Influence of sediment grain size and mineralogy on testate amoebae test construction

Testate amoebae are increasingly used for environmental monitoring as well as paleoenvironmental reconstructions. Paleoecological interpretations of testate amoebae assemblages depend on the understanding of the ecological processes operating today. We then ask the question of the link between testate structure and its environment. This study analyses both the grain size and mineralogical assemblage of tests of common species belonging to the genus Centropyxis and Difflugia. It is concluded that grain size is a limiting factor for test construction, whereas mineral composition is not. Hence, when analyzing agglutinated testate amoebae for paleoenvironmental reconstructions, it should be taken into account the mean grain size of the sediment. A non-appropriate grain-size probably inhibits the development of a testate amoebae specific assemblage.     

Remobilisation of deep Na-Cl waters by a regional flow system in the Alps: Case study of Saint-Gervais-les-Bains (France)

The hydrothermal system of Saint-Gervais-les-Bains, France is located in a south western low-elevation point of the Aiguilles Rouges crystalline Massif. The crystalline rocks are not directly outcropping in the studied area but certainly exist beyond 300 m depth. Uprising waters are pumped from two different aquifers below the Quaternary deposits of the Bon Nant Valley. In the Lower Trias-Permian aquifer crossed by De Mey boreholes (27–36 °C), the ascending Na-SO₄ and high-Cl thermal water from the basement (4.8 g/L) is mostly mixed by a Ca-SO₄ and low-Cl cold water circulating in the autochthonous cover of the Aiguilles Rouges Basement. The origin of the saline thermal water probably results from infiltration and circulation in the basement until it reaches deep thrust faults with leaching of residual brines or fluid inclusions at depth (Cl/Br molar ratio lower than 655). The dissolution of Triassic halite (Cl/Br > 1000) is not possible at Saint-Gervais-les-Bains because the Triassic cold waters have a low-Cl concentration (< 20 mg/L). Water–rock interactions occur during the upflow via north–south strike-slip faults in the basement and later on in the autochthonous cover. For the De Mey Est borehole, gypsum dissolution is occurring with cationic exchanges involving Na, as well as low-temperature Mg dissolution from dolomite in the Triassic formations. The aquifer of imbricated structures (Upper-Middle Trias) crossed by the Lépinay well (39 °C) contains thermal waters, which are strongly mixed with a low-Cl water, where gypsum dissolution also occurs. The infiltration area for the thermal end-member is in the range 1700–2100 m, close to the Lavey-les-Bains hydrothermal system corresponding to the Aiguilles Rouges Massif. For the Ca-SO₄ and low-Cl end-member, the infiltration area is lower (1100–1300 m) showing circulation from the Mont Joly Massif. The geothermometry method indicates a reservoir temperature of probably up to 65 °C but not exceeding 100 °C.     

祁连山摆浪河谷地的冰川地貌与冰期

祁连山摆浪河上游是一个以前研究者未曾涉足的地方，我们在这里发现6套保存完好的古冰川沉积和与之对应的冰水阶地以及上覆较厚的黄土 堆积，根据地貌地层学研究和^14C、TL、ESR测年，确认它们分别代表了小冰期、新冰期、同位素2阶段、4阶段、6阶段和12阶段6次冰川作用，是迄今在祁连山地区发现的相对比较确定的清晰齐全的第四纪冰川序列，发生于氧同位素12阶段的中梁赣冰期，表明抬升中的祁连山至少于460kaBP前与冰期气候耦合，进入了当时的冰冻圈。     

Ice-marginal environment and ecosystem prior to initial advance of the late Palaeozoic ice sheet in the Mount Butters area of the central Transantarctic Mountains, Antarctica

Basal rocks of the Upper Carboniferous to Lower Permian Pagoda Formation at Mount Butters provide an unusual view of periglacial conditions in the central Transantarctic Mountains region prior to the initial advance of the Gondwanide ice sheet. These rocks were deposited on a high relief unconformity that developed on granite. Deposition within relief on the unconformity, possibly in the lee of a granite buttress, protected the rocks from erosion during subsequent overriding by the ice sheet. The succession reflects deposition in a glacial‐fed to ice‐contact lake that contained a freshwater crustacean fauna. Centimetre‐ to decimetre‐scale basal layers include breccia and coarse‐grained sandstone. The occurrence of breccia resting on weathered granite suggests sedimentation as scree and as mass flow deposits. Overlying decimetre‐to metre‐scale stratified diamictites interbedded with metre‐scale, coarsening‐upward successions of siltstone to cross‐laminated sandstone suggest lacustrine deposition by suspension settling, rain out of ice‐rafted debris, and deltaic progradation. Thin zones with abundant conchostracans and/or with prolific trace fossils, in addition to less common remains of other crustaceans, attest to the presence of a low diversity benthic fauna. Conchostracans are concentrated in a series of thin beds that reflect moderately lengthy, perhaps seasonal, periods of free‐flowing water. Patchy vertical and lateral distribution of intense bioturbation and profuse trace fossils probably reflect repeated colonization events during times of favourable environmental conditions. Massive diamictite overlies the basal rocks and indicates that the ice‐marginal lake was subsequently overridden by the late Palaeozoic ice sheet. Occurrences of lodgement till, glacitectonite and deformation till suggest deposition from temperate or warm‐based ice, whereas underlying lacustrine and deltaic deposits, along with a crustacean and trace fossil fauna, suggest temperate periglacial conditions. Previous studies have stressed that upper Palaeozoic glacigenic deposits in Antarctica, and in Gondwanaland, record deglaciation events. In contrast, rocks at Mt. Butters provide an unusual glimpse into an ice‐margin lake and its fauna just prior to ice sheet advance.     

