MAGNETIC STRATIGRAPHY OF THE PACIFIC COAST CENOZOIC: SUMMARY

Magnetostratigraphic studies of most of the classic type sections of marine Cenozoic rocks of the Pacific Coast have now been completed, and greatly improve our correlations of these rocks with the global time scale, as well as the resolution of our dating of these rocks. Where once we were only able to date most of these sections to the nearest 2-3 million years or worse, now most of them can be dated to the nearest 100,000 years or better. Several conclusions are now apparent from these studies. First, as Ager (1963) first suggested, most of these sections represent relatively short intervals of time, so the longest and most complete sections we have of most Pacific Coast biostratigraphic stages are much shorter than the time intervals of the stages they represent. The Pacific Coast Cenozoic record is much less complete and much more full of gaps than previously realized, even though these beds were deposited in rapidly subsiding forearc basins with high sedimentation rates. Secondly, many of the classic benthic foraminiferal and molluscan stages are extremely long in duration (and low in resolution), making them poor for dating; many of the benthic foraminiferal stages are time-transgressive as well. Thus, whenever planktonic microfossils can be combined with magnetic stratigraphy, much better dates can be obtained.