Complex sentence: The Cromerian Complex in Europe is currently subdivided into 3 glacial periods and 4 interglacial periods, which are equivalent to Marine Isotope stages 13 to 21.
Split into simpler sentences: The Cromerian Complex in Europe is subdivided into 3 glacial periods and 4 interglacial periods. Both the Cromerian Stage and Complex are equivalent to Marine Isotope stages 13 to 21.