Magnetic Stratigraphy of Cenozoic Terrestrial Sediments and Mammalian Dispersal

Abstract

The existing literature on the correlation of the magnetic polarity timescale to vertebrate mammalian chronology for the Cenozoic is reviewed for all continents except the Soviet Union. The magnetostratigraphic data from North America is the most complete, followed by the Indian sub-continent. Ten criteria for rating magnetostratigraphic studies are established, and the papers reviewed are rated from 1-10, with 10 being the maximum score. The timing of mammalian dispersal is examined against the background of information from magnetostratigraphic studies allied with radiometric dating. North American Land Mammal ages are partly defined on immigrant taxa and the boundaries of the NALMA are based on dispersal events. It has been suggested that dispersal and evolutionary episodes observed in Siwalik sediments were correlative to sea level change deduced from data from benthic Foraminifera. To test this possibility in the general case, dispersal events into North America were determined by using updated values of the boundaries of the NALMA. These boundaries (dispersal events) were compared to the master sea level curve from analysis of benthic Foraminifera. In a majority of cases the dispersal events correspond to inferred drops in sea level. Since dispersals proceed in both directions once a corridor is open, it follows that European Land Mammal ages will tend to be coincident with the North America Land Mammal ages. As close as can be determined this seems to be a correct inference for the Neogene of Europe.