A relationship between alluvial backswamps and avulsion cycles: an example from the Willwood Formation of the Bighorn Basin, Wyoming

Stratigraphically limited intervals from the Lower Eocene Willwood Formation contain laterally extensive carbonaceous shales and ribbon sandstone networks associated with channel avulsion. We present data from one such interval that documents the avulsion sequence. Vertical sections measured along the outcrop of this interval are similar and comprise a basal carbonaceous shale overlain by fine-grained deposits on which weakly developed, hydromorphic paleosols formed. The paleosols enclose and are locally incised by ribbon sandstones, some of which cut down to and partly through the carbonaceous shale. The ribbons have width/thickness ratios between 3 and 13. Some ribbons cluster at a particular stratigraphic level, which, together with paleocurrent trends, suggests that they formed channel networks. Sections are capped by yellow-brown paleosols showing moderate pedogenic development. We suggest that the carbonaceous shales developed in low-lying topogeneous swamps in distal portions of the floodplain far from the trunk channel. Such a location set limits on the sediment that they received. The mudrocks with weakly developed paleosols and associated ribbon sandstones are interpreted as crevasse-splay complexes resulting from avulsion of the trunk river. The ribbon sandstones represent ancient feeder channels of the avulsion complex. The rapid influx of avulsion deposits appears to have been crucial to preserving the organic material, and this study reveals an important and as yet uncharacterized link between trunk channel processes and the accumulation of organic-rich deposits in distal alluvial swamps. Similar deposits are found in other stratigraphic units in the Rocky Mountain region, and the development of these and other organic-rich deposits should be reassessed in terms of channel avulsion.     

Precession‐scale cyclicity in the fluvial lower Eocene Willwood Formation of the Bighorn Basin,Wyoming (USA)

Little is known about controls on river avulsion at geological time scales longer than 10⁴ years, primarily because it is difficult to link observed changes in alluvial architecture to well‐defined allogenic mechanisms and to disentangle allogenic from autogenic processes. Recognition of Milankovitch‐sale orbital forcing in alluvial stratigraphy would provide unprecedented age control in terrestrial deposits, and also exploit models of allogenic forcing enabling more rigorous testing of allocyclic and autocyclic controls. The Willwood Formation of the Bighorn Basin is a lower Eocene fluvial unit distinctive for its thick sequence of laterally extensive lithological cycles on a scale of 4 to 10 m. Intervals of red palaeosols that formed on overbank mudstones are related to periods of relative channel stability when gradients between channel belts and floodplains were low. The intervening drab, heterolithic intervals with weak palaeosol development are attributed to episodes of channel avulsion that occurred when channels became super‐elevated above the floodplain. In the Deer Creek Amphitheater section in the McCullough Peaks area, these overbank and avulsion deposits alternate with a dominant cycle thickness of ca 7·1 m. Using integrated stratigraphic age constraints, this cyclicity has an estimated period of ca 21·6 kyr, which is in the range of the period of precession climate cycles in the early Eocene. Previous analyses of three older and younger sections in the Bighorn Basin showed a similar 7 to 8 m spacing of red palaeosol clusters with an estimated duration close to the precession period. Intervals of floodplain stability alternating with episodes of large‐scale reorganization of the fluvial system could be entirely autogenic; however, the remarkable regularity and the match in time scales documented here indicate that these alternations were probably paced by allogenic, astronomically forced climate change.     

The relationship between channel avulsion, flow occupancy and aggradation in braided rivers: insights from an experimental model

Experimental modelling of an aggrading braided river has allowed investigation of the relationship between the frequency of channel avulsion ( A _f), the duration of time that the braidplain is occupied by flow, the spatial pattern of braidplain sedimentation and how these respond to a change in sediment supply ( S _s). Model results demonstrate a strong, positive relationship between S _s and A _f and that there is no downstream change in A _f over the short braidplain distances ( ca 100 m) modelled herein. Although A _f is strongly dependent on S _s, the degree of channel switching does not influence the rate, or spatial pattern, of braidplain sedimentation. All experiments used a single, central input for water and sediment, and the channels occupied the centre of the alluvial basin for a longer period of time than the margins for all sediment supply rates and distances downstream. Despite this spatio-temporal pattern in flow occupancy, braidplain sedimentation rates were nearly uniform both downstream and across the basin, and increased at approximately the same rate as increases in S _s. As a consequence, less frequent, and possibly short-lived, flows at the margins of the braidplain deposited and preserved more sediment per unit time in comparison with the centre of the basin where flow occupancy was higher. An approximate order of magnitude change in sediment supply resulted in only a factor of two change in bed slope, probably due to both an increase in channelization and adjustment of the channel form that maintained sediment transport through the basin. This result suggests that linear diffusion models are unlikely to be applicable in landscape evolution models that possess aggrading multi-thread rivers, which are capable of self-adjustment in channel number and form.     

