Several thousand feet of late Tertiary marine sediments crop out across Heceta Bank on the central Oregon shelf. Rock samples from two east-west profiles (44°05^prime and 44°10^prime N) have yielded large, well-preserved foraminiferal faunas. The stratigraphic sequence of the samples has been determined using sparker subbottom profiles.

Two possible stratigraphic units are delineated on the basis of their foraminiferal content, seismic-reflection characteristics, and lithology. The older is characterized by Bolivina seminuda foraminata, B. semiperforata, B. spissa, Bulimina subacuminata, B. subcalva, Buliminella cf. B. exilis, Epistominella pontoni californica, and Uvigerina peregrina; less than 10 percent planktonic foraminifers; and right-coiling Globigerina pachyderma. This fauna represents paleodepths of 500-1,000 m and is dated as Pliocene. The younger unit is characterized by Cassidulina minuta, Eilohedra levicula, Epistominella exigua, Nonionella spp., Trifarina angulosa, and Uvigerina juncea; more than 50 percent planktonic foraminifers; and left-coiling G. pachyderma. This unit was deposited at depths of 100 200 m. This fauna could be Pliocene or Pleistocene. Paleoenvironmental data require minimal uplifts ranging from approximately 1,000 m for the oldest sampled strata to 100 m for the youngest. There was a general shoaling throughout the deposition of the units.

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