Jk. Child et al., 3 HOLOCENE TEPHRAS IDENTIFIED IN LACUSTRINE SEDIMENT CORES FROM THE WONDER LAKE AREA, DENALI-NATIONAL-PARK AND PRESERVE, ALASKA, USA, Arctic and alpine research, 30(1), 1998, pp. 89-95
Eighteen percussion piston cores were recovered from Wonder Lake and t
hree nearby kettle ponds in Denali National Park and Preserve, Alaska.
Three prominent tephra deposits, two felsic and one mafic, have been
recognized in the upper 1 to 3 m of the cores. Because of the relative
ly low magnetic susceptibility (MS) of the lacustrine sediment, tephra
s appear as prominent MS peaks allowing confident correlation of core
stratigraphies. These MS-based correlations are supported by microprob
e geochemical analyses of 11 tephra samples from six of the cores. Fiv
e accelerator mass spectrometer (AMS) radiocarbon ages, determined fro
m terrestrial plant remains, closely constrain the timing of these ash
fall events. Microprobe results indicate that the youngest tephra is c
orrelative with the Jarvis Ash, which has an accepted age of 3660 +/-
125 C-14 yr BP. The next older felsic tephra is correlative with the m
iddle Holocene Oshetna tephra. New C-14 ages reported in this study su
ggest that this regionally extensive tephra was deposited about 6000 C
-14 Yr BP. Neither of these tephras has previously been identified thi
s far west, indicating that both are significantly more extensive than
previously thought. A fine-grained basaltic ashfall deposit, identifi
ed in several of the Wonder Lake cores and dated to ca. 10,000 C-14 yr
BP, is a newly discovered tephra that provides an important stratigra
phic marker horizon at the Pleistocene-Holocene boundary in central Al
aska.