ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The coast, i.e., the zone where land, sea, and atmosphere meet, is one of earth's most varied and variable environments. Its tectonic and climatic history have produced a configuration which is being altered by physical, chemical, and biological processes. Because these processes operate at different intensities in various parts of the world, the degree of alteration varies greatly.Coastal processes cause both erosion and deposition but the overall effect is a tendency toward smoothing out the coastline. Some of the most common forms along coasts of today are cliffs, beaches, lagoons, estuaries, deltas, dunes, and reefs. Many of these are ephemeral and are present today mainly because coastal processes are operating at a level only recently reached by a rising sea. Even though stillstand has prevailed only 3000–5000 years, there already has been a major reduction in the size and variety of many of these forms and also a major reduction in the quantity of sand available for the nourishment of the world's beaches and coastal dunes. As long as stillstand continues, variety in coastal forms is destined to be reduced even more.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Geochemical facies of sediments and soils (the chemical indicators of the environment) provide geologists with a means to reconstruct fossilized environments of past ages. Facies diagnosis may be based on analysis of fossil bionomy, paleobiochemistry, or geochemistry. Geochemical facies diagnosis may be based on main constituents (lithology, sedimentology, and soil profile); minor components (concentrations in the order of 10−2or 10−3, or less: salinity, ion concentrations of Cl, Br, I, F, and P; Ca: Sr and12C:12C as well as18O:16O ratios, and indications on redox potentials), or the type and nature of organic substances preserved (C: N ratios, biochemistry of carbohydrates, and enrichment in certain elements of coals, oil, and gas). Analysis of chemical facies from remains in lithified sediments should incorporate the physical chemistry of the compounds studied, as well as the changes that will take at high burial pressures and possible increase in temperature.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Changes that may occur in terrestric soils upon inundation with sea water are due mainly to microbial activity. Most prominant changes occur in the clay fraction, where conversion of clay minerals into smectites and/or micas may take place. Iron minerals from terrestric soils may be stable at the sea bottom, but in other cases pyrite and siderite may form. Organic matter will generally decrease in the topsoil of buried terrestric soils and may vanish completely.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Redox processes are quite widespread in bottom sediments of modern water bodies. Decomposition of organic matter in the mass of sediments, taking place as a result of microbiological and chemical processes, changes the physicochemical conditions, thereby bringing about a decrease in the redox potential of pore liquids. Under the reducing conditions created by the decomposition of organic material, the valencies, forms, and geochemical mobility of compounds of certain elements become changed. A possibility is thus created for the redistribution and concentration of certain elements in bottom sediment. Based on geochemical measurements in some 27 sediment cores collected from bottom sediments in the northwest section of the Pacific Ocean, information on the forms of iron, manganese, and sulfur, as well as organic carbon, is given. The sediments studied can be divided into three major categories: (1) reduced sediments of the continental slope; (2) transitional sediments of the marginal oceanic zone; and (3) pelagic sediments of the open ocean (red oozes). Apart from data on the areal distribution of the geochemical factors measured, profiles of element distribution versus depth of sediment core are given.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Ferromanganese concretions and crusts on the floor of the deep sea are discussed as examples of ores formed in the marine sedimentary environment of the oceans. Their properties, the origin of their constituents, and their mode of formation, including the role of microbes in this process, are considered.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

A brief review has been given of the process of bacterial sulfate reduction in respect to other processes in ocean sediments. In particular, rates of sulfate reduction have been discussed in the context of control mechanisms and geochemical consequences. It is concluded that besides temperature and pressure, which are cosmopolitan parameters influencing most biological processes, the rate of sulfate reduction is dependent on (1) total organic carbon preserved in sediment; (2) state of complexing of the organic matter and its availability for biogenic degradation. These two parameters are in turn influenced by (3) the environment of deposition and (4) the rate of sediment accumulation. Correlations are presented that show a direct relationship between rate of sulfate reduction and rate of sediment accumulation. The consequences of different rates of sulfate reduction on pyrite formation and isotope fractionation are discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The natural history of aquatic and sedimentary humic substances in both marine and freshwater environments is reviewed. The ecological, geological, and economic importance of these compounds is discussed, and attention is drawn to problems requiring further research.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

With the exception of sediment deposited close to land, organic matter in marine sediments is derived mainly from planktonic debris from the local biomass. Since planktonic material is principally composed of proteins and carbohydrates (hemicellulose), it is of interest to compare the pathway of organic decay in a marine sediment with that of a terrestrial soil where lignin and cellulose is the chief organic input.The article briefly summarizes the present state of knowledge on early diagenesis of organic matter in marine soils. Information is based on the authors studies on distribution of amino acids and sugars in marine sediments deposited under reducing and oxidizing conditions. It is concluded that diagenesis is controlled by (i) biological degradation at the sediment-water interface, (ii) organic condensations, (iii) organic-metal ion interactions, and (iv) organicmineral interactions.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Changes in pH and Eh in open cultures of sulfate-reducing bacteria consisting of various mixtures of broken or powdered beach shells (Pekcypoda) and a marine culturing medium were measured during a 40-day experiment. Sulfate reduction started almost immediately, and was brought about mainly through the action of bacteria of theDesulfovibriotype. In the liquid above the carbonate sediments, redox potential minima of about —200 mV were measured after only 5 days. After the first 5 days, the lowered redox gradually increased again to reach about —100 mV after 40 days. In the sediment itself, however, a lowering of the redox potential to values of —250 to —300 mV was observed, and still lowering at the end of the 40-day observation period. Addition of small amounts of Mg ions was not found to influence the change in redox potential, but addition of iron sulfate markedly increased (made more positive) the Eh. By plotting the change in pH/Eh conditions in the course of the experiment into a mineral stability diagram involving the biologically essential elements C-N-S-H-O in their respective stable compounds, information on the effect of sulfate reduction on carbonate sediments was obtained. A lowering of the redox potential of seawater below values of some —250 mV will lead to the precipitation of calcium carbonate and the production of methane gas instead of the otherwise more stable calcium and bicarbonate ions.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID