东海外陆架EA01孔末次冰期最盛期的三角洲沉积

对东海 EA 0 1孔 (30°2 2 .96 15′ N、 12 5°4 5 .6 0 5 5′ E)岩心的沉积层序、粒度成分、沉积物年代、底栖有孔虫组合及其沉积环境的研究 ,揭示了东海外陆架末次冰期最盛期的三角洲沉积。钻孔 0 .36～ 2 9.6 5 m为一不完整的进积三角洲沉积层序 ,自下而上依次为前三角洲、河口沙坝和分流间湾的交替沉积 ;末次冰期三角洲的发育 ,表明了冰期低海面时期外陆架上的继承性沉降盆地仍被海水覆盖 ;盆地的区域沉降与海平面的共同作用形成了容纳沉积物的有效空间 ,捕获了河流带来的沉积物而形成三角洲 ,这是河流对海平面变化和构造下沉的响应 ,同时也反映了冰期陆架环境的多样性     

Hydrochemistry of carbonate terrains in alpine glacial settings

Nearly 200 analyses of meltwaters, ice and snow from three alpine glacial sites in carbonate terrain are summarized and discussed in terms of sources of solutes and kinetic controls on the progress of weathering reactions. Most data derive from the Swiss Glacier de Tsanfleuron which is based on Cretaceous and Tertiary pure and impure limestones. Two other sites (Marmolada, Italian Dolomites and the Saskatchewan Glacier, Alberta) are based on a mixed calcitic-dolomitic substrate. Most solutes originate from carbonate dissolution; moreover, where pyrite is present its oxidation supplies significant sulphate and forces more dissolution of carbonate. The ratios Sr²⁺/Ca²⁺ and Mg²⁺/Ca²⁺ are much higher in Tsanfleuron melt-waters than local bedrock, a phenomenon that can be reproduced in the laboratory at small percentages of dissolution. These anomalous ratios are attributed to incongruent dissolution of traces of the metastable carbonates Mg-calcite and aragonite. These phases also provide Na⁺ to solution. K⁺ is argued to originate mainly by ion-exchange on clays with solute Ca²⁺. Quartz and very minor feldspar dissolution are also inferred. Locally enhanced input from atmospheric sources is recognized by high Cl^? and associated Na⁺. The progress of weathering reactions has been evaluated by the trends in the data, computer modelling and some simple laboratory experiments. The most dilute samples show a trend towards removal of CO₂ to low partial pressures (c. 10^?5.5 atmospheres), reflecting initially rapid carbonate dissolution and relatively slow dissolution of gaseous CO₂. Later addition of atmospheric CO₂ or acid from pyrite oxidation allows further carbonate dissolution, but solutions show a wide range of saturations, and CO₂ pressures as high as 10^?2.2 where pyrite oxidation is important. In a carbonate terrain, measurement of electroconductivity (corrected to 25°C) and alkalinity in the field allows the following preliminary deductions (where meq stands for milliequivalents): where S is the minimum meq(Ca²⁺ + Mg²⁺) produced by simple dissolution of carbonate unconnected with pyrite oxidation. As with any proxy method, these deductions do not remove the need for chemical analysis of waters in a given study area.     

Mineralogy,geochemistry, and radiocarbon ages of deep sea sediments from the Gulf of Mexico,Mexico

The mineralogy, geochemistry, and radiocarbon ages of two sediment cores (GMX1 and GMX2) collected from the deep sea area of the Southwestern Gulf of Mexico (∼876–1752 m water depth) were studied to infer the sedimentation rate, provenance, heavy metal contamination, and depositional environment. The sediments are dominated by silt and clay fractions. The mineralogy determined by X-Ray diffractometry for the sediment cores reveals that montmorillonite and muscovite are the dominant clay minerals. The sections between 100 and 210 cm of the sediment cores GMX1 and GMX2, respectively, are characterized by the G. menardii group and G. Inflata planktonic foraminiferal species, which represent the Holocene and Pleistocene, respectively. The radiocarbon-age measurements of mixed planktonic foraminifera varied from ∼268 to 45,738 cal. years B.P and ∼104 to 25,705 cal. years B.P, for the sediment cores GMX1 and GMX2, respectively. The variation in age between the two sediment cores is due to a change in sediment accumulation rate, which was lowest at the location GMX1 (0.006 cm/yr) and highest at the location GMX2 (0.017 cm/yr).The chemical index of alteration (CIA), chemical index of weathering (CIW), and index of chemical maturity (ICV) values indicated a moderate intensity of weathering in the source area. The total rare earth element concentrations (∑REE) in the cores GMX1 and GMX2 vary from ∼94 to 171 and ∼78 to 151, respectively. The North American Shale Composite (NASC) normalized REE patterns showed flat low REE (LREE), heavy REE (HREE) depletion with low negative to positive Eu anomalies, which suggested that the sediments were likely derived from intermediate source rocks.The enrichment factor of heavy metals indicated that the Cd and Zn concentrations in the sediment cores were impacted by an anthropogenic source. The redox-proxy trace element ratios such as V/Cr, Ni/Co, Cu/Zn, (Cu + Mo)/Zn, and Ce/Ce* indicated that the sediments were deposited under an oxic depositional environment. The similarity in major element concentrations, REE content, and the NASC normalised REE patterns between the cores GMX1 and GMX2 revealed that the provenance of sediments remained relatively uniform or constant during deposition for ∼4.5 Ma. The major and trace element based multidimensional discrimination diagrams showed a rift setting for the core sediments, which is consistent with the geology of the Gulf of Mexico.     

179～129 ka B.P.时段千年尺度气候事件的湖北神农架石笋记录

根据湖北神农架1支石笋(SB11)13个230Th年龄和638个δ18O数据,重建了179～129 ka B.P.时段连续的高分辨率东亚夏季风历史.轨道尺度上石笋δ18O曲线呈现2个岁差旋回,指示东亚夏季风强弱变化受北半球夏季日辐射能量变化驱动.一系列千年尺度季风事件叠加于轨道尺度季风气候旋回上,与已有的东亚季风事件、北大西洋冰漂碎屑事件及地中海降温事件具有比较相似的变化规律,进一步证明了倒数第二次冰期千年尺度气候事件在北半球具有普遍性.山宝洞石笋记录与葫芦洞石笋记录的对比结果表明,最后两个冰期旋回千年尺度事件发生频率及变化幅度非常相似,有力地支持了千年尺度气候事件的冰量驱动模式.     

Late Pleistocene glaciers in Darhad Basin, northern Mongolia

Late Pleistocene glaciers around Darhad Basin advanced to near their maximum positions at least three times, twice during the Zyrianka glaciation (at ∼ 17-19 ka and ∼ 35-53 ka), and at least once earlier. The Zyrianka glaciers were smaller than their predecessors, but the equilibrium-line altitude (ELA) difference was < 75 m. End moraines of the Zyrianka glaciers were ∼ 1600 m asl; ELAs were 2100-2400 m asl. ¹⁴C and luminescence dating of lake sediments confirm the existence of paleolake highstands in Darhad Basin before ∼ 35 ka. Geologic evidence and ¹⁰Be cosmic-ray exposure dating of drift suggests that at ∼ 17-19 ka the basin was filled at least briefly by a glacier-dammed lake ∼ 140 m deep. However, lake sediments from that time have not yet been recognized in the region. A shallower paleolake briefly occupied the basin at ∼ 11 ka, but between ∼ 11 and 17 ka and after ∼ 10 ka the basin was probably largely dry. The timing of maximum glacier advances in Darhad appears to be approximately synchronous across northern Mongolia, but different from Siberia and western Central Asia, supporting the inference that paleoclimate in Central Asia differed among regions.     

Numerical simulation of the paleohydrology of glacial Lake Oshkosh, eastern Wisconsin, USA

Proglacial lakes, formed during retreat of the Laurentide ice sheet, evolved quickly as outlets became ice-free and the earth deformed through glacial isostatic adjustment. With high-resolution digital elevation models (DEMs) and GIS methods, it is possible to reconstruct the evolution of surface hydrology. When a DEM deforms through time as predicted by our model of viscoelastic earth relaxation, the entire surface hydrologic system with its lakes, outlets, shorelines and rivers also evolves without requiring assumptions of outlet position. The method is applied to proglacial Lake Oshkosh in Wisconsin (13,600 to 12,900 cal yr BP). Comparison of predicted to observed shoreline tilt indicates the ice sheet was about 400 m thick over the Great Lakes region. During ice sheet recession, each of the five outlets are predicted to uplift more than 100 m and then subside approximately 30 m. At its maximum extent, Lake Oshkosh covered 6600 km² with a volume of 111 km³. Using the Hydrologic Engineering Center-River Analysis System model, flow velocities during glacial outburst floods up to 9 m/s and peak discharge of 140,000 m³/s are predicted, which could drain 33.5 km³ of lake water in 10 days and transport boulders up to 3 m in diameter.     

Could ‘Snowball Earth’ have left thick glaciomarine deposits?

At least two of the Cryogenian (Neoproterozoic) glacials, viz. those of the Sturtian and the Marinoan, are said to have been so severe that the entire Earth was covered with ice (Snowball Earth). The most convincing evidence consists of diamicts with some glacial striae and of other glacial signatures (striated surfaces, polished rocks) that have been found in areas that are interpreted on the basis of paleomagnetic data as being positioned, at the time, at low latitudes. The extremely low temperatures must have contributed to entirely frozen oceans. Nevertheless, diamicts of exceptional thickness were formed in a marine environment. This cannot be explained satisfactorily, as icebergs cannot have floated in an entirely frozen ocean. It is suggested that at least a considerable part of the extremely thick Neoproterozoic ‘glaciomarine’ deposits represent syntectonic mass-flow deposits rather than glacial deposits. The existence of a huge mountain range between Eastern and Western Gondwanaland provided favourable conditions for such deposits.     

Heat flow variation with depth in Poland: evidence from equilibrium temperature logs in 2.9-km-deep well Torun-1

High-precision temperature measurements were carried out up to a depth of 2,930 m in the 5.5-km-deep well Torun-1, 26 years after completion of drilling. The temperature log provides equilibrium thermal state information for the Polish Lowland at the western margin of the Precambrian craton. Geothermal gradient calculated from the equilibrium temperature log, together with estimates of thermal conductivity from ‘net rock’ geophysical well logging analysis and available core measurements, yields heat flow in the range 50–60 mW/m² below 2-km depth. Heat flow of 50 mW/m² plus ∼10 mW/m² generated within thick sediments and highly metamorphosed sedimentary wedge is typical for the western margin of the Precambrian East European craton. Heat-flow variations with depth can be explained by a model of surface-temperature changes >10°C (glaciation to Holocene). Torun-1 Working Group: Marta Wróblewska, Jacek Majorowicz, Jan Szewczyk, Jan Šafanda, Vladimír Cermák     

末次盛冰期以来中国东部陆架层序地层研究现状

本文中笔者总结了多年来国内外中国东部陆架晚更新世地层结构研究的主要认识,系统阐述了层序地层与沉积环境演化。中国东部陆架沉积物输运量高、沉积作用受海平面变化影响强烈,是分析晚更新世沉积演化史的理想场所。末次盛冰期(22kaBP)之前,海面的持续下降形成以浅海、三角洲及海陆交互沉积为主的强制海退体系域。进入盛冰期后,一个新的旋回开始,在海退体系域之上,相继形成了包括低位体系域、海侵体系域及高位体系域在内新的4级层序:22～15kaBP盛冰期时期,海面降至最低,形成低位体系域,包括陆架深切河湖沉积及风成沉积,以及陆架边缘三角洲和潮流砂体等;盛冰期结束的15～7kaBP时期,全球海平面快速上升,形成含河道充填、湖泊、盐沼、潮坪、潮流砂体及浅海沉积的退积型海侵体系域;约7kaBP以后,海面与现今海面位置基本相当,形成高位体系域,主要为三角洲和潮流砂等近岸陆架的沉积。     

Tessellons,topography, and glaciations on the Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau has developed into a vast fortress-like structure that has recently presented a barrier limiting the egress of moisture-bearing air masses. Lower sea levels also affected the climate. This paper examines their effects on the current evidence for the timing of past glaciations, and the development and evolution of permafrost. There are two theories regarding glaciation on the Qinghai-Tibet Plateau(QTP). Kuhle suggested that there was a major, unified ice-cap during the Last Glacial Maximum(LGM), whereas major Chinese glaciologists and others have not found or verified reliable evidence for this per se. There have been limited glaciations during the last 1.1 Ma B.P. but with increasing dominance of permafrost including both primary and secondary tessellons infilled with rock, sand or loess. The East Asia Monsoon was absent in this area during the main LGM, starting at 30 ka B.P. on the plateau, with sufficient precipitation reappearing about 19 ka B.P. to produce ice-wedges. A weak Megathermal event took place between 8.5 and 6.0 ka B.P., followed by Neoglacial events exhibiting peak cold at 5.3–4.7 ka, 3.1–1.5 ka, and the Little Ice Age(LIA) after 0.7 ka. Subsequently,mean annual air temperature has increased by 4 °C.