Paleoecologic and Biostratigraphic Implications of Eocene Planktonic Foraminiferal Assemblages, California: ABSTRACT

Abstract

Correlations and age assignments based on the system of benthic-foraminiferal faunizones and provincial stages developed for the California region are contravened by those based on planktonic species, notably within the Eocene. For example, the and provincial stages are presently assigned to the middle and upper Eocene, respectively. Our data indicate that strata containing benthic-foraminiferal assemblages range in age from late early Eocene to early middle Eocene whereas sequences are of early to late middle Eocene age and further, that the Ulatisian Rose Canyon and the Narizian Cozy Dell formations are correlative. Significantly, none of the sequences for which planktonic foraminiferal data are available are of late Eo ene age. Inasmuch as the presently available stages and faunizones are time-transgressive, it is urged that this system no longer be used for West Coast Paleogene correlations. The development of a faunizonal succession based on planktonic foraminiferal species provides an adequate chronostratigraphic framework for paleogeographic interpretation, but the absence or rarity of thermophilic species important in standard faunizonations necessitates use of regionally dominant forms. Delineation of dominance and diversity trends reveals modification by shifting watermass boundaries of planktonic-foraminiferal assemblages occurring over End_Page 365------------------------------ the Paleogene California continental margin. Diverse subtropical upper Paleocene-lower Eocene faunas containing Morozovella pass upward into temperate middle Eocene ones characterized by diminished diversity, lack of Morozovella, and by high dominance values for truncorotaloidid and subbotinid species, thus lending support for the concept of a bipolar middle Eocene cooling interval. End_of_Article - Last_Page 366------------