摘要:

ABSTRACTRelatively pure lacustrine carbonates referred to as marl are being deposited in Littlefield Lake, central Michigan, a hard‐water lake with little terrigenous clastic influx. Thick accumulations of marl form both progradational marl benches along lake margins, and islands or lakemounts in the lake centre. Marl benches develop flat platforms up to 20 m wide in very shallow water and steeply inclined slopes, up to 30°, extending into deep water. The flat landward platform is frequently covered by algal pisoliths while the upper portion of the lakeward‐sloping bottom is overgrown byCharawhich in the summertime becomes thickly encrusted with low‐magnesian calcite. Marl islands are flat‐topped features that formed over relict highs on Pleistocene drift which underlies the lake basin. These are fringed by marl benches identical to those found along lake margins. Marl benches are composed of four units: two thin facies deposited on the shallow‐water bench platform and two thicker faces deposited on the bench slope developed in moderate water depths. These in turn overlie a fifth facies deposited in deep water. A coarsening‐upward sequence is developed in these sediments as a result of both mechanical sorting, and primary production of carbonate sand and gravel in shallow water. In addition to facies sequences and size grading, trends upsection of increasing carbonate content and decreasing insoluble content may serve to identify temperate‐region lacustrine carbonate deposits in t

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1980.tb01164.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

ABSTRACTCampanian (Upper Cretaceous) Chalk exposed in a quarry near Portsmouth is unusual in the occurrence of a contemporaneous anticlinal fold, probably diapiric in origin. Hardgrounds and local slumps developed over the structure, and part of the chalk succession thins considerably over its crest. Erosional channels, sometimes containing bioclastic lag deposits, formed at two levels. Movement on the anticline occurred three times during the part of the Lower Campanian represented in the section; the third phase resulted in extensive fracturing of the crestal region of the fold. Burial of the structure and the onset of normal chalk deposition concluded the Cretaceous phase of its history.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1980.tb01165.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

ABSTRACTAbundant wave ripples with wavelengths of up to 0.3 m, top‐surface granule lags and tabular sand‐stone beds suggest that the interbedded sandstones and siltstones of the Skaergårdnes Formation are shallow marine deposits. A simple orthogonal relationship between crestal trends of wave ripples and trough axes/cross‐bed dip directions indicates that bottom currents and surface waves were closely related, suggesting that wind‐drift currents were responsible for deposition. Interbedding of the tabular sandstones with siltstone is more probably due to the patchy nature of sand cover on the sea floor than to episodic sand derivation from the coast. The top‐surface granule lags indicate local, temporary excess of sand removal over supply, and were probably formed by both wave‐winnowing and non‐depositional megaripple migration. The well developed lags in this and similar ancient sediments suggest that winnowing, leading to bed armouring and sediment bypassing may be an important shallow

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1980.tb01166.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

ABSTRACTThe identification of the remains of organisms contributing to carbonate sediments by means of scanning electron‐microscopy is limited to particles of the 2–20 μm size class. Mineralogy and the content of Mg, Sr and trace elements alone are usually insufficient to solve the problem of identification, especially in the differentiation between algal and coral aragonite. The organic matrix of calcareous organisms consists of stable biopolymers such as polysaccharides and glycoproteins which are intimately associated with the carbonate skeleton. Analysis of these hydrolysed compounds gives rise to characteristic arrays of monosaccharides which provide independent criteria for producer identification. The calcareous green algaeHalimeda, PenicillusandUdoteashow high xylose and low fucose levels. Xylose and fucose levels are elevated in the red algaeAmphiroabut only fucose is prominent in the brown algaePadina.The coralsOculina, Porites, MilliporaandMontastreaare relatively rich in fucose and show little or no xylose. In the bivalvesArca, Codakiaand inArgopectenmannose may be characteristic. Analysis of artificial and natural sediments demonstrates that coral and algal aragonite can be distinguished on the basis of the total sugar concentration and respective xylose and fucose levels. The applicability of the technique in comparison to geochemical and mineralogical methods has been demonstrated for surface sediments from varying water depths of Harrington Sound, Ber

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1980.tb01167.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

ABSTRACTDiagenetic transformation of clay minerals, zeolites and silica minerals in Cretaceous and Tertiary argillaceous rocks from deeply drilled wells in Japan were studied. Transformations of these minerals during diagenesis were as follows: in clay minerals, montmorillonite → montmorillonite‐illite mixed‐layer mineral → illite; in zeolites, volcanic glass → clinoptilolite → heulandite and/or analcite → laumontite and/or albite; in silica minerals, amorphous silica → low‐cristobalite → low‐quartz. Maximum overburden pressures and geothermal temperatures corresponding to these transformations in each well studied were calculated. For clay minerals, a pressure of approximately 900 kg cm−2and a temperature of about 100°C are necessary for the transformation from montmorillonite to mixed‐layer mineral and 920 kg cm−2and 140°C for mixed‐layer mineral to illite. Transformation from kaolinite to other minerals requires much higher pressures and temperatures than from montmorillonite to mixed‐layer mineral. For zeolites, 330 kg cm−2and 60°C are required for the transformation from volcanic glass to clinoptilolite, 860 kg cm−2and 120°C for clinoptilolite to heulandite and/or analcite, and 930 kg cm−2and 140°C for heulandite and/or analcite to laumontite and/or albite. For silica minerals, 250 kg cm−2and 50°C are necessary for the transformation from amorphous silica to low‐cristobalite and 660 kg cm−2and 70°C for low‐cristobalite to low‐quartz. Based on these diagenetic mineral transformations, seven mineral zones are recognized in argillaceous sediments. On the other hand, from the porosity studies of argillaceous sediments in Japan, the process of diagenesis is classified into the following three stages. The early compaction stage is marked by shallow burial and viscous rocks with more than 30% porosity. The late compaction stage is characterized by intermediate burial and plastic rocks with 30‐10% porosities. The transformation stage is marked by d

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1980.tb01168.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

ABSTRACTAn early diagenetic non‐hydrothermal deposit of Na‐alunite [(Na,K)Al3(SO4)2(OH)6] is described from the Miocene Ras Maalab Group at Ras Sudar Sinai. The alunite is nodular and occurs along two horizons parallel to bedding. Displacive growth structures and disrupted bedding within the host rock, together with enterolithic growth structures within the nodules, indicate a period of growth prior to compaction. Linear arrays of fabric elements within the nodules, observed under the microscope, further support early diagenetic growth. The host sequence, believed to be the product of sedimentation within barred coastal lagoons has been subdivided into two lithofacies, one reflecting a subtidal open‐lagoonal environment, the other an intertidal restricted‐circulation environment. Anaerobic conditions of early diagenesis conducive to generation of H2S and FeS2preceded an oxidation event produced either by contact with free‐circulating oxygenated waters or by emergence. The sulphuric acid generated lowered the pH and clay minerals were converted t

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1980.tb01169.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

ABSTRACTThe pattern of empirical distributions, in particular size distributions, is often best brought out by drawing a log‐histogram. The Gaussian or ‘normal’ distribution furnishes a description of the empirical distribution if the log‐histogram approximates to a parabola. In many cases, however, the log‐histogram is far from parabolic but may be closely approximated by a hyperbola. It is therefore natural to consider those theoretical probability distributions for which the graph of the log‐probability (density) function is a hyperbola. The theory and applicability of suchhyperbolic distributionshave been the subject of a number of recent investigations and it is the purpose of the present paper to summarize these developments, with regard to the interest they may have to sedimentologists. A precise description of the hyperbolic distributions is given and their wide applicability is indicated. Methods for fitting these distributions to data are discussed and a number of sedimentological examples are presented. Furthermore, the question of finding dynamical explanations for the occurrence of the hyperbolic shape is considered from various poi

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1980.tb01170.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

ABSTRACTCalculations of the critical dimensionless bed stresses that obtain when upper‐stage plane beds should revert to ripple and dune bed forms are presented. Strong support is given to the Bagnold ‘universal’ plane‐bed instability criterion and to a modified criterion suggested by Allen over a wide range of solids grain size. A reinterpretation of the mechanism of plane bed instability is based upon the extent to which significant grain concentrations in plane bed flows increase apparent fluid viscosity and decrease turbulence production over potential bed defects, thereby preventing ripple or dune propagation and

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1980.tb01171.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

ABSTRACTElutriation from a fluidized bed provides an accurate, economical, direct method of sediment grading by terminal velocity. This is of particular value in studying populations of irregular particles in the range medium sand to granule (e.g. carbonate sands). A column suitable for such material (terminal settling velocity 1‐30 cm s−1) is described and sample results from ConnemaraLithothamnionbeach material are gi

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1980.tb01172.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

ABSTRACTThe flows above ripples of glass beads and ripple models have been visualized in an oscillatory water tunnel. Some ripples were observed to form without flow separation. Two types of vortices, the standing vortices without flow separation and the separation vortices have been observed, and their similarity is discussed.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1980.tb01173.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY