Abstract

The Paleogene-Early Neogene sedimentary sequence of southwestern Santa Cruz Island contains a rich macrofauna. These fossils are useful for separating lithologically similar units. This paper presents a roster of the known macrofossils from the area.

The Paleocene-Eocene Pozo Formation is dominated by the large Paleocene gastropod, Turritella pachecoensis. The unit also contains T. infragranulata, T. ocoyana, Neverita spp., and the pelecypods Dosinidia cf. D. margaritana and Glycymeris sp. Between the Pozo Formation and the overlying Canada Formation is a lithologically and biostratigraphically transitional unit, the Pozo-Canada Transitional Biozone (PCTB). The PCTB is characterized by Ostrea idriaensis, unidentified gryphaeids, Turritella uvasana, and two varieties of “sabellariid” tubes.

The Eocene Canada Formation contains a diverse fauna of low overall abundance. The most diagnostic fossils are the large pelecypod Venericardia, echinoid (?Eucidaris) spines, and resistant wood molds. Macrofossils from the overlying Jolla Vieja Formation (and Rincon and Monterey Formations) are rare.

The Eocene Cozy Dell Formation is also sparse in macrofossils, particularly when compared with the lithologically similar Canada Formation. Small pelecypods and gastropods (e.g., Neverita sp., Rimella sp.) are rare and of little biostratigraphic use.

The Miocene Vaqueros Formation contains a rich macrofauna dominated by Lyropecten miguelensis, Ostrea miguelensis, and unidentified balanomorph(s). Similar forms also occur in the San Onofre Breccia, however, the latter is noted for abundant oysters (Ostrea vespertina and O. eldridgei).

In addition to the established turritellid and pectinid zonations, it is proposed that oysters may be important specimens for identifying Paleogene and Eocene units. The occurrence of unique gryphaeids and ostreins within the Pozo-Canada transition beds (=Lower Eocene) may be useful in fine-tuning correlations within the Channel Islands and with the mainland.