Tidal and residual circulation in the St. Andrew Bay system,Florida

Two 24-h surveys were conducted in St. Andrew Bay, Florida, during spring and neap tides to describe the tidal and non-tidal circulation patterns and to determine the factors that affect these patterns. In particular, the effect of tidal forcing in modulating such circulation patterns was explored. Observed velocities were fitted to diurnal and semidiurnal harmonics separating tidal motions from sub-tidal motions. Residual flows were compared with an analytic model that allowed variations in the relative contributions from Coriolis acceleration and friction using the Ekman number. A solution with an Ekman number of 0.04 resembled the observations best and indicated that the hydrodynamics were governed by pressure gradient, Coriolis and friction. Locally, advective accelerations became important around headlands in sub-estuaries in the system. The consistency of the mean pattern from October to March suggests that tides play a minor role in modulating the exchange flow. Deviations from the long-term mean are mainly caused by wind-driven coastal setup and setdown.     

Volatile-induced magma differentiation in the plumbing system of Mt. Etna volcano (Italy): evidence from glass in tephra of the 2001 eruption

Mount Etna volcano was shaken during the summer 2001 by one of the most singular eruptive episodes of the last centuries. For about 3 weeks, several eruptive fractures developed, emitting lava flows and tephra that significantly modified the landscape of the southern flank of the volcano. This event stimulated the attention of the scientific community especially for the simultaneous emission of petrologically distinct magmas, recognized as coming from different segments of the plumbing system. A stratigraphically controlled sampling of tephra layers was performed at the most active vents of the eruption, in particular at the 2,100 m (CAL) and at the 2,550 m (LAG) scoria cones. Detailed scanning electron microscope and energy dispersive x-ray spectrometer (SEM-EDS) analyses performed on glasses found in tephra and comparison with lava whole rock compositions indicate an anomalous increase in Ti, Fe, P, and particularly of K and Cl in the upper layers of the LAG sequence. Mass balance and thermodynamic calculations have shown that this enrichment cannot be accounted for by “classical” differentiation processes, such as crystal fractionation and magma mixing. The analysis of petrological features of the magmas involved in the event, integrated with the volcanological evolution, has evidenced the role played by volatiles in controlling the magmatic evolution within the crustal portion of the plumbing system. Volatiles, constituted of H₂O, CO₂, and Cl-complexes, originated from a deeply seated magma body (DBM). Their upward migration occurred through a fracture network possibly developed by the seismic swarms during the period preceding the event. In the upper portion of the plumbing system, a shallower residing magma body (ABT) had chemical and physical conditions to receive migrating volatiles, which hence dissolved the mobilized elements producing the observed selective enrichment. This volatile-induced differentiation involved exclusively the lowest erupted portion of the ABT magma due to the low velocity of volatiles diffusion within a crystallizing magma body and/or to the short time between volatiles migration and the onset of the eruption. Furthermore, the increased amount of volatiles in this level of the chamber strongly affected the eruptive behavior. In fact, the emission of these products at the LAG vent, towards the end of the eruption, modified the eruptive style from classical strombolian to strongly explosive.     

济南地区闪长岩残积土的工程地质性质研究

残积土作为一种特殊土,其工程地质性质往往因母岩类型、地质环境及风化条件的不同差异很大。通过对野外资料、室内试验及原位测试等手段所获得的大量数据的整理分析,对济南地区闪长岩残积土的工程地质性质进行了研究,结果表明该地区的残积土地层剖面在垂直方向上具有分带性,由于残积土体的不均匀性,在力学性质的取值上存在着较大的离散性,在残积土物理、力学性质试验的基础上,结合当地的工程实践经验,提出了c、、a、Es、fak的建议值,以便能进一步指导工程实践。同时,也提出了一些在该地区当采用残积土作为地基持力层及地质条件中有残积土存在时施工、设计中应该充分重视其地层的互层性及不均匀性。     

Evaluation of ESR residual dose in quartz modern samples,an investigation on environmental dependence

Luminescence and ESR dating methods of quartz sediment are based on the natural resetting of the signal by light exposure (optical bleaching). When the bleaching is incomplete, a residual dose (D_eR) is added to the post-depositional dose accumulated since the deposit and hence the age is overestimated.Insufficient bleaching is usually linked to the environment and conditions of transport/deposition of the quartz grains affecting the light exposure duration. Indeed, each transportation mode – fluvial, marine or aeolian – is associated to specific conditions of light exposure, depending mainly to the location of grains in the transport agent during the transport phase, the opacity of the transport environment and the velocity of the transport.The present study attempts to discriminate the modes of transport/deposition providing a satisfying reset of the ESR signals of quartz grains. For this purpose, we investigated bleaching rates and ESR residual doses of aluminum centers from “present-day” aeolian, fluvial and marine sediments sampled in various sedimentary environments. The bleaching efficiency evaluation in these different environments may help for a better understanding of the resetting phenomenon for quartz signals which represents presently the main difficulty for ESR dating.The results show that the residual doses are small enough to allow an ESR dating of the main part of the sediment transported in almost all the context examined in this study. The smallest residual doses are obtained from quartz grains within the range of 100–200 μm and transported in clear water. Some limits for the application of optically bleached quartz ESR dating appears nevertheless, mainly when the residual dose and the dose accumulated after the deposit are quite similar, i.e. for Upper Pleistocene samples.     

碳酸盐岩残积红粘土微观结构的扫描电镜研究

根据大量的扫描电镜照片和辅助的X射线能谱分析资料,对残积红粘土微观结构进行了分类研究,指出前人研究不足之处是没有充分考虑土的形成条件、形成环境、土的成因以及组成矿物成分和形态。经研究认为,残积红粘土具有叠片状、絮凝状、粒斑状、斑状、斑块状、球粒状等结构,这些结构与组成红粘土的矿物形态及其成因密切相关。      

电离层残差对掩星反演温度精度的影响

本文以MSIS90大气模式和3D NeUoG电离层模式为大气背景,用三维射线追踪法模拟研究了太阳活动强度、地方时、掩星平面方位角对弯曲角电离层残差和温度电离层残差的影响,以及电离层残差对全球日平均温度的影响.结果表明：电离层残差是平流层顶部（35~50 km）和中间层底部（50~70 km）掩星大气温度反演的主要误差.在太阳活动活跃期,电离层残差对单一掩星事件的平流层顶部平均温度的影响可达1.8 K,中间层底部平均温度的影响可达7 K;对全球日平均温度的影响在平流层顶可达-0.6 K,在70 km高度处可达1.2 K.发展新的电离层改正方法或电离层残差修正算法对提高掩星大气反演精度和全球气候监测意义重大.     

Occurrence and influence of residual gas released by crush methods on pore structure in Longmaxi shale in Yangtze Plate,Southern China

The composition of gas released under vacuum by crushing from the gas shale of Longmaxi Formation in Upper Yangtze Plate, Southern China was systematically investigated in this study. The effect of residual gas release on pore structures was checked using low-pressure nitrogen adsorption techniques. The influence of particle size on the determination of pore structure characteristics was considered. Using the Frenkel-Halsey-Hill method from low-pressure nitrogen adsorption data, the fractal dimensions were identified at relative pressures of 0−0.5 and 0.5−1 as D₁ and D₂, respectively, and the evolution of fractal features related to gas release was also discussed. The results showed that a variety component of residual gas was released from all shale samples, containing hydrocarbon gas of CH₄ (29.58% −92.53%), C₂H₆ (0.97% −2.89%), C₃H₈ (0.01% −0.65%), and also some non-hydrocarbon gas such as CO₂ (3.54% − 67.09%) and N₂ (1.88%−8.07%). The total yield of residual gas was in a range from 6.1 μL/g to 17.0 μL/g related to rock weight. The geochemical and mineralogical analysis suggested that the residual gas yield was positively correlated with quartz (R²=0.5480) content. The residual gas released shale sample has a higher surface area of 17.20−25.03 m²/g and the nitrogen adsorption capacity in a range of 27.32−40.86 ml/g that is relatively higher than the original samples (with 9.22−16.30 m²/g and 10.84−17.55 ml/g). Clearer hysteresis loop was observed for the original shale sample in nitrogen adsorption-desorption isotherms than residual gas released sample. Pore structure analysis showed that the proportions of micro-, meso- and macropores were changed as micropores decreased while meso- and macropores increased. The fractal dimensions D₁ were in range from 2.5466 to 2.6117 and D₂ from 2.6998 to 2.7119 for the residual gas released shale, which is smaller than the original shale. This factor may indicate that the pore in residual gas released shale was more homogeneous than the original shale. The results indicated that both residual gas and their pore space have few contributions to shale gas production and effective reservoir evaluation. The larger fragments samples of granular rather than powdery smaller than 60 mesh fraction of shale seem to be better for performing effective pore structure analysis to the Longmaxi shale.     

山西2015地壳速度模型研究

针对山西测震台网缺少适合本地区地壳速度模型的现状,在前人工作成果的基础上,基于山西测震台网2009～2014年间产出的大量震相数据,采用"线性拟合"和"折合走时"法分别确定了模型参数中速度和深度的波动范围;利用Hyposat定位程序,使用46489组模型,分别批量定位76个地震事件,并选取残差最小的一组参数作为山西2015地壳速度模型;最后运用批量定位比较残差、PTD测定深度和人工爆破等3种方法对山西2015地壳速度模型进行了验证。结果表明:在山西地区进行地震定位时,山西2015地壳速度模型相较于现有的修正J-B模型残差更小,精度更高,具有更好的适用性。     

Numerical investigation of the factors influencing the vertical profiles of current,salinity, and SSC within a turbidity maximum zone

The flow-sediment interaction plays a considerable role on the vertical (internal) profiles of current,salinity and suspended sediment concentration (SSC) within a turbidity maximum zone (TMZ).Numerical modeling provides valuable insights into the complex estuarine physical processes.By combining numerical modeling with field observations,the influencing factors of fine sediment dynamics within the TMZ of Yangtze Estuary have been explored in this study.Firstly,during the neap tide,the measured data present that the current is too weak to break the density stratification,and the vertical flow structure is effectively altered.Secondly,a three-dimensional numerical model based on the Delft3D has been developed and a range of numerical sensitivity analyses were carried out to distinguish the dominant mechanisms and physical processes responsible for the phenomena observed from the measurement data.The numerical investigation highlights the following findings.(1) The vertical profile of currents within the TMZ is largely affected by saltwater intrusion,especially during lower currents when the baroclinic pressure gradient can significantly reshape the local vertical profiles of velocity.(2) The baroclinic effects are primarily determined by the stratification of salinity.(3) In addition to salinity,SSC also influences the local density stratification when its contribution to fluid density is comparable to that of salinity.(4) The settling velocity determines the overall sediment distribution and vertical profiles of the SSC in the water column.The SSC-dependent settling velocity (including the flocculation-induced acceleration and hindered settling deceleration phases) affects the longitudinal movement of the sediments.(5) The vertical profiles of current,salinity and SSC within the TMZ are highly associated with the turbulence determined by the model.The approach to modulate the vertical eddy viscosity in the model,based on the empirical dependency between Rig and Prt,may lead to a numerical instability in the stratified flow.In order to improve the stratification of SSC,additional turbulence damping effect is suggested to be implemented in the model.