The Dawson Cut Forest Bed lies in the lower part of thick, late Cenozoic loess deposits in the Fairbanks area. It is associated with several distal tephra beds that provide age control and offer the opportunity of its recognition elsewhere in central Alaska. EC tephra (named herein) occurs in the uppermost part of the Dawson Cut Forest Bed and its petrographic and chemical properties point to a co-magmatic relationship with PA tephra, which has not been found in direct association with the forest bed. Both tephra beds are pink and have unusually high Cl in their glass shards, which readily separates them from all other tephra beds in the Fairbanks area. They were produced by discrete eruptions, closely spaced in time. PA tephra has a glass-fission-track age of 2.02 ± 0.14 myr, indicating that the Dawson Cut Forest Bed must be about 2 million years old. The Palisades tephra (named herein) has very similar properties to these two tephra beds, suggesting that the buried forest bed just above it at the Palisades site on the Yukon River, about 250 km west of Fairbanks, correlates with the Dawson Cut Forest Bed.

Land snails have been investigated isotopically in tropical islands and mid-latitude continental settings, while high-latitude locales, where snails grow only during the summer, have been overlooked. This study presents the first isotopic baseline of live snails from Fairbanks, Alaska (64°51’N), a proxy calibration necessary prior to paleoenvironmental inferences using fossils. δ13C values of the shell (– 10.4 ± 0.4‰) and the body (– 25.5 ± 1.0‰) indicate that snails consumed fresh and decayed C 3-plants and fungi. A flux-balance mixing model suggests that specimens differed in metabolic rates, which may complicate paleovegetation inferences. Shell δ18O values (– 10.8 ± 0.4‰) were ~ 4‰ higher than local summer rain δ18O. If calcification occurred during summer, a flux-balance mixing model suggests that snails grew at temperatures of ~ 13°C, rainwater δ18O values of ~– 15‰ and relative humidity of ~ 93%. Results from Fairbanks were compared to shells from San Salvador (Bahamas), at 24°51’N. Average (annual) δ18O values of shells and rainwater samples from The Bahamas were both ~ 10‰ 18O-enriched with respect to seasonal (summer) Alaskan samples. At a coarse latitudinal scale, shell δ18O values overwhelmingly record the signature of the rainfall during snail active periods. While tropical snails record annual average environmental information, high-latitude specimens only trace summer season climatic data.