Early-Middle Pleistocene transitions: an overview and recommendation for the defining boundary

Abstract

Abstract The Early-Middle Pleistocene transition ( c. 1.2–0.5 Ma), sometimes known as the ‘mid-Pleistocene revolution’, represents a major episode in Earth history. Low-amplitude 41-ka obliquity-forced climate cycles of the earlier Pleistocene were replaced progressively in the later Pleistocene by high-amplitude 100-ka cycles. These later cycles are indicative of slow ice build-up and subsequent rapid melting, and imply a transition to a strongly non-linear forced climate system. Changes were accompanied by substantially increased global ice volume at 940 ka. These climate transformations, particularly the increasing severity and duration of cold stages, have had a profound effect on the biota and the physical landscape, especially in the northern hemisphere. This review assesses and integrates the marine and terrestrial evidence for change across this transition, based on the literature and especially the following 17 chapters in the present volume. Orbital and non-orbital climate forcing, palaeoceanography, stable isotopes, organic geochemistry, marine micropalaeontology, glacial history, loess-palaeosol sequences, pollen analysis, large and small mammal palaeoecology and stratigraphy, and human evolution and dispersal are all considered, and a series of discrete events is identified from Marine Isotope Stage (MIS) 36 ( c. 1.2 Ma) to MIS 13 ( c. 540–460 Ma). Of these, the cold MIS 22 ( c. 880–870 ka) is perhaps the most profound. However, we here endorse earlier views that on practical grounds the Matuyama-Brunhes palaeomagnetic Chron boundary (mid-point at 773 ka, with an estimated duration of 7 ka) would serve as the best overall guide for establishing the Early-Middle Pleistocene Subseries boundary.