INTERNATIONAL COMMISSION ON STRATIGRAPHY (ICS)
The International Commission on Stratigraphy is the largest and oldest constituent scientific body in the International Union of Geological Sciences (IUGS). Its primary objective is to precisely define global units (systems, series, and stages) of the International Chronostratigraphic Chart that, in turn, are the basis for the units (periods, epochs, and age) of the International Geologic Time Scale; thus setting global standards for the fundamental scale for expressing the history of the Earth.
ICS website: http://www.stratigraphy.org/
Global Stratotype Section and Point (GSSP)
version 2015/1: pdf; html (see below: to view pages of the links, click the right button of your mouse, then click to open the link in another page of your browser)