Glaciofluvial channels formed prior to the last deglaciation: examples from Swedish Lapland

At four localities in area east of the Sarek and Kebnekajse massifs in Swedish Lapland, glaciofluvial channels seem to have been overhidden by glaciers without having extensively modified. It is suggested that the channels were formed during an Early Weichselian stade. The last glaical advance had little effect on the pre-exiting landforms at these localities and probably also at many other places in the area. Earlier theories about glacial development and deglaciation patterns in this area are based on morphology and the assumption that the landforms were formed during the last deglaciation. These theories need to be revised.     

Role of permeability barriers in alluvial hydromorphic palaeosols: The Eocene Pondaung Formation,Myanmar

This study examines the lateral distribution of hydromorphy in the fine‐grained alluvial deposits of the Eocene Pondaung Formation, central Myanmar. Through detailed outcrop analysis and using a combined sedimentological and pedological approach, this study proposes a reconstruction of Pondaung overbank floodplain palaeoenvironments. The variations of hydromorphic features in the different overbank sub‐environments are then discussed and used to build a model of hydromorphic variability in alluvial deposits. Two main architectural associations with distinctive lithofacies and pedogenic features were identified, corresponding to different sub‐environments: heterolithic deposits and extensive mudstone successions. The heterolithic deposits display variegated fine‐grained lithofacies and contain poorly developed palaeosols with gley and vertic features, which are interpreted to reflect a seasonal wetlands landscape, developed in actively aggrading avulsion belts. Extensive mudstone successions with Vertisols that locally exhibit mukkara‐style pseudogley features are interpreted to represent a distal open‐forested environment. The palaeosols of both sub‐environments display dense local hydromorphic variations they are also characterized by a gradual shift from gley‐dominated to pseudogley‐dominated features with increasing distance from the avulsion belt. The clay‐dominated lithology of the floodplain parent material, which forms numerous subsurface permeability barriers, is shown to have acted as a fundamental control in limiting water‐table dynamics in coarse‐grained parts of the succession, thereby favouring hydromorphic variability. Palaeosol sequences of the Pondaung Formation contrast with the soil‐landscape associations described in other studies and provide an alternative model with which to account for the hydromorphic variability in poorly drained, alluvial soils. The model proposed as an outcome of this study demonstrates that hydromorphic variations can be dramatic in floodplains where permeability barriers are numerous. Further, the model stresses the importance of undertaking detailed lateral palaeosol analyses prior to making interpretations regarding hydromorphic variability.     

Spatial variability of palaeosols across Cretaceous interfluves in the Dunvegan Formation, NE British Columbia, Canada: palaeohydrological, palaeogeomorphological and stratigraphic implications

A basic sedimentological and palaeopedological framework is now in place for non-marine sequence models. The variability of interfluve palaeosols has not, however, been systematically documented, nor have the stratigraphic implications of that variability been incorporated into sequence models. Interfluve palaeosol variability in the deltaic Dunvegan Formation, NE British Columbia, Canada, is investigated, for which a detailed allostratigraphic and palaeogeographic framework has been developed, based on abundant well (> 2300 logs) and outcrop (> 60 sections) control. Regionally extensive valley fills and interfluves have been mapped in coastal plain deposits over an area of about 50 000 km². This palaeogeographic framework permits interfluve surfaces exposed in outcrop to be located in terms of distance from the margins of coeval valleys. The micromorphological, geochemical and mineralogical characteristics of five representative sequence-bounding palaeosols located from 250 m to more than 15 km from coeval valley margins are described. These interfluve palaeosols are similar to modern Alfisols and all record (i) aggradation on an alluvial/coastal plain; (ii) a subsequent static and/or degradational phase related to valley incision, non-deposition and soil thickening; and (iii) a final aggradational phase related to valley filling and renewed sedimentation across the coastal plain. Within this overall template, however, variations in palaeosol thickness, redoximorphic features, illuvial clay content and geochemistry suggest developmental control by hydrological characteristics that were influenced by both the nature of the underlying alluvial sediments and distance from the valley margin. The presence of mature interfluve palaeosols with complex developmental histories suggests that landscape dissection may have been related to terrace development associated with valley incision. Palaeosols closer to valley margins are thicker, contain more illuvial clay and display characteristics suggesting better drained conditions relative to those palaeosols that developed further from valley margins. Subsequent deposition on interfluves also reflects distance from valleys, with those sites close to valleys accumulating cumulic soils with evidence of brackish groundwater, whereas far from valleys (> 10–15 km), groundwater was fresh and clastic supply minimal, encouraging peat formation. Variations in drainage and palaeotopography during landscape dissection resulted in different palaeosol development styles on interfluve surfaces that can be shown, on the basis of physical correlation, to have the same geomorphic age. These observations support the concept of the soil-forming interval as a basis for pedostratigraphic correlation in ancient terrestrial deposits. Palaeosol variability on interfluves is to be expected, and recognition and documentation of this variability is an important prerequisite to palaeogeomorphological, palaeoclimatic and sequence stratigraphic interpretations.     

绿河油页岩中的开链醇化合物

研究了美国绿河盆地的23个未成熟的露头油页岩样品,其中 13个样品取自Laney组,为半温湿半干燥气候下沉积于较浅的封闭水体的盐湖中心,含有丰富的有机质;另外 10个样品取自LumanTongue组,为潮湿气候下沉积于近岸的水体开放的淡水环境,其有机质含量较低。所有样品均富含从C₁₁至C₂₀ 的同分异构体丰富的饱和类异戊二烯醇类化合物。此外还检出了一整套直链一元仲醇同系物,其碳数从 10至 33,而羟基可在任何理论上可能的碳位上。伯醇含量较低。研究结果表明,绿河油页岩中的有机质分别在沉积过程中和被抬升之后遭受了两次微生物降解。除伯醇的分布有生物来源特征外,其余的开链醇化合物是在绿河层系抬升至地表后微生物对其中烃类化合物降解的产物。文中将绿河油页岩有机质中异常高的氧指数归因于微生物降解,并探讨了其开链醇化合物的分布与物源、沉积环境及微生物降解程度的相关性。盐湖相Laney组的直链醇以低碳数组分为主,反映其有机质以菌藻为主的物源,与干燥的古气候相一致;淡水相LumanTongue组则以高碳数组分为主,有着明显优势的高等植物来源,与其潮湿的古气候相吻合。在沉积过程中,淡水相的LumanTongue组中的有机质遭受了比盐湖相的Laney组中的有机质更强的微生物降解,这意味着盐湖环境。     

Compound paleovalley fills in the Lower Pennsylvanian New River Formation, West Virginia, USA

Ancient paleovalley fills are typically interpreted in the rock record using over-generalized models without carefully considering modern analogs, especially in light of recent discoveries. It is now known that many Quaternary paleovalleys are compound in origin, exhibit considerable stratigraphic complexity, contain multiple incisions, and can be orders of magnitude larger than their putative ancient counterparts. Compound paleovalley fills in the Lower Pennsylvanian New River Formation (NRF) are directly comparable to these Quaternary analogs, stimulating a paradigm shift in the interpretation of ancient paleovalleys. In the NRF, multiple laterally- and vertically-juxtaposed fill successions, separated by incision surfaces, record high-frequency fluvial responses to external controls within lower-order sequences. Lowstand incision and sediment bypass, as predicted in sequence stratigraphy, is largely discounted by the available evidence and the definition of regional sequence boundaries is not straightforward. The identification of genetic sequences may be the most effective approach to understanding the NRF and, by inference, many other ancient paleovalleys. Results from this study of the NRF promote a revised model for ancient paleovalleys that incorporates: 1) the pre-eminence of compound architecture, 2) periodic episodes of incision and subaerial exposure occurring in response to high-frequency changes in climate or relative sea level, 3) fluvial downcutting as the primary cause of paleovalley incision, although some sediments are still preserved in a net-erosional regime, and 4) composite, time-transgressive sequence boundaries that may be difficult or impossible to correlate regionally.     

Formation and reorientation of structure in the surge‐type glacier Kongsvegen,Svalbard

Kongsvegen, a surge‐type glacier in Spitsbergen, Svalbard, shares a tide‐water margin with the glacier Kronebreen. The complex has been in retreat since a surge advance of Kongsvegen around 1948. The surface of Kongsvegen displays suites of deformational structures highlighted by debris‐rich folia. These structures are melting out to form a network of sediment ridges in the grounded terminal area. The structures are also visible in a marginal, 1 km long, 5–20 m high cliff‐face at the terminus. Current models for the evolution of deformational structures at Kongsvegen divide the structures into suites based on their orientation and dip, before assigning a mechanism for genesis based on structure geometry. Interpretation of aerial photographs and field mapping of surface structures suggest that many structures were reorientated or advected during the surge. We suggest that many of the deformational structures highlighted by debris‐rich folia represent reorientated, sediment‐filled crevasses. Some evidence of thrusting is apparent but the process is not as ubiquitous as previously suggested. Many deformational structures also appear to have been offset by more recent structures. Mechanisms of structural development must, therefore, be considered within the context of distinct stages of glacier flow dynamics and multiple surge episodes. Furthermore, evidence for thrusting and folding within the glacier systems of Svalbard has been used as the basis for interpreting Quaternary glacial landforms in the UK. The findings of this paper, therefore, have implications for interpretations of the Quaternary record. Copyright © 2002 John Wiley & Sons, Ltd.     

Evolution of an ancient coastal plain: palaeosols, interfluves and alluvial architecture in a sequence stratigraphic framework, Cenomanian Dunvegan Formation, NE British Columbia, Canada

To date, discussion of changes in alluvial style and in the character of palaeosols in relation to changes in accommodation and sediment supply on floodplains has primarily been from a conceptual standpoint: few case studies are available against which to test ideas. One hundred and thirty metres of non-marine strata of the Dunvegan Formation were examined in 14 closely spaced sections in the canyon of the Kiskatinaw River, NE British Columbia, Canada. This site was located about 120 km inland from the transgressive limit of the contemporary marine shoreline and represents almost exclusively freshwater environments. Fluvial channels in the Kiskatinaw River section are of two types. Small, single-storey, very fine- to fine-grained sandstone ribbons with W/T ratios <30, encased in fine-grained floodplain sediments are interpreted as anastomosed channels. Fine- to medium-grained, laterally accreted point-bar deposits forming multistorey sand bodies with individual W/T ratios >30 are interpreted as the deposits of meandering rivers filling incised valleys. Interchannel facies include the deposits of crevasse channels and splays, lakes, floodplains and palaeosols. Floodplain palaeosols consist of laterally heterogeneous, simple palaeosol profiles and pedocomplexes similar to modern Entisols, Inceptisols and hydromorphic soils. Interfluve, sequence-bounding palaeosols adjacent to incised valleys are laterally continuous, up to 3 m thick and can be reliably identified using a combination of (1) stratigraphic position; (2) field observations, such as thickness, structure, colour, degree of rooting; and (3) micromorphological features, such as evidence of bioturbation, clay coatings, ferruginous features and sphaerosiderite. Interfluve palaeosols are similar to modern Alfisols and Ultisols. Correlation of the local stratigraphic succession with the regional sequence stratigraphic framework, based on 2340 well logs and 60 outcrop sections, shows that the vertical changes in coastal plain character (more coals and lakes vs. more pedogenesis) can be related to relatively high-frequency base level cycles (eustatic?) that are expressed as transgressive–regressive marine cycles in downdip areas. Regional isopach maps show that these cycles were progressively overprinted and modified by an increasing rate of tectonic subsidence in the north and west. The character of palaeosols developed on aggrading floodplains primarily reflects local sediment supply and drainage. In contrast, well-developed interfluve palaeosols record pedogenesis during periods of reduced or negative accommodation (base level fall). Vertical changes in floodplain palaeoenvironments and palaeosol types reflect changes in accommodation rate. The detailed micromorphological analysis of interfluve palaeosols represents a powerful application of an under-used technique for the recognition of key surfaces in the geological record. This has broad implications for non-marine sequence stratigraphy.     

Water quality impacts from mining in the Black Hills,South Dakota,USA

The focus of this research was to determine if abandoned mines constitute a major environmental hazard in the Black Hills. Many abandoned gold mines in the Black Hills contribute acid and heavy metals to streams. In some areas of sulfide mineralization local impacts are severe, but in most areas the impacts are small because most ore deposits consist of small quartz veins with few sulfides. Pegmatite mines appear to have negligible effects on water due to the insoluble nature of pegmatite minerals. Uranium mines in the southern Black Hills contribute some radioactivity to surface water, but the impact is limited because of the dry climate and lack of runoff in that area.     

Multi‐scale classification of fluvial architecture: An example from the Palaeocene–Eocene Bighorn Basin,Wyoming

Fluvial channel geometry classification schemes are commonly restricted in relation to the scale at which the study took place, often due to outcrop limitations or the need to conduct small‐scale detailed studies. A number of classification schemes are present in the literature; however, there is often limited consistency between them, making application difficult. The aim of this study is to address this key problem by describing channel body geometries across a depositional basin to ensure that a wide range of architectures are documented. This was achieved by studying 28 locations over 4000 m of vertical succession in Palaeocene‐aged and Early Eocene‐aged deposits within the Bighorn Basin, Wyoming, USA. Five different channel body geometries have been defined based on the external geometric form, and internal arrangement and nature of storey contacts. These include the massive channel body geometry, semi‐amalgamated channel body geometry, internally amalgamated channel body geometry and offset stacked channel body geometry, which are considered to be subdivisions of the sheet geometry of many other classifications. An isolated channel body geometry has also been recognized alongside splay channel and sheet sandstone geometries in the floodplain facies associations. Field evidence, including the stacking style of storey surfaces, suggests that the different geometries form a continuum. The nature and degree of amalgamation at the storey scale are important in producing the different geometries and are related to the degree of channel migration. It is speculated that this is the result of differences in sediment supply and available accommodation. In contrast to previous schemes, the classification scheme presented here recognizes the importance of transitional geometries. This geometrical range has been recognized because of the basin‐scale nature of the study.     

Trench-slope channels from the New Zealand Jurassic: the Otekura Formation, Sandy Bay, South Otago

The Otekura Formation (Early Jurassic, Pseudaucella zone) at Sandy Bay comprises part of a 10+ km thick, regressive, forearc shelf and slope sequence, the Hokonui facies belt of the Rangitata Geosyncline. The Otekura Formation is dominantly fine grained, being mostly mudstone, silty mudstone and siltstone. The sediments are volcanogenic throughout. The upper 150 m of the formation contains two 20 m thick, channelized bodies of medium-thick bedded sandy flysch, each associated with thin bedded muddy flysch interpreted as overbank turbidites. Directional indicators within the channel sequence indicate emplacement from the south-southwest. In contrast, rare turbidites that occur below the channel sequence, within the background mudstone sediment, were emplaced from the east, i.e. at right angles to the channelized flows. The immediately overlying Omaru Formation contains more abundant macrofossils, intraclastic conglomerates, and appreciable amounts of traction-emplaced cross-bedded sand. Bioturbated calcareous siltstones with an in situ molluscan fauna follow (Boatlanding Formation), and are of shelf origin. The Omaru Formation is therefore interpreted as a shelf-slope break deposit, and the Otekura Formation as an upper slope facies. Reconnaissance studies indicate that the Otekura Formation is underlain by several kilometres of dominantly fine grained, deep water slope sediments, containing occasional sand and conglomerate filled channels similar to those here described in detail from the Otekura Formation. Such channels are inferred to form when a mass-transported sand, derived from failure higher on the slope, ploughs erosively into the sea floor. After their incision, the channels served for a short time as conduits for downslope transport of sediment, the redeposited deposits of which are found filling each channel. Both channel fills at Sandy Bay are capped by thin-bedded turbidites inferred to have overspilled from similar channels nearby on the slope.     

湖相重力流水道沉积特征与沉积模式:以鄂尔多斯盆地瑶曲铁路桥剖面三叠系延长组为例*

陆相深水重力流水道的类型细分及其沉积模式是制约其油气勘探开发的重要因素,但研究程度低。通过对鄂尔多斯盆地南缘瑶曲铁路桥剖面三叠系延长组实测、水道形态参数统计及岩相、粒度等分析,开展了湖相重力流水道的沉积特征、沉积过程及沉积模式研究。结果表明:(1)研究区内可识别出4期复合水道,主要为洪水重力流成因。根据其内部单一水道及单砂体形态特征、岩相组成,将其细分为沉积型和过渡型两类。(2)剖面下部2期复合水道为沉积型,以悬浮载荷成因岩相为主,常见块状净细砂岩、薄层泥岩岩相组合和鲍马序列岩相组合;上部2期复合水道为过渡型,岩相以底床载荷与悬浮载荷共存为特征,自下而上以交错层理细砂岩或叠瓦状泥砾细砂岩与含泥砾/泥岩撕裂屑块状细砂岩、平行层理粗粉砂岩及薄层泥岩的岩相组合为特征。(3)结合单一水道规模及其相互关系,建立了区内过渡、沉积型重力流水道的半定量沉积模式。过渡型水道内部侵蚀与沉积作用共存,单一水道宽度小、宽厚比低,呈透镜状,水道间切割性强,砂体横向稳定性较低,表现出不定向叠加、侧向拼接样式;沉积型水道内部由沉积作用主导,单一水道宽度较大、宽厚比较高,呈似板状—透镜状,砂体横向稳定性较高,表现出稳定的垂向加积样式。     

Formation of fluidization pipes during liquefaction: examples from the Uratanna Formation (Lower Cambrian), South Australia

ABSTRACT Usually well preserved fluidization pillars and sand filled fluidization pipes occur within submarine channel sands of the basal Uratanna Formation (Lower Cambrian) in the Adelaide Geosyncline of South Australia. The morphology of these structures reflects complex lateral and vertical movement of fluids during liquefaction and dewatering. Fluidization pipes acted as conduits for highly concentrated, upward directed fluid flow. The formation and maintenance of these pipes was dependent upon the development of a pipe wall composed of clay plugged fine sand. Formed during initial fluidization, this lining acted as a permeability barrier, confining and concentrating fluidized flow within the pipe. Each of the pipes is surrounded by a cylindrical fluidization halo in which leakage through the pipe lining produced partial fluidization of the surrounding sediment. Fine scale structures within these haloes indicate that fluids flowed radially and upward out of the fluidization pipes at an acute angle. These fluids merged with and influenced the orientation and size of adjacent fluidization pillars. The fluidization pipes of the Uratanna Formation may represent unusual preservation of the unstable fluid flow conditions that occur during incipient fluidization of sand beds.     

Geological controls on the geometry of incised‐valley fills: Insights from a global dataset of late‐Quaternary examples

Incised valleys that develop due to relative sea‐level change are common features of continental shelves and coastal plains. Assessment of the factors that control the geometry of incised‐valley fills has hitherto largely relied on conceptual, experimental or numerical models, else has been grounded on case studies of individual depositional systems. Here, a database‐driven statistical analysis of 151 late‐Quaternary incised‐valley fills has been performed, the aim being to investigate the geological controls on their geometry. Results of this analysis have been interpreted with consideration of the role of different processes in determining the geometry of incised‐valley fills through their effect on the degree and rate of river incision, and on river size and mobility. The studied incised‐valley fills developed along active margins are thicker and wider, on average, than those along passive margins, suggesting that tectonic setting exerts a control on the geometry of incised‐valley fills, probably through effects on relative sea‐level change and river behaviour, and in relation to distinct characteristics of basin physiography, water discharge and modes of sediment delivery. Valley‐fill geometry is positively correlated with the associated drainage‐basin size, confirming the dominant role of water discharge. Climate is also inferred to exert a potential control on valley‐fill dimensions, possibly through modulations of temperature, peak precipitation, vegetation and permafrost, which would in turn affect water discharge, rates of sediment supply and valley‐margin stability. Shelves with slope breaks that are currently deeper than 120 m contain incised‐valley fills that are thicker and wider, on average, than those hosted on shelves with breaks shallower than 120 m. No correlation exists between valley‐fill thickness and present‐day coastal‐prism convexity, which is measured as the difference in gradient between lower coastal plains and inner shelves. These findings challenge some concepts embedded in sequence stratigraphic thinking, and have significant implications for analysis and improved understanding of ‘source to sink’ sediment route‐ways, and for attempting predictions of the occurrence and characteristics of hydrocarbon reservoirs.     

Architecture of a tide-influenced river delta in the Frontier Formation of central Wyoming, USA

The Frewens sandstone is composed of two elongate tide-influenced sandstone bodies that are positioned directly above and slightly landward of a more wave-influenced lobate sandstone. The 20-km-long, 3-km-wide Frewens sandstone bodies coarsen upwards and fine away from their axes, have gradational bases and margins and have eroded tops abruptly overlain by marine shales. These sandstones are superbly exposed in large cliffs on the banks of the South Fork of the Powder River in central Wyoming, USA. The deposits change upwards from thinly interbedded sandstones and mudstones to metre-thick heterolithic cross-strata and, finally, to metres-thick sandstone-dominated cross-strata. There is abundant evidence for tidal modulation of depositional flows; however, palaeocurrents were strongly ebb-dominated and nearly parallel the trend of sandstone-body elongation. Detailed mapping of stratal geometry and facies across these exposures shows a complex internal architecture. Large-scale bedding units within sandstone bodies are defined by alternations in facies, bed thickness and the abundance of shales. Such bedsets are inclined (5°–15°) in walls oriented parallel to palaeoflow and gradually decrease in dip over hundreds of metres as they extend from the sandstone-dominated deposits higher in a sandstone body to muddier deposits lower in the body. Where viewed perpendicular to palaeoflow, bedsets are 100-metre-wide lenses that shingle off the sandstone-body axis towards its margins. The sandstone bodies are interpreted as sand ridge deposits formed on the shoreface of a tide-influenced river delta. Metres-thick cross-strata in the upper parts of sandstone bodies resemble deposits of bars (sandwaves) formed where tidal currents moved across shallows and the tops of tidal ridges. Heterolithic deposits lower in sandstone bodies record fluctuating currents caused by ebb and flood tides and varying river discharge. Erosion surfaces capping sandstone bodies record tidal ravinement. The tidal ridges were abandoned following transgression and covered with marine mud as waters deepened.     

Biostratigraphic and biogeographic implications of a hadrosaurid (Ornithopoda: Dinosauria) from the Upper Cretaceous Almond Formation of Wyoming,USA

The results of Barnum Brown's 1937 expedition to the Almond Formation of Wyoming consisted of two unidentified ceratopsian skulls and a partial hadrosaurid specimen (AMNH 3651). The hadrosaurid is here attributed to the Maastrichtian genus Saurolophus, verifying previous biostratigraphic correlations of this formation using ammonite zones. Fossiliferous lower Maastrichtian formations occurring latitudinally between those of Alberta, Canada, and southwestern Texas, USA, such as the Almond Formation, are essential for testing the effects and duration of apparent hadrosaurid faunal segregation earlier in the Campanian, and indirectly aiding in the placement of faunal boundaries that are currently unknown for the late Campanian. The discovery of Saurolophus in Wyoming, a close relative of the Campanian genus Prosaurolophus, affirms that the segregation of hadrosaurid faunas established in the late Campanian (～75 Ma) continued for at least 3 million years. Combining occurrences of Saurolophus from Mongolia and the Moreno Formation of California with those of Alberta, Canada, this genus appears to have had one of the largest geographic ranges of any equivalent clade of hadrosaurid dinosaur, although species level distributions are still uncertain.     

Abandoned mines drainage: impact assessment and mitigation of discharges from coal mines in the UK

The UK has a legacy of pollution caused by discharges from abandoned coal mines, with the potential for further pollution by new discharges as groundwaters continue to rebound to their natural levels. In 1995, the Coal Authority initiated a scoping study of 30 gravity discharges from abandoned coal mines in England and Scotland. Mining information, geological information and water quality data were collated and interpreted in order to allow a preliminary assessment of the source and nature of each of the discharges. An assessment of the potential for remediation was made on the basis of the feasibility and relative costs of alternative remediation measures. Environmental impacts of the discharges and of the proposed remediation schemes were also assessed. The results, together with previous Coal Authority studies of discharges in Wales, were used by the Coal Authority, in collaboration with the former National Rivers Authority and the former Forth and Clyde River Purification Boards, to rank discharge sites in order of priority for remediation.