PLEISTOCENE SERIES

worldwide division of rocks deposited during the Pleistocene Epoch (1,600,000 to 10,000 years ago). It overlies rocks from the Pliocene Epoch (5.3 to 1.6 million years ago) and is itself overlain by rocks of the Holocene Series; together these two latter divisions make up the Quaternary System. By international agreement, the global stratotype section and point for the base of the Pleistocene Series coincides with the base of marine claystones that overlie the e marker bed in the Vrica section in Calabria, Italy. This bed, a distinctive stratum of sapropelic rocks (i.e., those containing carbon-rich material from a swampy environment), is 1.9 m (6.25 feet) thick and is very conspicuous in the Vrica section's massive cliffs, which lie 4 km (2.5 miles) south of Crotone on the Marchesato Peninsula of Calabria. The most significant fossil found in Pleistocene strata is the mollusk Arctica islandica. The base of the Pleistocene is marked by the last occurrence of the nannoplankton Calcidiscus macintyrei and of the foraminiferan Globigerinoides obliquus extremus, as well as by the first appearance of the tiny plankton Gephyrocapsa oceanica. More importantly, the Pleistocene's boundary with the Pliocene occurs just above the position of the magnetic reversal that marks the Olduvai Normal Polarity Subzone, thus allowing the worldwide correlation of Pleistocene rocks with reference to the magneto-stratigraphic timescale.