Record details

    Factors influencing the Al2O3/Na2O ratio in Paleozoic siliceous shales
Statement of responsibility
    Jaroslav Dvořák
    Dvořák, Jaroslav
Source title - serial
    Věstník Českého geologického ústavu (Bulletin of the Czech Geological Survey)
    Vol. 72, no. 1
    p. 57-59
    2 obr., 1 tab., 9 bibl.
    České resumé
    Zkr. název ser.: Věst. Čes. geol. Úst. (Bull. Czech geol. Surv.)
Subject group
    břidlice jílová
    index zralosti
    moravskoslezský devon a spodní karbon
    sedimentace mořská
Geographical name
Abstract (in english)
   The Al2O3/Na2O ratio can be considered good evidence for the chemical maturity of clastic sediments. It represents the ration of the most and least stable oxides. The values between 12 and 15 can be taken as boundary limits between mature and immature clayey sediments (see Kukal 1985). Some difficulties might arise in the evaluation of paleozoic siliceous shales. Black siliceous graptolithic shales show an anomalously low Al2O3/Na2O ratio. Moravian Lower Carboniferous shales can be help in the explanation of this anomaly. It is supposed that they were deposited in shalow bays with warm water and intense evaporation. Chemical weathering released silica and also mobile sodium, which were washed into the basin. The sodium could have been fixed in the structure of clay minerals
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
Entered date
    21. 2. 2008
Import date
    8. 8. 2012