The influence of salt withdrawal subsidence on palaeosol maturity and cyclic fluvial deposition in the Upper Triassic Chinle Formation: Castle Valley, Utah

Integrated fluvial sequence stratigraphic and palaeosol analysis can be used to better reconstruct depositional systems, but these approaches have not been combined to examine halokinetic minibasins. This study characterizes the temporal and spatial patterns of lithofacies and palaeosols in a sequence stratigraphic framework to reconstruct a model of minibasin evolution and identify halokinetic influences on fluvial deposition. This research documents fluvial cycles and stratigraphic hierarchy, palaeosol maturity and apparent sediment accumulation rates in the Chinle Formation within the Big Bend minibasin. This study also uses palaeosols to help identify fluvial aggradational cycle (FAC) sets. The Chinle is divided into two hectometre‐scale (10² m) fluvial sequences, six decametre‐scale (10¹ m) FAC sets, and variable numbers of metre‐scale FACs depending on proximity to the minibasin. Ten pedotypes representing 225 palaeosol profiles are recognized. The pedotypes include palaeosols similar to modern Entisols, Inceptisols, Aridisols, Vertisols and Alfisols. A maturity index (1–5) is assigned to each pedotype to assess its variability in palaeosol development. Estimated palaeosol development time is used to approximate apparent sediment accumulation rates. Increased subsidence resulted in a greater number and thicker FACs, thicker FAC sets and fluvial sequence sections, and lithofacies associations reflecting more rapid sedimentation along the minibasin axis. Palaeocurrent indicators converge towards the minibasin axis and indicate that it formed and drifted through time. Relative palaeosol maturity is inversely related to stratal thickness, and decreases towards the minibasin where episodic burial by fluvial sediment was more frequent. Metre‐scale FACs are most abundant towards the minibasin axis, and locally have Entisols and Inceptisols developed upon their upper boundaries reflecting increased sediment accumulation rates. Areas outside the minibasin are characterized by fewer FACs that are associated with more mature palaeosols. Palaeosol‐derived apparent sediment accumulation rates are as much as two orders of magnitude greater within the minibasin than in marginal areas. The combined stratigraphic, palaeocurrent and palaeosol evidence is used to develop a model for the evolution of the Big Bend minibasin that illustrates the halokinetic affect on fluvial and landscape processes.     

Provenance of Jurassic accretionary complex: Mino terrane, inner zone of south-west Japan – implications for palaeogeography of eastern Asia

Provenance and tectonic history of the Jurassic accretionary complex, Mino terrane, located in the Inner Zone of south‐west Japan, were studied using sandstone framework composition and mudrock geochemistry. Modal analysis of sandstones shows that the tectonic setting of the source area for the studied Mino terrane clastic rocks was uplifted basement, largely dominated by high‐grade metamorphic terrain composed of quartz and feldspar, especially plagioclase. The textural and mineralogical immaturity, extent of alkali and alkaline earth element leaching, low chemical index of alteration values and depleted rare earth element (REE) contents suggest rapid uplift and erosion within the source terrain and a relatively weak weathering intensity. Factor analysis revealed that grain‐size effects governed compositional heterogeneity in the studied sediments. Provenance of the sediments is interpreted as being plagioclase‐enriched felsic basement rock, such as granodiorite, within a continental margin and evolved arc tectonic setting rather than active volcanic arc. Lack of a contribution from active volcanic arcs may have resulted from the cessation of volcanism during the reorganization of the subducting plate system and/or erosion of arc volcanics and exposure of basement. Considering the previous studies on palaeogeography and palaeocurrent reconstruction, the north‐eastern part of the Yeongnam massif in the Korean Peninsula is interpreted as the most probable source area for the studied turbidites. The results of mixing calculation for Mino terrane sediments suggest that Precambrian leucocratic granite and the basement rock of the Cretaceous Gyeongsang Basin shed large amounts of sediments to the Mino trench, whilst Precambrian granitic gneiss and the Triassic pluton supplied lesser amounts. The results of this study reveal that, although active subduction–accretion processes were occurring, the Mino trench was bordered by continental basement rocks. This knowledge contributes to enhanced understanding of the Jurassic palaeogeography of the east Asia continental margin.     

Contact metamorphism in the Malashan dome, North Himalayan gneiss domes, southern Tibet: an example of shallow extensional tectonics in the Tethys Himalaya

Combined petrographic, structural and geochronological study of the Malashan dome, one of the North Himalayan gneiss domes, reveals that it is cored by a Miocene granite, the Malashan granite, that intruded into the Jurassic sedimentary rocks of Tethys Himalaya. Two other granites in the area are referred to as the Paiku and Cuobu granites. New zircon SHRIMP U-Pb and muscovite and biotite ⁴⁰Ar-³⁹Ar dating show that the Paiku granite was emplaced during 22.2–16.2 Ma (average 19.3 ± 3.9 Ma) and cooled rapidly to 350–400 °C at around 15.9 Ma. Whole-rock granite chemistry suggests the original granitic magma may have formed by muscovite dehydration melting of a protolith chemically similar to the High Himalayan Crystalline Sequence. Abundant calcareous metasedimentary rocks and minor garnet-staurolite-biotite-muscovite ± andalusite schists record contact metamorphism by three granites that intruded intermittently into the Jurassic sediments between 18.5 and 15.3 Ma. Two stages of widespread penetrative ductile deformation, D1 and D2, can be defined. Microstructural studies of metapelites combined with geothermobarometry and pseudosection analyses yield P – T conditions of 4.8 ± 0.8 kbar at 550 ± 50 °C during a non-deformational stage between D1 and D2, and 3.1–4.1 kbar at 530–575 °C during syn- to post-D2. The pressure estimates for the syn- to post-D2 growth of andalusite suggest relatively shallow (depth of ∼15.2 km) extensional ductile deformation that took place within a shear zone of the South Tibetan Detachment System. Close temporal association between intrusion of the Malashan granite and onset of D2 suggests extension may have been triggered by the intrusion of the Malashan granite.     

Evidence of Specific MJO Phase Occurrence with Summertime California Central Valley Extreme Hot Weather

This study examines associations between California Central Valley(CCV) heat waves and the Madden Julian Oscillation(MJO). These heat waves have major economic impact. Our prior work showed that CCV heat waves are frequently preceded by convection over the tropical Indian and eastern Pacific oceans, in patterns identifiable with MJO phases. The main analysis method is lagged composites(formed after each MJO phase pair) of CCV synoptic station temperature, outgoing longwave radiation(OLR), and velocity potential(VP). Over the CCV, positive temperature anomalies occur only after the Indian Ocean(phases 2-3) or eastern Pacific Ocean(phases 8-1) convection(implied by OLR and VP fields). The largest fractions of CCV hot days occur in the two weeks after onset of those two phase pairs. OLR and VP composites have significant subsidence and convergence above divergence over the CCV during heat waves, and these structures are each part of larger patterns having significant areas over the Indian and Pacific Oceans. Prior studies showed that CCV heat waves can be roughly grouped into two clusters: Cluster 2 is preceded by a heat wave over northwestern North America, while Cluster 1 is not. OLR and VP composite analyses are applied separately to these two clusters. However, for Cluster 2, the subsidence and VP over the CCV are not significant, and the large-scale VP pattern has low correlation with the MJO lagged composite field. Therefore, the association between the MJO convection and subsequent CCV heat wave is more evident in Cluster 1 than Cluster 2.     

平面P1波斜入射下海底洞室地震响应解析分析

基于无黏性可压缩理想流体介质波动理论和Biot流体饱和多孔介质波动理论,考虑水下饱和土的流固耦合,借助Hankel函数积分变换法(HFITM)给出入射平面P1波在海底洞室周围散射问题的解析解。相比传统研究中的"大圆弧假定",Hankel函数积分变换法可以较好地处理半空间表面边界条件。利用该解析解,计算分析了洞室表面透水条件、入射角度、入射频率、海水水深和饱和土的孔隙率等因素对水-土交界面处水平位移、竖向位移和洞室表面动水压力、环周总应力的影响。结果表明:洞室表面透水条件对水-土交界面处水平位移和竖向位移影响较小;随着斜入射角的增加,水-土交界面处竖向位移减小;随着入射频率的增加,水-土交界面处水平位移随之增加;海水水深为2.5倍SV波的波长时,水-土交界面处水平位移及洞室表面动水压力最大值最大;随着孔隙率的增加,水-土交界面处水平位移、竖向位移和洞室表面环周总应力减小,而洞室表面动水压力随之增加。     

Study on the current structure of the thermohaline front in the southeastern entrance of the Yellow Sea during winter

A thermohaline front is located at the southeastern entrance of the Yellow Sea in winter, and it is generated by the intrusion of warm saline water into the Yellow Sea caused by a strong northerly wind. Recently, a westward transversal current traveling away from the west coast of Korea toward the open sea area along the front was reported. The westward transversal current is dominant in the surface layer during the temperature inversion period. The formation and structure of this current are examined using a numerical vertical ocean-slice model. When two different water masses meet, a front is formed and adjusted geostrophically. In this frontal zone, a horizontal pressure gradient flow by the vertically inclined isopycnal occurs under the thermal wind process in a baroclinic effect, and the cold fresh coastal water moves westward along the front in the upper layer. The barotropic effect across the front and the bottom friction effect strengthen the westward component of the velocity. The velocity of the bottom layer decreases remarkably in the increase of the bottom drag coefficient. This means that the bottom friction with the strong background tidal current causes a reduction in the current in the bottom layer.     

瓦里关山与观风山近地面空气7Be浓度季节性变化对比

7Be广泛应用于大气物质传输、表土季节性迁移和微粒混合作用的示踪。它在不同地域空气中的浓度分布构成了多领域研究的基础。7Be在对流层空气中的浓度随地表海拔高度而增加。基于瓦里关山和观风山的位置差异和海拔高差,对比观测其近地面空气7Be浓度变化不仅有益于区域尺度的大气和地表环境过程的示踪,而且对全球尺度的研究也将具重要意义。2002-10-09～2004-01-21,利用美国环境测量实验室的低水平核素表层大气采样系统在瓦里关山和观风山同步连续进行每周1个大气气溶胶样品的采集工作。7Be的比活度系用多道能谱仪进行γ谱测定,测量误差小于6%。中美两实验室对逐周样品测量结果表明两实验室的数据具有很好的可比性。两个站点7Be浓度逐周变化趋势总体相似,具有2～6周的短周期波动,波峰与波谷具有良好的对应关系,其高值或低值波动延迟或超前的差异与区域尺度的天气过程传播一致。瓦里关山和观风山7Be的年均浓度分别为(14.7±1.5)mBq/m3和(4.1±0.9)mBq/m3,前者约为后者的3.6倍。近地面空气7Be浓度与同期降水量的比较表明,在周时间尺度上,两者呈现出较好的预期负相关变化;而在月平均尺度上,两地7Be浓度变化比较稳定。位于内陆地区的瓦里关山受低海拔气团上升的影响较小,其空气中7Be浓度变化较真实地反映了中纬度、高海拔地区的背景水平。观风山地区虽然受到低纬度海洋性上升气团的影响,但7Be浓度变化仍然显示出低纬度、较高海拔地区的预期水平。     

三峡库区泄滩滑坡非饱和渗流分析及渗透系数反演

泄滩滑坡的水文地质结构比较复杂,滑体、滑带及滑动影响带为多孔连续介质,透水层基岩为裂隙介质。采用等效连续介质模型模拟裂隙岩体,建立了泄滩滑坡饱和－非饱和渗流的有限元计算模型。然后采用BP网络对非饱和有限元渗流计算进行了模拟,并根据蓄水期水库水位及滑坡体地下水位监测资料,采用遗传算法对泄滩滑坡各地层渗透系数进行了反演。反演的滑体饱和渗透系数为4.89?10?2 cm/s,与现场原位试验值1.78?10?2 3.2?10?2 cm/s相当;反演的滑带饱和渗透系数为4.66?10?5 cm/s,远比室内试验值2.74?10?7 5.73?10?7 cm/s大。这种差异在一定程度上反映了土体参数的尺度效应。     

局地气候分区框架下城市热岛时空分异特征研究进展

局地气候分区（LCZ）框架自2012年提出以来,在城市热岛研究领域备受重视,但目前对LCZ框架下城市热岛（简称LCZ城市热岛）时空分异特征仍缺乏系统性总结。本文以统计和“荟萃分析”为手段,系统梳理了2012—2019年LCZ城市热岛研究在数据获取手段、时空格局和影响因素3个方面的进展,并对今后研究进行了初步展望。结果表明,迄今为止全球范围内已在超过130座城市开展了LCZ城市热岛研究,这些城市主要集中于中纬度（35°N~55°N）的亚洲和欧洲地区,且主要聚焦于以近地表气温表征的“冠层热岛”和以地表温度表征的“地表热岛”。具体而言：① 在温度数据获取方面,站点观测（文献数量占比42.5%）、模型模拟（38.3%）与移动测量（19.2%）是获取气温的主要方法,其中模型模拟方法占比逐年升高。而卫星热红外遥感是获取地表温度的主要手段（86.5%）。② 在时空格局方面,就全球而言,LCZ气温的类间极值差（均值为3.1 K）显著低于地表温度的类间极值差（9.8 K）,且该极值差通常在夏季或冬季较大;冠层热岛与地表热岛均存在显著的“LCZ类内热岛”现象。③ 在影响因素方面,多数研究局限于定性分析地表结构、覆盖、材质和人类活动的影响,而普遍忽略了建筑布局与邻近LCZ类型等潜在因素的作用。本文将有利于从整体上更好地把握LCZ城市热岛的研究进展与今后的发展趋势。