The lowest part of the Clamgulchian has a flora characterized by the presence of the exotic genus PTEROCARYA, which may be accompanied by ULMUS/ZELKOVA. TSUGA and pollen of Cupressaceae/Taxodiaceae are consistently present, as is the fern OSMUNDA. Radiometric ages on this interval indicate an age range from 6.8 to 7.9 m.y. Among the sample you submitted, 11518 (DT75-200), 11519 (DT75-210), and 11520 (DT75-212) are clearly lowest Clamgulchian. My sample 11114 (5 miles south of Clam Gulch) also represents this assemblage.

The upper part of the lower Clamgulchian lacks broadleaved exotics (PTEROCARYA and ULMUS/ZELKOVA), but contains the conifers Cupressaceae/Taxodiaceae and TSUGA and the fern OSMUNDA. Samples from 11518 (DT75-200) and D1943 (see Wolfe et al, 1966) represent this assemblage, as do my samples 11116 and 11117, which were collected from beach level just north of Clam Gulch. The radiometric data of 6.6 m.y. appeas to be in the right age range. The pollen samples from Seward Peninsula dated at 5.7 m.y. represent this assemblage. Also included is sample D1945 (Wolfe et al, 1966), which probably came from between beds P and Q of Barnes and Cobb (1959) on Swift Creek. Thus, this assemblage apparently ranges from 5.7 to 6.6 m.y.

The upper Clamgulchian is known palynologically from my samples 11118 and 11119, which are 2.3 and 3.0 miles, respectively, north of Clam gulch. In addition, samples from D5379 from Hoodoo Creek (reported on for Weber; see E&R A-74-9D) are similar, in that TSUGA and Cupressaceae/Taxodiaceae are not present. The Hoodoo age of 5.3 m.y. would indicate that the sample you dated from the upper part of the Swift Creek section (4.1 - 4.6 m.y.) should produce an upper Clamgulchian flora; it is unfortunate that no pollen samples were obtained to confirm this suggestion.