Record details

Title
    Oncoidal and Ooidal Ironstone in the Lower Devonian Limestone Sequence, Barrandian, Czech Republic
Statement of responsibility
    Vladimír Skoček, Zdeněk Kukal
Author
    Kukal, Zdeněk, 1932-
    Skoček, Vladimír, 1934-
Language
    anglicky
Source title - serial
    Věstník Českého geologického ústavu (Bulletin of the Czech Geological Survey)
Vol./nr.
    Vol. 73, no. 1
Pages
    p. 23-32
Year
    1998
Notes
    5 obr., 3 diagr., 1 pl., 2 tab., 2 s.bibl.
    České resumé
    Zkr. název ser.: Věst. Čes. geol. Úst. (Bull. Czech geol. Surv.)
Subject group
    Barrandien
    chemismus hornin
    devon-spodní
    ferolity
    onkoid
    ooid
    prvky stopové
    rudy Fe
    sedimenty karbonátové
    textury sedimentů
Geographical name
    ČR-Čechy
    Svatý Jan pod Skalou (Beroun)
Keyword
    Barrandian
    Czech
    Devonian
    Ironstone
    Limestone
    Lower
    Oncoidal
    Ooidal
    Republic
    Sequence
Abstract (in english)
   Small lenses of ironstones were found in the sequence of red nodular limestones (the Řeporyje Limestone, locality Stydlé vody). These ironstones exhibit unique composition and structure and differ from other Barrandian ironstones. They contain great amount of allochems of considerable size among which oncoids, pisoids, cortoids and ferricrete fragments prevail. Ooids and peloids occur in lower amounts. Hematite is the main iron mineral accompanied by Fe-chlorite (berthieroid). The ironstone also contains small amounts of kaolinite, illite and clastic quartz. Fe tot content ranges between 8.20 and 35.12%. This variability is caused mainly by the irregular distribution of carbonate in the form of bioclasts, limeclasts and neomorphic crystalline calcite. Iron content in noncarbonate fraction of the same samples reaches as much as 50% Fe tot which corresponds to high-quality sedimentary iron ore.
   Lens-like form, variability in composition and poor sorting of allochems show the deposition of ironstones near intertidal and supratidal environments. Lateritic regolith on the exposed carbonate platform can be considered main source of iron. Secondary enrichment of iron compound took place due to the reworking by mechanical processes. The association of trace elements, mainly Ti and V and their correlation to the silica, alumina and total iron corroborate combined mechanical and biogenic depositional process. Close association of the ironstones and red nodular limestones might throw a new insight on the history of iron compounds during deposition and diagenesis of limestones. Facies relations between red and grey limestone units indicate an essential role of active organic matter in iron mobilization and reduction
Contributor
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
    U
Entered date
    31. 3. 2008
Import date
    8. 8. 2012