Ultimate grout-to-soil bond strength of micropiles in glacial deposits

Acta Geotechnica - This paper analyzed the ultimate grout-to-soil bond strength based on a database of 40 full-scale static load tests conducted on micropiles in glacial deposits in the province of...     

Sedimentology of glacial and glacial marine deposits on the George V-Adelie continental shelf, East Antarctica

Mineralogic and textural data suggest that glacial ice derived from the region of the present day Cook Ice Shelf extended to the edge of the d'Urville Sea continental shelf. As part of this glacial maximum, basal tills and glacial marine sediments were deposited over an irregular subglacial surface. Extensive redeposition of eroded material took place in the middle and outer portions of the continental shelf. Retreat of glacial ice was relatively rapid and was associated with widespread deposition of a thin residual glacial marine unit and turbidity current deposits in the far western and eastern parts of the region. Today, sedimentation on the continental shelf of the d'Urville Sea is controlled by biogenic and physical oceanographic processes. Deposition of ice-rafted detritus from icebergs undoubtedly occurs but is relatively insignificant. Glacial advances along this periphery of East Antarctica appear to the regulated by adjacent outlet glaciers rather than direct advance of the grounded ice sheet.     

Palaeolatitude of glacial deposits and palaeogeography of Neoproterozoic ice ages

At the end of the Neoproterozoic, the Earth may have experienced important environmental changes, with a transition between two supercontinents (from Rodinia to Gondwana), extensive glaciations with ice caps reaching the Equator and the beginning of metazoan diversification. In such a context, the palaeomagnetic record can be used to constrain both the palaeogeography and the palaeoclimate (palaeolatitudinal distribution of glacial deposits). Here we present an up-to-date geochronological and palaeomagnetic database for the Neoproterozoic glacial deposits, including poles recently obtained on ‘cap carbonates’ from China, Oman, and Amazonia. The database comprises ten poles (from eight different cratons), obtained directly on the glacial deposits or on the overlying ‘cap carbonate’, and two other palaeolatitudes derived from reference poles coeval to well-dated glacial units in the same craton. The occurrence of glacial deposition at low latitudes (<30 °) is attested by some good-quality poles, two of them well dated at ∼740 and ∼635 Ma. Based on these poles and on reference poles obtained on igneous rocks, tentative palaeogeographic reconstructions for ∼750, ∼620, and ∼580 Ma (ages for which the database has limited but still sufficient entries) were performed in order to investigate the tectonic context within which the glacial events were produced.     

Fossil remnants of up-turned debris bands in Pleistocene glacial deposits of Poland

Fossil remnants of up-turned debris-rich bands of glacial ice are recorded from three localities in the Polish Lowlands. In each case the fossil debris bands occur in proximal parts of hills built of glacitectonically disturbed sediments. The characteristics of these remnants and of the associated deposits and structures are described, and they are compared to present-day examples from Spitsbergen.     

Lichenometry in dating recent glacial landforms and deposits, southeast Iceland

Lichenometry curves were derived for the glacier forelands of Breidamerkurjokull and Skalafellsjökull using measurements of the collective species, Rhizocarpon geographicum , from independently dated surfaces deglaciated during the period since the late-19th century ice maximum episode in the area. The form of the curves appears to be linear. Several methods of predicting the ages of undated surfaces were compared for specific test examples, including single lichenometry curves, families of curves and multiple curves based on randomly selected largest lichens. The last method provided a useful means of assessing the reproducibility of predicted ages. Where substrate conditions were highly variable, a lichenometry curve based on single largest lichens provided a preferred result.     

基于数字图像处理技术的冰川堆积物粒度分析——以川西贡嘎山冰川堆积物为例

冰川堆积物的粒度组成在很大程度上控制了其物理力学性质,但常规试验无法得到连续的冰川堆积物的粒度组成数据。应用数字图像处理技术和室内试验相结合的分析方法,首先借助图像处理技术,对冰川堆积物剖面的砾石形态进行分析,获取粗粒部分(>2cm)的粒度组成,然后采用室内颗分试验获得细粒(<2cm)部分的粒度组成,将2类粒度数据进行叠合即可获取连续的冰川堆积物的粒度组成。结果表明：研究区冰川堆积物的粒度组成极不均匀且颗粒分析曲线呈现多峰性,具有良好的级配和工程性质;冰川堆积物的粒度组成、砾石形态和排列特征都有很好的分形特征。     

The high-level marine shell-bearing deposits of Clava, Inverness-shire, and their origin as glacial rafts

The enigmatic high-level, till-covered, cold water marine shell-bearing deposits at Clava, Inverness-shire, are described systematically in the light of new observations made at sites documented in the literature. The marine deposits, named here as the Clava Shelly Formation, include three members, the unfossiliferous Clava sand, the underlying Clava shelly clay and a shelly diamicton known as the Clava shelly till. The first two members form a conformable coarsening-upwards sequence containing a shallow water, high-boreal to low-Arctic fauna and flora. The Clava shelly till is essentially glacially re-sedimented glaciomarine clay containing a sparse fauna, but its stratigraphic relationship and age are not absolutely clear. The shelly clay is ascribed to a Mid-Devensian interstadial episode on the basis of amino-acid dating.It is concluded that the Clava shelly clay, and several discrete masses of Clava sand and shelly till, are glacially transported allochthons derived from the Great Glen. The rafts were probably detached as a result of high pore water pressure building up in laterally restricted aquifers beneath a confined glacier that flowed north-eastwards across the Loch Ness basin. This glacier was deflected eastwards and upwards towards Clava by ice flowing from the northern Highlands along the Beauly Firth during the build-up of the last Scottish ice-sheet. The rafts were stacked at the ice margin when the glacier entered the Nairn Valley before being overriden by the expanding ice-sheet.     

基于数字图像处理技术的冰川堆积物粒度分析——以川西贡嘎山冰川堆积物为例

冰川堆积物的粒度组成在很大程度上控制了其物理力学性质,但常规试验无法得到连续的冰川堆积物的粒度组成数据。应用数字图像处理技术和室内试验相结合的分析方法,首先借助图像处理技术,对冰川堆积物剖面的砾石形态进行分析,获取粗粒部分(>2cm)的粒度组成,然后采用室内颗分试验获得细粒(<2cm)部分的粒度组成,将2类粒度数据进行叠合即可获取连续的冰川堆积物的粒度组成。结果表明：研究区冰川堆积物的粒度组成极不均匀且颗粒分析曲线呈现多峰性,具有良好的级配和工程性质;冰川堆积物的粒度组成、砾石形态和排列特征都有很好的分形特征。     

Jet-efflux deposits of a subaqueous ice-contact fan,glacial Lake Rinteln,northwestern Germany

The coarse-grained, ice-contact, Porta Subaqueous Fan/Delta Complex was deposited in glacial Lake Rinteln at the margin of the Saalian ice sheet that advanced south of the Weser Chains, NW Germany. The ice-proximal depositional system was up to 15 km long and 10 km wide. The present study deals with ice-proximal subaqueous fan deposits, which are interpreted as products of a subcritical plane-wall outflow jet that periodically passed into a supercritical jet with hydraulic jump. The proximal facies assemblage consists of the coarse, clast-supported gravelly deposits of a hyperconcentrated (high-density) effluent and of related cohesionless debris flows attributed to the conduit or immediate proximal jet outflow zone of flow establishment. The intermediate facies assemblage, attributed to the outflow jet proximal zone of flow transition, is dominated by normally graded and cross-stratified gravels with scour structures at their bases; these gravels were deposited by a high-density effluent capable of forming mouthbar-like features. These deposits pass downcurrent into an assemblage of planar parallel-stratified and planar and trough cross-stratified sands and pebbly sands (partially interpreted as antidunes), with abundant scour structures and intercalated layers of fine sand/silt and silty mud, attributed to the jet distal zone of flow transition. The distal facies assemblage consists of trough cross-stratified sands and pebbly sands, and is attributed to the outflow jet proximal zone of established flow. The sedimentary succession as a whole has wedge-shape geometry, with a gentle fan-shaped inclination of the bedding from the southeast to the southwest. Repeated vertical alternations of supercritical and subcritical deposits and muddy interlayers can be attributed to temporary fluctuations in the meltwater outflow, whereas the overall upward fining of the succession indicates a net decline of meltwater discharges.     

Pleistocene glacial deposits along the eastern periphery of the Scandinavian ice sheets - an overview

The Quaternary glacial sequences in the Baltic region in Estonia. Latvia and Lithuania are relatively complete and reasonably well studied. The maximum thickness of deposits (200 300 m) is found in the uplands and ancient valleys. Tills of several genetic types have been described and in this paper the present view on the structure of the Pleistocene cover is given. The ice movement and glacial sedimentation were controlled by climate. underlying topography and tectonic processes.     

On the nature of lead–lag relationships during glacial–interglacial climate transitions

Analysis of leads and lags between different paleoclimate records remains an important method in paleoclimatology, used to propose and test hypotheses about causal relationships between different processes in the climate system. The robust lead of Antarctic temperature over CO₂ concentration during several recent glacial–interglacial transitions inferred from the Antarctic ice cores apparently contradicts the concept of CO₂-driven climate change and still remains unexplained. Here, using an Earth system model of intermediate complexity and generic scenarios for the principal climatic forcings during glacial–interglacial transitions we performed a suite of experiments that shed some light on the complexity of phase relationships between climate forcing and climate system response. In particular, our results provide an explanation for the observed Antarctic temperature lead over CO₂ concentration. It is shown that the interhemispheric oceanic heat transport provides a crucial link between the two hemispheres. We demonstrate that temporal variations of the oceanic heat transport strongly contribute to the observed phase relationship between polar temperature records in both hemispheres. It is shown that the direct effect of orbital variations on the Antarctic temperature is also significant and explains the observed cooling trend during interglacials. In addition, an imbedded δ¹⁸O model is used to demonstrate that during glacial–interglacial transitions, the temporal evolution of deep calcite marine δ¹⁸O in different locations and at different depths can considerably deviate from that implied by the global ice volume change. This finding indicates that the synchronization of different marine records by means of foraminiferal calcite δ¹⁸O yield large additional uncertainties. Based on our results, we argue that the analysis of leads and lags alone, without a comprehensive understanding and an adequate model of all relevant climate processes, cannot provide direct information about causal relationships in the climate system.     

Dislocated Quaternary deposits in southeastern Kattegat – a glacial or gravitational phenomenon?

The Quaternary deposits in the Store Middelgrund–Rørdebanke area midway between the island of Anholt and Hallandsåsen on the Swedish coast are described on the basis of reflection seismic profiles with a vertical resolution of 5–10 m. The Quaternary rests on Upper Cretaceous limestone, the surface of which is nearly horizontal. Three Quaternary sequences are defined and interpreted as: (1) Late Weichselian marine or lacustrine deposits, (2) Late Weichselian glaciogenic deposits, and (3) Late Saalian–Eemian and Early–Middle Weichselian deposits. Sequence 3 is probably comparable to the upwards-coarsening sequence known from Skaerumhede in Vendsyssel. The layers in sequence 3 are dislocated in the eastern part of the Store Middelgrund–Rødebanke area mainly by gentle folding, but other types of deformations occur. Folding could be the result of horizontal push from an ice sheet approaching from the east. Alternatively the folding is an effect of vertical, gravitational forces acting on the sediments due to an unstable density profile, as described by the Rayleigh–Taylor instability model. The zone of deformation is located close to the northern flank of the tectonically active Sorgenfrei–Tornquist Zone. It is suggested that the initiation of the folding process was facilitated by tremors from small earthquakes.     

Stratigraphy and sedimentology of Devensian (Dimlington Stadial) glacial deposits,east Yorkshire,England

The stratigraphy and sedimentology of the glacial deposits exposed along the coast of east Yorkshire are reviewed. Critical sections at Filey Brigg, Barmston and Skipsea are examined to reassess the stratigraphy of Devensian Dimlington Stadial glacial deposits in the light of recent developments in glacial sedimentology. Sedimentary and glaciotectonic structures studied in the field and by using scanning electron microscopy are emphasised. Two hypotheses are considered for the genesis of the interbedded diamictons and stratified sediments. The first involves the deposition of lodgement till and/or deformation till followed by meltout till, which was overridden to produce more deformation till, reflecting periods of ice stagnation punctuated by glacier thickening. The second hypothesis, which is favoured on the basis of field evidence and micromorphology, involves the vertical accretion of a deforming till layer associated with cavity/channel or tunnel valley fills, beneath active ice. At Barmston the upper part of the diamicton contains elongate pendant structures containing gravels, indicating that the diamicton was saturated and able to flow. The diamictons, therefore, represent a complex sequence of tills deposited and deformed by active ice during the Dimlington Stadial. Previously published stratigraphical schemes involving classifications of multiple tills in east Yorkshire should be simplified and it is more appropriate to assign these to a single formation, the Skipsea Till Formation. Rhythmic glaciolacustrine and proglacial glaciofluvial sediments overlie the tills at Barmston and Skipsea. These were deposited in sag basins during deglaciation as the tills settled and deformed under thickening sediment and as buried ice melted out. Extensive sands and gravels cap the succession and were deposited on a sandur during the later stages of deglaciation.