摘要:

ABSTRACTAnalyses of the chemistry of the earth's sedimentary shell (and the crystalline crust) reveal evolutionary trends in sedimentary rock composition, depositional environments, and the intensity and relative importance of geochemical processes. Successive changes in the mode of crustal movement, the intensity of volcanic and intrusive activity, and in the structural plan of continents (reduction of the area of active geosynclines, increase of the area of platforms) caused a regular transformation of the petrographic composition of ancient erosion areas and corresponding changes in the composition of terrigenous material that at different stages was supplied to depositional areas (gradually lower amounts of greywacke, decrease of average Na, Mg, Fe and Al content, inverse development of K and Ca). Sediment‐composition and lithological proportion in the sedimentary shell changed in the course of time: the abundance of volcanogenic rocks decreased, the abundance of carbonates and evaporites increased, the types of prevailing carbonate accumulation changed (siderite→dolomite→calcite), the degree of compositional differentiation of terrigenous sediments increased. These changes were accompanied by regular evolutionary changes in the chemical composition of the most important sedimentary rock types: the lowering of average Na and Fegencontents, the increase of Corg, Ssulfand Spyrconcentration, the inverse K development, the increase of the Ca/Mg ratio, the rise of the iron oxidation degree, the displacement of isotope ratios of oxygen and sulfur, etc.A definite trend in the development of the main types of sedimentary geochemical processes is established. The processes of clastogenesis and hydrolysis developed inversely: the importance of the first process decreased, but that of the second increased in the course of time. The intensity of oxidation and precipitation processes also increased through time; chemical precipitation was predominant during the early development stages, and biogenic precipitation predominated during the later stages. Characteristic boundaries in the evolution of sedimentary rock composition and geochemical processes are traced, which correspond to the boundaries A and Pt1, Pt1and Pt3, Rf3and V, Pz3and Mz. Discontinuous variations in the concentrations and ratios of elements in sediments and in the intensity of some geochemical processes are confined to these boundaries. They were determined by changes in the composition of erosion areas, by the increasing importance of platform types of sedimentary processes, by large changes in the biosphere, by the evolution of the atmosphere and ocean composition, and by changes in the types of surface equilibria in the dynamic system: atmosphere‐ocean‐str

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00019.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

ABSTRACTBedforms are defined and their variety outlined. Aeolian bedforms are shown to arise spontaneously by a two‐way interaction between surface form and airflow involving piecemeal material transfer between them. They eventually reach a dynamic equilibrium and transverse elements migrate downwind.Aeolian bedforms may be compounded of elements from four groups i.e., draas, dunes, aerodynamic ripples and impact ripples, each subdivided into transverse and longitudinal elements. There are no transitional forms between the elements of one of these eight subgroups and those of another and they are interpreted as being formed by different mechanisms. The possible nature of these mechanisms is considered and qualitative models for the development of generalised transverse and longitudinal elements given. Transverse and longitudinal elements may be combined in three different ways according to whether or not one element is displaced half a wavelength on crossing the othe

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00020.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

ABSTRACTAuthigenic quartz crystals formed within skeleton walls frequently contain carbonate inclusions which may characteristically differ from the composition of the skeletons. Whereas the skeletons suffered diagenetic alteration, the inclusions in the quartz crystals were more or less preserved and thus may indicate the original composition of the skeletons, provided the quartz crystals formed not too late in diagenesis. Because they generally grew after the aragonite‐calcite transformation, original aragonite skeletons are characterized by low‐Mg calcite inclusions in the quartz crystals whereas original high‐Mg calcite skeletons differ clearly by the Mg‐content of the inclusions. There is no difference between inclusions within quartz of original low‐Mg calcite and transformed aragonite skeletons, but the former skeletons are well and the latter are poorly preserved.By this method, it is shown that PaleozoicStromatopora and Actinostromaas well as Triassic Ammonoidea presumably were composed of aragonite, whereas the shells of articulate brachiopods (Stringocephalus, Terebratula, Rhynchonella, Gigantoproductus) were composed of low‐Mg calcite. The skeletons of Crinoidea (Devonian, Muschelkalk, Jurassic) and of Devonian rugose and tabulate corals, however, were composed of high

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00021.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

ABSTRACTMarine, mid‐Tertiary mudstones and siltstones of northwestern Oregon and western Washington contain unusual calcite pseudomorphs that commonly form the nuclei of carbonate concretions. These pseudomorphs typically have the shape of rhombic prisms, with dipyramidal terminations, that are much elongated due to multiple twinning (?). They appear similar to the glendonite pseudomorphs of New South Wales, however, their rhombic (orthorhombic?), prismatic form is at variance with the reported monoclinic form of the glendonite pseudomorphs. Internally, the pseudomorphs consist of granular calcite that takes the form of large ovoid crystals, radial or spherulitic crystals, fibrous but non‐radiating crystals, and mosaic crystals of clear spar.The original mineral, believed to be aragonite or one of the hydrated carbonates, probably formed in soft, organic‐rich mud, possibly in the burrows of marine organisms. Changes in physico‐chemical conditions caused early solution of the original mineral, leaving hollows or molds that quickly filled by precipitation of granular calcite. Judging from the low δC13values of the pseudomorphs, the carbonate carbon of this granular calcite was supplied from CO2produced through decay of local masses of organic matter. Concretionary calcite, supplied from a different source as shown by much higher δC13values, formed around the pseudomorphs. The entire pseudomorphic and concretionary process took place only a short distance below the depositional interface, prior to compaction and lithification of the host

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00022.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

