Evolution and sedimentology of a channel fill in the sandy braided South Saskatchewan River and its comparison to the deposits of an adjacent compound bar     

PHILIP J. ASHWORTH  GREGORY H. SAMBROOK SMITH  JAMES L. BEST  JOHN S. BRIDGE  STUART N. LANE  IAN. A. LUNT  ARNOLD J. H. REESINK  CHRISTOPHER J. SIMPSON  ROBERT E. THOMAS 《Sedimentology》2011,58(7):1860-1883

The depositional stratigraphy of within‐channel deposits in sandy braided rivers is dominated by a variety of barforms (both singular ‘unit’ bars and complex ‘compound’ bars), as well as the infill of individual channels (herein termed ‘channel fills’). The deposits of bars and channel fills define the key components of facies models for braided rivers and their within‐channel heterogeneity, knowledge of which is important for reservoir characterization. However, few studies have sought to address the question of whether the deposits of bars and channel fills can be readily differentiated from each other. This paper presents the first quantitative study to achieve this aim, using aerial images of an evolving modern sandy braided river and geophysical imaging of its subsurface deposits. Aerial photographs taken between 2000 and 2004 document the abandonment and fill of a 1·3 km long, 80 m wide anabranch channel in the sandy braided South Saskatchewan River, Canada. Upstream river regulation traps the majority of very fine sediment and there is little clay (< 1%) in the bed sediments. Channel abandonment was initiated by a series of unit bars that stalled and progressively blocked the anabranch entrance, together with dune deposition and stacking at the anabranch entrance and exit. Complete channel abandonment and subsequent fill of up to 3 m of sediment took approximately two years. Thirteen kilometres of ground‐penetrating radar surveys, coupled with 18 cores, were obtained over the channel fill and an adjacent 750 m long, 400 m wide, compound bar, enabling a quantitative analysis of the channel and bar deposits. Results show that, in terms of grain‐size trends, facies proportions and scale of deposits, there are only subtle differences between the channel fill and bar deposits which, therefore, renders them indistinguishable. Thus, it may be inappropriate to assign different geometric and sedimentological attributes to channel fill and bar facies in object‐based models of sandy braided river alluvial architecture.  相似文献   

The Lower Permian Wasp Head Formation,Sydney Basin: high‐latitude,shallow marine sedimentation following the late Asselian to early Sakmarian glacial event in eastern Australia     

MICHAEL C. RYGEL  CHRISTOPHER R. FIELDING  KERRIE L. BANN  TRACY D. FRANK  LAUREN BIRGENHEIER  STUART C. TYE 《Sedimentology》2008,55(5):1517-1540

The Lower Permian Wasp Head Formation (early to middle Sakmarian) is a ～95 m thick unit that was deposited during the transition to a non‐glacial period following the late Asselian to early Sakmarian glacial event in eastern Australia. This shallow marine, sandstone‐dominated unit can be subdivided into six facies associations. (i) The marine sediment gravity flow facies association consists of breccias and conglomerates deposited in upper shoreface water depths. (ii) Upper shoreface deposits consist of cross‐stratified, conglomeratic sandstones with an impoverished expression of the Skolithos Ichnofacies. (iii) Middle shoreface deposits consist of hummocky cross‐stratified sandstones with a trace fossil assemblage that represents the Skolithos Ichnofacies. (iv) Lower shoreface deposits are similar to middle shoreface deposits, but contain more pervasive bioturbation and a distal expression of the Skolithos Ichnofacies to a proximal expression of the Cruziana Ichnofacies. (v) Delta‐influenced, lower shoreface‐offshore transition deposits are distinguished by sparsely bioturbated carbonaceous mudstone drapes within a variety of shoreface and offshore deposits. Trace fossil assemblages represent distal expressions of the Skolithos Ichnofacies to stressed, proximal expressions of the Cruziana Ichnofacies. Impoverished trace fossil assemblages record variable and episodic environmental stresses possibly caused by fluctuations in sedimentation rates, substrate consistencies, salinity, oxygen levels, turbidity and other physio‐chemical stresses characteristic of deltaic conditions. (vi) The offshore transition‐offshore facies association consists of mudstone and admixed sandstone and mudstone with pervasive bioturbation and an archetypal to distal expression of the Cruziana Ichnofacies. The lowermost ～50 m of the formation consists of a single deepening upward cycle formed as the basin transitioned from glacioisostatic rebound following the Asselian to early Sakmarian glacial to a regime dominated by regional extensional subsidence without significant glacial influence. The upper ～45 m of the formation can be subdivided into three shallowing upward cycles (parasequences) that formed in the aftermath of rapid, possibly glacioeustatic, rises in relative sea‐level or due to autocyclic progradation patterns. The shift to a parasequence‐dominated architecture and progressive decrease in ice‐rafted debris upwards through the succession records the release from glacioisostatic rebound and amelioration of climate that accompanied the transition to broadly non‐glacial conditions.  相似文献   

Trace fossils from proglacial lake sediments   总被引：1，自引：0，他引：1  

PHILIP L. GIBBARD  ANTHONY J. STUART 《Boreas: An International Journal of Quaternary Research》1974,3(2):69-74

Trace fossils have been discovered in Middle Pleistocene proglacial lake sediments from St. Albans, Hertfordshire, England. They indicate that this environment was capable of supporting a variety of benthonic animals. The fossils are described and tentatively assigned to several invertebrate groups.  相似文献   

The vertebrate fauna of the type Cromerian   总被引：1，自引：0，他引：1  

ANTHONY J. STUART 《Boreas: An International Journal of Quaternary Research》1975,4(2):63-76

The rich vertebrate fauna of the Upper Freshwater Bed of West Runton, Norfolk. England (pollen assemblage zone Cr II) is described and related to vegetational conditions based on analysis of fossil pollen and macroscopic plant remains. The general picture is of fishes associated with aquatic plants in a slow-flowing river, amphibious vertebrates living in water-side habitats, and a terrestrial fauna generally reflecting a regional mixed oak forest cover, but also including grassland voles associated with local herb-dominated communities on the river floodplain. The fossil assemblage appears to have accumulated largely from the remains of terrestrial vertebrates washed in as the river eroded its banks. A reassessment of the fossil voles indicates that only five species occur, although ten were previously described. The sparse fauna from the overlying marine gravel (zone Cr III) is also discussed. On the basis of vertebrate faunas and other evidence, sites in England and Germany arc correlated with the type Cromerian.  相似文献   

Out of the Rat Race     

CHARLES WALDEGRAVE  SHANE STUART 《New Zealand geographer》1997,53(1):22-29

After the social policy reforms of 1991 important changes in internal migration in New Zealand occurred. These resulted in changing housing costs and falling incomes which led to the movement of low income households, particularly beneficiaries and state house tenants, from urban to rural areas and small towns. A survey of 404 people who moved to the Southern Wairarapa towns of Carterton, Martinborough and Featherston from New Zealand urban areas since 1985 shows that a proportional increase in beneficiary movement occurred after 1991. Housing costs, relative to income, are important factors in the decision to move for a range of migrants. This pattern of migration has important regional development ramifications.  相似文献   

SUGGESTIONS FOR A CONSISTENT TERMINOLOGY FOR SEISMIC ANISOTROPY1     

STUART CRAMPIN 《Geophysical Prospecting》1989,37(7):753-770

Seismic anisotropy is an unfamiliar concept to many geophysicists and the use of misleading and ambiguous terminology has made it more difficult to understand. I suggest here a consistent terminology in which simple expressions have specific meanings similar to their colloquial meanings. It is hoped that use of such language will help to make the increasing number of papers reporting seismic anisotropy more readily comprehensible to the non-specialist. This not a manual of anisotropy, and it is not intended for theoreticians. It is a list of terms which may make anisotropy a little easier to understand for those more familiar with wave propagation in isotropic solids.  相似文献   

Diagenetic signatures of stratal surfaces in the Upper Jurassic Fulmar Formation, Central North Sea, UKCS   总被引：2，自引：0，他引：2  

FIONA E. BURNS  STUART D. BURLEY  ROB L. GAWTHORPE  JOHN E. POLLARD 《Sedimentology》2005,52(6):1155-1185

Sedimentation rate and changes in relative sea level affect early diagenetic cementation along key stratal surfaces within the deeply buried Upper Jurassic Fulmar Formation, South Central Graben, UKCS. As a result of the bioturbated nature of the shallow marine strata, variations in ichnofabrics and cross-cutting relationships between trace fossils are important in identifying and correlating stratal surfaces. Two transgressive and two regressive surfaces/sequence boundaries were studied, using petrographical, mineralogical and geochemical techniques. Cements, including early diagenetic pyrite framboids, grain-rimming apatite, microcrystalline dolomite and ankerite, occur at, above and immediately below both transgressive and forced regressive surfaces/sequence boundaries. Breaks or subdued rates of sedimentation associated with both types of surfaces meant that the sediment package resided within early diagenetic zones for prolonged periods of time, enhancing diagenetic reactions at and below the surfaces. The distribution of ankerite, despite being a deep-burial cement, was primarily controlled by concentrations of bioclasts that are particularly abundant at transgressive surfaces. The diagenetic character of the forced regressive surfaces/sequence boundaries is more complex than that of the transgressive surfaces, both in terms of mineralogy and paragenesis. This is attributed to the superimposition of diagenetic assemblages as a result of erosion, re-sedimentation and sediment by-passing. Although the diagenetic signature of the surfaces has been modified by dissolution/replacement reactions during deep burial, early diagenetic signatures can still be distinguished.  相似文献   

The Thames Embankment and the disciplining of nature in modernity   总被引：1，自引：0，他引：1  

STUART OLIVER 《The Geographical journal》2000,166(3):227-238

The embanking of the Thames was an emblematic stage in the construction of modernity's discourse of 'the natural', re-engineering the river as a concrete framing of nature between the embankment walls and a representational framing of the natural within an engineering ideology. The legitimacy of embanking's control was, therefore, about both physical mechanisms and a particular discourse of the natural, but the Thames embankments did not merely reflect modernity's discourse - they actively helped mould it. The creation of a discourse of embanking was slow and hesitant, the product of the interplay between the subsidiary discourses of urban improvement and sanitarianism, and an opposing discourse of tradition. When built, the embankments acted as a fixed, ordered boundary between the cultured nature of the drained, commodified land, and the regulated liveliness of the river. They acted literally and figuratively to sever culture from a nature that was enclosed and tamed by embankment walls.  相似文献   

List of Participants     

JOHN STUART GLADWELL 《水文科学杂志》2013,58(4):515-516

ABSTRACT

Assistance to developing nations in the area of water resources has shown mixed successes and failures. A major factor is the capacity of the receiving nations to make good use of the resources provided at their stage of development—their “absorptive capacity”. Programmes must be tailored to the situations. This requires planning that is specific to the national and cultural context, as well as careful sensitivity to positive interaction with those who will be expected to implement programmes whose real purpose should be to allow the entire population, especially its very poor, to become socially effective and self-aware as well as more productive and comfortable. It also requires careful preparation in the way of education, science and institutional responsiveness. Experts and government leaders must reconsider their approaches to the problems so that the nations can learn and think for themselves.  相似文献   

UK Developments in Environmental GIS     

ALAN J. STRACHAN  NEIL STUART 《International journal of geographical information science》2013,27(1):17-20

  相似文献