| Résumé | (disponible en anglais seulement)
Clastic strata exposed in the intertidal platform of Oyster Bay, approximately 10 km south of Campbell River, Vancouver Island, as well as along lower Oyster
River, an additional 4 km still farther south, have preoccupied paleontologists substantially over the past 25 years. No pre-glacial strata were recognized in this area by Muller and Jeletzky (1970). Richards (1975) described an abundant fauna in the
beds at Shelter Point, approximately 2 km north of the Oyster Bay exposures, including the crab Longusorbis and associated ammonites and inoceramid bivalves, and he assigned these beds to the Spray Formation of the Nanaimo Group. This information,
combined with the very low dip of the Oyster Bay strata and their general lithological similarity with the coarse clastic strata found commonly in the Nanaimo Group, suggested a Late Cretaceous (Campanian) age of the Oyster Bay strata.
Beginning
in the 1980s, amateur collectors from Vancouver Island began amassing significant collections of fossils from the strata of southern Oyster Bay that are found several hundred metres southeast of the local road called "Appian Way," thus providing the
informal moniker "Appian Way Beds" for these localized exposures. While these collections included a great diversity of gastropod, bivalve, nautiloid, scaphopod, echinoderm, and coral specimens, as well as impressive collections of plant materials,
much previously undescribed, no taxa found commonly in Campanian strata of the Nanaimo Group were noted in these collections; particularly lacking were ammonites and inoceramid bivalves. For this reason, the hypothesis began to emerge that the
"Appian Way Beds" of Oyster Bay were of younger, post-Cretaceous, age than thought previously. Just how young, however, has been a source of some controversy, with different parties continuing to favour the traditional Campanian age (based on
lithostratigraphy), others a Paleocene age, and still others an Eocene age (based on plant macrofossils).
We have studied the foraminiferal and marine mollusk faunas of the Appian Way Beds of Oyster Bay, and we have also collected sandstone
samples from the strata for detrital zircon analysis. The youngest detrital zircons present in our samples indicate the strata have a Maximum Depositional Age of 63.1±1.0 million years, or early Paleocene (Danian); the strata have to be younger than
this and we can thus rule out a Cretaceous age for them. The gastropod assemblage present in the beds is particularly diverse. Several of the gastropods found in the Appian Way Beds are found in the Martinez Formation of California, which was
originally described as Eocene (Dickerson, 1914), but is now considered to be late Paleocene in age (Squires, 2003). Important taxa of gastropod mollusks present in the assemblage include Eocypraea aff. martini (Dickerson 1914), Leptomaria aff.
vacavillensis (Hickman 1976), ?Serratocerithium usanium Compton 1944, Drepanocheilus aff. exilis (Gabb 1864), and Pseudoperissolax blakei (Conrad 1855), collectively suggesting a late Paleocene to Eocene age.
Based on foraminifers, we can also
rule out late Eocene and younger as a possible age for the Appian Way strata as late Eocene assemblages are well described from Vancouver Island, Washington, and Oregon, including the Keasey Formation of Oregon, and are not comparable to that from
Appian Way. There is no single foraminiferal assemblage in the literature that is identical to that seen in the Appian Way samples, but the closest is from the "Lodo Formation" of California, dated as latest Paleocene (Prothero, 2001).
Silicosigmoilina californica Cushman & Church 1927 is the most abundant foraminifer at Appian Way. Mallory (1959) established a S. californica Zone from the Ynezian (Paleocene) Lodo Formation at Media Agua Creek, Kern County, California, but this
species is not confined to that zone, and probably has a total range of Coniacian to Eocene. Several other species in the Appian Way collection appear similar to Lodo Formation foraminifers. Collectively, the faunal data from the Appian Way Beds
suggest the strata are earliest Eocene or possibly latest Paleocene in age. |