摘要:

SUMMARYAnalysis of influx and efflux of sediment and water to and from the ocean and of residence times of the elements indicates that the oceans and atmosphere are in a steady state with respect to erosion and sedimentation. A detailed examination of the ocean‐atmosphere model is needed to see how the system worked in the geological past. Weathering is characterized primarily by the absorption of H+by silicates and secondarily by liberation of SiO2,alkalies and HCO3—to the oceans. The H+is supplied mainly by the H2O‐CO2system via the ionization of H2CO3but some is supplied by HCI from volcanic emanations. Weathering of carbonate rocks results in the same absorption of H+, releasing Ca2+, Mg2+, and HCO3—. Sedimentation, silicate reconstitution, and diagenesis are seen as the reverse of weathering in that H+is released and SiO2and alkalies are precipitated from solution. Thus a constant H+release is necessary to keep constant the CO2pressure of the atmosphere by transforming the HCO3—of the ocean into CO2+ H2O. The sedimentary products that are part of the steady‐state model are reconstituted silicates (degraded clay minerals that become diagenetically altered to less hydrous, more siliceous illites and chlorites), limestone (precipitation reverses limestone weathering), salt (uses up alkalies), and chert (uses op free SiO2). It is concluded that the major site of silicate reconstitution is not on the open sea floor but in coastal subsiding sedimentation belts in which high‐grade diagenesis takes place and whose formation waters are ultimately connected with the ocean and so can buffer it. The obvious consequences of the model are that the global amounts of carbonate, reconstituted silicate, salt, and chert must be related in a systematic way for any time interval in which the system is steady. To keep CO2constant, the total of carbonate precipitation and silicate reconstitution must be conserved. Similarly, salt precipitation and silicate reconstitution must be related to keep alkali removal constant. Finally, chert must be related to silicate reconstitution so that all silica released by weathering is removed from the ocean. A careful examination of the stratigraphic record is needed to objectively determine from such parameters whether the steady‐state system has always been operating much as today or whether there have been major secular changes or periodi

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1968.tb00837.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYAlthough supplied to rivers, grains of about 1–6 mm diameters are notably deficient in fluvial deposits because they are more readily entrained and more rapidly transported than grains of larger or smaller size. Very coarse sand and fine gravel are rarely found in shallow‐water sediments for the same reason. Currents, mainly of wave origin, concentrate these grains in beaches, where they are present in more‐than‐ordinary ab

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1968.tb00838.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYThe Cape Fear Formation rests on basement rocks in the Cape Fear River valley of the North Carolina Coastal Plain. It consists primarily of graded muddy sand—sandy mud couplets. A typical sequence for each couplet starts with a disconformity, followed by a basal gravelly sand with megaclasts of quartz and clay pebbles, cross‐bedded sand, and finally a structureless mud bed. Fossils are absent. The sand fraction is poorly sorted and the sediment has a clayey texture. Structures and textures suggest that each couplet is the product of a current waning from an upper flow regime, to the lower part of a lower flow regime. Turbidity current and fluvial origins are considered. Cross‐bedding and textural criteria indicate that normal, low‐density currents are responsible for at least part of the typical sequence. A normal fluvial origin is rendered less likely by the absence of mud cracking, root casts, and textural criteria of a partitioned subaerial environment. Stratigraphic and geochemical considerations suggest that the formation may have been deposited in estuaries or coastal lagoons; if so, the stratification may record sedimentation during the periodic flushing of saline water by river

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1968.tb00839.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYThe Río de la Plata Drainage Basin is the second largest in South America, with more than 75% of its discharge provided by the Paraná River and the remainder by the Uruguay River. Erosion rates, and silt‐ and clay‐size mineralogy indicate that most of the basin loads are provided by the mountainous environment

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1968.tb00840.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYElectron microprobe analyses of skeletal carbonate structures in coralline algae and pelecypods show that the magnesian content of the calcite depends on skeletal growth rates. Growth rate is a function of certain variables, including water temperature, light, and physiological cycles. The Mg‐content of calcareous sediment from specific organisms is not, therefore, mainly dependent on water temperature, as is generally believed, but also on the other factors affecting growt

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1968.tb00841.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYThe basic differences between mechanical analysis of sand by Ro‐Tap sieving and by settling in a sedimentation balance are discussed. The Groningen balance can continuously and rapidly record settling times of the grains (50–1,000 μ) of a 1.5‐g sample with a maximum recording and reading error of about 2%.The theory of sieving is not fully developed yet, nor has the theory of settling of sand‐sized particles been adequately expressed by any mathematical law. The drag coefficient (CD) and Reynolds number (Re) relation often used to derive diameter (d) from settling velocity (v) in this size range, are calculated from experimental data on diameter and velocity. Conversion of settling times to “sedimentation diameters” with the help of experimental curves for single, spherical quartz grains and their comparison with the corresponding “sieve diameters” are often found to be unsatisfactory in the case of natural sands, because shape and density variations of every individual grain in a sample can never be taken into account. Therefore, the use of settling velocity as a new grain parame

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1968.tb00842.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYRipple, flaser and lenticular bedding are well known, but for describing profiles, they are not sufficiently defined and subdivided. It is, therefore, the intent of the following text to present such a definition and classification.The classification contains the following main bedding types and intermediary types (Fig.1):1Cross‐bedding with flasers.2Flaser bedding, subdivided in: (a) simple flaser bedding; (b) bifurcated flaser bedding; (c) wavy flaser bedding; (d) bifurcated wavy flaser bedding.3Wavy bedding.4Lenticular bedding with thick or flat lenses, subdivided in: (a) continuous lenticular bedding (with connected lenses); (b) broken lenticular bedding (with single lenses

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1968.tb00843.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYThis report describes an investigation by means of laboratory tests of the critical shear stress and bed erosion as a function of time and bed shear stress for a sediment consisting of alternating sand and clay layers 0.1–3 cm thick (sand‐clay laminae). This type of deposit occurs quite frequently in estuaries and tidal inlets. The tests were carried out on an original bed deposited in an estuary.The critical shear stress and the degree of erosion in relation to time for the sand‐clay lamination were found to agree in order of magnitude with those for clay layers. The resistance to erosion of the sand‐clay lamination is therefore comparable with that of clay

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1968.tb00844.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYTurbidity currents are thought to be the agency responsible for the transport and deposition of the sediments known as turbidites. The way in which such currents may arise has been studied experimentally in a glass‐walled tank.The starting point of the experiments was setting the sediments in motion by raising their pore pressure via a shock or vibration. This was achieved in the experiments by striking the metal bottom of the tank with a mallet.The response of a heap of homogeneous sand to such a shock was merely to change the angle of its slope. If a layer of sand was draped over a core of coarser, homogeneous sand, sliding occurred along the plane of permeability contrast and the less coarse sand was deposited at the toe of the slope. When the layer consisted of kaolin, which has a much lower permeability than sand, sliding again took place, but the clay subsequently mixed with the water and was moved along the bottom of the tank in the manner attributed to turbidity currents.An attempt is made to set up a scaling rule for experiments of this type and the consequences that such a rule may have in subsequent study are briefly discusse

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1968.tb00845.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Book reviewed in this article:Statistische Methoden für Erdwissenschaftler (Statistical Methods for Earth Scientists). D. Marsal. E. SchweizerbartPetroleum Microbiology. J. B. Davis.Geology of Shelf Seas. D. T. Donovan(Editor). Oliver Boy

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1968.tb00846.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY