摘要:

SUMMARYThere are a series of basins off southern California, all presumably due to faulting of the broad continental borderland. Of these, San Diego Trough is the only one where sedimentation has gone on sufficiently to fill the basin depressions so that there is a continuous slope southward to where the trough connects with the deeper San Clemente Basin. This deposition has apparently come to a very great extent from turbidity currents moving down submarine canyons developing channeled fans at the canyon bases. All along the canyons and channels as well as across the fans and in San Diego Trough there are sequences of turbidite sands alternating with muddy sediments that represent the normal deep water sedimentation. Comparison of the coarse fraction from the sands and from the interbedded muds shows that the former are predominantly terrigenous in character whereas a large proportion of the latter are biogenous. Mica is quite low in the coarser sand layers but is abundant in the coarse fraction of the muds. Diatoms and radiolarians are largely confined to the mud layers where they may constitute a large percentage of the sand fraction.Study of the heavy and light minerals shows that the sediments of San Diego Trough are derived largely from the nearby land masses rather than having a considerable admixture from the north as would be the case if sediments were being brought down by turbidity currents coming into the trough from the north. The alterites are appa‐rently lower in San Diego Trough than in the near shore source area which suggests that a supply of sediments may be picked up from the canyon or channel walls along the way to the trough. Also the finding of the only coarse sands in the middle reaches of the channels suggests local sources as does the general make up of these coarse sands. Despite these locally derived coarse sands the prevalence of very fine sand and the “mud” layers between sand layers suggest that the turbidity currents supplying sediments to San Diego Trough have low velocities or at any rate little erosive cap

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1962.tb00029.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

In order to explain why the magnetic directions of naturally and artificially deposited fine silts show deviations from the direction of the ambient field a theoretical model has been postulated of the process of deposition.The deviations have been explained satisfactorily on the assumption that the sediment consists of quasi‐spherical, non‐cohesive particles which roll into hollows in the existing bed. A model of this kind provides a theoretical basis for the quantitative study of certain sedimentological questions which may be applied to the study of such problems as the apparent anomalous resistance to erosion of very fine grained sediments, their mechanism of compaction and the determination of current direction and velocity.Since it does not depend on direct observation either visual or mechanical the magnetic method may be particularly fruitful for sediments of fine silt grade where such observation is very diffic

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1962.tb00030.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

The observation that the results of line and point counting analyses of the particle size distribution of the same sand are different leads to the conclusion that these results are biased by the sampling technique1. The influence of the currently used sampling techniques on the numerical results of a particle size analysis is discussed. Evidence is presented to show that the use of line and point counting methods in granulometric analysis leads to results in which the influence of the sampling method is so strong that the practical value of these techniques is doubtful. It is therefore considered advisable to discontinue line and point counting techniques in granulometric analysis in favour of ribbon sampling methods.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1962.tb00031.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1962.tb00032.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1962.tb00033.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY