Anatomy and evolution of a Lower Cretaceous alluvial plain: sedimentology and palaeosols in the upper Blairmore Group, south-western Alberta, Canada     

PAUL J. MCCARTHY  I. PETER MARTINI  DALE A. LECKIE† 《Sedimentology》1997,44(2):197-220

The Lower Cretaceous (Albian) upper Blairmore Group is part of a thick clastic wedge that formed adjacent to the rising Cordillera in south-western Alberta. Regional transgressive intervals are superimposed on the overall regressive succession. Alluvial conglomerates, sandstones and mudstones were deposited in east-north-eastward draining fluvial systems, orientated transverse to the basin axis. Five facies associations have been identified: igneous pebble conglomerate, thick sandstone, interbedded lenticular sandstone and mudstone, thick mudstone with thin sandstone interlayers, and fossiliferous sandstone and mudstone. The facies associations are interpreted as gravelly fluvial channels, sandy fluvial channels, sand-dominated floodplains, mud-dominated floodplains, and marine shoreline deposits, respectively. Five types of palaeosols are recognized in the upper Blairmore Group based on lithology, the presence of pedogenic features (clay coatings, root traces, ferruginous nodules, slickensides, carbonate nodules) and degree of horizonization. The regional distribution of the various types of palaeosols enables a refinement of the palaeoenvironmental reconstruction permitting an assessment of the controls on floodplain evolution. In source-proximal areas, palaeosol development was inhibited by high rates of sedimentation. In source-distal locations, poor drainage resulting from high watertables, low topography and lower rates of sedimentation also inhibited palaeosol development. The best-developed palaeosols (containing Bt horizons) occur in intermediate alluvial plain positions (tectonic hinge zone) where the floodplains were most stable due to a balance between sedimentation, erosion and subsidence rates. Extrapolating from the upper Blairmore Group suggests that the tectonic hinge zone of continental foreland basins can be established by palaeosol analysis. At the hinge zone, soil development is controlled primarily by climate and tectonics and their effect on sediment supply, whereas closer to the palaeoshoreline, relative sea level fluctuations, resulting in poor drainage, may have a more significant influence.  相似文献   

Hurricane control on shelf-edge-reef architecture around Grand Cayman   总被引：3，自引：0，他引：3  

PAUL BLANCHON  BRIAN JONES 《Sedimentology》1997,44(3):479-506

Rimming the outer shelf of Grand Cayman is a submerged, 87 km long shelf-edge reef that rises to within 12 m of mean sea level. It consists of an array of coral-armoured buttresses aligned perpendicular to shore and separated by steep-sided sediment-floored canyons. Individual buttresses have a diverse coral-dominated biota and consist of three architectural elements: a shield-like front wall colonized by platy corals, a dome-shaped crown colonized by head corals, and a shoreward-projecting spur covered by varying amounts of branching coral. Buttresses are commonly fronted by coral pinnacles that, in some areas, have amalgamated with buttress walls to produce pinnacle-and-arch structures. As margin orientation changes, shelf-edge-reef architecture shows systematic variations that are consistent with changes in fetch and height of hurricane waves. Along margins exposed to fully developed storm waves, shelf-edge-reef buttresses are deep, have large amplitudes, and are dominated by robust head corals. These characteristics are consistent with hurricane-induced pruning of branching corals and the flushing of significant quantities of sand from buttress canyons by return flows. Along margins impacted by fetch-limited storm waves, reef buttresses are shallower, have intermediate-amplitudes, and have a significantly higher proportion of branching corals. These characteristics are consistent with less coral pruning and sand flushing by weaker hurricane waves. Along margins fully protected from storm waves, the buttresses-canyon architecture of the shelf-edge reef breaks down producing a series of shallow, undulating, branching-coral-dominated ridges that merge laterally into an unbroken belt of coral. These characteristics correspond with negligible amounts of pruning and flushing during hurricanes. In addition to differences between margins, local intra-marginal changes in shelf-edge reef architecture are consistent with changes in the angle of hurricane-wave approach. Open sections of the shelf-edge reef, which face directly into storm waves, are pruned of branching corals and the fragments swept back onto the shelf producing extensive spurs. By contrast, on more sheltered, obliquely orientated sections, storm-waves sweep debris along and off shelf producing little or no spur development. Instead, the debris shed seawards accumulates in front of the buttress walls and initiates the development of coral pinnacles. Over time, repeated buttress pruning and canyon flushing during hurricanes not only controls reef architecture but may also influence accretion patterns. Vertical accretion is limited by the effective depth of storm-wave fragmentation. Once this hurricane-accretion threshold is reached the reef moves into a shedding phase and accretes laterally via pinnacle growth, amalgamation, and infilling. Consequently, the reef steps out over its own debris in a kind of balancing act between lateral growth and slope failure — a pattern widely recognized in ancient reefs.  相似文献   

ETHNIC RESIDENTIAL SEGREGATION IN BELFAST,NORTHERN IRELAND, 1971–1991*     

PAUL DOHERTY  MICHAEL A. POOLE 《Geographical review》1997,87(4):520-536

ABSTRACT. The segregation of Catholics and Protestants varies spatially and temporally in Belfast, Northern Ireland. Using small-area statistics from the censuses of 1971, 1981, and 1991, taken during the recent “Troubles,” a strongly rising level of ethnic segregation is noted for the 1970s, followed by a more gentle rise in the 1980s. Segregation is shown to vary among subunits of the urban area. The basic cause of this segregation is ethnic violence, and the spatial variation in segregation can be attributed to spatial variation in this violence.  相似文献   

Origin and Evolution of the Kerguelen Plateau, Broken Ridge and Kerguelen Archipelago: Editorial     

WALLACE  PAUL J.; FREY  FREDERICK A.; WEIS  DOMINIQUE; COFFIN  MILLARD F. 《Journal of Petrology》2002,43(7):1105-1108

  相似文献   

Sedimentology and preservation potential of carbonate sand sheets deposited by the December 2004 Indian Ocean tsunami: South Baa Atoll,Maldives     

SCOTT L. NICHOL  PAUL S. KENCH 《Sedimentology》2008,55(5):1173-1187

  相似文献   

A rendzina from the Lower Carboniferous of South Wales     

V. PAUL WRIGHT 《Sedimentology》1983,30(2):159-179

ABSTRACT A thin calcrete-crust horizon from the Lower Carboniferous Llanelly Formation of South Wales consists of two parts; an upper laminated unit and a lower peloidal unit. The former is interpreted as a subaerial stromatolite and the latter as an A horizon of a palaeosol. Comparisons are made with the A horizons of rendzinas and it is concluded that the calcrete-crust represents a complete rendzina profile. This fossil rendzina contains abundant evidence of a soil fauna in the form of fecal pellets and small burrows.  相似文献   

The McIntosh Layered Troctolite-Olivine Gabbro Intrusion, East Kimberley, Western Australia     

MATHISON  CHARTER I.; HAMLYN  PAUL R. 《Journal of Petrology》1987,28(1):211-234

The well-preserved ?lower Proterozoic McIntosh intrusion consistsof 96 macro-layers with a total stratigraphic thickness of about6 km. The lowermost rocks in this possible cone-shaped intrusionare hidden, and the roof and the upper layers were removed byerosion. The layered sequence is dominated by 40 bimodal cyclicunits of troctolite and olivine gabbro. Minor gabbronorite layersoccur throughout the sequence, and are more abundant and morefractionated higher in the sequence. Six imperfect megacycicunits are developed in the upper 2700 m, each unit consistingof several troctolite-olivine gabbro cyclic units followed bya Fe-Ti oxide-bearing gabbronorite. The overall cumulus crystallizationorder in each megacyclic unit was plagioclase first, closelyfollowed by olivine, then augite, orthopyroxene, and magnetitesuccessively. Cryptic composition data for troctolites and olivine gabbrosshow a slight overall decrease of 10 mol per cent An and Fofrom the base to the top of the layered sequence (approximateranges An_80–70 and Fo_78–68). Several major fluctuationsoccur however, and are generally associated with the oxide gabbronorites,which are significantly more fractionated than the adjacentlayers (plagioclase An_53–60, orthopyroxene Mg_52–69Each fluctuation comprises a marked progressive discontinuity(rapid normal fractionation) followed by a gradual to rapidregressive discontinuity (or reversal) in the overlying troctolitesand olivine gabbros. Apparently, such marked progressive discontinuitieshave not been described in layered intrusions. A chilled margin and the overall composition of the intrusionsuggest an olivine tholeiite parent magma, inferred to havecrystallized at P 6 kb, relatively low _PH2O and high f_O2 (>NNO buffer). The troctolite-olivine gabbro cyclic units areinferred to have formed by fractional crystallization of periodicadditions of new magma. However, the oxide gabbronorites seemtoo fractionated relative to the underlying layers to have formedby conventional crystal fractionation mechanisms, and they couldhave resulted from a ‘liquid fractionation’ processin which fractionated residual magma, instead of rising, periodicallybecame denser and ponded on the temporary floor (a density crossover).Gradual, reversed cryptic trends in the cyclic units above theoxide gabbronorite layers may reflect mixing of this fractionatedmagma with successive magma additions.  相似文献   

The role of fungal biomineralization in the formation of Early Carboniferous soil fabrics   总被引：7，自引：0，他引：7  

V. PAUL WRIGHT 《Sedimentology》1986,33(6):831-838

Paleosols in the Lower Carboniferous limestones of South Wales commonly contain needle-fibre calcite which is an unusual form of calcite recently shown to form by the calcification of fungal hyphae in present day soils. The needle-fibre calcite occurs in two associations in the paleosols: as coatings on sediment grains and as rhizocretions. The former can be compared with the microbial grain coatings of Quaternary calcretes. The latter represent the sites of fungal coats on roots and are interpreted as probable ectomycorrhizae, a symbiotic fungal sheath-root association. These findings suggest that biomineralization was important in the formation of soil fabrics during the Carboniferous as it is in present day soils.  相似文献   

Flow regimes in debris flow   总被引：4，自引：0，他引：4  

PAUL ENOS 《Sedimentology》1977,24(1):133-142

The Bingham model has been suggested for the rheological behaviour of debris flow. Velocity plotted against yield strength uniquely defines turbulent and laminar flow in published experimental data on flow of Bingham materials. These regimes are not defined by a unique value of the Bingham number even though it includes both of the critical parameters, yield strength and velocity. Laminar flow in at least the final stages natural debris flows is suggested by sediments with parallel-to-flow or inclined clast fabric, preservation of delicate clasts, blocks projecting from the top of the deposit(?), and an absence of flutes.  相似文献   

The changing photochemistry of the troposphere   总被引：5，自引：0，他引：5  

PAUL J. CRUTZEN  PETER H. ZIMMERMANN 《Tellus. Series B, Chemical and physical meteorology》1991,43(4):136-151

  相似文献