ABSTRACTSedimentary structures are examined in recent alluvium that was deposited in an environment transitional between fluvial and estuarine. The depositional sequence in vertical section reveals three units, that vary according to type and association of sedimentary structures, and lithology.1The lower unit is characterized by large‐scale trough cross‐stratification. Sedimentary structures suggest a fluvial environment in which water and sediment movement were uni‐directional but subject to periodic fluctuations.2The middle unit displays an alternation of small‐and large‐scale cross‐stratification, which is directionally bi‐modal due to tidal action. Both water and sediment movement were bi‐directional and highly variable in intensity. A vertical gradation in dimension of structures shows successive weakening of tidal currents as deposition proceeded.3The upper unit is characterized by flaser and lenticular bedding and small‐scale trough cross‐stratification, ascribed to an estuarine regime of low intensity.The observed transition from a fluvial to an estuarine environment is tentatively related to increased tidal action, caused by the destruction of large parts of reclaimed land bordering the Oude Maas, following severe floods in this area during the 14th and

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00023.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

ABSTRACTThree main kinds of syndepositional deformation are found in cross‐bedded sand‐grade sediments. The first type is characterized by simple recumbent folds of broadly parabolic form. The second is marked by series of folds, with or without overturning. The third type is much more complex, presenting a combination of faulting, folding, and the local destruction of bedding.The type marked by recumbent folds is interpreted as due to the deformation of a liquefied (or perhaps fluidized) sand by current drag following an event in the majority of cases suspected to be an earthquake shock. By reference to empirical and theoretical studies of sedimenting systems, and the behaviour under small shear stresses of liquids of high viscosity, this physical model is developed analytically to yield equations describing the geometry of the deformations in terms of the thickness of the deformed bed, the settling velocity and concentration of particles in the liquefied sand, the viscosity of the liquefied sand, and the magnitude of the deforming force. The equations describe a fold surface that is a portion of a flat‐lying parabola, and show that the proposed circumstances of deformation are plausible in terms of what is known of the real situation. They further reveal that, under the assumptions made in the analysis, the vertical height of the fold hinge above the base of the bed is a function only of the initial shape of the deformed cross‐stratum, the shear rate in the liquefied materials, and the falling velocity and concentration of particles in the liquefied bed. The shapes of deformations calculated from the equations agree well with patterns observed from the geological

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00024.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

ABSTRACTSince Galliher's studies on the sediments from the Monterey bay (California), vermicular pellets have been considered to be derived from mica flakes by a transformation phenomenon. Generally, it is considered that all the glauconite pellets result from the transformation of degraded smectitic‐ or illitic‐type sheets into more ordered sheets. In the present study, it is shown that the vermicular pellets cannot be derived from the transformation of a mica flake. The mass obtained is several orders higher than the initial mass. Secondly it is noticed that the transformation process invoked do not allow for the continuing existence of the sheets. Finally, the ions of the micaceous sheet are never involved in the “transformation”, for sometimes they are found intact in the vermicular pellet. A study carried out through an electron microscope by reflexion indicates that there is crystal growth between the mica sheets. These sheets are merely a support favourable for glauconite neoformation. If the ions of the mica flake are involved in this genesis to any extent, they yield only a very low quantity of the mass of the final granule. As in the cracks of quartz grains, in feldspar cleavages or in limestone pores, the important surface constituted by the mica sheets is a catalyst for glauconite neofo

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00025.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

ABSTRACTA synthetic rubber base spray adhesive was used to obtain high‐relief, rapidly drying peels of moist unconsolidated beach sand. Samples from vertical planar trench walls and box coring devices were obtained instantaneously and completely hardened in about fifteen additional minutes, with drying times dependent primarily on air temperature. This technique can also be used for preservation of sediment‐core structures in the laborat

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00026.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

ABSTRACTRonov and Migdisov (1971) very effectively document and explain the apparent compositional evolution of the shield and platform rocks of the world in terms of secular changes in source composition, the mode and intensity of weathering (in turn a reflection of secular variations in the composition of the biosphere, atmosphere, and hydrosphere), and compositional differentiation resulting from repetitious episodes of granitization, metamorphism, erosion, and sedimentation. Based on modifications of my own analysis of geosynclinal sediment compositions (Schwab, 1971), I suggest some additional comparisons and interpretations (Fig.1, Table I).

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00027.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Book reviewed in this article:The Crystalline State: an Introduction. P. Gay.Analytical Geochemistry. (Methods in Geochemistry and Geophysics, 5.)The LordEnerglynand L. BrealeyMineralogy for Students. M. H. Battey.Bauxites. IdaValeton.Evolution of Sedimentary Rocks. R. M. Garrels andF. T. Mackenzie.The Origin of Life by Natural Causes. M. G. RuttenOptische Bestimmung der gesteinsbildenden Minerale. Teil 1, Bestimmungstabellen. W. E. Tröger(4th revised edition, prepared by H. U. Bambauer, F. Taborszky, and H. D. Trochim).Chemical Weathering of the Silicate Minerals. F. C. Loughnan.Manual of Planktonic Foraminifera. J. A. Postuma.Procedures in Sedimentary Petrology. RobertE. Carver(Editor).Les Grès du Paléozoïque inférieur au Sahara. Sédimentation et Discontinuités‐Evolution structurale d'un Craton. S. Beuf, B. Biju‐Duval, O.deCharpal, P. Rognon, O. Garielet A. Bennacef.Karst‐Important Karst Regions of the Northern Hemisphere. MilanHerakand VictorT. Stringfield(Editors).Carbonate Sediments and Their Diagenesis. (Developments in Sedimentology, 12.)R. G.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1972.tb00028.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY