ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00011.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

ABSTRACTApplication of sieve and size‐shape analyses (Moss, 1962) to natural and artificial bed‐load deposits of shallow, unidirectional currents revealed that a textural sequence parallels one of primary structures. With increasing grain size and/or transporting power, sedimentary characteristics followed the stepwise pattern: fine ripple bed stage → coarse ripple bed stage → dune bed stage → rheologic bed stage.Bed roughness (A population grain size) strongly influences sedimentation in the first three, the “bare bed” stages. Respectively, they evidently represent enclosure of the A population particles within the viscous sublayer, their protrusion above the layer which remains influential in their interstices, and the contraction of the layer to insignificance allowing almost fully turbulent flow. Transitions between these bed stages cause major changes in the A and B populations and take place on the bed. Transitions involving the rheologic bed stage, however, take place above the bed, reflecting changes in saltation intensity. The rheologic layer, a moving mass of particles kept dispersed by collisions but gravitationally held to the bed, produces distinctive sediments. Bed‐load sediments can form from arbitrary mixtures in seconds of time or centimetres of travel.Ripples and dunes form only if flow conditions near the bed are fairly steady. Ripples, evidently sensitive to temporal current direction changes, are more readily prevented from forming than are dunes. Whereas structures dominate beds between parallel flume walls, in natural flows, often rife with temporal flow perturbations, plane beds are the more common. The characteristic textural features of the bed stages are shown whether or not the structures develop.Evidently temperature‐sensitive, the fine to coarse ripple bed stage transition could probably be used as a basis for water

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00012.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

ABSTRACTThe Donjek is a proglacial braided river with a coarse heterogeneous bedload ranging from −7 to +8 φ. The three reaches studied comprise, in downstream order, a zig‐zag reach formed by the interaction of the river and tributary fans, a straight reach, and a meandering reach, all with internal braids. The straight to meandering junction is unusual in that slope and discharge both increase.The dominant bed‐forms are longitudinal gravel bars, which migrate only during flood. Their internal structure is poorly defined horizontal bedding, which suggests that gravel deposition takes place on the upper bar surfaces, rather than on foreset slopes at the downstream margins. At lower stage sand accumulates in wedge‐shaped units lateral to the bars, with internal high‐angle cross‐stratification and ripple cross‐lamination; other sedimentary structures are rare. A simple facies model can be constructed on the basis of two trends: a proximal‐distal trend, and an active‐stable trend. Both result in the increased abundance of fine‐grained sediment.Random directional measurements give good estimates of the river trend from small‐scale structures (mainly ripples) and from channels, the latter giving the closest approximation. The variability of ripple orientation always exceeds that of channels. Both increase in the meandering reach, although the divergence of the vector mean from the river trend is not significantly greater than

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00013.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

ABSTRACTAll core evidence supports the conclusion that abyssal plains are sites of graded‐bed sequences deposited from turbidity flows. The deposits appear to be present‐day equivalents of thin‐ to medium‐bedded, graded, flysch‐type sands and silts of many ancient geosynclines and sedimenta

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00014.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

ABSTRACTIn the Lower Breccia Formation (Lower Jurassic), variations in thickness of the breccia sequence, in individual bed thickness, and in size of clasts suggest separate sources to the southwest and north of the study area. Large clasts, poor clast rounding, grading, and restriction of stratification towards the tops of individual beds indicate deposition by mechanisms other than normal marine bottom currents. The deposits are too thick to have been deposited from the bed load of many successive sandy turbidity currents. A mass‐flow origin is therefore favoured. The stratification in the breccias is believed to have formed at a late stage in their deposition. It is considered to be a result of traction of clasts at the tops of beds by fluid entrained by the flow, or turbidity currents associated with the flo

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00015.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

ABSTRACTThe fine carbonate fraction (less than 63 μ in diameter) in 175 sediment samples collected from the Carolina continental margin has been studied. This fraction, generally under 5% of the total sample, averages 43% CaCO3. By comparison, the CaCO3fraction of the total samples averages only 25%. On the inner shelf, the percentage CaCO3in the fine fraction is twenty or more times greater than the percentage CaCO3in the total sample. With increased distance offshore, the percentages of CaCO3in the fine fraction and the total sample approach equality. Beyond the shelf break the percentage of CaCO3in the total sample is greater than that in the fines.The CaCO3faunal components are primarily foraminifera, fragments of foraminifera, mollusc‐barnacle fragments and echinoid material. Minor constituents include alcyonarian and tunicate spi‐cules,Halimedaand other calcified green algae. Many grains are bored and show solution effects. The coarse carbonate fraction shows distinct regional faunal assemblages, but the fines are essentially uniformly distributed. Two exceptions are a zone of mollusc fragments around Cape Hatteras and a foraminifera zone on a portion of the outer shelf. The average carbonate mineral assemblage consists of 44% low‐Mg calcite, 38% aragonite and 18% high‐Mg calcite. The principal modes of origin of calcareous fines on the Carolina continental margin are probably biological and physical destruction of coarser particles and primary formation in fine size fraction (as in the case of some foram

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00016.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Book reviews in this article:Shallow‐water Sedimentation, as illustrated in the Upper Devonian Baggy Beds. R. Goldring.Desert Sedimentary Environments (Developments in Sedimentology, 14). K. W. Glennie.Geology of Clays. Weathering, Sedimentology, Geochemistry. G. Millot.Introduction to Quantitative Paleoecology. R. A. Reymen

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00017.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00018.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY