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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 63 (1979)

Issue: 3. (March)

First Page: 494

Last Page: 494

Title: Paleoecologic Evaluation of Late Eocene Zonations of West Coast: ABSTRACT

Author(s): Kristin McDougall

Article Type: Meeting abstract


Investigations of the late Eocene benthic forams along the West Coast indicate that the current zonal schemes can be modified to accommodate the constraints imposed on the organisms by ecologic conditions and thus become less provincial. The benthic foraminiferal assemblages of northwestern Oregon and southwestern Washington are used to develop a series of ecologic facies indicative of bathymetry and/or water mass. Upper depth limits, trends, clines, and morphologic variations of this group provide tools for determining ecology. The faunas of the type sections of the California and Washington stages, zones, and subzones, when analyzed in terms of this ecologic model illustrate some of the deficiencies inherent in these schemes. The late Eocene zones of California have a s rong association with depth; that is, Narizian zones are lower or middle bathyal whereas Refugian zones are outer neritic or upper bathyal. The late Eocene zones of Washington are diagnostic of middle bathyal depths with considerable transport; as a result partial rather than total ranges are used in the development of these zones.

Although no new zones are proposed, it is possible to revise the existing zones to recognize the total ranges and bathymetric or other ecologic controls. The late Narizian Stage encompasses a bathyal and neritic facies. The bathyal facies is correlative with a modified Bulimina corrugata Zone of California and the Uvigerina cf. U. yazooensis Zone of Washington. The neritic late Narizian facies corresponds to a modified Bulimina schencki-Plectofrondicularia cf. P. jenkinsi Zone of Washington and a modified Amphimorphina jenkinsi Zone of California. The Refugian Stage can also be divided into a neritic and bathyal facies. However, the early and late subdivision of this stage is weak. The Refugian is equivalent to the modified versions of the Cibicides haydoni Subzone, Uvigerina atwilli ubzone, and the Uvigerina vicksburgensis Zone of California and a modified Sigmomorphina schencki Zone of Washington. The Cibicides haydoni Subzone is the neritic facies of the Refugian whereas the faunas of the Uvigerina atwilli Subzone, Uvigerina vicksburgensis Zone, and Sigmomorphina schencki Zone represent the bathyal Refugian facies.

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