A significant change from dextral to sinistral populations of Globigerina pachyderma occurred at the Pliocene-Pleistocene boundary in southern California, as recorded in deep-water deposits. By using modern populations as a basis for comparison, it can be shown that this represents a major shift from dextral warm temperate to sinistral subarctic populations, and it defines a point in time which should coincide more dependably with the Pliocene-Pleistocene boundary than a boundary based upon benthic species. Use of this method shows that the upper limit of the Wheelerian Stage, which is based on the upper limits of the Epistominella pacifica-Uvigerina peregrina faunas, ranges from more than 200 meters below to more than 300 meters above the Pliocene-Pleistocene boundary. >

A second problem is recorded in the Eocene of the Santa Barbara embayment. Planktonic Foraminifera suggest that the Eocene Narizian Stage, based primarily on benthic species, is as young as late Eocene in the Santa Rosa Hills and as old as middle Eocene elsewhere. Similarly, planktonic Foraminifera indicate that the Ulatisian Stage, also based upon benthic species, is early to middle Eocene in some places and is entirely middle Eocene in others.

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