ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00259.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTIn May 1974 a powerful flood flushed the Grand River basin, Ontario. The effects on the bedload were drastic in a narrow (30 m) and deep (40 m) rock walled and floored gorge near Elora, Ontario. Along Irvine Creek, the tributary occupying the gorge, the gravel cover was reworked in several types of bars, predominantly transverse and point bars. The bars formed very rapidly in response to essentially steady, non‐uniform flow that developed during a brief period of high flood.Superimposed on major bars are several minor sedimentary features such as coarse transverse ribs, chute channels and bars, longitudinal ribs, imbrication clusters, backsets with well developed imbrication, that were formed under very high stream discharge. Structures like imbrication clusters, transverse ribs and small riffle bars require a ‘live bed’ situation to form, and they develop when stones come to a stop either because they cluster during transport, or because keystone effects occur along shallow channels. In Irvine Creek, very few sedimentary features were formed during waning and low flood stages: only some shadow deposits and a few Ostler lenses. The few fines that were available were lost downstream or filled in lower parts of gravel beds.This study confirms that in streams that experience strong seasonal fluctuations in discharge, bedforms that develop during high floods have a high probability of preservation. In gravelly deposits, foreset structures and plane beds are most commonly preserved, although they may be difficult to recognize in old deposits, which may appear massive, particularly if the gravel has been infilled with finer pebbles and sand. In the case of Irvine Creek, all deposits are organized, and lateral and vertical variations in textures, particularly imbrication and packing, are very useful in the recognition of sedimentary struc

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00260.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTThe Guelph esker (Ontario, Canada) consists of a sinuous, steep‐sided and segmented ridge which comprises poorly sorted, matrix‐supported sands and gravels. These sands and gravels were probably deposited during the sliding bed stage which has been observed by others in closed‐conduit hydraulic experiments. The poor sorting probably resulted from a high concentration of bed‐material load in the lower part of a subglacial tunnel, sorting being restricted to that produced by particle collisions. Inclusive graphic standard deviation is characteristically large for the sands and gravels, indicating that virtually all sizes available were in transport. The overall grain size distribution shows a characteristic undulatory shape on arithmetic probability paper, mostly because of selective removal of pebble gravel and granule sizes. This poorly sorted fades is believed to be diagnostic of transport in a subglacial tunnel flowing full of water, and may be used to identify subglacial conditions in other eskers. Deltaic sands and gravels occur downcurrent of the esker and contain a greater diversity of structures; climbing‐ripple cross‐laminae, parallel laminae and massive structure, deposited in large‐scale foresees at the end of a subglacial tunnel. These deltaic sands and gravels grade distally into outwash sand

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00261.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTIn growing sedimentary sequences range and velocity of vertically ascending pore water (advection) can be determined quantitatively by using a simple graphical method. During continuing deposition and maintenance of compaction equilibrium, the pore water from deeper layers cannot reach the sediment‐water interface. Range and velocity of advective flow decrease from top to bottom of a sequence and depend on the thickness affected by compaction. The velocity of pore water flow as well as the transport of solutes by advective flux are proportional to the sedimentation rate. Compaction flow can also result from under‐con‐solidation and diagenetic reduction of pore space. At the sediment‐water interface, a direct contact between the ascending pore water and the overlying water body is feasible only under special conditions (interrupted sedimentation over under‐consolidated material, erosion). These results are demonstrated on geometric models of sedimentary sequences, on experimentally deposited clay, and on selected examples of the Deep Sea Drillin

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00262.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTA sequence of gradational lithification events can be observed in caliche profiles, in the Saldanha Bay area (South Africa), from friable lightly cemented aeolian calcarenites or littoral shelly deposits through an intermediate semi‐indurated zone to an upper strongly indurated zone (calcrete).Lightly cemented sediment fabrics exhibit bridge and meniscus cements, micritic druses and vadose compaction phenomena. The middle semi‐indurated zones exhibit coated grains in which irregular borings and/or tubules with tangential acicular fibres contribute to coated grains. Random networks of acicular fibres also occur in void spaces. In fully indurated upper layers of the caliche profiles, fabrics of micriteand microspar (in voids) occur in complex brecciated macro‐fabrics.The features represent changes in a sequence from the friable primary sediments to the calcretes. Fresh‐water vadose flushing leaches grains and causes formation of meniscus and bridge cements and uneven druses. In the middle zone, inorganic processes are aided by the action of micro‐organisms; fungi, bacteria or algae which produce tubules and irregular borings; the overall effect of which is to break down original detrital carbonate particles and enclose them in a crypto‐crystalline micrite. The acicular fibres probably result from evaporation of supersaturated solution. Mechanical processes cause fracturing, which repeated many times gives complicated brecciated fabrics within the upper ind

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00263.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTIllite, illite‐montmorillonite (I‐M) mixed layer, kaolinite and chlorite are the principal clay minerals identified in the carbonate and terrigenous carboniferous rocks in the South Wales coalfield. Mineralogic changes and illite crystallinity are the main modifications in the studied rocks. Progressive illitization of I‐M mixed layers (decrease in their expandabilities) towards the western part of the coalfield (i.e. in the direction of increase in coal‐rank and grade of metamorphism), and the development of vermicular kaolinite, dickite, allevardite and pyrophyllite in the anthracite area are the main mineralogic changes. Illite crystallinity was determined by Weaver's sharpness ratio (S.R.) and isosharpness ratio maps of illite in the carbonate and terrigenous rocks are produced showing a gradual increase in illite crystallinity towards the west. Illites in the terrigenous rocks tend to be aluminous (evidenced by the increase in their intensity ratios, ‘I.R.’) with increase in coal‐rank and grade of metamorphism towards the west. These changes are controlled to some extent by lithology. Correlation of illite S.R. with either its I.R. or expandability of I‐M mixed layer, has outlined two diagenetic zones in the coalfield: zone I, the Diagenetic zone, in the eastern and southern regions; and zone II, the Metadi‐agenetic zone, covering the central and northern parts of the central region. The Anchimetamorphic zone (zone III), which corresponds to the anthracite area in the northwestern region, was differentiated by correlating the illite S.R. with coal‐rank. The occurrence of the above mentioned diagenetic zones and modifications of the clay minerals in the carboniferous rocks of the South Wales coalfield are mainly lateral without variation wit

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00264.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTA variety of finely laminated, subfossil, aragonitic stromatolites and oncolites occur on a regressive marginal flat surrounding Marion Lake, South Australia. These algal forms overlie a substrate of coarse, highly porous, moldic aragonitic limestone which passes progressively towards the take centre through a zone of interstatified aragonite and gypsum and ultimately to pure crystalline gypsum. All of these facies overlie Holocene marine carbonate bank sediments which unconformably overlie at least one upper Pleistocene marine unit. Detailed petrographic and stratigraphic studies, combined with comparative studies of related nearby lakes containing a variety of living aragonitic cryptalgalaminates, provide a model for development of the Holocene sedimentary sequence. Marion Lake last became inundated by the sea around 6500 years ago during the Holocene transgression, when a protected marine environment was initiated. Lateral sediment accretion sealed marine passes into the resulting lagoon system soon after sealvel stabilized, and a variety of gypsum and gypsum‐carbonate‐algal facies evolved. Pure gypsum was deposited in waters 2–3 m deep in the central basin area concurrently with formation of seasonally alternating gypsum and aragonite layers towards basin margins. Blue‐green filamentous algae thrived in the shallower marginal areas and at least partly controlled carbonate deposition, which must have occurred during seasonal outflow of carbonate‐rich ground water from the calcareous dune aquifer over denser gypsum‐saturated waters. These systems eventually migrated towards the centre of the lake to produce the relationships preserved today. The fresher waters also leached the gypsum from the marginal gypsum‐carbonate facies. Collapse due to gypsum dissolution, along with aragonite crystallization, combined to form a lake‐marginal mega‐polygonal facies. Teepee structures formed around polygon margins, with optimum conditions for stromatolite development occurring on the teepee crests. The actual stromatolites which occur around Marion Lake are strongly indurated and involve a variety of morphologies, the most common of which are laterally linked hemispheroids. Stacked hemispheroids and oncolites are also relatively common, along with irregular forms, many of which encrust a variety of substrate irregularities. Vertical relief of the stromatolites varies from centimetres to tens of centimetres and all forms are characterized by extremely fine internal interlaminations of alternate light and dark grey laminae which typically occur several per millimetre. The microstructure comprises micritic aragonite crystals with fibrous habit associated with organic matter, and occasional zones of abundant algal filament molds which are generally oriented norm

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00265.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTGeneralized curves for grain threshold under liquid flow and under gas flow (air), based on laboratory data summarized in a previous paper, are utilized to generate a series of threshold curves for unusual sedimentary environments and little‐studied sedimentary materials of interest to geologists. These are aeolian and water flow threshold on the planet Mars, and the threshold of foraminiferal sands in the deep‐sea. Such extrapolations from the generalized curves are necessary because of the difficulty or impossibility of obtaining satisfactory data for these sediments or environments, and the procedures demonstrate the importance of the general threshold cur

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00266.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTCM grain‐size diagrams of clastic deposits were introduced in 1957. Since that time a large number of diagrams representing most environments were constructed. Discussions of parameters C and M by the writer and by others showed that these parameters are indicators of hydraulic conditions under which sediments were deposited. In a 1975 paper Vandenberghe discussed the CM diagram of the Boom Clay, Belgium, and excluded that CM diagrams gave indications on the mechanism of sediment deposition.In order to answer Vandenberghe's assertions, the writer systematically compared the numerous CM diagrams representing suspension deposits with the characteristics of the environments. Result of this comparison is that CM diagrams give coherent indications on deposition which agree with the known environment characteristics. The Boom Clay diagram is no exception.Another result of the present study is that, in environments as a whole, two types of currents can be recognized, distinguished by the relation between bottom turbulence and grain‐size of sediment in suspension. Deposits of these two current types and distribution of bottom turbulence are indicated by CM diagrams. Characteristics of these currents vary with the environment and help the reconstruction of ancient environments.Information given by CM diagrams has limits and should be integrated with other evidence on the environment. However, contrarily to the information given by ecology or sedimentary structures, the evidence provided by grain‐size has the advantage of being universal, as it can be obtained in all clastic deposits. This evidence therefore is a means for comparing and classifying clastic deposits as a

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00267.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTThis short note reports a series of density current experiments designed to model turbidity underflows caused by flood‐stage discharge of lake‐tributaries. In a 5.8 m long tank filled with freshwater, saltwater was fed in continuously, flowing down a 15°‘delta’ slope onto a horizontal floor. These density currents maintained steady state characteristics. The main objectives of this investigation were to determine (1) the flow regime of the density currents and (2) the underflow‐induced movements in the freshwater. Reynolds numbers for thirty‐five runs ranged from 70 to 4100. Experiments with laminar flow reproduced kinematic (Froudian) models of underflows measured in the Walensee (Switzerland). Flow was rapid on the slope (Froude number, Fr>1) and tranquil (Fr<1) on the floor. Turbulent flow experiments yielded velocity profiles (with a maximum at the flow interface) which approximate natural conditions. Movements in formerly stagnant water body are induced by interfacial shear stress: a layer of freshwater is dragged along by the density current and replaced by the backward flow of an equal amount of overlying water (mass conservation). Extrapolated to a natural setting, circulation induced by underflows is probably an important mechanism for oxygenating deep lacus

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00268.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY