Preliminary Revaluation of Late Miocene Biostratigraphy of California: ABSTRACT

Preliminary studies of the type Mohnian and Delmontian Stages and regional biostratigraphic studies of other late Miocene sections of California by the use of benthonic Foraminifera and fish indicate the following. 1. The Delmontian Stage of Kleinpell is correlative with his Mohnian Stage on the basis of the occurrence of (a) Epistominella gyroidinaformis (Cushman and Goudkhoff) in the lower part of the type Delmontian (this species does not range stratigraphically above early Mohnian in California); (b) Bolivina hughesi Cushman (=Bolivina sinuata alisoensis Cushman and Adams of others), Bulimina delreyensis Cushman and Galliher, and Etringus scintillans Jordan in the upper part of the type Mohnian in California; and (c) Late Miocene megafossils in the Santa Margarita Sandstone, which overlies with apparent conformity beds that are near, and correlate with, the upper part of the type Delmontian. 2. Kleinpell's Bolivina obliqua Concurrent-range Zone (Delmontian) overlaps the range of species characteristic of his subjacent Bolivina hughesi Zone in the type are of the Mohnian Stage and all other Mohnian zones at other localities in California. 3. Many of the species characteristic of his late Mohnian Bolivina hughesi Zone overlap both his subjacent Bulimina uvigerinaformis Zone and his superjacent Bolivina obliqua Zone. 4. Many of the species characteristic of his Bulimina uvigerinaformis Zone overlap both his subjacent Bolivina modeloensis Zone and his superjacent Bolivina hughesi Zone. 5. Bulimina uvigerinaformis Cushman and Kleinpell and Bulimina delreyensis Cushman and Galliher have the same stratigraphic range and appear not to range above "middle" Mohnian in California. Therefore, all of Kleinpell's late Miocene concurrent-range zones are in need of revision or redefinition. End_of_Article - Last_Page 559------------