The collections represent far more detailed paleontologic sampling than was previously available (an earlier report on this area was written by F. S. MacNeil, A-65-1M).

Age:
the stratigraphically highest collection (M4390) may represent the Pliocene as that epoch has been recognized in previous work on Gulf of Alaska Tertiary faunas. This call is based on the Chlamys and the Neptunea that seem to be restricted to strata that have been previously assigned to the Pliocene. The age of the next to the highest collection (M4389) is indeterminate; it could also be Pliocene but the assemblage is too meager to permit an age assignment.

Localities M4386 and M4387 probably are of late Miocene age; they include the highest stratigraphic occurrence of Neptunea aff. N. tabulata (Baird) which ranges downward to the base of the Yakataga Formation and contain the pectinid Swiftopecten which heretofore has only been recorded from strata assigned to the Miocene in the Gulf of Alaska. The immediately overlying collection contains a doubtfully identified specimen of Macoma arctata which is suggestive of late Miocene age. Accordingly, a provincial boundary between the Miocene and the Pliocene can be tentatively placed in the unfossiliferous interval between 4210 and 5110 ft above the base of your measured section.

The criteria utilized by MacNeil in differentiating the provincial middle Miocene from the late Miocene are not clear. There is a recognizable faunal break between M4378-80 and M4381 based upon the highest stratigraphic occurrences of Cyclocardia n. sp., a species heretofore recorded only from strata that MacNeil assigned to the middle Miocene, and Turritella hamiltonensis. Another boundary could be drawn between the highest stratigraphic occurrence of Lituyapecten cf. L. yakatagensis (Clark) MacNeil (M4375) and the presumably antecedent species L. lituyensis (M4377). This boundary would honor MacNeil’s assignment of a provincial post-middle Miocene age to the biozone of L. lituyaensis.

This appears to be an excellent section for potential correlation of the Yakataga Formation. The collections, together with the earlier material, leave much to be desired, however, in terms of diversity. It would be very helpful to have additional material from this section. The McCoy collections from Phillips are from a 2000 ft measured section on the east side of Kulthieth Mountain (5 localities). Unfortunately, there are only one or two species in each collection and only one, M4603 (1700 ft above the base of his measured section) includes a stratigraphically diagnostic species; Chlamys cf. C. tugidakensis MacNeil (this species is indicative of a Pliocene age).

Environment:
Collections from the base of the section (M4365) up to 2520 ft above the base (M4378-80) represent a sublittoral, or neritic, environment deeper than about 10-20 fathoms. The assemblage from M4381 (3585-3670 ft above the base) indicates shoaling to low intertidal or very high sublittoral depths. M4386 (3770-4070 ft above the base), again, is probably no shallower than 10-20 fathoms based upon the occurrence of Lituyapecten. The stratigraphically higher collections may record slight shoaling based upon the occurrence of Swiftopecten, a doubtful Mytilus, and the vermetid gastropod.

The molluscan genera are suggestive of cool temperate to cold surface water temperatures, almost all of them live today in shallow water along the Gulf of Alaska coast. An exception is the genus Turritella which today ranges no farther north than the southern part of the Oregonian (temperate) molluscan province which extends northward from central California to British Columbia. In view of the other genera in the assemblage it seems likely that the Turritella was adapted to somewhat cooler water temperatures than in which it lives today along the eastern North Pacific margin.