Sedimentology,geochemistry, and biota of Volgian carbonaceous sequences in the northern part of the central Russian Sea (Kostroma region)

Lithological, geochemical, stratigraphic, and paleoecological features of carbonaceous sediments in the Late Jurassic Volgian Basin of the East European Platform (Kostroma region) are considered. The shalebearing sequence studied is characterized by greater sedimentological completeness as compared with its stratotype sections in the Middle Volga region (Gorodishche, Kashpir). Stratigraphic position and stratigraphy of the shale-bearing sequence, as well as the distribution of biota in different sedimentation settings, are specified. It is shown that Volgian sediments show a distinct cyclic structure. The lower and upper elements of cyclites consist of high-carbonaceous shales and clayey-calcareous sediments, respectively, separated by transitional varieties. Bioturbation structures in different rocks are discussed. Microcomponent composition and pyrolytic parameters of organic matter, as well as distribution of chemical elements in the lithologically variable sediments are analyzed. Possible reasons responsible for the appearance of cyclicity and accumulation of organicrich sediments are discussed.     

Proglacial glaciotectonic deformation associated with glaciolacustrine sedimentation,Lake Pukaki,New Zealand

The Quaternary glaciogenic sediments exposed on the southwest shore of Lake Pukaki were investigated. The sections consisted of the Pukaki Diamicton, which is composed of four lithofacies: (i) homogeneous facies (PDH)—a grey matrix-supported homogeneous subglacial diamicton; (ii) coarse facies (PDC)—a very coarse matrix-supported diamicton, which was interpreted as a proximal glaciolacustrine sediment; (iii) laminated facies (PDL)—a cream coloured, fine-grained, matrix-supported diamicton, with grade laminations of silt, sand and gravel, interpreted as a more distal glaciolacustrine facies; and (iv) fine facies (PDF)—a cream coloured fine-grained, silt-rich matrix-supported diamicton, with lenses of sand and gravels, which was interpreted as the most distal glaciolacustrine facies. It is suggested that these sediments were produced by two small ice advances during a period of general retreat. Furthermore, the sections showed a combination of three types of glaciotectonic deformation; gravity tectonics, proglacial glaciotectonics and subglacial glaciotectonics. Two of the moraines showed an unusual style of glaciotectonic deformation, i.e. proglacial deformation on the proximal face and gravitational slumping on the distal face. It is suggested that this style of deformation is diagnostic of proglacial deformation into a waterbody associated with a retreating margin.     

Subglacial processes and drumlin formation in a confined bedrock valley,northwest Ireland

Knight, J. 2010: Subglacial processes and drumlin formation in a confined bedrock valley, northwest Ireland. Boreas, 10.1111/j.1502‐3885.2010.00182.x. ISSN 0300‐9483. Subglacial processes beneath the Late Weichselian ice sheet in northwest Ireland are deduced from sediments and structures within drumlins in a bedrock valley at Loughros Beg, County Donegal. Here, a glacially smoothed bedrock surface underlies the drumlins, which are composed on their up‐ice side of stacked, angular rafts of local bedrock. Overlying and down‐ice from these rafts are down‐ice‐dipping beds of massive to bedded diamicton that contain sand and gravel interbeds. In a down‐ice direction the diamicton matrix coarsens and the beds become laterally transitional to water‐sorted gravels. The down‐ice end of one drumlin shows a concentrically bedded stratified gravel core aligned parallel to ice flow and resembling the internal structure of an esker. With distance away from this core, the gravels become more poorly sorted with an increase in matrix content, and are transitional to massive to stratified diamicton. A four‐stage model describes the formation of drumlins in this sediment‐poor setting. The sediments that are located directly above the bedrock represent deposition in a semi‐enclosed subglacial cavity. A trigger for this process was the formation of subglacial relief by the thrusting up of bedrock rafts, which created the leeside cavity. Subsequent sediment deposition into this cavity represents a form of feedback (self‐regulation), which may be a typical characteristic of subglacial processes in sediment‐poor settings.     

A comparison of mineral magnetic, geochemical and mineralogical techniques for compositional studies of glacial diamictons

Data from heavy mineral analysis, X-ray fluorescence spectrometry (XRF) and X-ray diffractrometry (XRD) are compared with those obtained from mineral magnetic analysis for a range of glacial diamicton samples taken from the Quaternary sequence in the Isle of Man. These data show that the mineral magnetic approach offers a useful means of characterizing glacial sediments for purposes of lithostratigraphic correlation and provenance indication and that the magnetic data are of a comparable quality to those obtained from standard applications of the more traditional techniques. The heavy mineral and XRD data indicate that little post-depositional chemical alteration of the detrital composition of the sediments has taken place. The mineral magnetic, heavy mineral and XRF analysis suggests both similar lithostratigraphic relationships between the various diamicton units and consistent indications of their likely provenance. These are consistent with published, field-based, stratigraphic relationships of the same sediments and ice-flow directions in the Irish Sea Basin during the Devensian.     

Origin of diamictons on the Barents Sea shelf

Occurrence conditions and lithological-paleontological characteristics of two diamicton units developed in the southeastern segment of the Barents Sea shelf are considered. It is shown that they are lithologically analogous to the present-day (undoubtedly aqueous) diamicton mud. Correlation between bulk densities of both varieties and consolidation degree (consistency) is described by a single regression equation. We present pieces of evidence contradicting the widespread point of view about the diamicton as a glacial till moving along the seafloor. They are primarily represented by paleontological remains, mainly foraminiferal assemblages. It is shown that dislocations observed in cores and traditionally considered as glaciotectonic movements are confined to fault zones in the acoustic basement and they represent fragments of secondary neotectonic structures. Ridges and hills mapped previously as glacial accumulation morphostructures reflect a relict topography of the recent subaerial shelf development not masked by sedimentation so far.     

山地冰川沉积相模式与特征

山地冰川沉积研究在中国有特殊重要性。因为欧、美对冰碛沉积研究多限于大陆冰盖,沉积环境比较单纯,冰水沉积比重很大,而中国山地冰川多限于山体内部,冰水沉积极不发育,且沉积环境很复杂,亚相变化也大。此外中国山地冰川多属大陆性,与欧、美海洋性冰川在物理性质和沉积特征上都有不同。如冰川磨蚀作用弱,冰碛中粉砂少,冰上融出碛发育而流碛和滞碛不发育,原生(同生)构造如粗糙斜层很发育等。这些都将丰富冰碛沉积学内容,并对科学地鉴别中国东部各种混杂堆积的成因有重要意义。如据现代冰川沉积指标庐山就没有任何冰川堆积。     

Late Pleistocene glaciolacustrine sedimentation and paleogeography of southeastern Michigan,USA

The geomorphic, stratigraphic and sedimentological characteristics of glaciolacustrine sediments in the metropolitan Detroit, Michigan area were studied to determine environments of deposition and make paleogeographic reconstructions. Nine lithofacies were identified and paleoenvironments interpreted based on their morphostratigraphic relationships with relict landforms. The sediments studied are found southeast of the Defiance and Birmingham moraines lying beneath a lowland characterized by a low morainal swell (Detroit moraine) and a series of lacustrine terraces that descend progressively in elevation southeastward. The glaciolacustrine sediments were deposited approximately 14.3–12.4 kA BP during the Port Bruce and Port Huron glacial phases of late Wisconsinan time, and are related to proglacial paleolakes Maumee, Arkona, Whittlesey, Warren, Wayne, Grassmere, Lundy and Rouge. The glaciolacustrine section is typically 2–4 m thick and consists of a basal unit of wavy-bedded clayey diamicton overlain by a surficial deposit of stratified and cross-stratified sand and gravel. The basal unit is comprised of subaqueous debris flow deposits that accumulated as subaqueous moraine in paleolake Maumee along the retreating front of the Huron lobe. The surficial deposits of sand and gravel were formed by traction, resulting from lacustrine wave activity and fluvial processes, in lakebed plain, beach ridge and deltaic depositional settings. Much of the lake-margin sand and gravel was derived from clayey diamicton by lacustrine wave action and winnowing, and that associated with paleolakes of the Port Huron phase is largely reworked Port Bruce sediment. Paleogeographic reconstructions show that the Defiance, Birmingham and Detroit moraines, Defiance and Rochester channels, and the Rochester delta, were deposited penecontemporaneously as paleolake Maumee expanded northward across the map area. A unique type of wavy bedform is characteristic of clayey diamicton deposited by subaqueous mass flow in the study area that is useful for differentiating sediment: 1) deposited by mass flow in subaqueous vs. subaerial settings, and 2) deposited by subaqueous mass flow vs. basal till. These bedforms are a useful tool for identifying subglacial meltwater deposits, and facilitate the mapping and correlation of glacial sediments based on till sheets. The map area provides a continental record of ice sheet dynamics along the southern margin of the Laurentide ice sheet during Heinrich event H-1. The record reveals rapid glacial retreat (～ 0.8 km/yr) contemporaneous with the discharge of a large volume of meltwater. Evidence in the study area for subglacial meltwater is problematic, but indications that periglacial conditions persisted in the map area until ～ 12.7 kA BP, and extended for 200 km or more south of the ice front suggest that a frozen substrate may have contributed to instability of the LIS.     

Glaciodynamically upthrusted bands of englacially transported debris in the Pleistocene of central Poland

Two kinds of buried structures are described from Dzirżenin, north-east of Warsaw, where they occur within a glaciofluvial landform: (1) narrow till ridges, showing vertically oriented structures, excavated from stratified gravel and sands; and (2) a narrow vertical zone of massive gravelly/sandy material, involving vertically oriented lens-like layers composed of massive sand with pebbles, or of diamicton. The gravelly/sandy zone is also closely surrounded by stratified glaciofluvial sediments. In spite of their vertical position and internal deformation, the till ridges and gravelly/sandy zone show non-tectonic contacts with the surrounding, stratified, undisturbed sediments. The glaciofluvial sediments that occur immediately next to the structures under discussion are characterized by the occurrence of comparatively coarse material and interbeddings of diamicton, which wedge out away from these structures. The gravelly/sandy zone separates different kinds of water-laid deposits. The buried structures are interpreted as former debris-laden bands, thrust upwards within the frontal part of the ice sheet and then transformed into still-frozen debris ridges projecting over the already dead ice. Further melting of the decaying ice resulted in abundant glaciofluvial sedimentation, and the debris ridges also supplied material for the deposition of the neighbouring stratified deposits. One of the ridges separated different glaciofluvial environments. The glaciofluvial sediments completely buried the ice-cemented ridges, which were finally transformed by a melting-out process into the till ridges and the gravelly/sandy zone. The former are interpreted as having been transformed from upturned debris-laden bands with a high concentration of debris or from the bands composed of frozen-up sediment slabs. The gravelly/sandy zone is interpreted as having (most probably) been deposited from upturned bands characterized by a lesser concentration of debris.     

Brecciated diamictons from Mohawk Bay, S. Ontario, Canada

Examination of sediments along the north shore of Lake Erie at Mohawk Bay reveals a relationship between the formation of intensely brecciated diamictons and the presence of sand-block intraclasts. It is postulated that the sand blocks were subglacially deposited within a meltwater environment, and later frozen prior to being eroded and transported within a mobile subglacial debris layer. On immobilization the frozen sand blocks, encased within the diamicton, acted as a heat sink creating cryostatic stresses within the surrounding diamicton as a result of the advance of a frost front and related frozen ‘fringe’. The effect of these anisotropic stresses resulted in porewater migration to the frost front. Subsequent development of intense brecciation occurred as aureoles around the sand intraclasts due to localized high tensile stresses causing fracturing within the fine-grained matrix of the diamicton.     

金沙江金坪子堆积体形成过程对青藏高原东缘构造、气候的响应

金坪子堆积体位于金沙江河谷之中,处在＂康滇地轴＂的中部,类似一个大滑坡体。通过对金坪子堆积体的数字高程模型（DEM）、12个钻孔、1个平硐和1个竖井资料的分析,以及实地调查,对金坪子堆积体的沉积物进行沉积学、年代学和岩石地层学等多学科的研究。金坪子堆积体由12层不同的沉积物和8个地貌单位组成,其中1～9层为古金沙江河流...     

Stratigraphy and palaeoecology of a possible interglacial site,northernmost Ellesmere Island,Canada

An extensive stratigraphic section at Cape Alfred Ernest on the Wootton Peninsula, northwest Ellesmere Island contains six lithofacies which appear to record two glacial phases separated by an organic layer. (1) A lower massive gravel records a pre-ice advance outwash phase; (2) massive fine-grained sediments record a period of non-glacial marine deposition when sea-level was higher than present; (3) a massive diamicton records the advance of ice across the site; (4) intermediate stratified beds record supraglacial and proglacial outwash, and include an organic layer; (5) massive diamicton grading down-valley to stratified diamicton and then massive, sheared diamicton, overlain by laminated fine-grained sediments with dropstones, recording the last (late Wisconsinan) glaciation; (6) upward-coarsening sands and gravels record proglacial outwash and grade to raised marine deltas. Radiocarbon dates of 39270 ± 640 and > 51000 yr BP were obtained on samples from the organic layer by accelerator mass spectrometry and conventional radiocarbon dating, respectively. Palaeoecological data suggest that the organics accumulated in a wet sedge meadow environment when the climate was warmer than present. Stratigraphic considerations suggest that the organic layer represents an interglacial interval which, if valid, indicates that the site constitutes the northernmost interglacial stratigraphy in the Canadian Arctic. Alternatively, the organic layer may date to Plio-Pleistocene times.     

滇东南沱冰期质疑

本文较详细地研究了滇东南沱组紫红色杂砾岩的特征,认为它不是冰碛岩,而是泥石流堆积物。其形成环境以小江断裂为界,可大致划分为泥石流沟和泥石流扇两个亚相。古气候的分析结果表明.南沱冰期很可能不存在。     

Glacigenic clast fabrics: genetic fingerprint or wishful thinking?

The interpretation of glacigenic diamictons is a subjective process, for which quantitative support is frequently sought from parameters such as clast shape and fabric. It has been widely suggested that different glacigenic diamicton facies possess distinct clast‐fabric signatures. This paper examines this concept using a data set of 111 clast fabrics, and a synthesis of published results. Eigenvalues are calculated and compared for a variety sedimentary facies. It is concluded that clast fabric alone is not able to discriminate between different glacigenic facies, and it is argued that clast fabric offers little quantitative support in the interpretation of glacigenic sediments. It is suggested, therefore, that although clast fabric may continue to have a role as an indicator of relative strain at specific sites, its use in the discrimination of glacigenic facies is limited. Consequently, we should be much more selective in undertaking such analyses in the future. Copyright © 1999 John Wiley & Sons, Ltd.     

Sedimentology and history of a Late Wisconsinan glacial lake, Grande Prairie, Alberta, Canada

The Grande Prairie region of northwestern Alberta was partially covered by glacial Lake Peace, which was dammed against the retreating Laurentide ice sheet. Two levels of glacial Lake Peace are identified in the study are by closely spaced groups of strandlines and minor deltas lying at 805 to 840 m a. s. l., and 655 to 710 m a.s.l. Sedimentation associated with the upper of the two lake levels is marked by rhythmites of silt and clay deposited by turbid underflow, interbedded with diamicton deposited by debris flow. Dropstones and dump structures indicate common ice-rafting. Thick sequences are only found on the axes of major valleys, where sediment gravity flows were concertrated. Thin sequences of ice proximal glaciolacustrine sediments reflect topographic setting and do not indicate a short-lived lake. Retreat of the ice front resulted in a decrease in ice-rafted material and diamicton in sediments. The fall in lake level to the second stage resulted in deposition of sequences of vaguely laminated silt and clay close to the modern Beaverlodge River. These sediments were deposited by suspension settling from interflow or overflow of the Beaverlodge River as it entered the lake. Lake sedimentation was dominated by inflow from unglaciated areas, rather than the ice front.     

Glacial sedimentary processes and environmental reconstruction based on lithofacies

Glacigenic sediments exposed in pits around Villeneuve, near Edmonton, Alberta, are subdivided into facies based on grain size, sedimentary structure, glacially-induced deformation and faulting, and groove marks. Two diamicton facies are recognised, one of which is interpreted as a primary till, deposited directly from glacier ice, and the other as a product of mass-movement. The diamicton facies are closely associated with current bedded facies interpreted as fluvioglacial deposits. The stratigraphic sedimentological and tectonic aspects of these fluvial deposits suggest subglacial deposition in channels and cavities. At any one place the glacier appears to have alternated between being attached to the bed, causing thrusting and sole marking, and being separated from the bed by a cavity in which fluvial and mass-movement sediments accumulated. The net result is a highly complex and laterally variable stratigraphy produced by a single glacial advance. The correct interpretation of such sequences is essential if lithostratigraphy is to be used to establish glacial history. In addition, the interpretations presented here have implications regarding the formation of soft zones in ‘till’. They indicate that the soft zones are beds of sorted sediment redeposited by mass-movement.     

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.     

Fluvial deposits within the Pleistocene Crag at Thorpe St Andrew,Norwich, England

This paper records the findings at a temporary exposure at Thorpe St Andrew near Norwich, Norfolk, UK in Early and early Middle Pleistocene Crag deposits. The British Geological Survey (BGS) describes the particular formation exposed as Norwich Crag consisting of Early Pleistocene shallow marine sediments. The section shows a succession of sorted sands and gravels overlain by a sandy diamicton. Based on field evidence and clast analysis, the sands and gravels are interpreted as the product of point bar and overbank sedimentation and represent the product of a river cutting into and aggrading within the more widespread shallow marine deposits. Composition of the sediments indicates derivation, primarily from Wroxham Crag Formation, with a contribution from Norwich Crag. The sandy diamicton is interpreted as late Middle Pleistocene Corton Till that is recorded in the area. A distinct pattern of colour changes at the top of the sands and gravels is interpreted as a soil that developed on the fluvial sediments before being overridden by the glacier that deposited the Corton Till. The existence of the fluvial sediments within the regional shallow marine deposits suggests that a fall of sea-level, possibly due to climate cooling, while the elevation of the sediments and the adjacent Crag implies that the site has been uplifted since sedimentation. This is the first observation of terrestrial sediments within the shallow marine Crag. The paper also makes a contribution to understanding the diagenetic processes that give deposits within this region some distinctive colour and sediment patterns.     

伊洛瓦底盆地D区块及周缘古近系物源分析

缅甸D区块是伊洛瓦底盆地中西部与Letpanto油田相邻的区块, 具有一定的油气勘探潜力, 对物源方向的认识存在不同观点。笔者利用沉积物砾石成分、砂岩骨架成分、地球化学元素分析方法, 旨在明确伊洛瓦底盆地D区块及周缘古近纪物源方向和类型, 进而指导本区沉积相与油气资源勘探研究。砾石分析结果显示, 存在自西向东方向的物源, 古新世物源来自中、酸性火成岩, 始新世来自浅变质岩、中性及基性火成岩。砂岩骨架成分分析显示, 古近纪地层物源均来自弧造山带, 既有大陆切割、未切割、过渡型岛弧来源, 也有再旋回造山带来源。主量、微量、稀土元素分析结果判断物源区构造背景均属于大陆岛弧和主动大陆边缘, 具有安山岩物源区特征。综合分析认为, 本区古近纪物源演化具有一定继承和相似性, 物源主要来自盆内链状岛弧和东部掸邦高地, 喜马拉雅造山带不可能从北部直接提供物源。推测北部喜马拉雅造山带通过伊洛瓦底江从东部进入, 为盆地提供物源。