摘要:

ABSTRACTSedimentation processes forming a series of bipartite layers have been studied mathematically. Two types of sedimentation processes are recognized, i.e. concurrent deposition of sandstone and shale by a turbidity current (Type I) and alternate deposition of each of them (Type II). A time series of events in a sedimentation process is reasonably considered a first‐order Markov chain, and the process is described with a Markov matrix including four state‐variables such as deposition of sandstone, erosion of sandstone, deposition of shale, and erosion of shale. Analysis of Markov matrix yields a fixed probability vector, which for Type I process is different from that for Type II process. The vector bears a close relation to Kolmogorov's coefficient, which is the ratio of the number of beds deposited and the number of beds preserved in a given sedimentary section. This coefficient can be computed on the basis of field observations. Substitution of the computed data determined the values of the fixed probability vector for two sedimentary sections in Japan. The results permitted a theoretical conclusion as to the genesis of observed sandstone‐shale alternations. This conclusion is in good agreement with the deductions from more conventional sedimentological me

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01614.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

ABSTRACTMarkov chain analysis is a comparatively simple statistical technique for the detection of repetitive processes in space or time. Coal measure cyclothems or fluvial fining‐upward cycles are good examples of sedimentary successions laid down under the control of Markovian processes.Analyses of stratigraphic sections commence with a transition count matrix, a two‐dimensional array in which all possible vertical lithologic transitions are tabulated. Various probability matrices may be derived from this raw data, and these are then subjected to chi‐square tests to determine the presence or absence of the Markov property. This technique is applied to four types of stratigraphic succession which occur in the Devonian rocks of Prince of Wales Island, Arctic Canada.(1) A conglomerate succession of alluvial fan origin. Markov analysis is of little or no assistance in the interpretation of these rocks, in which only two principal lithologies are present.(2) A conglomerate‐sandstone succession. Fluvial fining‐upward cycles are detectable by visual examination of the sections and are strongly indicated by Markov analysis.(3) A sandstone‐carbonate succession, of marginal marine origin, and including both marine and non‐marine strata. Cyclicity is weak in these rocks, but analysis suggests that regressions took place much more rapidly than transgressions during their period of deposition.(4) A succession in which the relative proportions of the various lithologies vary markedly with age. The varying nature of the cyclic tendencies is emphasized in this case by dividing the succession into two subintervals, for the purpos

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01615.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

ABSTRACTRadiaxial fibrous calcite, a common cavity fill in ancient limestones, is characterized by curved twin lamellae, optic axes that converge away from the substrate and subcrystals which diverge in this same direction. The optic axes radiate about three or four axes located in positions between adjacent crystals and orientated parallel with the crystal elongation. The crystals are commonly turbid with inclusions, which may be concentrated along twin lamellae and subcrystal and inter‐crystalline boundaries, or form zones parallel to the substrate. Some inclusion patterns reveal the position of former crystal faces.From a consideration of the occurrences, gross morphological characters, the fabrics of the crystals and the inclusion patterns, radiaxial fibrous calcite is interpreted as a replacement of an early diagenetic acicular cement, composed of interfering bundles of radiating crystals. It is suggested that replacement takes place by a solution‐precipitation process and the migration of a fluid film through the acicular host, with replacement occurring most rapidly between bundles of acicular carbonate. The optic axis pattern of the fibrous calcite is considered to be inherited from thec‐axis orientations of the host acicular crystals. Fibrous calcite intercrystalline boundaries form as fractures after replacement. Some inclusion patterns record the characters of the replaced acicular cement; others, formed of impurities reorganized during the replacement, reveal the form of the replacement

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01616.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

ABSTRACTThe total mineralization of solutions squeezed out of montmorillonite clay saturated in sea water was determined at different overburden pressures. The subsequent fractions of expelled solutions were also analysed for various anions (Cl−, SO2‐4, HCO−3, F−) and cations (Na+, K+, Mg2+, Ca2+, B3+).The results indicate that the concentrations of squeezed‐out solutions during the initial stages of compaction (at pressures up to 35 kg/cm2) are slightly higher than that of interstitial solution present initially. The concentration of squeezed‐out solution goes through a maximum, or at least remains constant, before starting to decrease with increasing overburd

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01617.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

ABSTRACTBasaltic boulders dredged from the Mid‐Atlantic Ridge contain lithified coccolith‐foraminiferal ooze in fractures and small pockets. Textural and isotopic studies of this sediment provide no evidence for high temperature metamorphism. The lithified carbonate sediment occurs together with palagonitized basaltic glass and zeolitic tuff, and appears to have been squeezed into cracks and other voids within the congealed margins of partly‐cooled basalt pillows which intruded soft carbonate ooze. Thermal metamorphism probably was precluded by rapid heat dissipation in convecting pore waters and by the thermal stability of calcareous microplankton. Low temperature alteration of basaltic glass appears to have provided the chemical milieu for precipitation of calcite cement as well as zeolites in the sed

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01618.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

ABSTRACTWholesale removal of the unstable carbonate phases aragonite and Mg‐calcite, and precipitation of calcite and dolomite is currently taking place where phreatic waters (the modern water table) invade 120,000‐year‐old Pleistocene biolithites (Falmouth Formation), North Jamaica.Pleistocene rocks presently in the vadose zone are relatively unaltered, and consist of mineralogically unstable scleractinian biolithites. At the water table, a narrow zone of solution, a ‘water table cave’ is commonly encountered. Below the water table the rocks are invariably more highly altered than those above. Mg‐calcites are very rare, and considerable dissolution of aragonite has commonly occurred.Dolomite occurs as 8–25 μm, subhedral to euhedral crystals replacing micrite, or precipitated as void linings. The isotopic composition of the dolomite (δO18=‐1·0 %0, δC13=‐8·4 %0), and its high strontium content (3000 p.p.m.) suggest precipitation as CO2‐oversaturated meteoric groundwaters invade the mineralogically unstable biolithites, dissolve Mg‐calcites and Sr‐rich aragonites, and de‐gas. Because some dolomitized rocks are enriched in magnesium relative to unaltered biolithites, addition of magnesium to the system is necessitated, and is probably derived from sea water in the mixing zone.Phreatic meteoric diagenesis is thus demonstrated to be a rapid process, and t

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01619.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

ABSTRACTThrough an analysis of their coarse‐grain composition (>63 μm), pumice‐rich sandy layers from deep sea cores were identified as shelf‐derived turbidites rather than deposits due to ash rain or drifting pumice. A comparison of median sizes of individual grain types and total samples yielded significant vertical and horizontal sorting trends, which allowed apparently unrelated samples from different cores to be grouped into proximal and distal parts of one turbidite type. A discrimination of samples belonging to unrelated turbidite layers was also possible. In addition, whatever the grain size, planktonic molluscs and foraminifera have Md‐diameters 1·1–2·75 times larger than those of pumice. Weathered shallow‐water skeletals have Md‐diameters approximately equal to pumice, whereas those of augite and hornblende are 1·25–2·3 times smaller. This results in a different proportion of components in proximal and distal turbidite samples. The Md‐values of planktonic foraminifera reach their upper natur

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01620.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

ABSTRACTMineralogical analysis of calcite and Mg‐calcite by X‐ray diffraction requires that the samples be ground to a powder. Such grinding determines the particle size of the powder and the structural damage of the minerals. Both of these in turn affect the peak intensities recorded by the X‐ray machine. Most carbonate sediments are inhomogeneous; they contain both calcite and Mg‐calcite which are affected differently by grinding. Such differences cause quantitative analytical results to be inconsistent with the true mineralogical abundance. The two acceptable methods of analysis—(1) measurement of peak height from the base and (2) measurement of the area under the peak—were compared to determine if sample preparation affects the quantitative results. In samples with variable and relatively small amounts of calcite and Mg‐calcite the measurement of peak height yields more reproducible results than does the measurement of peak areas. Different proportions of particle size of the mineralogical components in a sample powder, affect proportionally more the peak areas than the peak heights. Extensive grinding causes structural damage of the component minerals which affects much more the peak areas than the peak heights. Thus for quantitative analyses of calcite and Mg‐calcite in inhomogeneous carbonate samples which require differing grinding times and have greatly variable amounts of calcite and Mg‐calcite, the peak height measurement seems to be a better method than peak

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01621.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01622.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01623.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY