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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
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JOSÉ F. GARCÍA-HIDALGO JAVIER GIL MANVEL SEGURA CARMEN DOMÍNGUEZ† 《Sedimentology》2007,54(6):1245-1271
The Late Cenomanian–Mid Turonian succession in central Spain is composed of siliciclastic and carbonate rocks deposited in a variety of coastal and marine shelf environments (alluvial plain–estuarine, lagoon, shoreface, offshore‐hemipelagic and carbonate ramp). Three depositional sequences (third order) are recognized: the Atienza, Patones and El Molar sequences. The Patones sequence contains five fourth‐order parasequence sets, while a single parasequence set is recognized in the Atienza and El Molar sequences. Systems tracts can be recognized both in the sequences and parasequence sets. The lowstand systems tracts (only recognized for Atienza and Patones sequences) are related to erosion and sequence boundary formation. Transgressive systems tracts are related to marine transgression and shoreface retreat. The highstand systems tracts are related to shoreface extension and progradation, and to carbonate production and ramp progradation. Sequences are bounded by erosion or emergence surfaces, whose locations are supported by mineralogical analyses and suggest source area reactivation probably due to a fall in relative sea‐level. Transgressive surfaces are subordinate erosion and/or omission surfaces with a landward facies shift, interpreted as parasequence set boundaries. The co‐existence of siliciclastic and carbonate sediments and environments occurred as facies mixing or as distinct facies belts along the basin. Mixed facies of coastal areas are composed of detrital quartz and clays derived from the hinterland, and dolomite probably derived from bioclastic material. Siliciclastic flux to coastal areas is highly variable, the maximum flux postdates relative sea‐level falls. Carbonate production in these areas may be constant, but the final content is a function of changing inputs in terrigenous sediments and carbonate content diminishes through a dilution effect. Carbonate ramps were detached from the coastal system and separated by a fringe of offshore, fine‐grained muds and silts as distinct facies belts. The growth of carbonate ramp deposits was related to the highstand systems tracts of the fourth‐order parasequence sets. During the growth of these ramps, some sediment starvation occurred basinwards. Progradation and retrogradation of the different belts occur simultaneously, suggesting a sea‐level control on sedimentation. In the study area, the co‐existence of carbonate and siliciclastic facies belts depended on the superimposition of different orders of relative sea‐level cycles, and occurred mainly when the second‐order, third‐order and fourth‐order cycles showed highstand conditions. 相似文献
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ANDRÉS ALASTUEY XAVIER QUEROL AURA CHAVES ANGEL LOPEZ&#;SOLER CARMEN R. RUIZ 《Tellus. Series B, Chemical and physical meteorology》2001,53(1):40-52
The present work summarises the results of a 2‐year study of wet‐only sequential deposition in 2 rural areas (Alcan¯iz and Morella) located at different distances from a large coal‐fired power station. Precipitation chemistry was characterised by relatively high , Ca2+ and average concentrations. Sequential study of single precipitation events showed that concentrations of most of the ions studied decreased exponentially throughout single precipitation events, with a sharper decrease in concentrations at the beginning of the event. Usually, 40 to 80% of the wet‐only deposition of major ions occurred in the first 2 mm. pH measurements, ranging from 5.6 to 8.1, showed a decrease in the pH values throughout a precipitation event. Deposition levels of Ca2+ and accounted for the neutralisation of major acidic species in the precipitation events except in 5 rain episodes sampled at Morella. The sequential study of the evolution of the ratio during a single precipitation allowed us to identify potential acidic rainfall fractions after an initial volume of precipitation, after most of the Ca2+ in atmospheric particles had been scavenged. A higher neutralisation capacity was deduced for Alcan¯iz owing to the higher atmospheric levels of natural carbonates and . 相似文献
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