第三系・第四系境界問題の現状

Abstract

The recommendations of the commission appointed to advice on the definition on the Pliocene- Pleistocene boundary at the 18th International Geological Congress held in London, 1949, are thought to have been accepted generally as a current resolution of the problem. However, some revision shall be made on the recommendations on account of progress in stratigraphy. Among the significant knowledges obtained after the 18th IGC, 1948, are as follows.1) The Calabrian formation is much older than the glacial Pleistocene. 2) The Villafranchian is lower than the Calabrian. 3) No remarkable world-wide change in evolution, climate, water temperature, or vegetation occurred at the beginning of the Pleistocene as compared with other events during the Pliocene and Pleistocene. 4) Many fossil hominids have been found from the Lower Pleistocene and below at various localities including the Olduvai Gorge, where the lowest horizon of hominid corresponds to the Olduvai Event in magnetic polarity chronology. 5) Combined bio- and magnetostratigraphic method is widely applied to sedimentary sections, in which the evolutional appearance of Globorotalia truncatulinoidesfrom G. tosaensis was found in or near the correlative with the Olduvai Event, though the horizon varies locally.On the other hand, in the stratigraphic classification, more importance has been attached to the boundaries than the characteristics of the main part of the unit, and distinction of the Pleistocene from the Pliocene implies to define the boundary between them at the type locality. Perhaps the Pliocene-Pleistocene boundary stratotype finds universal approval when it is designated in the classical area of Calabria, southern Italy. If the stratotype is appropriately designated in a well studied section, precise correlation of the boundary is possible applying the modern methods of stratigraphy. Early designation of the boundary between the Pliocene and Pleistocene is desirable. Of the present state of the Pliocene-Pleistocene boundary problem it may be said that the designation of the stratotype has been long awaited.