摘要:

SUMMARYPenecontemporaneous calcareous algal products are very complex in both texture and mode of origin. For example, all gradations exist between stromatolites and pseudo‐stromata, different types of oncolites are transitional and are often difficult to distinguish from other allochthonous algal material, algal pellets form the final product of abrasion and they too are very similar despite variations independent of their original source; and some Algae may break down into “algal dust” or carbonate needles.Algal limestones of different ages and environments may supply detritus that is indistinguishable from one another. Therefore, in petrographic investigations of carbonate sediments the descriptive term “limeclast” is less ambiguous than the genetic terms “intraclast” and “calclithite”. If a combination of field‐work and thin‐section studies permits precise genetic and environmental interpretations, the limeclasts can be genetically described as “intraclasts” and “extraclasts”. If the extraclasts form the predominant components, the sediment is a “calclithite” and is a type of terrigenous rock (FOLK, 1959).In general, four possible relations exist between limestone frameworks and micrite matrices. Both allochthonous fragment accumulations and autochthonous growths may have either detrital matrices or matrices that formed in situ. The autochthonous algal micrite matrices give no indication of a degree of turbulence and winnowing in contrast to allochthonous matrices.Apparently minute differences, which are, however, significant in the genesis of limestone components may become more important with an increase in isotope, trace element and diagenetic investigations where the identity of the carbonate

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1965.tb01556.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SUMMARYA noteworthy feature of parts of the Series is the development of cyclothems which consist of: scoured surface, coarse member, fine member, scoured surface. General environments, suggested by this and fossil evidence, are: erosion in river bed, deposition in river bed, deposition in overbank area, erosion in river bed. Structures within the sets of strata include: no lamination, flat bedding, small and large‐scale cross‐lamination, parting lineation. The significance of each is discussed. Sole structures, occurring on the scoured surfaces, are described. They include: groove casts, crescents, flute casts, a variety of long welts, and unoriented structures. These are mainly scour structures but some may be subaerial marks, and there is also evidence for post‐depositional flowage. The value of these structures as indicators of palaeocurrent and ultimately palaeoslope directions is discussed with examples. Measurements of sole structures, parting lineations and ripples have been more profitable than large‐scale cross‐stratification or contorted l

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1965.tb01557.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SUMMARYThe Meridian Sand is recognized as neritic bar sand because it is overlain and underlain by prodominantly marine strata, contains a marine microfauna and is glauconitic. Cross‐bedding is the large scale planar type and has a regional variance of 10,302. No maximum is present where dip azimuths of sets are plotted on a stereogram. It is suggested that the wave path, topography of the depositional surface, and local rates of subsidence varied during deposition of the cross‐bedded sand resulting in a uniform distribution of the cross‐bedding

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1965.tb01558.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1965.tb01559.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1965.tb01560.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY