Sedimentological and diagenetic controls on the reservoir quality of marginal marine sandstones buried to moderate depths and temperatures: Brent Province, UK North Sea
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W artykule przedstawiono wyniki badan rentgenostrukturalnych i derywatograficznych mineralow ilastych z utworow triasu gornego monokliny śląsko-krakowskiej. W osadach kajpru wystepują zespoly: chloryt, illit i illit-smektyt oraz illit, chloryt i illit-smektyt, natomiast w osadach retyku zespoly: illit-smektyt, chloryt i illit oraz illit, kaolinit, illit-smektyt i ślady chlorytu. Zawartośc chlorytu wzrasta ku osadom starszym, zaś kaolinitu, wystepującego tylko w utworach bezwapiennych, ku osadom mlodszym. CLAY MINERALS IN THE UPPER TRIASSIC SEDIMENTS IN ENVIRONS OF KLUCZBORK The mineral composition of the clay fractions of the Upper Triassic sediments, which are under exploitation in the environs of Kluczbork, the Silesia-Krakow monocline, has been analysed by X-ray and DTA methods. They are composed mostly of the following clay minerals: illite, irregularly interstratified minerals of the illite-smectite series and chlorite. Kaolinite is usually lacking. It appears only in the limeless sediments of the Rhaetic. In the Keuper, two different assemblages of clay minerals are present: chlorite, illite, irregularly interstratified illite-smectite and illite, chlorite irregularly interstratified illite-smectite. They differ from the assemblage comprising kaolinite, illite, irregularly interstratified illite-smectite and traces of chlorite, which is characteristic for the Middle Triassic sediments. In the Lower Rhaetic, irregularly interstratified illite-smectite prevails over ,chlorite and illite. The Middle Rhaetic sediments yield illite, irregularly interstratified illite-smectite, chlorite and kaolinite. The mineral ratios are changed again in the uppermost Rhaetic sediments yielding the following series: illite, kaolinite, irregularly interstratified illite-smectite and traces of chlorite. Chlorite is represented by clinochlore-like clay mineral and its content increases along with the age of the layers. Illite has a clearly dioctahedral disordered structure and may be classified as Md polytype. It is associated by the swelling-faze of the various content, from 20 volume per cent in the old layers, up to about 90 volume per cent in the youngest layers of the Triassic. The minor constituents of the clay fractions in the Triassic sediments are the following accessory minerals: quartz, calcite, dolomite and anatase.
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Abstract The use of field emission electron microscopy for the study of clay mineral petrography in mudrocks and sandstones is discussed. The methodology including sample preparation is outlined and three examples of the application of the technique are described: the formation of authigenic illite in mudrocks, the multiple generation of authigenic illites in sandstones and the effects of KCl drilling muds on shale fabrics. In the study of authigenic illite formation in Palaeocene mudrocks from the North Sea, the FESEM analyses have demonstrated the formation of illites with increasing burial depth that conventional SEM and XRD analyses had failed to show. The FESEM analyses of the authigenic illites in Carboniferous sandstones from the southern North Sea revealed at least three different habits representing different generation episodes rather than one illite formation event.This has important repercussions with regard to the interpretation of stable isotope and dating data for the illites. Significant petrographic changes in shales after treatment with KCl drilling muds have been observed from FESEM analyses, suggesting reactivity between the shales and the KCl muds.
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Based on the previously available data of clay minerals in the surface sediments of the Southern Yellow Sea,this paper mainly deals with the distribution of 4 types of the clay minerals(illite,kaolinite,smectite and chlorite).The research results show that the content of the illite in this area is the highest,the smectite or kaolinite are the second and chlorite is the lowest;the illite-smectite-kaolinete-chlorite-type rock is the main type of the clay minerals assemblage in the area,and the second one is illite-kaolinete-smectite-chlorite-type;the material source of clay mineral is mainly from the Yellow River and theYangtze River.
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