The sedimentary signature of ice-contact sedimentation and deformation at macro- and micro-scale: A case study from NW Scotland

Studies on the genesis of subaerial debris flows and associated deposits are relatively rare in the literature, especially in an ice-marginal context of moraine formation. The present contribution reports results from both the macro- and micro-scales of a subaerial depositional setting in order to contribute to closing this gap. At the macroscale, alternating loose, stratified, clast- and matrix-supported diamicts and finely laminated sand units indicate deposition of debris flows and fluvial units in a subaerial, ice-marginal setting that were stacked up to form a terrestrial ice-contact fan. Macroscale and micromorphological analyses show that this fan displays evidence of a three-phased formation: (a) overriding and glaciotectonisation of pre-existing sediments followed by retreat and burial of this core by (b) ice-contact fan deposition dominated by water-rich fluvial deposition with relatively little debris flow activity and (c) a switch to a gravitational sedimentation style with dominantly debris flow deposition and fewer and thinner fluvial units. Thin sections of both the diamict and laminated sand units show evidence of deposition of a mud and fine sand-rich slurry being expelled from the tops of advancing mass flows. Water-rich fine-grained slurries appear to have been progressively overridden and deformed in response to ductile shear occurring at the base of individual flows. Liquefaction and remobilisation of sand within laminated deposits occurred during such basal shear events, resulting in the injection of liquefied sediments into variably deformed laminated sands and clays. Deformation is more likely to have taken place through internal movement of the sediment due to changing porewater conditions and loading upon emplacement. Our approach confirms previous results that highlight the possibilities of increasing the accuracy of sedimentological investigations through combined sedimentological analyses at varying scales.     

Marine spatial planning in Scotland. Levelling the playing field?

Marine spatial planning (MSP) is the leading tool for managing human activities at sea. It is designed to assist in decision making for marine resource access and use by considering the actions of those using the resources, interactions between these groups, and their cumulative impact on the natural environment. Being informed by ecosystem based management, MSP recognises that socio-natural systems are complex and that stakeholder and public input are key components of well-informed decision making. Therefore, MSP is rooted in the principles of good governance, including those of participation and transparency. This paper considers MSP processes in Scotland's inshore waters in the context of these good governance principles. The focus is on the institutional arrangements that allow stakeholders and the public to contribute to planning Scotland's seas and coasts. Whilst acknowledging the significant challenges faced by planners, and the work conducted so far, this research suggests that improvements could be made in how – and when – engagement takes place. It appears that at an early stage of introducing MSP in Scotland powerful stakeholders shaped the images, values and principles that guide it, and that including a broader range of actors early on might positively affect the legitimacy and acceptance of MSP in its later stages. The current institutional arrangements do not appear to allow for this. Ultimately, MSP in Scotland is in danger of institutionalising – and thus legitimising – existing power relations between marine resource users, and it does little to level the playing field.     

滇东北铅锌成矿带成矿条件分析

滇东北地区铅锌矿产资源丰富,就其原因可归于区内具有特征性地质环境:含矿地层是一套局限性滨-浅海环境沉积作用形成的以碳酸盐为主与砂、泥岩层呈不等厚交替出现的沉积建造,区内有较好的含矿层(碳酸盐层)与遮挡层相结合的地层成矿条件;矿区地质构造复杂,因经历了多期的构造运动,形成近于等间距排列的逆冲推覆体构造及与之相伴生的次级断裂和褶皱构造;同时,多期次的构造运动,也引起岩浆多次沿深大断裂发生侵入或喷发作用;在成矿作用上,复杂、多层次的地质构造为成矿作用提供了不同类型的导矿、容矿构造,岩浆作用一方面为成矿提供物源,另一方面为成矿作用提供热动力,为矿液加热,促使成矿热液得以循环运动,从而在有利部位发生交代作用而成矿。     

A preliminary study of PGE in the Late Caledonian Loch Borralan and Loch Ailsh alkaline pyroxenite-syenite complexes,north-west Scotland

The Siluro-Ordovician Loch Borralan (c. 430 Ma) and Loch Ailsh Complexes (c. 439 Ma) comprise a suite of intrusive rocks ranging in composition from clinopyroxenites, through potassic melasyenites to quartz syenites. The rock suite at Loch Borralan also includes nepheline syenite. Geochemical data in the literature indicate that the intrusions are alkaline, with pronounced enrichments in LILE and LREE relative to contemporaneous calc-alkaline magmatic centres further to the south-east, although they share similar high LILE/Nb, subduction-related characteristics. The Loch Borralan Complex is associated with marginal gravity and magnetic anomalies which can be interpreted in terms of a shallow body less than 400 m thick. Analysis of rocks and drill core revealed widespread elevated Pt and Pd values in pyroxenites and syenites in both complexes. The highest concentrations, up to about 900 ppb Pt+Pd, occur in pyroxenites in the Loch Borralan Complex. Extensive archived drill core provides an excellent section through the marginal pyroxenites, which host the PGE at Loch Borralan. The pyroxenites show unusual petrological features; early clinopyroxene is followed by biotite, apatite, magnetite, sphene and plagioclase with later garnet, which might be metasomatic in origin. Sulphides occur in minor amounts. High-temperature shearing produced local granulation and mylonitisation. Later brittle deformation caused extensive micro-fracturing and the introduction of minor carbonate veining. Platinum-group minerals (PGM) were located in a number of samples with high PGE assay values. These occur as clusters of grains around 1–2 m in diameter, and are difficult to identify uniquely. A few grains appear to be magmatic; these are Pt and PtPd sulphides that occur enclosed in clinopyroxene or garnet. All other grains occur in late fractures or along grain boundaries. These include sperrylite (PtAs₂), Pd antimonides and PdBi tellurides, along with hessite (Ag₂Te). They occur in microfractures accompanied by carbonate and barite and fine-grained sulphides and are probably of secondary origin. The PGE in the pyroxenites may have been introduced during the magmatic phase of the intrusion but the observed distribution of PGM results from low-temperature, hydrothermal remobilisation following brittle deformation and introduction of fluids.

The enigma of fine-grained alluvial basin fills: the Permo-Triassic (Cumbrian Coastal and Sherwood Sandstone Groups) of the Solway Basin,NW England and SW Scotland)

The late Permian to Triassic sediments of the Solway Basin consist of a layer-cake succession of mature, predominantly fine-grained red clastics laid down in semi-arid alluvial plain to arid sabkha and saline marginal marine or lacustrine environments. The Cumbrian Coastal Group consists of Basal Clastics and Eden Shales. The Basal Clastics are thin regolith deposits resting unconformably on all-underlying units and are composed of mixtures of angular local gravel and far-transported fine to very fine-grained sands deposited as basal lag. The Eden Shales are predominantly gypsiferous red silty mudstones, with thin very fine-grained sandstone beds, and with thick marine gypsum beds at the base, deposited at a saline lake margin. The overlying Triassic Sherwood Sandstone Group consists of the Annan and Kirklinton Sandstones. The Annan Sandstones are predominantly thick-bedded, multi-storied, fine-grained mature red quartz sandstones in which coarse sand is practically absent despite channels with clay pebbles up to 30 cm in diameter. The overlying, predominantly aeolian, Kirklinton Sandstones consist of festoon cross-bedded and parallel-laminated fine-grained sandstones, almost identical to the Annan Sandstones except that mica and clay are absent. The Stanwix Shales, located above, consist of interbedded red, blue and green mudstones, siltstones, and thin very fine-grained sandstones, with gypsum layers. Although the entire succession can plausibly be interpreted as deposited in a large desert basin opening into a hypersaline marine or lacustrine embayment to the southwest, the uniformly fine-grained nature of the succession is unusual, as is the absence of paleosols, and body and trace fossils. There is almost no coarse sand even in the river channel units, and it seems likely that the basin was not only extremely arid but supplied predominantly by wind rather than water.     

黄河黑山峡口最高阶地宇宙核素的初步年龄 及所反映的新构造运动*

黄河深切于青藏高原东北缘的构造山地中,留下了山地和黄河形成演化的记录,但其高阶地年龄因超出常规测年技术的范围而存在困难。文章尝试用原地成因宇宙核素¹⁰ Be和²⁶ Al以及垂直剖面取样技术,通过剖面X²最小统计同时求出了年龄、侵蚀速率、继承浓度以及阶地沉积物密度等参数,所获得的黑山峡口247m最高基座阶地的参考年龄和剥蚀速率分别约为2.4Ma和15.5 ＋8 -4 m/Ma,这是该河段高阶地测年的一次新探索。根据这一结果及相关的构造地貌特征,认为香山-天景山断裂带西段2.4Ma前以逆冲为主,以后逐渐过渡到左旋走滑,该段黄河诞生于逆冲作用减弱时期。     

Late Devensian and Flandrian palaeoenvironmental changes on the Scottish continental shelf west of the Outer Hebrides

Examination of two radiocarbon-dated vibrocores taken from south of St Kilda at a water depth of about 155 m, a short distance within the maximum position of the Late Devensian (Dimlington Stadial) ice sheet, suggests that the St Kilda Basin became free of glacier ice after 15250 yr BP. Sedimentation in a shallow, low energy, high arctic, muddy environment continued until after 13500 yr BP. There followed a higher energy temperate episode during which water depths were roughly about 40 m: this is correlated with the latter part of the Windermere Interstadial and with the warmer interval known in shallow Scottish seas about or a little before 11 000 yr BP. The Loch Lomond (Younger Dryas) Stadial is marked in the vibrocores by the return of muddy sediments and a cold-water fauna. Relatively shallow water conditions seem to have persisted into the earliest Flandrian, when the water depth was still roughly 60 m, corresponding to a sea-level in the area 90–100 m below present. It is suggested that pack ice was widespread in the northeast Atlantic before the Windermere Interstadial and also during the Loch Lomond Stadial, when it transported shards of Icelandic volcanic ash into the St Kilda basin. Estimates of sea-surface temperature for the last part of the Windermere Interstadial are close to those derived from the deep-sea record for the same period.     

A Holocene tsunami deposit in eastern Scotland

A thin, regionally extensive, laterally persistent sand layer identified within the Holocene coastal sequences of eastern Scotland, dated to 7000 years BP, is suggested to be a tsunami deposit. The likely source of the tsunami wave is the earthquake induced second Storegga Slide on the Norwegian continental slope at least 750 km northeast of the deposit.     

The shell of Mytilus as an indicator of zonal variations of water quality within an estuary

Variations in the mineralogy and chemistry of the shells of the filter-feeding organism Mytilus edulis have allowed discrimination of subenvironments of growth within the Tay estuary. Aragonite proportions higher than those predictable for the temperate, tidal, growth conditions are associated with stretches of the estuary affected by organic pollution. Accumulation and concentration of copper (Cu) in the organic periostracum suggest that Mytilus shell may also prove useful as a monitor of metallic element pollution.The relatively fragile nature of the polylayer shell of Mytilus and the layer specific distribution of components require the use of either complete, undamaged specimens or population groups to discriminate significant variations.