Original paper

Reassessment of the Zemorrian foraminiferal Stage and Juanian molluscan Stage north of the Olympic Mountains, Washington State and Vancouver Island

Nesbitt, Elizabeth A.; Martin, Ruth A.; Carroll, Neil P.; Grieff, Jeff


The Oligocene biozonation of marine formations exposed along the Straits of Juan de Fuca, western USA and Canada, are re-evaluated with a greatly increased fossil data set. The Pysht, Sooke and Clallam formations are the type sections of the Juanian and Pillarian molluscan stages, the Liracassis rex and Liracassis apta biozones of the Juanian Stage, and they have also been assigned to the Refugian, Upper and Lower Zemorrian and Saucesian benthic foraminiferal stages. Based on these stages, paleomagnetic signatures have been used to assign Chrons and numerical ages. Reassessment of the index fossils has resulted in the lack of definition of the biozones and the benthic foraminiferal stage boundaries and the entire Pysht and Sooke formations falls within the Zemorrian Stage, but could not be subdivided into early and late substages. The lack of delineation of subzones within the Oligocene in this region is attributed to both the original characterization of the stages/zones and complex faulting and folding of the exposed Tofina-Fuca depositional basin of the Cascadia subduction margin.


oligocenebiostratigraphymagnetostratigraphytofino-fuca basincascadia