摘要:

SUMMARYA simple method of determining the strike and dip of the AB planes of mica flakes in etched slides of arenaceous sediments by means of a universal stage mounted on a stereomicroscope is described.The polar stereograms constructed from such measurements in fluviatile sandstones show monoclinic symmetry due to up‐current imbrication which compares well with the orientation of plant fossils, current bedding structures and the general current pattern. An angular discordance exists between these features and the direction of sole marks.An example is given of how analyses of the orientation and imbrication of mica flakes can assist in the solution of sedimentation problems of coalfield geolog

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01591.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

SUMMARYThe objective characterisation of sedimentary structures has not had as robust a development as more qualitative approaches. Using KRYNINE'S definition (1948, p. 145) that sedimentary structure is the “visible expression of non‐uniformity in texture and composition”, a method is here developed that yields data which are a function of the thickness and orientation of the visually homogeneous elements that, juxtaposed, comprise a sedimentary structure. This method, based upon a progressive enlargement of the field of vision about a point until the included area is first non‐uniform, yields a series of diameters which are related to both structural type and sampling plan. Exposures of sediment on a point‐bar in the Mississippi River were studied in this manner and it was determined that the method efficiently discriminated between structural varieties, and additionally allows the structural complexity of a point‐bar to be given a succinct quantitative

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01592.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

SUMMARYDispersal patterns, based upon the frequency distribution of rock types in the submarine gravels of Foveaux Strait, indicate a connection between the gravels and the present terrestrial drainage systems to the north and south of the Strait. It is inferred that the submarine gravels were initially deposited as fluviatile sediments during a former period of low sea‐level. It is further suggested that the significant factor regulating the proportions of the various rock types wasnotdistance from the periphery of the present marine environment or the proximity or relief of the source areas. More important were the actual sizes of the water catchment and source areas on opposite sides of the Strai

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01593.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

SUMMARYAncient geosynclinal coastal deposits, preserved and exposed for present‐day examination, probably represent interior—and hence protected—shores, and were therefore characterized by low‐to‐moderate breaker energy levels, as is the modern Gulf of Mexico. Modern low‐energy beach sand size distributions are distinguished by an inflection, here called the surf “break”, formed by a winnowing or statistical filtering process, by the breakers, in the finer sizes. The result is a two‐segment curve having an intersection in many cases not far from 1.5 phi. If the energy level is very low, a tail of fines may be added, producing a three‐segment curve having two inflection points. Along high energy beaches, the surf “break” occurs at such large grain sizes that it cannot be preserved in sand; whether or not it can be recognized in gravel is not known.Ancient sandstones which represent the breaker zone, along a low‐to‐moderate energy coast, should also exhibit the surf “break”. The Lyons Sandstone, a known Permian beach deposit, provides an example. Other examples are cited.Any useful indicator of the shoreline position, in lithified rocks, should have three characteristics: ease of recognition, high reliability, and strong probability of preservation. The surf “break” scores reasonably well on all three points. Hence it may be an important key to paleogeography. Nevertheless, there still remains a question inasmuch as certain river sands have similar inflections. Whether these kinks were inherited from near‐by, but older, beach deposits, or were formed by stream action, is not known. The reliability of the surf “break” is estimated at 80% or better, except for the case where near‐shore sands, of whatever

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01594.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

SUMMARYIn contrast with the commonly accepted notion regarding ancient turbidites, non‐greywacke sandstones are not uncommon in the typically graded turbidite facies of the Cambrian and Silurian sediments in north Wales. The sandstones are the arkosic and lithic types of PETTIJOHN (1957) or the feldspathic and lithic arenites of GILBERT (1954) and occur at the bottom of graded beds when the grain size tends to be above medium grade. Petrological features suggest that debris forming the sandstones in north Wales was not significantly modified during transportation and original provenance characters are well preserved.The occurrence of such sandstones implies that: (1) the current concept of ancient graded greywackes in the turbidite facies should be revised; (2) non‐greywacke sandstones in ancient turbidites are comparable in petrological features to recent deep‐sea sands; (3) these sandstones are important in connection with the origin of the clay matrix in grey

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01595.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

SUMMARYData from Ordovician and Tertiary turbidites and from the Hekla ash fall show good correlation between bed thickness and grain size. Most of the thicker beds are coarser grained. The relation between bed thickness and grain size in graded beds can be explained by a theory which uses a sedimentation formula based on the decay law of turbulence in the deposition zone of a turbidity current.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01596.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

SUMMARYSolutions of calcium bicarbonate were allowed to lose carbon dioxide and evaporate to dryness under controlled temperature conditions. With filtered solutions prepared from spar calcite, precipitates were 100% calcite in the 2° to 100°C temperature range. When, in analogous experiments, coralline aragonite was the starting material, the precipitates were 100% calcite. Essentially the same was true when carbonate rocks from karst areas were used to prepare the experimental solutions. An artificially prepared mixture (maximum crystal size of about 7 u) of 70% aragonite and 30% calcite was also used in the study. The precipitates from this starting material were apparently affected by seed nuclei which passed through the filter. The stability of calcium carbonate seed nuclei appears to vary with temperature. Natural calcium bicarbonate solutions from caves yielded only calcite at 25°C.Calcite should be the dominant or only polymorph of CaCO3formed by the loss of carbon dioxide and evaporation of natural calcium bicarbonate solutions if temperature is the controlling factor. Since appreciable amounts of aragonite are found in many cave deposits, factors other than temperature must influence the polymorphs formed.POBEGUIN (1955) proposed that rapid evaporation and slow diffusion of solutions favor aragonite. If so, layers of aragonite and calcite in speleothems may reprsent alternate wet and dry paleoclimates. During these periods, rate of introduction of solution and rate of evaporation would change marked

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01597.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

SUMMARYIn the light of present‐day requirements and the author's personal experience, existing systems of nomenclature and classification of sediments on a textural basis need revision. A system is proposed that is based on a three end‐member relationship involving sand‐, silt‐ and clay‐size particles. The construction, nomenclature and application proposed, fulfils the purpose of a classification because it is simple, easily remembered, practical, has wide application, is needed; and above all it groups sediments into useful categories that make communication more effective a

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01598.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

SUMMARYThe weight‐frequency size distribution is generally accepted to be log‐normal (phi‐normal) for sandstones, but the nature of number‐frequency distribution of particles in sandstones is largely unknown. This paper develops the theory of correction procedure for the observed weight‐frequency moments obtained by thin‐section analysis of sandstones (and clastic sediments in general) which was not avail

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01599.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

SUMMARYCriticisms by VAN DER PLAS (1962) of thin‐section point counting as a method of size analysis appear to be based on confusion betweennumber percentandvolume percent.Points are samples of volume, and point counts yield volume percents. This is as much true of size classes as of other types of constituents, though distortions are caused in the distribution by the sectioning effect. The “ribbon” method advocated by Van der Plas counts individuals rather than points and hence yields number percents. The two types of statistic are fundamentally diff

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01600.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY