Geologic Studies in Alaska by the U.S. Geological Survey, 1992

8 GEOLOGIC STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1992
limiting radiocarbon age for the dune, however, is pro-
vided by a collapsed rodent nest that underlies an
unconformity that truncates the paleosol and forms the
base of the south arm of the dune. The unconformity was
most likely produced by deflation as the dune began to
form, and the nest was probably collapsed by the weight of
the accumulating dune. A radiocarbon age of 3,690*90 yr
B.P. was determined for herbaceous plant material from
the nest (table 1). A pause in dune activity is marked by a
paleosol 10 cm thick composed of sandy humus that oc-
curs 50 cm below the top of the dune. This paleosol has a
radiocarbon age of 1,100+80 yr B.P.
METERS
0
Correlative paleosols in eolian sand are found at sites
4 through 9 (fig. 1). Five of these paleosols consist of
peat 10 to 30 cm thick within eolian sand and the sixth of
sandy humus. Radiocarbon ages on the paleosols range
from 890 to 2,500 yr B.P. (table 1).
CALIBRATION OF RADIOCARBON AGES
Radiocarbon yr B.P. do not correspond to calendar yr
B.P., because the rate of production of I4c in the atmosphere
and other reservoirs has not been constant over geologic time.
Tundra mat
Eolian sand, hehacaw roots and
sparsewoody~~
Sandy humic horizon
Eolian sand with thin humic horizons
in the lower put
Sandy humic m e slightly cryuturbated
2,42M80 yr B.P. (I-13,041)
Eolian sand, cryo*
Figure 6. Measured section at site 2 (fig. 5) showing location of dated paleosol.
Figure 7. Oblique aerial photograph, looking west-southwest, showing parabolic dune truncated by coastal bluff at site 3.