研究,并估算了沉降量和剥蚀量。在此基础上,提出苏北盆地的形成经历了挤压的前陆盆地、弧后扩张的裂陷盆地、大规模拉张的断陷盆地和热沉降的坳陷盆地等四个演化阶段;认为盆地沉积物主要来自5个蚀源区：NE面的滨海隆起、NW面的鲁苏隆起、西面的大别山、SW面的张八岭以及南面的扬州一宁镇古生代沉积岩区;提出建湖隆起从始新世末期以来长期处于暴露和剥蚀状态,有条件为北侧的盐阜坳陷、南侧的东台坳陷提供部分成油气物质的认识。进一步确定苏北盆地曾经历过仪征、吴堡、真武和三垛等4次抬升剥蚀事件,这些事件对不对称箕状盆地的形成起了很大的作用。区内盆地的南侧边界多呈上陡下缓的“犁式”正断层,并呈阶梯状逐次朝北下掉,盆地北侧岩层与下伏层多呈超覆关系,形成“南断北超”的盆地面貌。主断层常出现上部下滑（新）、下部逆冲（老）的反转构造现象,因而苏北盆地具有多期复合迭加的特点。本区沉积中心多表现为不对称的深凹区,沉积厚度巨大,是研究区生油层系的重要场昕。     

伸展构造盆地的平衡剖面及其构造意义——以松辽盆地南部为例

挤压构造的平衡地质剖面分析已经广泛应用于造山带构造分析, 但伸展构造区的平衡地质剖面分析实例仍然很少.运用盆地分析的技术与方法, 分层序或阶段将地质构造依次恢复、地层逐层回剥, 并通过在松辽盆地南部吉林两井油田扶余油层4条剖面的实践, 复原出不同时代盆地构造与地层发育的连续剖面, 揭示出松辽盆地南部主要构造样式是以浅表构造层次的负花状构造及深层剥离断层发育为特征; 断层生长指数、盆地的伸展史和伸展量等参数显示, 晚白垩世是构造转型的重要阶段, 此前主要为走滑构造样式形成阶段, 此后则主要为伸展滑脱构造发育阶段.在此基础上, 提出松辽盆地具有伸展-走滑双重力学构造性质, 可能是一个弧后构造盆地.      

极地海冰的研究及其在气候变化中的作用

极地海冰作为全球气候系统的一个重要组成部分,通过影响大洋表面的辐射平衡、物质平衡、能量平衡以及大洋温、盐流的形成和循环而影响全球气候变化.从最初研究极地海冰的强度和承载力到目前海/冰/气相互作用全球气候耦合模型的建立,使海冰变化和全球气候变化紧密结合起来.这些研究领域主要有:海冰及其表层雪的物理特性和过程、海冰区域生态特征、海冰区与气候相关的反照率和物质平衡研究以及海冰气候耦合模型等大的领域.模拟显示,21世纪因为全球变暖,南北极海冰都将减少.海冰和全球气候系统其它要素之间的相互作用问题、极地海冰的厚度季节性区域性分布问题、极地海冰边界及范围变化趋势问题、生消关键过程及其影响因素问题、冰间湖的作用以及海气相互作用等将是未来重要的研究方向.     

地震历史对砂土抗液化性能影响的试验研究

为探讨地震历史对饱和砂土抗液化性能的影响,通过离心机动力模型试验,观测了遭受过不同强度地震的饱和砂土水平场地在再次地震荷载作用下的响应,包括超静孔隙水压力的发展和土体的变形。研究表明,小地震有利于增强砂土颗粒之间的咬合及结构的稳定性,极大地提高了其抗液化能力,而遭受强地震并且发生液化的砂土,由于在沉积过程中形成的不稳定结构,则可能在将来强度相对较小的地震中再次液化。试验结果说明了地震历史对砂土液化性能有重大影响及进一步开展砂土细观结构研究的重要性。     

Stress history effects on 1‐D consolidation of soft soils: a rheological model

Stress history plays an important role in controlling the consolidation behavior of soft clays, but few models exist that can provide quantitative estimate of its influence. In this paper, the Gibson–Lo rheological model is used to simulate the coupled processes of drainage and creep of soft soils that takes stress history into account. A hybrid combination of analytical and numerical methods is adopted to solve the governing equations of consolidation with the nonlinear rheological model. The methodology is applied to a saturated soft soil subjected to surface loading. The soil profile is separated into normally consolidated and overconsolidated layers by a boundary that is allowed to move. Comparisons of the model predictions and its simulations are used to evaluate the effects of stress history, model parameters, and loading pattern on consolidation behavior. It is shown that stress history influences the location of the moving boundary, variations of the profiles of excess pore water pressure dissipation, stress and deformation‐based average degrees of consolidation. Parametric studies conducted show that when soil is stiffer, the excess pore water pressure dissipates much more quickly, and thus the soil consolidates much faster especially at the early stages. The results also show that soil viscosity influences the deformation‐based average degree of consolidation at the latter stages. The consolidation process of soil layer under linear loading is shown to lag behind those under instantaneous loading: the longer the loading period is, the smaller the average degrees of consolidation are no matter how they are defined. Copyright © 2012 John Wiley & Sons, Ltd.     

