Modelling controls on aeolian dune‐field pattern evolution     

ERIN EASTWOOD  JOANNA NIELD  ANDREAS BAAS  GARY KOCUREK 《Sedimentology》2011,58(6):1391-1406

A second‐generation, source‐to‐sink cellular automaton‐based model presented here captures and quantifies many of the factors controlling the evolution of aeolian dune‐field patterns by varying only a small number of parameters. The role of sediment supply, sediment availability and transport capacity (together defined as sediment state) in the development and evolution of an aeolian dune‐field pattern over long time scales is quantified from model simulations. Seven dune‐field patterns can be classified from simulation results varying the sediment supply and transport capacity that control the type and frequency of dune interactions, the sediment availability of the system and, ultimately, the development of dune‐field patterns. This model allows predictions to be made about the range of sediment supply and wind strengths required to produce the dune‐field patterns seen in the real world. A new clustered dune‐field pattern is identified from model results and used to propose an alternative mechanism for the formation of superimposed dunes. Bedforms are hypothesized to cluster together, simultaneously forming two spatial scales of bedforms without first developing a large basal dune with small superimposed dunes. Manipulation of boundary conditions produces evolving dune fields with different spatial configurations of sediment supply. Trends of spacing and crest length increase with decreasing variability as the dune field matures. This simple model is a valuable tool which can be used to elucidate the dominant control of aeolian sediment state on the construction and evolution of aeolian dune‐field patterns.  相似文献   

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

  相似文献   

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   

Is there a Need for Sedimentary Rock Reference Samples ?     

A. PARKER 《Geostandards and Geoanalytical Research》1977,1(2):147-147

Six sedimentary rook types are proposed as geochemical standards: an arkosic sandstone, a quartzitic sandstone, a shale, a marl, a dolomitic limestone and an evaporite. Localities where these might be obtained are given, and alternative suggestions invited.  相似文献   

Bedrock lithology control on contemporaneous alluvial fan facies, Oligo-Miocene, southern Pyrenees, Spain   总被引：1，自引：0，他引：1  

GARY NICHOLS†  BEN THOMPSON 《Sedimentology》2005,52(3):571-585

Climate and tectonics play important roles in controlling processes of transport and deposition on alluvial fans, but the bedrock lithology in the fan catchment area is also a significant, independent factor. Adjacent Oligo-Miocene alluvial fan deposits on the northern margin of the Ebro Basin display contrasting depositional characteristics with one dominated by the deposits of debris flows and the other by deposition from flows of water. A difference in clast compositions indicates that the two studied fans (the Nueno and San Julián fans) had contrasting bedrock lithology in their drainage basins. The proximal facies of the Nueno fan body contains matrix-supported conglomerate beds with up to 80% pebble clasts of gypsum in a matrix of gypsiferous sand, interbedded with gypsarenite beds. The drainage basin of this fan was dominated by Triassic bedrock consisting of beds of gypsum, marl and micritic limestone. The San Julián fan body comprises clast-supported, polymict conglomerate beds containing pebbles from Triassic, Cretaceous and Palaeogene limestone units that are exposed in the adjacent part of the basin margin. The interfingering of the deposits of these two fans demonstrates that they were contemporaneous. Given the consistent climate, the differences in fan depositional processes must therefore be attributed to the contrasting bedrock lithology in their drainage basins. A drainage basin consisting mainly of marl and gypsum bedrock provided sufficient fine-grained material to generate debris flows, whereas more dilute, water-lain processes dominated where the drainage basin was largely limestone strata.  相似文献   

Assessing uncertainty due to elevation error in a landslide susceptibility model     

MICHELLE L MURILLO  GARY J HUNTER 《Transactions in GIS》1997,2(4):289-298

A landslide susceptibility model, employing a digital elevation model (DEM) and geological data, was used in a GIS to predict slope stability in a region of the H J Andrews Long-Term Research Forest, located in the Western Cascade Range in Oregon, USA. To evaluate the contribution of error in elevation to the uncertainty of the final output of the model, several different, but equally probable, versions of the input DEM were created through the addition of random, spatially autocorrelated noise (error) files. The realized DEMs were then processed to produce a family of slope stability maps from which the uncertainty effects of elevation error upon landslide susceptibility could be assessed. The ability to assess this uncertainty has the potential to help us better understand the inherent strengths and weaknesses of applying digital data and spatial information systems to this application, and to facilitate improved natural resource management decisions in relation to timber harvesting and slope stability problems.  相似文献   

Late Proterozoic periglacial aeolian deposits on the West African Platform, Taoudeni Basin, western Mali     

MAX DEYNOUX  GARY KOCUREK  JEAN NOËL PROUST 《Sedimentology》1989,36(4):531-549

The Late Proterozoic Bakoye 3 Formation is a predominantly aeolian unit deposited in the glacially influenced cratonic Taoudeni Basin of western Africa. The Bakoye 3 can be divided into five distal units, two proximal units, and a local upper massive sandstone. The basal Unit 1 shows a complex interfingering of aeolian and subaqueous structures, and is interpreted as the precursor of the overlying erg sequences. Unit 2 consists of compound, trough cosets of aeolian cross-strata dominated by grain-flow strata. The unit is interpreted to represent draas with superimposed, small, crescentic dunes. A super bounding surface marks the termination and planation of the erg. Unit 3 is distinguished from the underlying Unit 2 by its larger, overall simple sets of trough cross-strata, interpreted to represent simple, large, crescentic dunes. Unit 4 occurs only locally in laterally discontinuous, large troughs. In one case the trough is filled by small sets of tabular cross-strata dominated by grain-flow deposits. At another section, wedges of coarse-grained wind-ripple strata fill the trough. Unit 4 may represent remnants of ergs or, more likely, local deposition in depressions. The depressions, in the latter scenario, formed with the development of a second super surface that truncates Unit 3. Unit 5 consists of very large sets of wind-ripple cross-strata with less common sets of grain-flow deposits. These deposits are believed to represent enormous dunes with large plinths and subordinate slip face development. A third super surface separates Unit 5 from overlying marine deposits. Together, Units 1–5 represent the core of the ergs in a distal position relative to adjacent upland source areas. Proximally, aeolian deposits are simple, smaller, trough sets interpreted as moderate sized crescentic dunes. Coarse-grained braided stream deposits are prominent. Locally, the top of the Bakoye 3 is marked by channelized mass-flow deposits containing aeolian blocks, and is believed to have resulted from iceberg grounding. An overall environment for the Bakoye 3 is one of uplands marked by ice sheets, with outwash plains extending distally to aeolian ergs. Super surfaces, all marked by polygonal fractures and coarsegrained sediment, represent periods of erg termination that may be linked to glacial-fluvial-aeolian cycles.  相似文献   

Sedimentology of proximal to distal volcaniclastics dispersed across an active foldbelt: Ellensburg Formation (late Miocene), central Washington   总被引：1，自引：0，他引：1  

GARY A. SMITH 《Sedimentology》1988,35(6):953-977

Late Miocene volcaniclastics of the Ellensburg Formation (Washington, northwestern USA) are exposed in basins within an integrated palaeodrainage over the depositional reach from 15 to 120 km eastward from a Cascade Range source area. Two facies associations are recognized. The first is composed of laterally restricted, well-sorted, polymictic conglomerates representing a gravel-bedload regime during inter-eruption periods. The second comprises laterally extensive sheets, bounded by deeply-developed paleosols, composed of monomictic pebbly, pumiceous dacitic sandstones with intercalated debris-flow and hyperconcentrated flood-flow deposits. These sheets aggraded in response to eruptive events that are sometimes recorded by air-fall tephras at the bases of sequences. Debris-flow and hyperconcentrated flood-flow deposits occur as far as 120 km from source, but are uncommon beyond 50 km. Hyperconcentrated flood-flow deposits initially increase in abundance away from source as debris-flow deposits diminish, suggesting formation of hyperconcentrated flood flows by dilution of debris flows. Sandy facies form broad sheets dominated by scour-fill bedding, in proximal and medial settings, and grade to narrower, trough cross-bedded sheets in distal settings, suggesting moderation of flood discharges with distance. Base-level changes associated with episodic sediment influx caused incision-aggradation cycles in mainstream settings, and episodic impoundment of tributaries to form lakes or rapidly aggrading, poorly drained floodplains. Although volcanism was the primary control on depositional style, concurrent development of the Yakima fold belt produced a structure-consequent drainage pattern that determined sediment dispersal, and basin subsidence permitted preservation of both syn-eruption and inter-eruption facies. Detritus from rising anticlines was generally diluted by the volumetrically superior extrabasinal volcaniclastics, but dominates deposits of small tributary streams flowing toward, rather than from, the Cascades.  相似文献