The stratal succession along the southern perimeter of the San Joaquin Valley affords a unique opportunity to observe the late Eocene to early Miocene passage within sequential marine episodes where faunal relations of the upper Narizian (Late Eocene), Refugian and Zemorrian (Oligocene), and Saucesian (early Miocene) Stages can be studied.

A monophyletic group of species of Uvigerina and Siphogenerina aids in defining successive faunal zones or biozones that correlate in part with the type sections of the Refugian, Zemorrian, and Saucesian Stages. For example, Uvigerina jacksonensis ( = U. cocoaensis) characterizes the Refugian, U. tumeyensis characterizes a provisionally defined lower Zemorrian, Siphogenerina nodifera characterizes a provisionally defined upper Zemorrian and S. transversa characterizes a provisionally defined Saucesian. The application of these biozones offers a feasible method to account for all of past geologic time within this depositional continuum, something which is not possible using existing time-rock units or stages.

Vaqueros mollusks occur consistently in lowermost Saucesian strata. This suggests that the Uvigerinella sparsicostata Zone (Zemorrian of current usage) of the Santa Barbara embayment, which overlies the Vaqueros Formation, is mostly coeval with early Saucesian as applied in the San Joaquin Valley. This requires an expanded concept of the Saucesian Stage as the type section for the Saucesian overlies the U. sparsicostata Zone in the Santa Barbara embayment.

Faunal bases for comparing the Eocene--Oligocene and Oligocene-Miocene boundaries in California with those of the Middle Americas are discussed. In both regions the boundaries seemingly coincide with eustatic lowering of sea level, as observed in other parts of the world.

End_of_Article - Last_Page 435------------