Middle to Late Pleistocene palaeoenvironmental evolution of the southeastern Alpine Valeriano Creek succession (northeastern Italy)

The Middle–Late Pleistocene alluvial and lacustrine succession of Valeriano Creek (southeastern Alpine foothills, 190 m a.s.l.) documents the environmental evolution of the piedmont plain before the onset of the Last Glacial Maximum (LGM). The sedimentary record was investigated by multidisciplinary stratigraphical and sedimentological studies coupled with petrographic and palaeobotanical analysis. A chronology has been provided by luminescence, radiocarbon dating and pollen biochronology. The succession developed at the valley mouth of a small catchment and is confined in the piedmont plain by the alluvial fans of major rivers. The oldest deposits were formed during a cold phase during the late Middle Pleistocene. This part of the piedmont plain was generally stable until Termination II, when it was trenched more than 15 m deep by watercourses. The infilling succession of the trench, mostly by low‐energy alluvial sediments interbedded with mire and peat deposits, documents, for the first time on the southern side of the Alps, the relationships between fluvial activity, vegetation and climate change at the foothills piedmont plain during late Marine Isotope Stage (MIS) 5. The stadial–interstadial climate forcing implies a local reorganisation of fluvial dynamics and of forest composition, although substantial plant cover persisted even during cooler stadials. In accordance with coeval alluvial and speleothem records from the northern side of the Alps, this environmental evolution supports a very restricted Alpine glaciation of the main fluvial catchments of the southeastern Alps during MIS 5a–d. Copyright © 2009 John Wiley & Sons, Ltd.     

Pliocene‐Quaternary history of Futuna Island,south Vanuatu,southwest Pacific

U‐series ages from thermal ionisation mass spectrometry are reported here for the raised coral reefs of Futuna Island, which lies adjacent to the eastern margin of the backarc Futuna Trough in south Vanuatu, southwest Pacific. U‐series ages from coral from the lowest raised reef indicate that its upper part is most likely to be ca 210 ka, whereas the most elevated raised reef has a likely age of ca 520 ka (range 600–440 ka). The inferred Pliocene‐Quaternary history for Futuna Island and the adjacent Futuna Trough is: (i) formation of the Pliocene—Early Quaternary basaltic‐andesite cone in a southeast part of the Vanuatu Island Arc; (ii) inception of the Futuna Trough (adjacent to the west margin of Futuna Island) since 1.8 Ma; (iii) subsequent uplift of the volcanic cone above sea‐level caused ～500 m of its upper part to be removed by marine erosion; (iv) the island then subsided and at least 160 m of limestone was deposited on the truncated cone; and (v) during the period 520 ka to ca 210 ka seven fringing reefs formed at the margin of the cone as the island was uplifted. Since ca 210 ka Futuna further subsided and, as a result, the post ca 210 ka history of the island is obscure.     

A continuous Holocene beetle record from the site Stavsåkra,southern Sweden: implications for the last 10 600 years of forest and land use history

Beetle remains from a small bog in southern Sweden contribute information concerning the forest history of the study area. The study shows that beetles are valuable indicators of woodland structures such as openness, field vegetation, presence of dead wood and disturbance factors such as climate change, fire regimes, grazing and land use. The early Holocene, ca. 8600–6450 cal. BC, was characterised by open, pine‐dominated woodlands maintained by fire and grazing disturbances. The changes in the wetland fauna, between 8600 and 7500 cal. BC, correlate well with low lake levels in southern Sweden. During the mid Holocene, ca. 6450–2400 cal. BC, the woodlands were relatively dense, with few openings in the canopy. Around 4200 cal. BC, there was a shift to a dominance of deciduous trees. Fire and grazing pressures were particularly low. Numbers of aquatic and hygrophilic beetles indicate dry conditions between ca. 5000 and 3000 cal. BC. During the late Holocene, ca. 2400 cal. BC to present, the woodlands opened up mainly through increased land use. The main disturbance factors were fire and grazing. The beetles indicate the formation of heather‐dominated heathland around 800 cal. BC. Copyright © 2008 John Wiley & Sons, Ltd. This article was published online on 23 December 2008. An error was subsequently identified. This notice is included in the online and print versions to indicate that both have been corrected (5 August 2009).