Reply: Redepositional or Climate Event in Iberia During the Boreal     

JUDY R. M. ALLEN  BRIAN HUNTLEY  WILLIAM A. WATTS 《第四纪科学杂志》1997,12(1):75-75

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Unravelling the conundrum of river response to rising sea‐level from laboratory to field. Part II. The Fly–Strickland River system,Papua New Guinea     

GARY PARKER  TETSUJI MUTO  YOSHIHISA AKAMATSU  WILLIAM E. DIETRICH  J. WESLEY LAUER 《Sedimentology》2008,55(6):1657-1686

The most recent deglaciation resulted in a global sea‐level rise of some 120 m over ca 12 000 years. A moving boundary numerical model is developed to predict the response of rivers to this rise. The model was motivated by experiments at small scale, which have identified two modes describing the transgression of a river mouth: (i) autoretreat without abandonment of the river delta (no sediment starvation at the topset–foreset break); and (ii) sediment‐starved autoretreat with abandonment of the delta. In the latter case, transgression is far more rapid, and its effects are felt much further upstream of the river mouth. A moving boundary numerical model that captures these features in experimental deltas is adapted to describe the response of the Fly–Strickland River system, Papua New Guinea. In the absence of better information, the model is applied to the case of sea‐level rise without local climate change in New Guinea. The model suggests that: (i) sea‐level rise has forced the river mouth to transgress over 700 km since the last glacial maximum; (ii) sediment‐starved autoretreat has forced enough bed aggradation to block a tributary with a low sediment load and create the present‐day Lake Murray; (iii) the resulting aggradation was sufficient to move the gravel–sand transition on the Strickland River upstream; (iv) the present‐day Fly Estuary may be, in part, a relict river valley drowned by sea‐level rise and partially filled by tidal effects; and (v) the Fly River is presently reforming its bankfull geometry and prograding into the Fly Estuary. A parametric study with the model indicates that sediment concentration during floods plays a key role in determining whether or not, and to what extent, transgression is expressed in terms of sediment‐starved autoretreat. A sufficiently high sediment concentration can prevent sediment‐starved autoretreat during the entire sea‐level cycle. This observation may explain why some present‐day river mouths are expressed in terms of deltas protruding into the sea, and others are wholly contained within embayments or estuaries in which water has invaded landward.  相似文献   

Sedimentology and architecture of the Douglas Creek terminal splay,Lake Eyre,central Australia     

JOHN A. FISHER  CARMEN B. E. KRAPF  SIMON C. LANG  GARY J. NICHOLS  TOBIAS H. D. PAYENBERG 《Sedimentology》2008,55(6):1915-1930

Douglas Creek terminal splay, sited on the western shoreline of Lake Eyre North, central Australia, covers a surface area of approximately 4 km² with a down‐system length of 2·5 km from the distributary channels terminus to the splay fringe. Two distributary channels feed two sediment lobes which have amalgamated to form the terminal splay. Three primary facies associations have been identified sub‐dividing the creek terminus into distributary channel, proximal and distal splay sections. Proximal splay sediments are characterized by erosionally based, relatively thick (> 100 mm), stacked sheets of coarse to medium sand which commonly display trough and planar cross‐bedding, whereas the distal splay is characterized by thin (generally < 50 mm) massive beds of very fine sand, silt and clay. The change in splay sedimentology is interpreted as reflecting the transition from bedload‐dominated deposition to suspended load‐dominated deposition from decelerating sheetfloods as they spread out from the channel onto the dry lake bed. A proximal to distal splay transition zone is also noted where deposits of both facies associations interfinger laterally and vertically. In scale, geometry and facies associations, the Douglas Creek terminal splay is very different to the often cited Neales terminal splay complex located 70 km to the north. It is suggested that these architectural differences reflect variations in discharge volume, input sediment distribution and the degree of vegetation cover. Understanding the variation in terminal splay architecture has very significant implications for the modelling of analogous subsurface petroleum systems, which at present relies on few modern‐day analogues.  相似文献   

Greenhouse carbon balance of wetlands: methane emission versus carbon sequestration   总被引：6，自引：0，他引：6  

GARY J. WHITING  JEFFREY P. CHANTON 《Tellus. Series B, Chemical and physical meteorology》2001,53(5):521-528

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Fusain in Carboniferous shallow marine sediments, Donegal, Ireland: the sedimentological effects of wildfire   总被引：2，自引：0，他引：2  

