甘孜- 理塘洋可能存在北向俯冲：来自松潘- 甘孜道孚- 炉霍岩浆岩的证据

松潘- 甘孜造山带巨厚的三叠系复理石沉积盖层给探讨其基底性质、俯冲- 碰撞过程和深部岩浆作用增添了难度，使得带内广泛出露的花岗质岩体和少量镁铁质岩体成为解开松潘- 甘孜造山带构造演化谜团的重要研究对象。锆石U- Pb定年结果表明道孚花岗闪长岩形成于223. 5~217. 4 Ma，炉霍二长岩结晶年龄为219. 4 Ma，辉长岩为218. 9 Ma，均属于晚三叠世岩浆活动的产物。化学成分研究结果表明，花岗质岩石都表现出I型花岗岩特征，其中炉霍二长岩具有较高的Ba、Sr含量，相对较高且均一的εHf(t)值（-3. 69~-1. 65），表明其可能来源于富集玄武质新生下地壳的熔融。道孚花岗闪长岩具有分散的εHf(t)值（-13. 51~0. 41），野外和地球化学特征指示其形成于幔源熔体与古老壳源熔体的混合。辉长岩在微量元素蜘蛛图上具有类似的模式，不同程度富集Ba、Sr、Pb、Th和U元素，出现Nb、Ta、Ti元素亏损，具有岛弧玄武岩的特征，来源于流/熔体交代的地幔楔部分熔融。综合区域已有资料，我们对甘孜- 理塘洋的演化历史提出新的认识，认为甘孜- 理塘洋不仅仅存在向南俯冲的可能性，同时也具有北向俯冲的历史，晚三叠世道孚- 炉霍岩浆岩的形成受控于甘孜- 理塘洋向北边松潘- 甘孜地块俯冲的背景之下。     

祁连山南部地区三叠纪弧后前陆盆地——基于沉积填充与大地构造的证据

本文通过对祁连山南部地区三叠纪沉积充填特征的研究,建立了盆地形成过程中沉积充填与区域构造演化的关联。依据沉积充填特征、构造接触关系及区域地质背景,认为祁连山南部地区三叠纪盆地具有弧后前陆盆地的构造属性;综合分析年代学、沉积物性和盆地内部填充单元的差异划分出与柴达木岛弧带和祁连山南部弧后前陆盆地相关的区域大地构造单元。认为早三叠世-中三叠世中期,南部遭受俯冲作用持续向北挤压推覆导致盆地挠曲沉降;中三叠世中期-晚三叠世中期发生弧(东昆仑-柴北缘)-陆(巴颜喀拉地块)碰撞,祁连山南部盆地挠曲沉降增大,其间形成区域性断裂和不整合等盆地记录的地质事件;晚三叠世晚期祁连山南部盆地发生过补偿陆相填充,弧后前陆盆地消亡。     

论四川盆地三叠系地下水水文地质条件

四川盆地三叠系地下水可划分出碎屑岩孔隙裂隙和碳酸盐岩岩溶裂隙两大储集类型。按此处构造开启程度和埋深条件等的不同,下中三叠统地下水有沉积变质水和渗入淋滤水两种基本成因类型,水动力特征各异。沉积变质水处于深埋封闭条件,受地静压力驱动控制;渗入淋滤水分布于背斜露头区和浅部地区,受静水压力驱动控制。并由此控制了盆地三叠系盐类的保存条件。     

Depositional environments and facies of the Late Triassic Abu Ruweis Formation, Jordan

