THE INCREASING FREQUENCY and intensity of gla-cial-interglacial cycles toward the end of the Pliocene (1.806–5.332 million years ago) set the stage for the Pleistocene epoch (11.8 thousand years ago-1.806 million years ago), which is the final phase of the Quaternary period. Some argue that the lower Pleistocene boundary maybe set too late because the general trend toward significant cooling and glaciation had begun in the mid-late Pliocene (2.75 million years ago). Hence, the term Plio-Pleistocene may be used to delineate this transitional phase between the two epochs.

Strong glacial-interglacial phases are the key climatic features that characterize the Pleistocene epoch [Page 795]and have shaped much of the modern landscape. Glacial stages maybe referred to as ice ages, and are used to describe a period of extensive ...