摘要:

ABSTRACTOrigin of the longitudinal dune form is reviewed. The spectacular longitudinal dunes of the Simpson desert are caused by helicoidal wind flow of the prevailing south‐southeastern winds, acting upon ancient alluvial plains. Critical in this theory is the evidence from tuning‐fork junctures, which open upwind as do similar features in other geologic realms of primarily one‐directional currents undergoing second‐order helicoidal circulation.A summary of previous work on using grain size to distinguish beach from dune sands reveals the consistent good sorting and positive skewness of coastal dunes. Simpson desert dunes are also positively‐skewed, but are not as well sorted as coastal dunes because they are only recently derived from poorly‐sorted alluvial source sediments. Dune crests are coarsest and best sorted because they are made out of the most easily saltated fine sand (about 2.5 ø); windward flanks, leeward flanks, and reg are progressively finer and also show regular and explainable changes in the higher‐order grain‐size parameters. Both dune and reg sediments are made of polymodal mixtures, giving rise to a “quantum theory” o

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb00217.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTThe northeast corner of the Pacific Ocean is a region of turbidity‐current activity. Cores from this area are dominated by very fine‐grained sand and medium‐grained silt that grade upward to clay. The results presented in this article are based on 217 textural analyses of turbidite layers comprising 30 piston cores.It is possible to distinguish proximal and distal facies of turbidites using characteristics of layering, grading and texture. Features of the proximal facies include wide range of layer thickness, maximum layer thickness, non‐grading, truncation of grading, textural reversals, and sand at the base of graded layers. Areas beyond main routes of submarine flows are sites of episodic addition of silt‐through clay‐sized sediment. The proportion, thickness, and mean grain size of the silt decreases with increasing distance from the main aven

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb00218.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTA series of carefully controlled marine experiments, in which sand of known grain diameter and essentially perfect sorting was exposed to waves of various sizes, was supplemented by study of lakes of various widths (and hence differing values for fetch), in an effort to obtain relationships between parameters measurable in sedimentary rocks (i.e., ripple‐mark spacing) and paleogeo‐graphic information (water depth, wave height, wave length, and fetch). The results were subjected to regression analysis.Two equations were obtained, relating ripple‐mark spacing to grain size, water wavelength and water depth, with predictive abilities higher than 80%. Two equations were obtained, relating ripple‐mark spacing to grain size, water wave‐height and water depth, with a predictive ability of 75%‐80%. Two useful equations involved water wave‐length, and two involved water wave‐height; in general those based on water wave‐length were superior to those based on water wave‐height.In shallow‐water work, the pairs of values which can be obtained from equations included in this paper are highly limited in range, and thus define the paleogeographic unknowns reasonably closely. These pairs (or single values, as may be appropriate) can be inserted into three additional equations, which relate fetch to various wave parameters.An application is made to Jurassic rocks (lower Morrison sandstones) in northern New Mexico, which are interpreted as deposits of a large, shallow lake. Shorelines, where they cannot be located by inspection of the rocks, can be inferred fairly closel

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb00219.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTMicritic envelopes are commonly believed to develop from the lime‐mud infillings of circumferential perforations made in skeletal particles by algae. Because “algae” are usually taken to mean photosynthetic algae, the corollary has been proposed that micritic envelopes would not appear on carbonate skeletal particles originating in waters too deep for active growth of photosynthetic algae. Extensions of this “photosynthetic‐algae‐only” origin of micritic envelopes implies that: (1) the disappearance of envelopes with depth could mark a useful paleobathymetric datum; and (2) preservation of outlines of skeletal particles should be much better in “shallow”‐water carbonates than in “deep”‐water carbonates.We doubt the validity of the depth‐limiting concept of the origin of micritic envelopes for two reasons: (1) petrographic study of a large number of thin sections thought to be representative of various paleo‐depth levels does not indicate any systematic variations in the preservation of the outlines of skeletal particles; and (2) molluscan skeletal debris displaying micritic envelopes and effects of borings identical with those generally ascribed to the activities of photosynthetic algae have been found in an aragonite‐cemented sandstone from the Atlantic shelf where geologic evidence indicates that the water at time of boring was too deep for active growth of photosynthetic algae.Accordingly, we re‐emphasize the fact that organisms other than photosynthetic algae can bore into calcareous materials. In particular, fungi, bacteria, and heterotrophic algae (whose distribution does not depend on the penetration of light into seawater) are known to be active borers. Bacteria can be eliminated as producers of bores having diameters greater than approximately 10 μ. Fungi create boring structures with radiating or branching patterns or bores with nonuniform size. Some fungal bores appear to be indistinguishable from excavations known to have been bored by photosynthetic blue‐green algae. At present we do not know how to distinguish the results of boring activity of photosynthetic algae from thos

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb00220.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTContinuous seismic profiles from the upper continental slope east of North Islands, New Zealand, show that surface sediment 10–50 m thick has slumped down bedding planes sloping at 1°–4°.There are four slumps, the Kidnappers Slump which has an area of 250 km2, the Paoanui Slump of 80 km2, a small slump of only several square kilometers and a slump of undetermined extent. All occurred during the last 20,000 years in Last Glacial Age sediments. A glide plane is exposed at the head of each slump and beds are thrust or contorted at the toe of some slumps.Slumping was probably caused by the failure of loosely packed sandy silt during major earthq

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb00221.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTSediment cores originating from the Indian and the Atlantic Ocean were investigated. The declination of the cores was measured non‐destructively. In both regions it was possible to correlate several cores on the basis of their magnetization (intensity correlation in contrast to correlation of paleomagnetic reversals). Additional layers of turbidity‐currents and a layer of volcanic material were detec

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb00222.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTEven small colloidal clay fractions in suspension affect markedly the results from a hydrometer test. The discrepancies are due to non‐consideration of specific gravity and relative viscosity of the actual clay‐water suspension. Therefore, actual—i.e., experimentally or otherwise determined—values of specific gravity and relative viscosity should be used instead of the conventionally used values for the specific gravity and the coefficient of viscosity. Expressed in terms of this study, in equations 1 and 2 the values ofG1andnshould be replaced byG11andnr,respectively. Another simple but time‐consuming remedy is to remove the clay content from the soil by repeated decantation before conducting the hydrometer

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb00223.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTIn studies of particle‐size distribution of the less than 20‐mm fraction of glacial clays in eastern Durham it is noted that one particular characteristic seems common to them all. When the particle‐size data obtained by sieving and hydrometer analysis are plotted on semi‐logarithmic graph paper (BRITISH STANDARDS, 1961) it is seen that almost all the curves are made up of two shallow concave or straight sections separated by a small section of varying convexity. What is perhaps most surprising is that this convexity or marked break of slope is nearly always found in the range 0.2–0.8 mm. The break of slope shows that the material in the finer grain sizes is more abundant than the coarser material.The question arises as to what is the cause of this break of slope and whether it is a sorting characteristic of sub‐glacial processes or is explicable in terms of parent‐mater

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb00224.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTThe bulk of the material comprising the pocket beach at the mouth of the Manndraperelv, Tanafjord, northern Norway, is supplied by the river. The stream bed consists of poorly sorted coarse sediments which show a crude upstream imbrication. Dampening of wave activity near the mouth of the stream by the outflow of water has caused relatively fine‐grained material to accumulate on spits. Size‐shape sorting by waves concentrates the finest pebbles on landward moving swash bars.Away from the stream mouth beach deposits become finer grained landward, and are zoned in a manner similar to that described by BLUCK (1967). If similar deposits were preserved in the geological record they might be confused with coarse‐grained fluviatile sequences. Study of the textures of the Manndraperelv deposits establishes criteria for distinguishing between these two possibil

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb00225.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

The Geology of Western Europe. M. G. RUTTEN. Elsevier, Amsterdam, 1969, 520 pp., 303 illus., Dfl. 65.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb00226.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY