ABSTRACT

Late Neogene planktonic foraminiferal datums and epoch boundaries in Italy, as proposed by the Committee on Mediterranean Neogene Stratigraphy, are compared with those in the Caribbean and Gulf of Mexico. Datums recognizable in these regions include 1) appearance of Globorotalia margaritae in Early Pliocene, 2) appearance of the G. crassaformis lineage in Middle Pliocene, 3) appearance of G. tosaensis and Sphaeroidinella dehiscens in very late Pliocene, and 4) appearance of Globorotalia truncatulinoides within the Early Pleistocene (Middle or Late Calabrian).

Initiation of the Pleistocene in these regions is recognized by abrupt onset of climatic deterioration, as indicated by marked changes in the planktonic and benthonic foraminiferal populations, and marked eustatic lowering of sea level, as demonstrated by regressive facies, nondeposition, or deep-water turbidites, depending upon basinal position. Evidence given by paleontology (typological studies), paleoclimate records, eustatism, and geomagnetic dating of earliest Pleistocene glacial rocks favors a Pleistocene epoch beginning at 2.5 to 3.0 million years ago within the Gauss normal epoch. This time corresponds to the extinction horizon of Globoquadrina altispira and withdrawal of other warm-water species from the Caribbean and Gulf of Mexico. There is no reason to assume that worldwide onset of Pleistocene climate deterioration was diachrononous, as would need be the case if the Pleistocene had begun only 2.0 m.y. ago in warm-water regions as postulated by some workers. A new species is described and discussed in an appendix.