摘要:

ABSTRACTThe number of paired horizontal laminae in an ephemeral channel‐fill increases systematically down‐catchment from stream headwaters, and is shown to be functionally related to tributary confluence. Under moving storm conditions, each tributary sub‐catchment delivers a sediment‐laden discharge pulse that finds sedimentary expression in paired laminae of light and heavy minerals. Lamina differentiation is attributed to a congregational sorting mechanism. The direct relationship (r, = 0.903) between paired laminae and confluencing tributaries permits palaeoenvironmental inference of drainage‐net character, and palaeoclimatic va

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00116.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTThe Troodos Massif of Cyprus is overlain by a variety of cherts in pelagic chalks, volcanogenic sediments, radiolarites and radiolarian mudstones, all of Campanian to Upper Eocene age.There are two chert types, granular chert and vitreous chert. X‐ray diffraction (XRD) reveals the silica polymorphs, disordered cristobalite and quartz.Silicification of the chalks varies from incipient, to bedded, granular cherts, all with disordered cristobalite as the main silica phase. Quartzitic cherts are restricted to the base of Upper Palaeocene and Lower Eocene calciturbidite beds. Disordered cristobalite predominates in the radiolarian mudstones at the foot of the sequence.The form of disordered cristobalite in cavities ranges from microspherules of radiating bladed crystals, the ‘lepispheres’ of the Deep Sea Drilling Project (DSDP) to bladed overgrowths, and fibrous silica. In contrast, within the fine grained matrix, the disordered cristobalite takes the form of partly coalescent crude microgranules and microspherules.Most of the chalcedonic quartz in Cyprus is derived by recrystallization of previously inorganically precipitated disordered cristobalite rather than by direct precipitation.According to the concept of impurity‐controlled maturation the composition of host sediment controls the incorporation of exchangeable cations and other impurities into inorganically precipitated disordered cristobalite. With time (up to 100 million years) internal solid state reorganization of the disordered cristobalite is accompanied by gradual expulsion of impurities, until the cristobalite dissolves followed by quartz precipitation. Complete conversion to quartz takes place first in porous calcareous sediments free of impurities, as in the Cyprus calciturbidites; in fine grained clay‐rich sediments, like Cyprus radiolarian mudstones, disordered cristobalite persists much longer. Impurity‐controlled maturation also helps explain the diagenesis of Cyprus ch

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00117.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTGrain‐size parameters derived from the mechanical analysis of acid‐insoluble residues from mixed terrigenous‐shell beach sediments from Auckland, New Zealand, are more effective for interpreting the depositional processes, and for characterizing the beach environment on textural scatter plots, than are parameters based on the analysis of the total beach samples. This results mainly from the wide variations in size of hydraulically equivalent skeletal carbonate grains in the sediment, especially in the coarser size grades, but may also be accentuated by the local origin and susceptibility to alteration of the shell material. Compared with the total sediment grain‐size distribution, the insoluble residues from the beach deposits are characteristically finer‐grained, better sorted, and more consistently coarse‐skewed and leptokurtic.The grain‐size distribution characteristics of insoluble residues from several stratigraphic units in a sequence of Oligocene mixed terrigenous‐skeletal shelf sediments in the South Auckland region distinguish depositional mechanisms and environmental energy levels for each unit that are consistent with interpretations made on the basis of carbonate petrography and palaeontology. With regard to the bulk content of terrigenous mud in the insoluble residues, the grain‐size distribution of the fraction coarser than 4φ is alone diagnostic of the energy‐time trends in these sediments.The grain‐size parameters of the acid‐insoluble residues in modern and ancient mixed terrigenous‐skeletal carbonate sediments may provide more reliable criteria for distinguishing and characterizing the depositional environment of these deposits than do the parameters obtained from the size distribution of

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00118.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTTwo sets of empirical data on the relationship of the plan shape of current ripples to flow conditions previously thought incompatible are reconciled by taking explicit and necessary account of the effects of flow width relative to flow depth. The aspects of plan shape considered are the mean streamwise ripple wavelength and the wavelength, measured across the flow, of longitudinal features due to centrifugal instability formed on the backs of the ripples. A regression analysis connecting these attributes with flow conditions including the width‐effect shows that the amount of unexplained variability is of the same order as the accumulated experimental errors, and suggests that the two sets of data are in excellent agreement. The relationship of the plan geometry to flow conditions is less simple than has sometimes been supposed, but ways are suggested in which the experimental results can be used to establish the hydraulics of past environment

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00119.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTThe structural state of an alkali feldspar is determined by the nature of the distribution of Al and Si in the tetrahedral sites of the feldspar structure. This state is a function of a number of genetic controls including temperature, cooling rate, deformation, crystal size, and several chemical factors. Together these controls constitute a genetic regime. Identification of the structures of detrital feldspars may enable recognition of genetic regimes and be useful in provenance interpretation and mineral province definition.A 2‐peak method of X‐ray diffraction (XRD) determination as a variant of an earlier proposed 3‐peak method of structural state determination is used in this study. Total analytical time for each determination is about 50–55 min per grain. Results of structural state identification of 126 detrital feldspars from Holocene stream sands derived from volcanic, plutonic and metamorphic rocks are presented in order to illustrate the application and potential of the technique. Detrital feldspars from the metamorphic rocks are all maximum microcline; those from the plutons range from orthoclase to microcline depending on the age of the pluton, whereas those from the volcanic rocks are sa

