Paleoceanography 



135 



from basin to basin when plotted according 

 to temperature (or to depth of basin sills) but 

 a poor zonation when plotted by depth sam- 

 ples. In contrast, Bandy (1953fl) discovered 

 that some of the shallow-water species off 

 San Diego occur in deeper and colder water 

 off San Francisco and that there is a marked 

 difference in the Foraminifera at equivalent 

 depths off northern and southern California, 

 even though temperatures are similar. A 

 related discrepancy exists in the faunas off 

 Alaska and Panama. In addition, Resig 

 (1958) detected differences in living faunas 

 at various depths in the isothermal water 

 below the sill of Santa Cruz Basin. Depth 

 zonation of foraminiferal populations also 

 exists in the isothermal waters in lagoons of 

 the Marshall Islands (Cushman, Todd, and 

 Post, 1954). 



It is possible that the depth variation of 

 foraminiferans is such a complex function 

 of temperature, oxygen content, food supply, 

 nature of substrate, and other factors that a 

 precise evaluation of oceanographic charac- 

 teristics from faunas alone is almost hopeless. 

 However, empirical extrapolation of biozones 

 from the present southern California basins 

 to ancient ones can still be made more or less 

 safely. This was first accomplished for the 

 now-filled Ventura Basin by Natland (1933) 

 and was later somewhat extended and modi- 

 fied to include effects of turbidity currents 

 (Natland and Kuenen, 1951) and rate of 

 sedimentation and subsidence (Bandy, 

 1 953b). Later, Nadand and Rothwell ( 1 954) 

 and Natland (1957) applied the same tech- 

 nique to the Los Angeles Basin. Durham 

 (1950, 1954) extended the general method 

 back in time to the beginning of the Tertiary 

 Period, using as criteria the horizontal distri- 

 bution of living corals and shallow-water 

 mollusks, instead of the vertical distribution 

 of foraminiferans. The results of all studies 

 suggest that the temperature of accumulation 

 of the predominantly shallow- water strata of 

 Paleocene and Eocene Epochs can be gener- 

 alized at about 25 °C, and of the Oligocene 

 Epoch at about 23°, both higher than present 

 water temperatures (Fig. 84). 



The depths of the Miocene Epoch and 

 particularly those of the Pliocene Epoch, 



when sediments accumulated in deep water 

 of the now-filled Los Angeles and Ventura 

 Basins, may be identified by use of modern 

 foraminiferal biozones (Fig. 121). Some 

 support for estimates of ancient depths is 

 provided by comparison offish remains with 

 the modern depth distribution of closely re- 

 lated fishes (David, 1943; Pierce, 1956). If 

 the temperature variation with depth was the 

 same during the past as now, the biozones 

 may also indicate the paleotemperatures. 



MILLIONS OF YEARS 



Figure 121. Depth of Los Angeles and Ventura Basins 

 during past 50,000,000 years with possible temperature 

 of bottom waters. Areas beneath bottom show thickness 

 of various strata before and after physiographic basins 

 were formed during the Miocene Epoch. Present state of 

 compaction is assumed at all stages of accumulation be- 

 cause of lack of data on grain size for the strata. Time 

 scale from Simpson (1947), depth and thickness data 

 from Natland (1957), adaption of plot by Bandy (19536). 



