Record details

    Compositional changes in Silurian shales: conclusions based on calcite concretions research
Statement of responsibility
    Josef Šrámek
Other titles
    15th Conference on Clay Mineralogy and Petrology, Brno, September 6-10, 1998 - Proceedings (Variant.)
    Šrámek, Josef
Source title - serial
    Scripta facultatis scientiarum naturalium Universitatis Masarykianae brunensis. Geology
    Vol. 28-29
    p. 89-98
    1 obr., 1 fot., 3 tab.
    Obsahuje bibliografické odkazy
    Zkr. název ser.: Scr. Univ. Masaryk. brun., Geol.
Subject group
    břidlice jílová
    minerály jílové
Geographical name
    Bykoš (Beroun)
    Karlštejn (Beroun)
    Praha - Lochkov
    Suchomasty (Beroun)
Abstract (in english)
   The subject of the study were calcite concretions collected and studied eight localities of the Barrandian Silurian shales. The comparion of the results of detailed laboratory research of concretions and their host shales is as follows: In the concretions, calcite as the sole carbonate mineral, represent 60-90 wt% (arithmetic mean 78 ˝ 16wt%), while in the host shales its content is only about 7 to 26% (arithmetic mean 15,4 ˝ 8,7wt%). In insoluble residue of concretions the amount of Na-feldspar (occasionally also potassium feldspar) and quartz are distinctly higher than in the insoluble residue of the shales, which are richer in K2O and MgO. In the latter, beside quartz, diostahedral mica - illite/muscovite, 14 A chlorite and smectite constitute a substantial portion of the rock.
   The semiquantitative X-ray analyses of insoluble residues carried out on XRD as well as on Guinier chamber, supported by results of chemical, thermal (DTA-GTA) and infra-red absorption analyses were used for calculation of contents of albite and dioctahedral illite/muscovite. Both these minerals wer used as internal standards for fixing the content of further minerals - quartz, K-feldspar, chlorite and smectite. Mutual comparisons of the composition of particular concretions and their host sediments revelaed a decrease of clastic quartz and feldspars grains in insoluble residue of shales by 10-20 per cent. This dissolution was compensated by the formation of authigenic illite, chlorite and montmorillonite/smectite. The decrease in amount of clastic quartz and feldspars is inversely proportional to the present calcite content in the host shale.
   A possible wider exploitation of carbonate concretions as an appropriate instrument for the study and research of diagenetic changes of the original composition and structure of shales can be recommended. However, it has been debased by the fact that in insoluble residue of many carbonate rocks (e.g. limestine) we can often find diagenetic/authigenic growth of clastic quartz and feldspars grains
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
Entered date
    21. 3. 2008
Import date
    8. 8. 2012