摘要:

SUMMARYIn the Kinderscout Grit (Namurian, R1c) of the southern half of the Central Pennine Basin, England, there occur tabular, isolated, cross‐bedded sets of coarse sandstone, between 4 and 40 m thick. The sets are up to 1 km wide and the foresets, in plan, are convex in the direction of dip. The sets interfere laterally to form extensive sheets. Foresets dip at up to 27° and are sometimes themselves internally cross‐bedded in trough‐shaped sets, here termed “intrasets”. The large sets are thought to be deltaic sedimentation units rather than sandwaves. In the delta top environment in which these sets were deposited, a high rate of bed‐load sediment supply and a sudden deepening were required to initiate the sets.Medium‐scale cross‐bedding, thought to have been laid down in migrating, fluviatile channels overlies the large‐scale sets and represents the topset member of the sedimentation units. From the spatial arrangement of the large‐ and medium‐scale cross‐bedding, it is possible to distinguish those areas where deposition took place during the deepening, from those where it took place essentially after the deepening. The causes of the deepening, which must have been on at least a basinal scale, may have b

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1968.tb00833.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYElectron microscopic examination of Namurian bedded cherts in North Wales (Great Britain) has revealed the existence of two dominant surface textures, granular and spongy, with a range of textures intermediate between the two. These textures can be used to differentiate between three principal lithologies within the cherts and between laminae and colour bands within the lithologies. A positive relationship is demonstrated between the presence of spongy texture and a high volume of impurities; there is a gradation, with increasing argillaceous/organic content, from granular through intermediate to spongy surfaces. It is suggested that this gradation reflects an increase in chalcedony over micro‐crystalline quartz resulting from: (l) an increase in impurities; (2) an increase in the rate of precipitation of silica. The relationship between surface texture and type of lithology is considered to be consistent with the order of crystallisation for silica put forward by MILLOT (1960

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1968.tb00834.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYThe sparitic Plassen Limestone (Tithonian, N.K.A., Upper Austria)The sparitic Plassen Limestone (Tithonian, N.K.A., Upper Austria) shows various types of calcite‐fabric. We distinguish fibrous, fibrous‐drusy, and drusy cavity fillings. While the fibrous fabric can be interpreted as submarine precipitation soon after sedimentation, an explanation of the drusy calcites as submarine or subaerial precipitation remains an open question. There are, however, indications of subaerial influences. For the origin of the dismicrites an interpretation as shrinkage structures may be conside

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1968.tb00835.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYIn this paper the problem of the evaluation of the grain‐size distribution of a spherical granular material embedded in a matrix, upon the basis of the measured distribution of the sizes of the figures formed by the intersection of the grains with a random plane, is discussed and a solution, based upon matrix algebra, is developed.There are no limitations on the method, with respect to the type of particle‐size distribution function involved and, in theory, the grain‐size distribution may be determined to any desired degree of accuracy by the use of a conversion table.Conversion tables, which are sufficiently comprehensive to give results of worthwhile accuracy in most practical cases, are presented and the necessary calculations can be carried out, without recourse to complicated mathematics, by the use of a slide‐rule or a desk calculating machine.If the grain‐size distribution must be divided into a number of classes greater than that covered by these tables, then extended tables must be prepared. This can be done, by application of the methods of the present work but evaluation upon a computer, by use of a standard fast‐running routine, is then practically unavoidable.The present treatment also leads directly to the number of particles of each size present in a unit volume of compact, this being a figure of technical importance which is not easily established by ot

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1968.tb00836.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY