Washington Department of Natural Resources Bulletin No. 62 Foraminifera, Stratigraphy, and Paleoecology of the Quinault Formation, Point Grenville-Raft River Coastal Area, Washington Weldon W. Rau

LOCAL CORRELATIONS—SOUTHWEST WASHINGTON

OCEAN CITY AREA

Until recently, essentially no local framework of biostratigraphic correlation had developed in the rocks of late Tertiary-early Quaternary age in western Washington. With increased interest in possible petroleum production from these relatively young rocks, some generalizations have developed during the past 15 years. Most of this information has been obtained from the subsurface, penetrated in a few wells drilled in the Ocean City area, some 20 to 25 miles south of the area of outcrop of the Quinault Formation. The faunal succession known in these wells suggests that the Quinault Formation represents an upper part of the local upper Tertiary-lower Quaternary sequence. It is perhaps best exemplified in the Union Oil Company of California-State No. 3 well, where some 3,600 feet of upper Tertiary-lower Quaternary strata were penetrated above older rocks of the Hoh Formation. Foraminifera from the upper 2,500 feet of strata in this well are typical of those of the Quinault Formation. Shallow-water forms found largely in the upper part of the Quinault Formation are dominant in the uppermost part of the well, and deeper water forms gradually become more abundant downward to a depth in the well of about 2,500 feet. At this horizon a substantial number of forms make their first appearance and continue to occur to the top of the Hoh Formation at a depth of about 3,600 feet. Many of these species represent substantial water depth, and most of them are either not known in the Quinault Formation, or occur only rarely in the basal part of the formation. A few of these species are:

Bolivina sinuata Galloway and Wissler
Bulimina rostrata Brady
Bulimina subacuminata Cushman and Todd
Rotalia garveyensis Natland
Valvulineria malagaensis Kleinpell

The fauna from this part of the well can best be compared with those assemblages generally regarded as late Miocene or earliest Pliocene in age in other basins of deposition along the coast, particularly in the southern California region.

From biostratigraphic relations known in the Ocean City area, it therefore is suggested that an uppermost part of the Tertiary sequence of that area correlates broadly with the Quinault Formation in its area of outcrop. However, a lower part of this sequence (from a depth of 2,500 feet to 3,600 feet in the Union Oil Company of California-State No. 3 well) may be stratigraphically below most, if not all, outcrops of the Quinault Formation.

MONTESANO AREA

The stratigraphic relation between the Quinault Formation and the Montesano Formation, exposed a few miles to the east, has long been pondered. Outcrops of the two units are separated by a covered area only a few miles wide, yet suggested correlations have been somewhat varied in the past. Weaver (1916a) at one time included all the Quinault Formation of this report in his Montesano Formation, and regarded it as late Miocene in age, but later (1942) he removed from the Montesano Formation at least the Cape Elizabeth section and regarded it as the Quinault Formation of Pliocene age. Still later (Weaver and others, 1944), it was suggested that perhaps the lower part of the Quinault Formation might be contemporaneous with a part of the Montesano Formation. Conclusions of Weaver and of other writers until that time were based largely on mollusks.

In recent years, studies of the Foraminifera of the Montesano Formation (Fowler, 1965; Rau, 1967) support a late Miocene age for the formation, or in part, extend its age into the early Pliocene, depending upon individual interpretations on where the Mohnian and Delmontian stages of Kleinpell should be placed with respect to the boundary between the Miocene and Pliocene epochs (Fig. 7). Even though assemblages of the Quinault and Montesano Formations have many species in common, particularly the assemblages of the Duck Creek-Pratt Cliff section of the Quinault Formation, and of the Montesano Formation in general, few if any elements in the faunas particularly indicate a precise correlation. Substantially represented forms of the Quinault Formation that are either conspecific or very similar to those common to the Montesano Formation, are listed below:

Buccella inusitata [B. frigida in Montesano Formation]
Buliminella curta
Cibicides mckannai
Epistominella pacifica
Florilus basispinatum
Globigerina bulloides
Nonionella miocenica
Pullenia salisburyi
Uvigerina, finely costate
Uvigerina subperegrina
Virgulina californica ticensis

FIGURE 7.—Generalized correlation chart showing suggested relations between the stratigraphy of the Quinault Formation and that of the Montesano Formation of southwest Washington.

On the Pacific coast several of these species, particularly B. curta and V. californica ticensis, typically occur in rocks of late Miocene age. Rotalia garveyensis, although not found by the writer in any of the measured sections of the Quinault Formation, has been reported from somewhere in the vicinity of the lower part of the Duck Creek-Pratt Cliff section by others (Boettcher, R. S., Mobil Oil Company, written communication, 1969). Furthermore specimens tentatively referred to this species were collected by the writer from an isolated locality (Q-97) near the mouth of the Raft River (Fig. 8), together with species typical of the lower part of the Duck Creek-Pratt Cliff section. The presence of this species may well be significant, inasmuch as its highest occurrence is regarded by many workers as generally marking the top of the Miocene, particularly in the Los Angeles basin. Furthermore, in the Montesano Formation it was found only in the upper part (Fowler, 1965; Rau, 1967). Because this species occurs in the basal part of the Quinault Formation and the top of the Montesano Formation and because in general the foraminiferal faunas in these parts of the respective formations are similar, foraminiferal evidence supports previous conclusions for a correlation of the lowermost part of the Quinault Formation (basal part of the Duck Creek-Pratt Cliff section) and the uppermost part of the Montesano Formation Fig. 7).

FIGURE 8.—Sketch map showing miscellaneous collecting localities along the coast north of the Raft River.

Essentially no foraminiferal evidence is available for a correlation of the Cape Elizabeth section with any part of the Montesano Formation. Although a number of identical or conspecific foraminiferal species are present in both the section south of Taholah and the Montesano Formation, none of these is particularly significant with respect to a correlation. Furthermore, species not recorded in the Montesano Formation but present in the section south of Taholah such as Cassidulina limbata and Elphidium hughesi, suggest that this Quinault section may be of slightly different age, possibly younger than any part of the Montesano Formation. The section north of Point Grenville contains even fewer forms known in the Montesano Formation, and therefore a correlation of these units also is not particularly supported by Foraminifera.