Refinement of lower Silurian chronostratigraphy: proposal of new GSSPs of the Aeronian and Homerian stages

Existing global stratotype sections of the lower Silurian Aeronian and Homerian stages have been found inadequate with respect to modern high-resolution tools of stratigraphic correlation and even standard biostratigraphy. In response to current ISSS initiatives, Rhuddanian/Aeronian and Sheinwoodian/Homerian boundary sections exposed at Hlásná Třebaň and Kosov in the Prague Synform will be examined in detail as prospective candidates for new global stratotypes. Biostratigraphic description and correlation of the sections based upon graptolites will be supplemented by chitinozoan and limited conodont data. Horizons and biozones formerly selected to mark the base of the respective stages are well recognizable in these sections. Apart from biostratigraphic markers, geochemical and petro-physical proxies will be studied since trends in carbon isotopic composition and potential changes or cycles in organic productivity and rate of black-shale sedimentation can serve as likely proxies of global environmental changes of chronostratigraphic significance.