Fig. 1From: Review of the Early–Middle Pleistocene boundary and Marine Isotope Stage 19The Quaternary System/Period and its official subdivision as currently approved by the ICS and ratified by the IUGS EC. Stage 4 corresponding to the Upper Pleistocene Subseries has yet to be officially defined. GSSP = Global Boundary Stratotype Section and Point (from Head et al. in press)Back to article page