Strontium isotope profile of Carboniferous-Permian Akiyoshi Limestone in southwest Japan

Abstract

The chemical and Sr isotope compositions of the Akiyoshi Limestone (SW Japan) were determined. This limestone is a continuous sequence ranging in age from Early Carboniferous to Late Permian and is considered as an organic reef complex deposited on a basaltic seamount. The Sr isotope compositions (⁸⁷Sr/⁸⁶Sr) of the Akiyoshi Limestone range from 0.7068 to 0.7088. The time dependent change of the Sr isotope compositions is approximated to the two decreases in Early Carboniferous and Early to Late Permian, and one smooth increase in Middle Carboniferous to Early Permian. Although it is assumed that post-depositional diagenetic alteration may more or less have modified the original isotope values, the profile of the Sr isotope compositions of the Akiyoshi Limestone is interpreted as preserving the temporal change of sea water Sr isotope compositions during Carboniferous to Permian.