摘要:

ABSTRACTThis study investigates the deposits of sand‐bed ephemeral streams within an area of 250,000 km2in the western Lake Eyre basin, central Australia, being initiated after the record floods of February–March 1967.Large‐scale ripples were the most common bed forms preserved in the majority of channels, covering 30–40% of the depositional area. Other bed forms included longitudinal, transverse and linguoid bars (20%), upper‐regime plane beds (<5%), small‐scale ripples (25–30%), and flute marks (<1%). Major bed forms could be related to flood stage: plane beds (upper regime), large‐scale ripples, and longitudinal bars usually were generated by high‐stage flow, and transverse and linguoid bars by waning and low‐stage flow.Trough cross‐stratification was produced by migrating small‐scale and large‐scale ripples, large‐scale sets comprising about 60% of the deposits. Tabular cross‐stratification (25% of deposits) resulted from the downstream and lateral growth of channel bars. Flat‐bedding with parting lineation (<5%) was dominant only along the middle reach of the Finke, the major stream in the western Lake Eyre basin. Disturbed bedding was almost totally absent. Bed forms, in order of increasing overall mean grain size (?) of deposits, are plane beds (upper regime), small‐scale ripples, transverse and linguoid bars, and large‐scale ripples. Sorting (σI) and skewness (SkI) are dependent on mean grain size (Mz).Lower‐regime flow prevailed for the majority of streams, upper‐regime flow being dominant only in the middle reach of the Finke. Using estimated Froude numbers and Darcy‐Weisbach resistance coefficients, the greatest mean velocities of flow h

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01128.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTSedimentologists have noted that turbidite sequences become thinner bedded and finer grained as traced downcurrent. We provide a semi‐quantitative explanation of this behavior based on the idea that turbulence in a turbidity current decays downcurrent so that in its zone of deposition both the total load in suspension and the grain size of that load decrease with increasing distance from the source. Semi‐empirical equations proposed by Chézy, Lokhtin and Sundborg are central to our argu

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01129.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTSingle‐set cross‐stratification, considered to have been produced by the upstream migration of antidunes, is present in the basal division of certain thick turbidite beds.The basal divisions of these turbidites consist of very coarse to medium sand with a smooth or fluted base and sinusoid top. Internal laminae are inclined upstream at a shallow angle (less than 15°), opposing the local paleocurrent direction shown by flutes and ripple‐drift cross‐lamination.The sinusoid (antidune) bed forms and their associated internal cross‐strata were preserved by the rapid fall‐out of sediment from suspension normal to the bed.A paleohydraulic analysis suggests that during the final stages of antidune growth and migration, the currents moved at approx. 1 m/sec over very low slopes (much l

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01130.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTAn abnormal relationship between quartz roundness and grain size, and unusual K‐feldspar accumulation in the medium sand fraction, quartz grains with overgrowths, and a differentiated heavy‐mineral community made it possible to calculate quantitatively the contributions of four sources to a modern beach sand in southeastern Bornholm. The quartz grains with overgrowths were particularly sensitive to transport and clearly showed an increase in roundness away from their origin, the Balka Quartzite. This rock, due to its high resistance, contributed only about 1% to the beach sa

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01131.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTThe experiments involved pouring aqueous starting suspensions of pumice sand and kaolinite silt into a submerged trough. The steepness of the bottom slope of the trough was varied from run to run. Heights of sand and silt were recorded at 10‐cm intervals away from source. The results: (1) support earlier suggestions that the ratio of sandstone to shale is a sensitive indicator of proximality in ancient turbidites, but do not support clearly the suggestion that the rate of decrease in that ratio away from source may indicate steepness of bottom slope; (2) suggest that the rate of decrease in sandstone thickness away from source in ancient turbidites may be inversely proportional to steepness of bottom slope.The possible application of the results to the geological record is discusse

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01132.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTThe examination, with a scanning electron microscope, of 200 quartz grains from a tropical environment (Uganda) shows the nature of chemical weathering on these grains. Five main types of features occur: solution pits; solution crevasses; chemical etching along quartz structures; blocky forms probably resulting from swelling; and widespread disintegration of the grain surface. Few of these features have previously been recorded.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01133.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTA significant recent advance in microscopy has been the introduction of differential‐interference contrast (DIC) optics. In reflected‐light instruments, one “Nomarski prism” (a modified Wollaston prism) is used both for beam splitting and combining. In effect, two deformed wave‐fronts are produced which are laterally separated by a distance below the resolving power of the microscope. They are brought to differential interference by the analyzer, the effect being one of oblique illumination of the object.This system can be used in the study of mineral‐grain surfaces. For this purpose, conventional replicas of the grains are placed on petrographic slides which in turn are placed over a silvered mirror on the microscope stage. The Nomarski prism is then adjusted until the best contrast is achieved.For a test study, samples were collected from the intertidal zone of the Atlantic shore of eastern Long Island, mostly at localities which earlier were sampled by Krinsleyet al. (1964) and studied in a classical investigation of quartz‐grain surface features by transmission electron microscopy. In the present study, a semi‐quantitative evaluation of surface features was attempted, using as guide the criteria set up by Krinsley and his school. The results of this study are tentatively interpreted as reflecting pronounced erosion in the study area, and increasing energy levels from East Hampton t

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01134.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01135.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01136.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTCoccoliths are the main constituents of the carbonate layers in several Oligocene bituminous shales as well as in the Oligocene “Helle Mergelkalke” limestone, Upper Rhine Graben and Bavarian Molasse Tro

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01137.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY