The Oligocene-Miocene boundary is equated with

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the Globigerinoides trilobus datum of the tropics; this is approximately equivalent to the base of the Saucesian Stage of California. In ascending order, the lower Miocene Catapsydrax dissimilis, C. stainforthi, and Globigerinatella insueta zones correlate with the Saucesian and basal Relizian Stages. Assemblages characterizing the Catapsydrax stainforthi zone have been identified in the upper part of the lower Saucesian Stage of Reliz Canyon, California. Further, Sphenolithus belemnos is a good index of the lower Miocene of tropical areas and of the Saucesian Stage of California.

The orbuline datum of the tropics, which is in the uppermost part of the Globigerinatella insueta zone, is the base of the middle Miocene. This level appears to correspond to the base or the lower part of the Relizian Stage of California. In ascending order, the middle Miocene Turborotalia peripheroronda and Globorotalia peripheroacuta zones correlate with the Relizian Stage, and the Globorotalia praefohsi and Globorotalia fohsi zones correlate with the Luisian Stage. Sphenolithus heteromorphus occurs in the Relizian Stage and also in the Globigerinatella insueta and Turborotalia peripheroronda zones of the tropics. Discoaster kugleri is an index of the uppermost zone of the G. fohsi sequence and it is identified in the upper Luisian Stage of Newport Bay, California. Orbulines first a pear in the Luisian Stage in California.

The Globorotalia menardii datum is the base of the upper Miocene in tropical areas, and it corresponds approximately to the Globigerina pachyderma datum of California or the base of the lower Mohnian. The dextral Globigerina pachyderma zone of the lower Mohnian contains Catinaster coalitus and Discoaster bollii, which are indices of the Turborotalia mayeri and Globorotalia menardii zones of the tropics. The sinistral Globigerina pachyderma zone of the upper Mohnian and basal Delmontian Stages represents the first major cool event in the middle Neogene; it correlates with the Turborotalia acostaensis (Globigerina bulloides) zone of tropical areas and with the sinistral G. pachyderma zone of the Messinian of Italy.

The base of the Pliocene is marked by the appearance of Sphaeroidinella dehiscens" and by the change from sinistral to dextral populations of Neogloboquadrina dutertrei.

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