GARY NICHOLS  TIM JONES† 《Sedimentology》1992,39(3):487-502

Evidence from fusain deposits in Lower Carboniferous rocks of western Ireland indicates that a catastrophic wildfire destroyed thousands of square kilometres of Carboniferous ‘forest’. In addition to yielding large quantities of charcoal, this wildfire event resulted in increased surface water runoff which affected sedimentation in an adjacent estuarine environment where the fusain is now preserved. This is the oldest documented evidence for a catastrophic palaeowildfire and a clear example of the sedimentological effects of large-scale fires. The Lower Carboniferous (Visean) rocks in the Largymore Syncline of western Donegal, Ireland, are shallow marine sandstones, mudstones and limestones. The Upper Shalwy Beds are mudstones and cross-bedded sandstones which show bi-polar cross-stratification and mud drapes on cross-bed foresets indicating deposition in a tidal environment, probably a large estuary. In three coastal exposures a bed containing up to 20% fusain is found at the same stratigraphic horizon. The fusain is interpreted as fossil charcoal produced by palaeowildfire in a land area to the north-west. The volume of fusain present in the unit can be estimated and by comparison with charcoal production in modern wildfires it has been calculated that around 95 000 km² (more than the present land area of Ireland) was burnt. Along with the fusain, other effects of the wildfire can be seen in the deposits, which are poorly sorted compared to the rest of the Upper Shalwy Beds and are characterized by inclined heterolithic stratification produced by the draping of underlying bedforms. These features are considered to be due to a considerably increased sediment load in the estuary, resulting from enhanced surface runoff and soil erosion due to the wildfire.  相似文献   

LOS LAVADORES: DISCOVERING PLACE IN THE ANDES     

CASEY D. ALLEN 《Geographical review》2012,102(3):364-371

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THE CLASSIFICATION OF CROSS-STRATIFIED UNITS. WITH NOTES ON THEIR ORIGIN   总被引：5，自引：0，他引：5  

J. R. L. ALLEN 《Sedimentology》1963,2(2):93-114

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Large transverse bedforms and the character of boundary-layers in shallow-water environments     

J. R. L. ALLEN 《Sedimentology》1980,27(3):317-323

Theoretical work, laboratory studies, and field observations indicate that the oscillatory boundary layers generated by the tidal wave differ fundamentally in dynamics and kinematic structure from the unidirectional boundary layers of rivers. Unique to the former are mass-transport currents attributable to: (1) the wave motion itself, and (2) bed curvature in the presence of the oscillatory flow. The implication of this difference for bed-material transport is that the larger flow-transverse bedforms of shallow-water environments are divisible hydraulically between two major classes: (A) those related to tidal conditions, under which the fluid reverses in direction of flow with each reversal of the tide, permitting the initiation and maintenance of bed features by the spatially reversing, curvature-related mass transport, and (B) those related strictly to rivers and river-like flows, in which the fluid motion is unidirectional, and therefore the only mechanisms available for bedform initiation and maintenance are those creating a finite spatial lag between the transport rate and the bed waviness. Forms of Class B are best called dunes and bars, and only those attributable to Class A should be termed sand waves. The latter, restricted to oscillatory boundary layers of tidal origin, apparently correspond to the very much smaller; but also commonly symmetrical, ripple marks produced in wind-wave oscillatory boundary layers.  相似文献   

ON BED FORMS AND PALAEOCURRENTS     

J. R. L. ALLEN 《Sedimentology》1966,6(3):153-190

Bed forms arise by interaction between a fluid flow and the sediment transported over or close to the bed. The geometry of bed forms is two-dimensional or three-dimensional. Two-dimensional bed forms generate two-dimensional internal sedimentary structures and are adjusted to two-dimensional flow-vector fields. Three-dimensional bed forms generate three-dimensional internal sedimentary structures and are adjusted to three-dimensional flow-vector fields. Many shallow-water flow systems observable today are each characterised by flow-vector fields of unequal rank, and hence are hierarchically structured. Hierarchies of bed forms and internal structures which parallel the hierarchies of flow-vector fields can also be established in the case of these flow systems. A single type of bed form or internal structure from an hierarchically structured flow system cannot specify that system fully with regard to either its directional or flow-dynamic characteristics. An approach to palaeocurrent analysis that is more flexible and comprehensive than previously attempted may therefore be desirable.  相似文献   

A QUANTITATIVE MODEL OF CLIMBING RIPPLES AND THEIR CROSS-LAMINATED DEPOSITS   总被引：1，自引：0，他引：1  

J. R. L. ALLEN 《Sedimentology》1970,14(1-2):5-26

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