冰臼与壶穴之争述评

一些地质学家在粤东揭西和丰顺所发现的U形谷、冰碛物和石海等第四纪冰川遗迹的证据不足，该区成群出现的“冰臼”，实际上是河床基岩为河流侵蚀所形成的壶穴。控制壶穴形成的构造、岩性、地貌和河流作用等条件，文中作了较为充分的论述。粤西北封开一怀集地区已发现一系列第四纪冰川遗迹，因此广东的第四纪冰川问题，今后仍值得进一步研究。     

Correlation between high-resolution climate records from a Nanjing stalagmite and GRIP ice core during the last glaciation

A 400-mm-long stalagmite from Tangshan Cave, Nanjing has been analyzed by a high-precision TIMS-U series dating method and also determined for oxygen and carbon stable isotopic compositions. The results provided a high-resolution paleoclimate record for eastern China during a time interval (from 54 000 to 19 000 aBP) of the last glaciation. The continuous record of oxygen-18 variations in the stalagmite, indicating a precipitation history of the East Asian monsoon, shows not only signals of the Heinrich events, but also the Dansgaard-Oeschger cycles which are first found in the last glacial climate record of the East Asian monsoon area. Although the stalagmite-based climatic signals match well with the GRIP ice core record, some differences between the two records can be recognized: (1) The last glacial climate changes in eastern China exhibited a long-term remarkably cooling trend, superimposed on which were four successive Bond’s cycles illustrated by the δ¹⁸O curve. This strong cooling tendency may be an effect of the strong summer monsoon event during the MIS 3 over the Tibetan Plateau. (2) There exist some phase differences of 1000–2000 years between the cooling events in the stalagmite-based climate signal and the GRIP ice core record. Such differences should be further verified by calibrations of multiple dating methods     

Physiographic and geological characteristics of shelves in north and west of Taiwan

In north of Taiwan the East China Sea Shelf extends from the coastline of mainland China to the southern Okinawa Trough, showing a shelf-slope-basin bathymetric profile. Sea floor of the East China Sea Shelf is generally smooth and flat. It is wide (230 km) and relatively shallow with an average shelf-break depth of 120 m, reflecting the effect of Quaternary glaciation about 15000 years ago. The Pliocene-Quaternary East China Sea Shelf is underlain by thin sequences of about 1000 m thick shallow marine sediments mainly derived from China, forming an eastward dipping sedimentary wedge due to regional tilting and subsidence and representing the youngest part of the Cenozoic rift margin in southeastern China. The Taiwan Strait Shelf has two phases in development: one is the early phase of the Paleocene-Miocene rift margin and the other is the late stage of the Pliocene-Quaternary foreland sedimentation. It is a foreland shelf and its present morphology results from the combined effects of tectonic subsidence and sedimentation overprinting that of the Late Pleistocene glaciation about 15000 years ago.     

西藏吉隆盆地的新构造运动及第四纪冰川

吉隆盆地七级阶地和一级山顶剥蚀面的存在说明：本区自早更新世沉积贡巴砾岩后，新构造运动抬升有８次，其中以早更新世Ｑ＿１晚期至中更新世Ｑ＿２抬升最强，共５次，相对于吉隆河河面（盆地基准面）的抬升幅度８９６ｍ；晚更新世Ｑ＿３和全新世Ｑ＿４两者共３次的抬升幅度较小（计７４ｍ）．区内第四纪以来经历过４次冰期：２次发生在Ｑ＿１晚期至Ｑ－２，２次分别出现于Ｑ＿３，Ｑ＿４．从漂砾数量推断，以Ｑ＿３冰期规模最大，Ｑ＿４冰期规模次之．     

The influence of soil interstitial waters on the physicochemistry of major,minor and trace metals in stream waters of the green lakes valley,Front Range,Colorado

The influence of soil interstitial waters on the physicochemical characteristics of major, minor and trace metals in stream waters of an alpine watershed, Front Range, Colorado was assessed. Dissolution of Ca-aluminosilicate minerals, ion exchange reactions and the magnitude of solute flux within the alpine soil environment account for most of the observed concentrations of major, minor and trace metals in the alpine stream waters. The rate of mineral dissolution and magnitude of solute flux during the summer of 1989 was greatly affected by anthropogenic disturbance which resulted in large amounts of colloidal material and freshly exposed mineral surfaces. The alpine ecosystem responded very quickly to this disturbance. The magnitude of solute flux in the soil environment was also highly dependent on the duration and intensity of rain events, as well as the location of the site along the slope. Transport of most trace metals in the stream waters was achieved by adsorption onto colloidal surfaces of Al–Si hydroxides smaller than 0·45 μm.     

哈纳斯湖地区地貌与湖的成因

哈纳斯湖位于阿尔泰山深处,最大水深188.5m,平均水深122.1m。横断面具典型的箱形形态,在其底部存在现代活动地堑。湖盆的成因是强烈的构造断陷加上山谷冰川的创蚀及终碛垄的堰塞。随着终绩垄被出流下切,湖泊面积变小。