Age and Depositional Environments of Tertiary Rocks of Nootka Island, British Columbia (92-E): Mollusks Versus Foraminifers

Conflicting interpretations of age and depositional environment of the Tertiary rocks of Nootka Island and adjacent areas of Vancouver Island resulting from studies of their molluskan and foraminiferal faunas appear to be caused by:1. A conflict of opinion concerning the correlation of regional molluskan, foraminiferal, and mammalian stages now applied to the Tertiary rocks of Western North America with units of the international biochronological standard based on the European faunas and type sections.2. Underestimation of the regional (i.e. within individual regions of the Western North American Tertiary province) biochronological value of Tertiary mollusks and other invertebrate macrofossils by many foraminiferal specialists.3. Neglect of mollusks as paleoecological indices by some foraminiferal specialists.4. Misinterpretation of paleoecological value of fossil foraminifers by some foraminiferal specialists. The application of general considerations 1 to 4 to the Tertiary rocks of Nootka Island and adjacent areas of Vancouver Island indicates that:1. A micropaleontological interpretation of the whole of Divisions A and B as bathyal deposits formed at depths of about 2000 ft (610 m) is unwarranted. The molluskan fauna present in the greater part of these units indicates they are predominantly littoral to outer neritic (0 to 800 ft (0 to 244 m)) deposits. Only the middle part of Division B could have been a bathyal (i.e. more than 800 ft (244 m) deep) deposit.A turbiditic redeposition of coarse clastics of Division A into the bathyal depth is ruled out by the state of preservation of its macrofossils, lithology of rocks, and the abundance of regular rows of early diagenetic concretions which maintain their stratigraphic position over considerable distances. The shales of Division B are not redeposited turbidites for the same reasons. If the abundance of allegedly bathyal foraminifers throughout the thickness of these two units will be confirmed by proper documentation and by further research it would be necessary to interpret their association with neritic macro-invertebrates as having been caused by the influence of strong upwelling currents which lowered the temperature of inshore waters and so made them habitable for these foraminifers.2. The recently proposed late Eocene dating of the upper part of Division A and the lower and middle parts of Division B cannot be justified either by the molluskan or by the foraminiferal fauna. The previously proposed early to mid-Oligocene age of these units remains valid regardless of whether one places them into the late Refugian foraminiferal stage or in the Lincoln molluskan stage.3. Even if it is valid, the unsupported claim of the presence of Bulimina schencki fauna does not indicate the correlation of these beds with the late Narizian, as this fauna is closely allied to and is probably contemporary with the early Refugian faunas of southern California. However, these beds may be of a latest Eocene age if the presence of Bulimina schencki fauna will be confirmed.4. The upper part of Division B contains an apparently Lower Blakeley macrofauna suggestive of late Oligocene age in terms of the generally accepted molluskan chronology. The early to mid-Zemorrian (=mid-Oligocene) dating of its foraminifer fauna reflects the divergent micropaleontological tradition which favors the placement of the Oligocene/Miocene boundary at the top of the Zemorrian stage.5. The suggested late Miocene to early Pliocene age of a shallow water foraminifer fauna of Division C of Nootka Island is contradicted by its stratigraphic position underneath the reliably dated Division D (see below). Only the upper part of Division C appears to be a neritic to ?littoral deposit. Its lower part is more likely an outermost neritic to uppermost bathyal deposit.6. The rich and diagnostic upper Blakeley (=lower Miocene) molluskan fauna of Division D is indubitably correlative with that of the type Sooke Formation of Southeastern Vancouver Island and with that of the "Sooke" Formation of the Seattle area. The early Miocene age of these three units is confirmed by the presence of a primitive whale tentatively referred to the order of Archaeoceti and the desmostylan genus Cornwallius in the type Sooke Formation. These data discredit the recently proposed early to early middle Pliocene dating of foraminifers of the Division D and the type Sooke Formation.7. No post-lower Miocene rocks are known to outcrop anywhere on the western coast of Vancouver Island contrary to the recent claims of some micropaleontologists. Also, there is no evidence of an unconformity separating the lower Miocene Division D from the underlying Oligocene to ?lowest Miocene Divisions A, B, and C. All four units appear to form part of a single invasion of a shelf-like (predominantly outer neritic to uppermost bathyal) Oligocene – early Miocene sea onto the southwestern part of Nootka Island. This sea, which may have been deeper and represented by a different facies elsewhere (i.e. Hesquiat Peninsula, Pachena–Sooke area), apparently withdrew completely and permanently from the west coast of Vancouver Island in the latest early Miocene.