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00120.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTChert distribution in the Lake Valley rocks is selective to mud‐supported facies; it is not related to proximity to unconformities. The facies selectivity of the chertification is believed to be a function of the depositional distribution of indigenous silica as sponge spicules, an interpretation that is supported by high positive qualitative correlation of chert with spiculitic rocks. Petrography indicates that the spicules were all originally siliceous, and that they all went through a moldic stage during which many molds were compactively destroyed and distorted. Remaining molds were subsequently cemented by calcite or chalcedony. Chert distribution and spicule petrography argue for an intraformational source for much of the silica.Chert micro‐fabrics are dominated by microquartz, a replacement of grains and lime mud; length‐fast chalcedony, a pore‐filling cement; and megaquartz, a post‐chalcedony pore‐filling cement.Petrography of compaction features within chert masses indicates that chertification occurred after some burial. Based on stratigraphic reconstruction this burial depth was a maximum of about 215 m. and was most likely a few metres to a few tens of metres.Petrography of chert‐calcite cement relationships indicates that chertification occurred before and during first generation, pre‐Pennsylvanian non‐ferroan calcite cementation, and was completed before late‐stage, post‐Mississippian ferroan calcite precipitation. Petrography of chert clasts in basal Rancheria (Meramecian) and basal Pennsylvanian conglomerates proves these clasts derived from the Lake Valley Formation and were chertified before redeposition. Thus, some cherts in the Lake Valley are pre‐Meramecian in age, but all are pre‐Pennsylvanian in age. Furthermore, association of the cherts with the non‐ferroan cements indicates the cherts were probably precipitated in meteoric phreatic lens established beneath the pre‐Meramecian and pre‐Pennsyl

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00121.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTThe vertical and lateral stratigraphic relations of facies and facies associations, palaeocurrent directions, and geometry and internal organization of associated thick‐bedded and coarse‐grained bodies of sandstone provide the framework for distinguishing five thin‐bedded turbidite facies in the Eocene Hecho Group, south‐central Pyrenees, Spain. Each facies is characterized by a number of primary features which are palaeoenvironmental indicators by themselves. These features and their palaeoenvironmental significance are summarized below.1The impressive regularity and lateral persistence of bedding and depositional structures, combined with the association of thin hemipelagic intercalations are typical characteristics of thebasin plainthin‐bedded turbidites. Lateral variations in bed thickness, internal structures, grain size, sand: shale ratio, and amounts of hemipelagic intercalations are present in these sediments, but take place so gradually that they cannot generally be recognized at the scale of even very large exposures. The basin plain facies has a remarkable character of uniformity over great distances and considerable stratigraphic thicknesses.2Thickening‐upward and/or symmetric cycles with individual thicknesses ranging from a few metres to a few tens of metres are typical oflobe‐fringethin‐bedded turbidites. The sediments that comprise the cycles contain small but recognizable variations in bed thickness and sand: shale ratio. The diagnostic cyclic pattern can be detected in relatively small exposures. It should be noted that in absence of coarse‐grained and thick‐bedded sandstone of the depositional lobes the above cyclic pattern is diagnostic offan‐fringeareas.3An extremely irregular bedding pattern with lensing, wedding, and amalgamation of individual beds over very short distances, sharp rippled tops of many beds, and internal depositional structures indicative of mainly tractional processes without substantial fallout, are typical and exclusive characteristics ofchannelmouththin‐bedded turbidites.4Bundles of interbedded thin‐bedded sandstone and mudstone as thick as a few metres that are separated in vertical sequences by mudstone units of roughly similar or greater thickness are typical ofinterchannelthin‐bedded turbidites. The most diagnostic feature of this depositional environment is the presence of beds of sandstone filling broad shallow channels as probable crevasse‐splays.5Thin, thoroughly rippled sandstone beds with marked divergence of the bedding attitude characterize thechannel‐marginfacies. The divergence or expansion in thickness, is consistently toward the channel axis. Small and shallow channels filled with thin‐bedded deposits, interpreted here as crevasses cut into channel edges or levees during period of severe ov

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00122.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTThe Bingham model has been suggested for the rheological behaviour of debris flow. Velocity plotted against yield strength uniquely defines turbulent and laminar flow in published experimental data on flow of Bingham materials. These regimes are not defined by a unique value of the Bingham number even though it includes both of the critical parameters, yield strength and velocity. Laminar flow in at least the final stages natural debris flows is suggested by sediments with parallel‐to‐flow or inclined clast fabric, preservation of delicate clasts, blocks projecting from the top of the deposit(?), and an absence of flu

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00123.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00124.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb00125.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY