西南极乔治王岛新生代古生物特征及古环境探讨

西南极乔治王岛发育有一套高钾低铝的拉斑玄武岩,夹火山碎屑岩,属于岛弧火山岩系列。该岛还保存了南极最长的冰川沉积记录,是研究南极冰盖演化历史的重要证据。乔治王岛出露的新生代陆相地层中含有丰富的植物叶、孢粉、茎干、无脊椎动物化石及鸟类足印的痕迹化石等,从始新世到早中新世,化石逐渐减少,表明植物多样性呈明显下降趋势,幸存的稀疏植被被严格限制在冰川周缘的苔原物种上。冰海相地层与古生物研究表明,晚渐新世海相地层主要对应高能环境,早中新世海相地层对应低能环境。对乔治王岛新生代古生物特征及古环境的探讨,不仅理解了古生物及多样性的变化趋势,也为重建南极古环境提供证据。      

南极长城站区寒冻风化特征

通过对南极长城站区寒冻风化速率的观测和分析，结合气温等因素的变化，讨论了该区寒冻风化与影响因素之间的关系。研究表明，该区夏季风化速率为冬季的36－7．5倍；海拔较高的地方风化速率比海拔低的高1．28－3．35倍；壁朝向东、东南的风化强度比朝向北、北西的大2．6－16倍。低温年份的风化速度仅有高温年份的7．2％－16．6％，与世界其它冰缘区的风化速率对比，本区寒冻风化速率属中等水平。     

西南极乔治王岛冰芯研究——冰雪层定年、微粒记录及离子迁移

在分析南极乔治王岛冰帽大冰穹顶部降水和成冰条件的基础上,利用冰芯上部层物理特征参数确定的5个年层及其附近气象站相应的降水记录,结合多年降水资料将大冰穹45m冰芯划分为15个年层.应用此年层剖面,证实了微粒含量的两个异常峰值分别对应于1987年Deception岛和1980年的SealNunataks两次火山喷发.乔治王岛冰帽属于温性冰帽,大、小冰穹冰芯阴阳离子受沉积后融水渗浸淋溶作用的影响.对冰芯阴阳离子的淋溶次序分析显示,大冰穹为SO₄^2->Mg²⁺>Ca²⁺>K⁺>Cl^->Na⁺>NO₃^->Br^-,而小冰穹为Mg²⁺>Ca²⁺>SO₄^2->K⁺>Cl^->Br^->Na⁺.     

The Polonez Cove Formation of King George Island, Antarctica: stratigraphy, facies and implications for mid-Cenozoic cryosphere development

The middle to late Oligocene Polonez Cove Formation, exposed on south‐eastern King George Island, South Shetland Islands, provides rare evidence of mid‐Cenozoic West Antarctic cryosphere evolution. A revised lithostratigraphy and facies analysis and a review of the palaeoenvironmental significance of the formation are presented here. The diamictite‐dominated basal member of the formation (Krakowiak Glacier Member) records the presence and retreat of marine‐based ice on a shallow continental shelf. Five overlying members are recognized. These consist of basaltic‐sourced sedimentary rocks and lavas and represent a variety of shoreface and shallow continental shelf environments in an active volcanic setting. These units contain diverse reworked and ice‐rafted exotic clasts that become sparse towards the top of the formation, suggesting a continuing but waning glacial influence. New ⁴⁰Ar/³⁹Ar dates from interbedded lava flows indicate a late Oligocene age (25·6–27·2 Ma) for the Polonez Cove Formation, but are slightly younger than skeletal carbonate Sr‐isotope ages obtained previously (28·5–29·8 Ma). There is evidence for wet‐based subice conditions at the base of the Polonez Cove Formation, but no sedimentary facies to suggest substantial meltwater. This may reflect a subpolar setting or may result from lack of preservation or a high‐energy depositional environment. A northern Antarctic Peninsula/South Shetland Islands provenance is probable for most non‐basaltic clasts, but certain lithologies with possible origins in the Transantarctic and Ellsworth Mountains also occur sparsely throughout the formation. There is evidence to suggest that the presence of such far‐travelled clasts within subglacially deposited facies at the base of the formation reflects the advance of a local ice cap across marine sediments containing the clasts as ice‐rafted material. The presence of these clasts suggests that extensive marine‐based ice drained into the southern Weddell Sea region and that a strong Weddell Sea surface current operated both before and during deposition of the Polonez Cove Formation.     

Geochemistry of soils of King George Island, South Shetland Islands, West Antarctica: Implications for pedogenesis in cold polar regions

Fine fractions of soils on the Barton Peninsula, King George Island, West Antarctica have been forming during the last 6000 yr since the last deglaciation. Texturally, they are mostly composed of mineral and rock fragments with some volcanic ashes, which are also indicated by geochemical compositions representing for the nonclay silicate minerals and low values of chemical index of alteration. No significant changes are observed in major- and trace element abundances. Such geochemical characteristics suggest that chemical weathering of bedrocks on the Barton Peninsula seems insignificant and that the soils are composed of physically weathered mineral and rock fragments which are mixed with eolian additions of volcanic ashes and Patagonian dusts. Chondrite-normalized rare earth element (REE) distribution patterns of the Barton Peninsula soils are slightly different from those of bedrocks, indicating that the REE abundances and characteristics were influenced by eolian additions. Mixing calculations, which mass-balance the REEs, suggest that volcanic ashes blown from Deception Island were the major eolian contributor, followed by atmospheric dusts sourced from Patagonia, South America. Even in the warmer and humid climatic conditions in the maritime Antarctic region, the chemical weathering of bedrocks appears to be insignificant, probably due to the relatively short duration of weathering since the last deglaciation.     

The Characteristics and Mechanism of Island-Arc Volcanism on the Central and Southern Fildes Peninsula, King George Island, Antarctica

The volcanic rock series on the Fildes Peninsula is the product of the later subduction of the Pacific platebeneath the Antarctic plate. It consists mainly of basalt, basaltic andesite and andesite with minor dacite. Itsisotopic ages range from 64.6±1 to 43±2 Ma, belonging to Palaeocene to Eocene. Volcanism in the area maybe divided into two phases. The contents of major oxides, rare earth elements (REE) and trace elements in vol-canic rocks formed in different phases show regular changes, which are mainly related to the rock associationsof these phases. Isotope geochemical studies indicate that the primitive magma in the area originating by par-tial melting in the upper mantle underwent fractional crystallization and ascended to the high-level (shallow)magma chamber. Before eruption the primitive basalt-andesitic magma was subjected to differentiation in thehigh-level magma chamber, forming zones of derivative magmas of different compositions. In various phasesmagma-conducting faults experienced periodic extension and cut through various derivative magma zones indifferent parts of the peninsula, leading to the eruption of magmas of different compositions on the surface andthe formation of volcanic rock associations of corresponding compositions.     

南极乔治王岛与象岛邻近海域表层沉积硅藻组成及分布特征

本文对“第33次南极科考—海洋六号航次”在乔治王岛南侧、象岛西侧海域内通过箱式取样获得的表层沉积物样品进行了硅藻组成和分布特征的研究。主要统计了硅藻丰度、简单分异度、属种组成等, 并结合沉积物粒度数据进行分析, 结果表明乔治王岛南侧站位丰度和分异度高于象岛西侧站位, 最高丰度达到1.96×106壳/g。丰度的差异分布可能主要与洋流有关, 别林斯高晋海表层洋流带入充足营养盐导致乔治王岛南侧站位硅藻繁盛, 而威德尔海涡流底层水影响下的象岛西侧站位则难以沉降保存包括硅藻壳体在内的细小沉积颗粒。各站位硅藻组成的差异主要体现在海冰相关种分布不均和半咸水种类繁盛情况等, 前者可能与漂浮海冰控制的时间长短有关, 而后者与淡水输入等综合环境因素有关。     

Late Holocene paleoenvironment in northern New Caledonia, southwestern Pacific, from a multiproxy analysis of lake sediments

Lithostratigraphic and palynological analysis of two cores recovered from the ‘Grand Lac’ (New Caledonia), combined with 35 ¹⁴C AMS dates, yields a paleoenvironmental record spanning the last 2000 yr. The lithology is represented mainly by clayey or laminated layers. A catastrophic event, which is marked by very coarse deposits, occurred probably between ca 1070-960 cal yr B.P. and possibly is associated with an unusually severe La Niña event. Before and after this event, a similar combination of the two main sediment types is recorded. The repeated alternation of laminated and clayey layers is interpreted as the response to local hydrologic forcing, which may reflect a shift from relatively wet to relatively drier conditions, respectively. Variable amount of micro-charcoal is detected all along the profile. Without additional evidence, notwithstanding the initial local human settlement documented since ca 2900 ¹⁴C yr B.P., micro-charcoal occurrence and variability cannot be linked directly to an anthropogenic origin. No distinct palynological zonations in relation to the lithology are observed, and the vegetation changes may only represent minor transitions across environmental limits.     

The importance of radiocarbon dates and tephra for developing chronologies of Holocene environmental changes from lake sediments,North Far East

Developing continuous chronologies of paleoenvironmental change in northern areas of the Far East using ¹⁴C can be problematic because of the low organic content in lake sediments. However, Holocene age-models can be supplemented by widespread tephra deposits reported in the Magadan region. The best documented of these tephras has been correlated to the KO tephra from southern Kamchatka dated to 7600 BP. Although a key chronostratigraphic marker, no detailed compendium of the distribution of this tephra and its associated ¹⁴C dates has been available from sites in the northern Far East. We provide such a summary. Known locally as the Elikchan tephra, lake cores indicate an ash fall that extended ~1800 km north of the Kamchatkan caldera with a ~500 km wide trajectory in the Magadan region. Other Holocene tephras preserved in lake sediments have poorer age control and possibly date to ~2500 BP, ~2700 BP and ~6000 BP. These ashes seem to be restricted to coastal or near-coastal sites. A single record of a ~25,000 BP tephra has also been documented ~100 km to the northeast of Magadan.     

Paleoclimatic implications of an early Holocene glacier advance on Disko Island, West Greenland

The paper describes studies of glacial deposits and raised beaches on the island of Disko. West Greenland. Two stades in the glacial history are defined, the Godhavn stade, which represents the last major glaciation on Disko, and the Disko stade, which defines a Preboreal readvance. During the Godhavn stade, only eastern and southern Disko were affected by the extended Inland Ice, while glaciation on western and northern Disko was local in character. In connection with the deglaciation, the sea transgressed to the marine limit at c. 9,250-9,000 BP. Immediately before, tentatively culminating around 9,300 BP, a significant readvance of glaciers on eastern Disko occurred. The marine limit rises on a transect from northwest to southeast across Disko from 60 m a.s.l. to 90 m. The paper discusses changes in equilibrium line altitude (ELA) during the deglaciation, and explains the Disko stade readvance in terms of variations in upper-air wind conditions.     

南极乔治王岛中——新生代岩浆岩Sr—Nd—Pb同位素组成及源区特征

对乔治王岛１１个火山岩和２个侵入岩样品做了Ｓｒ－Ｎｄ－Ｐｂ同位素分析，其中（８７Ｓｒ／８６Ｓｒ）ｉ＝０．７０３２６～０．７０３９２，εＮｄ＝３．０２～６．７２，２０６Ｐｂ／２０４Ｐｂ＝１７．７７６～１８．５１５，２０７Ｐｂ／２０４Ｐｂ＝１５．．５０６～１５．５７１，２０８Ｐｂ／２０４Ｐｂ＝３７．８６８～３８．３０８。根据以上同位素组成及其相互关系并结合岩石学和微量元素特征及火山岩中熔融包裹体成分，得出以下结论：（１）研究的乔治王岛岩浆岩起源于亏损地幔（ＤＭＭ）和地幔流体交代成因的富集地幔ＥＭＩ混合形成的源区；（２）该源区具有广义Ｄｕｐａｌ异常，它正是由于ＥＭＩ组份加入即通过流体交代作用而产生的；（３）流体主要是俯冲深海沉积物脱碳酸盐作用而释放出的富ＣＯ２流体。     

New Discovery of the Early Cretaceous Volcanic Rocks on the Barton Peninsula, King George Island,Antarctica and Its Geological Significance

Ages determined with the 40Ar/39Ar isotopic system affirms the Early Cretaceous volcanic activity in the Barton Peninsula, King George Island, Antarctica. Two specimens of basaltic andesite collected from the lowermost volcanic sequence of the peninsula were irradiated and analyzed in different experiments, yielding an identical age spectrum, and two magmatic thermal events of the Early Cretaceous (120.4± 1.6 Ma, 119± 1 Ma) and Early Tertiary (53.1± 1.5 Ma, 52± 1 Ma) are distinguished. The former is interpreted to represent the primary cooling age of basaltic andesite, whereas the latter is the thermal reset age caused by the intrusion of granitic pluton. These new ages clearly indicate that volcanism was active during the Early Cretaceous on the Barton Peninsula and that intensive hydrothermal alteration and mineralization of Mesozoic volcanic rocks resulted from Tertiary magmatism.     

Dissolution and depletion of ferromagnesian minerals from Holocene tephra layers in an acid bog,New Zealand,and implications for tephra correlation

This study examines the depletion of ferromagnesian silicate minerals from a sequence of thin, distal, mainly rhyolitic tephra layers of Holocene age preserved in an acid peat bog (Kopouatai), North Island, New Zealand. The rate of such depletion has been fast, as indicated by the complete loss of biotite from one tephra layer (Kaharoa Tephra), in which it is normally dominant, in only ca. 770 yr. Chemical dissolution is advocated as the likely cause for the depletion, with amphiboles and other mineral grains commonly showing etch pits, microcaves, and other characteristic surface solution features. Theoretical thermodynamic and kinetic models show a marked increase in the rate of dissolution of all ferromagnesian minerals under conditions of low pH (< 4), but that where silica concentrations in solution are high the relative proportions of minerals remaining are unaffected. However, where concentrations of dissolved silica are low, as in most bog environments, the relative proportions of ferromagnesian minerals are affected as well as absolute amounts being decreased. Amphiboles are depleted relative to pyroxenes, consistent with kinetic studies. The results show that the identification and correlation of tephras on the basis of relative abundances of ferromagnesian minerals alone may be unreliable, and emphasise the need to use multiple criteria in such studies.     

Rate of late Quaternary ice-cap thinning on King George Island, South Shetland Islands, West Antarctica defined by cosmogenic 36Cl surface exposure dating

Glacial landforms on the Barton and Weaver peninsulas of King George Island in the South Shetland Islands, West Antarctica were mapped and dated using terrestrial cosmogenic ³⁶Cl methods to provide the first quantitative terrestrial record for late Quaternary deglaciation in the South Shetland Islands. ³⁶Cl ages on glacially eroded and striated bedrock surfaces range from 15.5±2.5 kyr to 1.0±0.7 kyr. The ³⁶Cl ages are younger with decreasing altitude, indicating progressive downwasting of the southwestern part of the Collins Ice Cap at a rate of ∼12 mm yr⁻¹ since 15.5±2.5 kyr ago, supporting the previously published marine records for the timing and estimate of the rate of deglaciation in this region.     

The deglaciation of Upernavik trough,West Greenland,and its Holocene sediment infill: processes and provenance

Under glacial climates, continental ice sheets such as, e.g., the Greenland Ice Sheet, extended onto the continental shelves and often carved out deep cross-shelf troughs. The sedimentary infill of such troughs commonly is a product of the complex interactions between the ice sheets, largely driving sediment input into the ocean, and the surrounding water masses. Off West Greenland, research has focused on the Disko and Uummannaq troughs, leaving the northerly adjacent Upernavik trough relatively understudied. Hence, neither the chronology of deglaciation nor the details of its postglacial infill are sufficiently well understood. Here, we combine computed tomography image-derived information with geochemical and granulometric data from four sediment cores recovered from the Upernavik trough that point to (i) deglaciation of the mid-shelf probably around 13.4 cal. ka BP that was most likely driven by a northward advection of warmer Atlantic waters during the Bølling–Allerød, (ii) the presence of widespread mass wasting around 8 cal. ka BP on the inner shelf and (iii) the complex interplay between various modes of sediment input, transport and deposition under hemipelagic sedimentation afterwards. While this interplay complicates provenance studies, we identify two major sediment delivery mechanisms that control transport and deposition from four sediment source areas. Through the Early Holocene the relative contributions of sediments from the various sources changed from a predominantly local origin to more southerly sources, mainly driven by decreasing input from the local sources. The integration of relative sediment source contributions with varying sedimentation rates challenges previous studies postulating intensified sediment delivery from the south through a greater influence of the West Greenland Current and highlights the need for the integration of sediment input and transport mechanisms into provenance studies in the area.     

New relative sea-level curves for the southern Scott Coast,Antarctica: evidence for Holocene deglaciation of the western Ross Sea

Here we present new relative sea-level (RSL) curves developed from Holocene-aged raised beaches along the southern Scott Coast of the western Ross Sea, Antarctica. Fifty-four dates of marine shells, seal skin and elephant seal remains incorporated within raised beaches during storms afford a chronology for these curves. All of the curves show the same pattern and timing of RSL change within a small range of error. The best-dated curve suggests that final unloading of grounded Ross Sea ice from the southern Scott Coast and McMurdo Sound region occurred shortly before 6500 ¹⁴C yr BP. This age is consistent with glacial geological evidence that places deglaciation between 5730 and 8340 ¹⁴C yr BP. Our data strongly suggest that grounding-line retreat of the Ross Sea ice sheet southward through the McMurdo Sound region occurred in mid- and late Holocene time. If this is correct, then rising sea level could not have driven ice recession to the present-day grounding line on the Siple Coast, because global deglacial sea-level rise was essentially accomplished by mid-Holocene time. Copyright © 1999 John Wiley & Sons, Ltd.     

液态下冰芯微粒含量随时间的变化-南极乔治王岛冰芯微粒研究(英)

Re-measurement of microparticle content of surface 10 m ice core from the top of King George Island Ice Cap shows that, except samples in 8. 5～ 10 m depth, the microparticle content generally decreases 45%～ 85% within first 48 hours at melted state, afterwards, the content change is small. Content at each grain size interval has a decrease, but the main decrease is in particles of <3μm. Though particle content varies with depth, the decreases are much larger in peak areas than in valleys. From the tests, it can be considered that, the reason of particle content decrease at melted state is that some sea salt grains in samples dissolved. The microparticle content of samples in 8. 5～ 10 m depth has not decrease, the reason is that melting and re freezing have occurred at the depth, because the ice temperature is near 0 °C, and there are series of ice layers, the thickest is 7 cm, at that depth. The chemical analyses for same samples at same conditions show that, except irregular changes in NH4,NO, there are small changes in other ions, probably the content changes in micro-grain <3 μm can not obviously cause the chemical content change in samples.     

末次冰消期以来东海内陆架沉积物地球化学特征及其古环境意义

尝试对末次冰消期以来东海内陆架沉积物地球化学特征及其蕴含的古环境、古气候信息进行探讨。对位于浙-闽沿岸泥质沉积中心附近的EC2005孔岩性、粒度、常量元素、矿物以及AMS^14C测年数据进行了综合分析,得出以下主要结论：（1）东海内陆架沉积物不同常量元素与TiO2的比值具有不同的环境、气候意义,SiO2、Na2O与TiO2的比值可以用来反映沉积水动力条件的强弱,Al2O3、Fe2O3、MgO、K2O、MnO以及下部湖相沉积层中的CaO、P2O5与TiO2的比值则主要反映了沉积物源区的变化以及与风化程度相关的源区气候变化。（2）研究区自17．3k。BP以来沉积环境经历了剧烈变化,岩芯底部60．20m至41．00m（17．3～13．1kaBP）为湖泊三角洲沉积序列,海水自13．1kaBP开始侵入研究区,形成了41．00m的海相沉积地层。自12．3kaBP研究区受到沿岸流影响,7．3ka BP以来稳定的泥质沉积体开始形成。（3）自末次冰消期初期至末期,气候总体向暖湿方向发展,新仙女木事件、8．2k。冷事件在本孔中有明显的记录,显示出全球性重要气候事件在中纬度浅海陆架海域的区域性响应。