Palynology of organic beds below Devensian glacigenic sediments at Pen-y-bryn,Gwynedd, North Wales

Pollen diagrams from organic facies overlain by glacigenic sediments at Pen-y-bryn, North Wales (53°7′N, 4°16′W), suggest that it is the first locality in the British Isles to provide evidence for several Devensian interstadials prior to Devensian stadial glaciation(s). The evidence is not, however, unequivocal. At least two main episodes of organic sedimentation are indicated, separated by an interval of uncertain duration. One eposide records a Pinus-Picea-Betula forest. A second, possibly later, event, with tree pollen less than 10% of total land pollen (TLP), suggests a cool, largely unforested environment. A third episode, with tree pollen up to 25% of TLP, may be related to the latter or be of intermediate age, whereas a fourth and later episode of organic accumulation may be of reworked material. Radiocarbon dating of organic deposits and of a wood macrofossil enclosed in basal till is inconclusive, as is preliminary uranium-series dating. The principal biogenic episodes may correlate with Oxygen Isotope Substages 5c and 5a, but as the pollen records reflect facies floras, the correlation remains tentative; it is also possible that other temperate periods are recorded. Further resolution of the chronostratigraphy is required to help clarify the problematic correlation of interstadial and stadial events in northwest Europe and to correlate more accurately the biogenic and glacigenic facies at Pen-y-bryn with their Pleistocene equivalents elsewhere.     

Exploring till bed kinematics using AMS magnetic fabrics and pebble fabrics: the Weedsport drumlin field,New York State,USA

Gentoso, M. J., Evenson, E. B., Kodama, K. P., Iverson, N. R., Alley, R. B., Berti, C. & Kozlowski, A. 2012 (January): Exploring till bed kinematics using AMS magnetic fabrics and pebble fabrics: the Weedsport drumlin field, New York State, USA. Boreas, Vol. 41, pp. 31–41. 10.1111/j.1502‐3885.2011.00221.x. ISSN 0300‐9483. Thick, relatively homogeneous basal tills exposed in the drumlins and flutes of the Weedsport drumlin and flute field in New York State exhibit anisotropy of magnetic susceptibility (AMS) and pebble fabrics that are consistently oriented parallel to the streamlined bedforms. The pebble fabrics and AMS fabrics are concordant. In this study, six drumlins and five flutes were sampled. Thermally induced, incremental reduction of isothermal remanent magnetization indicates that AMS is caused by primarily elongate maghaemite grains. The orientations of principal axes of maximum susceptibility (k₁) are generally parallel to pebble long‐axis orientations, and tend to plunge mildly up‐glacier. Fabric directions are generally parallel to drumlin long‐axis orientations, but deviate by 12°–23° from flute directions. Fabrics of the flutes are stronger and more unidirectional than those of the drumlins. These results support the use of AMS as a fast and objective method for characterizing fabrics in tills, and suggest hypotheses about basal processes linked to glacially streamlined landforms.     

在陆相咸水沉积物中检出Δ5甾醇化合物及其生源意义探索

利用GC／MS分析技术在塔5井、官77井和狮23井下第三系陆相咸水沉积物样品中检测到了丰富的Δ^5-甾醇类化合物，并对其进行了定性研究，鉴定出19个化合物，碳数范围为C23－C31，丰度最高的化合物为24－乙基胆甾－5－烯－3β醇，占甾醇总量的75％左右。样品的母质类型甾醇的分布特征表明，样品中丰富的C29甾醇可能主要来自于咸水环境中的某种藻类而非陆源物质。     

现代河流沉积物碎屑及矿物组分研究新进展

现代河流沉积物忠实地记录了流域盆地内的母岩、风化、搬运和沉积过程中的化学、物理过程以及人类活动的改造作用,是探索和验证源- 汇系统等理论的重要媒介。本文以全球现代河流砂组分数据库为基础,总结了碎屑组分、重矿物组分在不同大陆的分布特征,探讨了其在物源识别、源区贡献率计算、沉积物产生及搬运过程中气候- 构造等影响因素的评估、对源- 汇系统的研究启示等方面的应用。今后建议加强基于大数据的沉积物组分对气候- 构造- 人类活动的响应、沉积物产生及通量、高时间分辨率的沉积物组分变异性、不同物源定量化方法的差异等方面的研究。     

石英ESR测年法在第四纪陆相沉积物测年中的应用

电子自旋共振（ESR）测年法是近40年来逐步发展起来的第四纪年代学方法。由于它的测年范围宽、测年物质种类多等优点,特别是对于老于20万年的早中更新世没有火山灰等定年物质的样品,有着特殊的优势,引起了第四纪研究者的关注。近年来,随着对ESR法基本原理认识的深入和实验技术的提高,在测年信号心的热稳定性、晒退回零特性、辐射剂量-信号增长特性、测年可靠性等方面的研究均取得了较大进展。本文结合国内外在ESR法基础原理、测年应用等成果,简要回顾了ESR法的历史发展,以及不同信号心在第四纪地质研究中的成功应用。     

Clay mineral variations in Holocene terrestrial sediments from the Indus Basin

We employed X-ray diffraction methods to quantify clay mineral assemblages in the Indus Delta and flood plains since ~ 14 ka, spanning a period of strong climatic change. Assemblages are dominated by smectite and illite, with minor chlorite and kaolinite. Delta sediments integrate clays from across the basin and show increasing smectite input between 13 and 7.5 ka, indicating stronger chemical weathering as the summer monsoon intensified. Changes in clay mineralogy postdate changes in climate by 5–3 ka, reflecting the time needed for new clay minerals to form and be transported to the delta. Samples from the flood plains in Punjab show evidence for increased chemical weathering towards the top of the sections (6–< 4 ka), counter to the trend in the delta, at a time of monsoon weakening. Clay mineral assemblages within sandy flood-plain sediment have higher smectite/(illite + chlorite) values than interbedded mudstones, suggestive of either stronger weathering or more sediment reworking since the Mid Holocene. We show that marine records are not always good proxies for weathering across the entire flood plain. Nonetheless, the delta record likely represents the most reliable record of basin-wide weathering response to climate change.     

Contourites: Their recognition in modern and ancient sediments

We suggest that publication of evidence that the continental rise of the western North Atlantic has been shaped by bottom currents flowing parallel to bathymetric contours (Heezen, Hollister and Ruddiman, 1966) marked the beginning of a revolution in sedimentology comparable to the turbidite revolution launched by Kuenen and Migliorini in their classical 1950 paper.Intensification of slow, thermohaline circulation on the western margins of the ocean basins leads to high-velocity, deep, boundary currents, capable of eroding, transporting and depositing fine-grained sediment. Long-period, direct current measurements suggest a complex, periodic flow for these currents, while bottom photographs indicate their influence on the sediment surface. Sediment ridges in the North Atlantic can be closely related to the deep-water circulation pattern. Other morphological features (ripples, furrows, waves), echogram characteristics, and the presence of well-developed nepheloid layers cannot be uniquely attributed to the action of bottom currents.Critical review of marine-based investigations reveals a lack of generally accepted criteria for the recognition of contourites on the basis of sediment character. We discuss the problems in establishing such criteria and recognize that: (a) a continuum may exist between dilute turbidity flows, bottom currents and hemipelagic settling; (b) interbedded turbidites, contourites and hemipelagites are common, especially in a rise environment; and (c) composition and other criteria may be only locally applicable. However, we can identify two main contourite groups, muddy contourites and sandy contourites, and have proposed new criteria for their recognition. Muddy contourites are generally bioturbated, have poorly defined bedding, and contain biogenic sand often concentrated into irregular layers. They may be texturally and compositionally distinct from interbedded turbidites, and have relatively high CaCO₃ and organic carbon contents. Sandy contourites occur as thin, bioturbated, irregular lag-deposits, or as reworked tops of sandy turbidites. In the latter case they may be clean, well sorted, parallel- or cross-laminated, but show no offshore trends or vertical structural sequence. Grain orientation shows the bottom current direction, often superimposed upon the original turbidite fabric.Reveiw of land-based work shows that there is growing recognition of the need for a new concept to complement turbidity-current theory, but that there have been relatively few claims of firm contourite identification. Recognition of ancient contourites has been based either on the application of previous sedimentological criteria, or on an interpretation of the broader environmental framework. It is suggested that it is lack of suitable criteria for the identification of contourites rather than a true scarcity of these rocks that has led to such a restricted literature.Mindful of problems created by diagenesis, tectonic activity and the limited preservation potential of many diagnostic features of marine contourites, we do suggest criteria, and a procedure, for the recognition of contourites in land-based work. Sandy contourites of the reworked-turbidite variety may be the most easily recognised; the presence of bimodal palaeocurrent directions at about 90° is an important indicator of this type.The geological significance of contourites in palaeo-oceanographical, palaeogeographical and tectonic reconstructions is emphasised, especially in relation to work on passive (Atlantic-type) continental margins. We also refer to the possible economic significance of contourites as exploration for hydrocarbons moves into deeper waters.     

Mineral magnetic analysis of a ‘weathering’ surface within glacigenic sediments at Glanllynnau,North Wales

A number of ‘weathering’ horizons have been identified within glacigenic sediment sequences in North Wales and have been instrumental in determining various proposed Late Quaternary event chronologies. This paper applies the techniques of mineral magnetic analysis to such a sediment sequence at Glanllynnau. The presence (or otherwise) of evidence for weathering processes on the upper surface of the Criccieth Till, which is overlain by further glacial materials, is examined. Despite a marked colour variation between the ‘weathered’ and non-weathered components of the Criccieth Till, their mineral magnetic properties suggest little or no variation in iron oxide assemblages. The consequences of this for the environmental interpretation of the sediment sequence are discussed.     

Characterization of sediments by high-frequency echo-sounding

A high-frequency echo-sounder (200 kHz) was used to characterize the sediments of the shallow Öre Estuary in the Gulf of Bothnia, northern Sweden. The acoustic signal patterns of the echogram were used to differentiate between fine-grained and coarse-grained sediment bottoms according to four major criteria: roughness of the line surface, line thickness, and occurrence of white line and double echo. The echogram characteristics were calibrated against physical properties of the sediment determined in the laboratory. It can be concluded that high-frequency echo-sounding offers an easily applied and reliable method for determining the spatial extent of different bottom sediments (e.g., fine-grained) in shallow waters.     

Petrologic studies of terrestrial organic matter in Carpathian flysch sediments, southern Poland

In the Carpathian Flysch, coal is present either as exotics of Carboniferous coal deposits or as autochthonous, thin layers of lustrous coal. This paper present the results of the studies of coal-bearing rocks that are coeval with the enclosing flysch sediments. These coals form lenses up to 0.15 m thick. Their morphology precludes an exotic origin. The main petrographic component is collinite with admixtures of poorly fluorescing telinite. Minor components are: exudatinite, sporinite, fusinite, micrinite and sclerotinite. Mineral matter consists of framboidal pyrite clay minerals and quartz.The random reflectance of telocollinite varies from 0.38% to 0.72%, which corresponds to subbituminous and bituminous ranks. Correlation between chemical analysis, coking properties and relfectance measurements, leads to the conclusion that boundary between subbituminous and bituminous coals should be defined by the following values: C=80wt%, VOLATILES=43wt%; calorific VALUE=32.3 MJ/kg; and R^o=0.56–0.57%.Atypical properties, such as: upper C value (75–80wt%); high volatile matter contents (over 43wt%) and low random reflectance (^o about 0.38–0.57%) in subbituminous coals; low C value (about 80–82wt%); low reflectance (0.56–0.72%); and good coking properties, of the bituminous coals are attributed to quick coalification during increasing temperature as a result of tectonic stress.     

First find of kutnohorite in modern sediments of the South Caspian basin

High-manganese kutnohorite was found in the surface layer of bottom sediments of the South Caspian basin by the method of X-ray diffraction for the first time. Bottom sediments were collected by a multicorer during the 39th voyage of R/V Rift in 2012. Study of the samples by a complex of methods (X-ray diffraction, scanning electron microscopy, atomic absorption, and analysis of the carbon isotope composition) allowed us to attribute kutnohorite to autigenic minerals of the early stage of diagenesis.     

Organic matter distribution in the modern sediments of the Pearl River Estuary

We determined biomarker concentrations and distributions for surface sediments from 54 sites in the Pearl River Estuary, China. We focus on a suite of four biomarker-based indicators for relative terrestrial to marine organic matter (OM) source: the branched-isoprenoid tetraether (BIT) index, the ratio of high/low molecular weight n-alcohols [(ΣC_26–34/(ΣC₁₆₊₁₈ + ΣC_26–34)], an analogous ratio for n-fatty acids and the ΣC₂₉-steroids/(ΣC₂₉-steroids + brassicasterol) ratio. All four exhibit the same terrestrial to marine transition seen in previous bulk δ¹³C studies, but with an abrupt decrease in the relative terrestrial contribution across the delta front to pro-delta transition. Concentrations of terrestrially-derived biomarkers show no systematic decrease across the transition. Instead, the decrease in the proportion of terrestrial OM is due to a decrease in the sedimentation rate and associated terrestrial OM burial across the delta toe. This suggests that diagenetic controls on the fate of terrestrial OM, such as increased biodegradation where sedimentation rate is low, are subordinate to sedimentological processes. Biomarker-derived temperature values are cooler than expected for the lower Pearl River catchment, suggesting that the dominant component of the terrestrial OM is derived from the cooler upland regions of the catchment. The dominance of input from more distal terrain with greater topographic relief is evidence for the importance of geomorphological control on terrigenous OM transport. Collectively, the results demonstrate the importance of sedimentological processes in the supply, deposition and transport of terrestrial OM.     

A mechanism for emplacement and concentration of diatoms in glacigenic deposits

The occurrence of diatoms (both marine and freshwater) in sediments beneath the West Antarctic Ice Sheet (WAIS) is suggestive of past ice-sheet collapse. However, it is not the only model explaining such occurrences. We propose another mechanism for introducing diatoms beneath ice sheets by considering the fate of a diatom placed (by eolian processes) on top of an ice sheet. Mathematical modeling indicates that the route the diatom will take through the ice sheet is dictated by the basal melting rate. If no basal melting takes place, flowlines will crop out at the ice-sheet margin. However, if basal melting is as low as 0.01 m/yr the trajectories of all Howlines except for those nearest the margin will intersect the bed, with those diatoms deposited near the dome reaching the bed about halfway down the Howband. Larger values of basal melting lead to the diatoms reaching the bed even faster and closer to the point of origin. In light of these results, the presence of diatoms in sediments beneath the WAIS does not lead to a unique solution; it is not necessary to invoke past ice-sheet collapse to account for their presence.     

The importance of atmospheric input of terrestrial organic material to deep sea sediments

The concentrations of lipids were determined in atmospheric particle, gas and rain samples collected from the tropical North Pacific to assess lipid sources, transport mechanisms and fluxes to the ocean surface. Four lipid compound classes (aliphatic hydrocarbons, fatty alcohols, fatty acid esters, and salts) all unequivocally show a terrestrial vascular plant source. These aerosol lipids originate from wind erosion of Asian and American soils and direct emission from vegetation. The major fluxes result from rain rather than dry deposition. These fluxes are large enough to have a major potential impact on the inventory of terrestrially derived lipid material found in deep-sea sediments. This has been showm for n-alkanes, fatty alcohols, fatty acids, total lipids and for organic carbon. By comparing atmospheric and sediment trap fluxes with sediment accumulation rates, it is suggested that some biogenic terrestrial material is more protected from degradation than marine-derived material.     

Transformation of arsenic compounds in modern intertidal sediments of Iriomote Island, Japan

The arsenic accumulation process in intertidal sediments of Iriomote Island, Japan, is analyzed as a naturally balanced arsenic-fixation system. Major and minor element chemistry is analyzed by X-ray fluorescence photometry, mineralogy is investigated by X-ray diffractometry, and four arsenic compounds are characterized by hydrogen-generated atomic absorption photometry. It is found that arsenic is accumulated by iron hydroxides/oxides precipitated following the decomposition of humic acids in the shallower sediment, and is subsequently incorporated into iron sulfide minerals at depth. The arsenic is immobile during incorporation into arsenic-bearing phases, suggesting that arsenic is unlikely to be released into the porewater under natural conditions in early diagenesis. The formation and decomposition of arsenic-bearing organic compounds appear to be associated with the formation and decomposition of arsenic in oxyhydroxides/oxides, suggesting that microbial activity may play an important role in controlling the behavior of arsenic and arsenic-bearing phases in the sediment column.     

Brittle deformation in pitted pebble conglomerates

The fracture patterns produced in pitted pebble conglomerates from the Alpine Molasse and the Carboniferous of northern Spain, have been studied in relation to the stress concentrations which were produced in the conglomerates during their deformation. The stress distributions which develop around pebble contacts at different stages of their pitting history have been determined from photoelastic experiments. The development of different types of fracture, having dominantly tensile or shear components, and their distribution within the pebbles, are shown to be related to the mineralogy of the pebbles, the strength of the matrix and the amount of deformation the conglomerate has suffered.     

四川盆地白垩纪沙漠沉积磁组构特征及其古风向意义

本文通过对四川盆地白垩纪沙漠沉积的磁化率各向异性测量和统计分析,揭示了该沙漠磁组构参数在不同层位的变化特征,获得了古风向及其变化趋势和气候带漂变规律。结果表明：（１）四川盆地白垩纪沙漠在早白垩世晚期的风向主要为ＳＥＥ向和ＳＷ向,二者交替出现。晚白垩世早期为ＳＥＥ向。（２）两组方向所示盛行风为西风和东北信风。（３）该沙漠早期处于副热高压带的西风和东北信风切变带上,切变带曾作短周期南北向漂变,晚期因切变带南移而处于西风带中,属于长周期漂变。（４）磁组构能很好地显示风沙沉积物中无宏观表征的风向特征。