The concept of sea-floor spreading has been examined in the Atlantic and Pacific oceans by paleontologic dating of the sediments that lie in contact with acoustic basement. Despite errors that could be introduced by burial of sediments by sills, paleontologic dating limitations, and deep-sea currents creating a hiatus at the basement-sediment contact, there is an extraordinarily good relation between age of the basal sediments and distance from the ridge crest. Based on these data, an average Cenozoic spreading rate in the north Atlantic is 1.2 cm/yr, in the south Atlantic 2.0 cm/yr, and in the equatorial Pacific 12 cm/yr. By extrapolating spreading rates Heirtzler et al. proposed an age scale for the identifiable magnetic anomalies that typify a spreading sea floor. The ges of the basal sediments recovered by drilling agree very well with the time scale to about 45 m.y. ago. From 45 to 70 m.y. ago the agreement is also good, but the age of the basal sediment appears consistently lower than the proposed time scale. The sediments indicate there may be significant mineralization associated with the basal sediments. Samples should make possible reconstruction of oceanic circulations of the past and the dependence of these circulations on arrangement and emergence above sea level of land masses. Migration of the crust relative to effects related to the rotational poles of the earth, such as the equatorial zone, can be deduced.

End_of_Article - Last_Page 357------------