714 AERHENIXJS [CHAP. 25 



20 and 35° could explain this intensified vertical circulation during glacial 

 times. The stratification of biotic components in the Equatorial Pacific under 

 these conditions provides a record of the general climatic evolution of the earth; 

 new drilling techniques now being introduced (Bascom, 1961) could extend the 

 time record beyond the few million years now accessible. 



Sediments from Eocene to Pliocene age, outcropping or covered by relatively 

 thin Quaternary strata, have been sampled on topographic highs within the 

 area in question (Arrhenius, 1952, 2.57; Riedel, Chapter 33, this volume). This 

 sedimentation information from the early Cenozoic has been summarized in the 

 lower disconnected part of the bottom graph of Fig. 36, and in the curves 

 marked "Lower Tertiary" in the upper graph of the figure. The northern 

 carbonate compensation line in Lower Tertiary was much farther north than at 

 present, probably north of latitude 45°. However, it was gradually displaced 

 southward, passed latitude 16°N in Miocene time, and approximately reached its 

 present location in Upper Miocene or Pliocene times. Oxygen isotope measure- 

 ments of benthonic Foraminifera from these strata indicate bottom-water 

 temperatures of approximately 10°C as compared to 1-2° throughout the 

 Pleistocene (Emiliani, ojp. cit.; Emiliani and Edwards, op. cit.). Apparently the 

 large meridional extent of carbonate sediments in Lower Tertiary times was due 

 to a decreased rate of dissolution rather than to an increased rate of pro- 

 duction. 



The meridional drop in concentration of fossils away from the equatorial 

 zone appears also in the Tertiary strata, indicating the operation of the Equa- 

 torial Divergence already in early Cenozoic times. Its accurate location in rela- 

 tion to the present equator is not yet known. 



4. Physical Stratification 



The detailed record on the ocean floor of the climatically induced oscillations 

 in the Equatorial Current system makes it possible to correlate the sedimentary 

 strata of this facies over large distances. Such a correlation is indicated in Fig. 

 38, which shows two sequences, 3200 km apart, or one-third of the earth's 

 quadrant. The identification of the individual strata is further corroborated by 

 the sequence of properties other than carbonate content, such as the distribution 

 of diatoms shown in Fig. 37. 



Attempts have been made to determine the absolute ages of the Pacific 

 equatorial Pleistocene strata by the radiocarbon activity of the carbonate 

 (Arrhenius, Kjellberg and Libby, 1951), and recently by the protactinium/ 

 ionium method (Sackett, 1960). Because the short half-life of i^C (5800 years) 

 limits direct age determinations by this method to the Late Glacial and Post- 

 glacial strata (stages 1 and 2.2), the age measurement was used to determine the 

 Late Pleistocene and Recent rate of deposition of inorganic constituents; and 

 the ages of older strata were extrapolated under the assumption of a constant 

 average rate of deposition of inorganic compounds throughout the Pleistocene 

 within the area selected. The error inherent in this assumption is probably not 



