ABSTRACT
The Pleistocene is characterised by cyclical climatic changes that were especially pronounced between oxygen stage 22 and the present. The changes induced concomitant marked changes in the geographic distribution of marine planktonic and benthic fauna that effectively prevent their use as chronostratigraphic markers after Stage 23. To insure isochroneity, the INQUA Working Group on Major Subdivisions of the Pleistocene proposed the Matuyama-Brunhes reversal as the Lower-Middle Pleistocene boundary. This was approved by both the Stratigraphic Commission and the International Council. This definition conflicts with the Supplementary chapter of the International Stratigraphic Guide on magnetostratigraphic polarity units. However, definition of a boundary stratotype that is both near the reversal and supported in time by biostratigraphic data, as at Vrica, would be acceptable. Use of the reversal as a guide to the chrono-stratigraphic boundary would make recognition of the position of the boundary possible in both marine and subaerial rocks.