The Abu Ruweis Formation is composed of carbonates, evaporites, and mudstones, with some locally developed pelletic, oolitic and stromatolitic limestones. The lateral persistence of bedding, the purity of the evaporite rocks, the alternating arrangement of marine carbonates and evaporites indicates periodic deposition in subaqueous conditions (salina). Petrographic investigations, X-ray diffraction analysis as well as chemical analysis have shown that the outcropping evaporite beds are mainly composed of secondary gypsum, with rare anhydrite relics. Five microfacies of gypsum were recognized according to their fabrics: porphyroblastic and granoblastic gypsum showing polarization texture, gypsum pseudomorph after anhydrite laths, and satin spar gypsum. The textures they display indicate a hydration origin of precursor anhydrite, which is in turn rehydrated from primary gypsum. Some of these anhydrites were formed as a result of replacement processes of the carbonate sediments associated with the evaporites, as evidenced from the textural relationships of the carbonate and sulfate minerals. The O¹⁸ content ranges from 1.45 to 8.38% PDB and the C¹³ content ranges from −1.52 to 4.73% PDB. Trace elements analysis has shown that the Abu Ruweis dolomites are rich in strontium (up to 600 ppm), and sodium (up to 835 ppm). The isotope composition and trace elements content, as well as the petrographic characteristics point to a penecontemporaneous hypersaline dolomitization origin for the Abu Ruweis dolomites. The evaporites were deposited during a regressive lowstand systems tract, whereas the carbonates were deposited under shallow water marine conditions during a highstand systems tract. The Abu Ruweis succession represents a relatively stable arid climate within a rapidly subsiding basin. Restricted conditions were provided by the development of beach barriers.     

Ophiomorpha irregulaire, rare trace fossil in shallow marine sandstones, Cretaceous Atane Formation, West Greenland

Ophiomorpha irregulaire is a large and extremely rare trace fossil. The type section is in the Book Cliffs, Utah, USA. A second on-shore locality is reported here, in the Nuussuaq Basin of West Greenland. Both occurrences date from the Late Cretaceous. Other reports of O. irregulaire are restricted to two-dimensional sections in well cores and are mostly Jurassic in age. The West Greenland occurrence is in the Atane Formation in shallow marine clean sandstone. The two on-shore localities lie in the same biogeographical region, in connection with the Cretaceous Western Interior Seaway of North America. O. irregulaire is characterized by a sinuous, branched meander maze lying mostly within a single horizontal plane, probably not far beneath the seafloor. The burrow lining has remarkably elongate pellets that probably were emplaced by the burrower. In some cases, diagenetic compression may have deformed the lining pellets to produce their elongated shape. The muddy sediment comprising the lining is almost unrepresented in the clean sands of the substrate, and it was probably trapped from suspension during suspension-feeding activity.     

Three-dimensional model and late stage warping of the Plattengneis Shear Zone in the Eastern Alps

The Plattengneis shear zone is a 250–600 m thick, flat lying, Cretaceous, eclogite facies, mylonitic shear zone, with north-over-south transport direction, that is exposed over almost 1000 km² in the Koralpe region along the eastern margin of the Alps. Although the shear zone is one of the largest in the Alps, its role in the Eoalpine metamorphic evolution and the subsequent exhumation of the region, remain enigmatic and its large-scale geometry is not well understood. The outcrop pattern suggests that the shear zone is made up of a single sheet that is folded into a series of open syn- and antiforms with wavelengths of about 10 km. Eclogite bodies occur above, within and below the shear zone and there is no metamorphic grade change across the shear zone. In the south, the fold axes strike east–west and plunge shallowly to the east. In the north, the fold axes are oriented in north–south direction and form a dome shaped structure of the shear zone. Total shortening during this late stage warping event was of the order of 5%. Indirect evidence constrains this folding event to have occurred between 80 and 50 Ma and the fold geometry implies that the final exhumation in the Koralpe occurred somewhat later than further north. Interestingly, the shear zone appears to strike out of the topography in the south and dip into the topography in the north, so that north of the shear zone only hanging-wall rocks are exposed and south of it only foot-wall rocks. Possibilities for the geometric relationship of the Plattengneis shear zone with the surrounding south dipping detachments are discussed.     

Paleoenvironmental records of water level and climatic changes from the middle to late Holocene at a Lake Erie coastal wetland, Ontario, Canada

Pollen and diatom assemblages, and peat stratigraphies, from a coastal wetland on the northern shore of Lake Erie were used to analyze water level and climatic changes since the middle Holocene and their effects on wetland plant communities. Peat deposition began 4700 cal yr B.P. during the Nipissing II transgression, which was driven by isostatic rebound. At that time, a diatom-rich wild rice marsh existed at the site. Water level dropped at the end of the Nipissing rise at least 2 m within 200 yr, leading to the development of shallower-water plant communities and an environment too dry for most diatoms to persist. The sharp decline in water level was probably driven primarily by outlet incision, but climate likely played some role. The paleoecological records provide evidence for post-Nipissing century-scale transgressions occurring around 2300, 1160, 700 and 450 cal yr B.P. The chronology for these transgressions correlates with other studies from the region and implies climatic forcing. Peat inception in shallow sloughs across part of the study area around 700 cal yr B.P. coincides with the Little Ice Age. These records, considered alongside others from the region, suggest that the Little Ice Age may have resulted in a wetter climate across the eastern Great Lakes region.     

Stratigraphic evidence for multiple drainings of glacial Lake Missoula along the Clark Fork River, Montana, USA

Glacial Lake Missoula, a source of Channeled Scabland flood waters, inundated valleys of northwest Montana to altitudes of ∼ 1265 m and to depths of  >600 m, as evidenced by shorelines and silty lacustrine deposits. This study describes previously unrecognized catastrophic lake-drainage deposits that lie stratigraphically beneath the glacial-lake silts. The unconsolidated gravelly flood alluvium contains imbricated boulder-sized clasts, cross-stratified gravel with slip-face heights of 2-> 35 m, and 70- to 100-m-high gravel bars which all indicate a high-energy, high-volume alluvial environment. Gravel bars and high scablands were formed by catastrophic draining of one or possibly more early, high lake stands (1200-1265 m). Most glacial-lake silt, such as the Ninemile section, was deposited stratigraphically above the earlier deposits, represents a lower lake stand(s) (1050-1150 m), and was not deposited in lake(s) responsible for the highest discharge events. The glaciolacustrine silt-covered benches are incised by relict networks of valleys formed during the drainage of the last glacial lake. Significant erosion associated with the last lake draining was confined to the inner Clark Fork River canyon.     

Secular variations of the upper crust composition: Implication of geochemical data on the Upper Precambrian shales from the Southern Urals western flank and Uchur-Maya region

In the mid-1980s, it was concluded based on geochemical study that Th, Sc, La concentrations and ratios Th/Sc, La/Sc and Eu/Eu* did not wary significantly in the post-Archean time. It was impossible to judge about compositional variations of upper crust during the Riphean and Vendian, because data of that time characterized a limited number of samples from the post-Archean basins of Australia, New Zealand, and Antarctic. Considered in this work are variations of Eu/Eu*, LREE/HREE, Th/Sc, and La/Sc ratios in Upper Precambrian fine-grained siliciclastic rock of the Southern Urals western flank (Bashkirian meganticlinorium) and Uchur-Maya region (Uchur-Maya plate and Yudoma-Maya belt). As is established, only the Eu anomaly in the studied siliciclastic rocks is practically identical to this parameter of the average post-Archean shale. Three other parameters plot on the Riphean-Vendian variation curves with positive and negative excursions of diverse magnitude, which do not coincide always in time. It is assumed that these excursions likely mark stages of local geodynamic activity, destruction of pre-Riphean cratons, and progressing recycling of sedimentary material during the Riphean.     

Diversity and stages in evolution of conodontophorids and bivalve mollusks in Triassic seas of Siberia and the Far East

Comparative analysis of taxonomic diversity dynamics of condontophorids from Boreal (Arctic regions of Russia) and Tethyan (Northwest Pacific) paleobasins showed that they had most favorable habitat environments in tropical seas. In the Boreal realm, condontophorids went through three stages of evolution comprising probably four substages and four phases, whereas three stages with six substages and twelve phases are distinguished in the Tethyan realm. The most important abiotic factors that controlled development of conodontophorids are paleotemperature of seawater and paleogeographic settings. Renewals in taxonomic composition conodontophorids and diversification of their assemblages have been confined to moments of paleotemperature and/or sea level rise. The comparative analysis of stages in evolution of conodontophorid and bivalve assemblages has been carried out. As is established, the peak taxonomic diversity of bivalves in Boreal seas was in the Late Triassic after the diversity minimum of the Early Triassic time. In contrast, conodontophorids were most diverse in the Olenekian Age.