Record details

Title
    Shrnutí nových poznatků: co nám říkají o genezi železivců v české křídě
Statement of responsibility
    Jiří Adamovič
Other titles
    Summary of new results: what do they say about the genesis of ironstones in the Bohemian Cretaceous
    Železivce české křídové pánve : katalog vybraných významných geologických lokalit pískovcových oblastí (Variant.)
Author
    Adamovič, Jiří, 1965-
Language
    česky
Source title - serial
    Knihovna České speleologické společnosti
Vol./nr.
    Roč. 38
Pages
    s. 146-151
Year
    2002
Notes
    1 obr., 1 tab.
    Anglické resumé
    il.
    Zkr. název ser.: Knih. Čes. speleol. Společ.
Subject group
    asociace minerální
    chemismus hornin
    česká křídová pánev
    ferikrusta
    ferolit
    křída-svrchní
    ochrana přírody
    petrogeneze
    pískovce
Geographical name
    ČR-Čechy
Keyword
    české
    Genezi
    Křídě
    Nových
    Poznatků
    říkají
    Shrnutí
    železivců
Abstract (in english)
   This volume provides descriptions of tens of localities with prominent ferruginization of sandstones in the Bohemian Cretaceous Basin (BCB) as regards sandstone lithology, distribution of intrusive bodies, tectonic deformation and the character and extent of ferruginization products. The distribution of Fe-oxyhydroxides in N and NE part of the BCB is of the same diversity and intensity as in the classical area of north-central BCB. Typology of Fe occurrences was proposed by ADAMOVIČ et al. (2001) and ADAMOVIČ (2001, 2002a). Quartz-poor ironstone consists of goethite I, kaolinite, anatase, +- opal, +- detrital quartz, and a younger generation of goethite II +- lepidocrocite. It contains 43.4 wt. per cent Fe tot. on average (20.98-67.01). Quartz-rich ironstone is dominated by detrital quartz with accessory detrital minerals, cemented by goethite +- lepidocrocite +- hematite, and contains 24.3 wt. per cent Fe tot. on average (11.75-32.68).
   The ironstones are enriched in incompatible elements relative to quartzose sandstones and, in the case of Fe tot., As and Zn, U, Th and REE, even relative to fresh volcanic rocks. With the exception of Ba and Sr, quartz-rich ironstones of macromorphological types 1-3 show similar major-element and trace-element composition (ADAMOVIČ 2001).Although a close spatial relation was generally proved between the distribution of intrusive bodies of basaltic rocks and Fe-oxyhydroxides, some prominent occurrences are developed in areas free of volcanic rocks. The most important in this respect are the finds of bodies of basaltic intrusive breccia and dyke systems at Špičák Hill near Střezivojice and in the Močidla Gorge, classical sites of type-2 and type-3 ferruginization products, respectively (ADAMOVIČ et al.
   2001).Transport of ferrous iron in low-Eh fluids of late magmatic origin and its precipitation in zones of mixing with oxygenated meteoric waters seem to be the most probable mechanisms producing macromorphological types 1-3. Minor redepositions of iron by cold groundwater cannot be excluded. Pyrite oxidation or supergene enrichment in iron from superficial volcanic products are the mechanisms to explain the genesis of morphological type-4 concretions. Hematitized sandstones of type 5 are sediments of red-beds type, formed by dehydration of weakly goethitized clayey sandstones during sediment burial. Ferruginization in sandstones of the BCB is viewed as a polygenetic process with a primary hydrothermal impulse.
   Geological and geochemical evidence indicates that the dissolved mineral content of iron-bearing fluids is of complex provenance, probably combining 1) primary magmatic source, 2) component leached from the adjacent upper crustal rocks (mostly granitic rocks in the area studied), and 3) component produced from decomposed volcanic rocks, the bodies of which represent principal ascent paths for the iron-bearing fluids. Source 3) was probably of major importance over most of the basin.
Contributor
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
    U
Entered date
    24. 10. 2007
Import date
    8. 8. 2012