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   

Experimental studies of the fluidization of layered sediments and the formation of fluid escape structures   总被引：6，自引：0，他引：6  

R. J. NICHOLS  R. S. J. SPARKS  C. J. N. WILSON† 《Sedimentology》1994,41(2):233-253

Experiments demonstrate that fluid escape structures can be produced as a result of unstable fluidization behaviour where a lower base layer of granular material is inhibited from fluidizing by the presence of an overlying non-fluidizing top layer. Before the base layer can fluidize the weight of the overlying material must be balanced, and this is accomplished by base layer material pressing against the bottom surface of the confining top layer forming a static layer. This static layer allows the top layer to lift away from the base layer which is then free to fluidize. A water-filled crack forms below the static layer and, as this grows, instability causes the static layer and top layer to bend and conical voids to form below the antiformal sections. Rupture occurs at the apex of the water void, allowing the underlying water and fluidizing material to burst out through the top layer. The fluidized base layer material then flows through the rupture until all of this material, except that in the static layer, is deposited above the previously overlying layer and a stable fluidization system results. The top layer material is bent upwards around the rupture, and the resulting pillar-type escape structure is preserved if flow then ceases. The vigour of the burst-out is greatest when the base layer material has a grain size 15% of the top layer material. If the base layer grain size is less than 8% of the top layer then base layer material will pass through the top layer pore spaces, without forming an escape structure. If cohesive material is present, escape structures form when a layer of fine grained cohesive material overlies a layer of cohesionless material. At low flow rates small pipes with scattered angular bends pierce the top layer, and base layer material passes through them. The base layer material is ejected on to the top layer and builds up around the mouth of each pipe to form constructional structures, sand volcanoes. This is in contrast to the cohesionless experiments, where the weight of material being deposited on the top layer caused an ejecta-filled depression to form around the rupture. If flow then ceases both the pipes and the sand volcanoes are preserved. At high flow rates, where the base layer fluidizes, the top cohesive layer becomes fragmented. Small fragments circulate within the fluidizing base layer and are preserved as floating clasts. Large fragments sink to the bottom of the fluidizing base layer. Erosion of the bottom surface of these larger fragments causes this surface to become convex downward. The experimentally derived structures are similar to pillar-type structures observed in the field and the processes described can be used to investigate the development of these structures. Fluidization experiments also demonstrate the genesis of dish structures, and the cohesive behaviour can be applied to the deformation of these structures after initial formation.  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   

Origin of first-order bounding surfaces in aeolian sandstones     

GARY KOCUREK 《Sedimentology》1984,31(1):125-128

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Atmospheric deposition to watersheds in complex terrain     

GARY M. LOVETT  JONATHAN J. BOWSER  ERIC S. EDGERTON 《水文研究》1997,11(7):645-654

Single collection stations for wet or bulk deposition are generally inadequate to describe atmospheric inputs to watersheds in complex terrain. Atmospheric deposition is delivered by wet, dry and cloud deposition processes, and these processes are controlled by a wide range of landscape features, including canopy type and structure, topographic exposure, elevation and slope orientation. As a result, there can be a very high degree of spatial variability within a watershed, and a single sampling point, especially at low elevation, is unlikely to be representative. Atmospheric inputs at the watershed scale can be calculated from the whole watershed mass balance if the outputs and within-watershed sources and sinks are known with sufficient accuracy. Alternatively, indices of atmospheric deposition such as Pb accumulation in the forest floor and SO²⁻₄ flux in throughfall can be used to characterize patterns of total deposition, and these indices can be used to model deposition to the entire watershed based on known landscape features such as elevation and canopy type. © 1997 John Wiley & Sons, Ltd.  相似文献