Gastropod shells are commonly preserved in Quaternary sediments, but are o
ften avoided
for radiocarbon dating because some taxa incorporate
14C-de
ficient carbon during shell
formation. Recently,
Brennan and Quade [(1997) Quat. Res. 47, 329–336]
found that some minute taxa (
Vallonia,
Pupilla, and
Succineidae) appear to yield reliable
14C ages
for late Pleistocene samples. A more rigorous evaluation o
f the
14C inventory o
f minute gastropods is presented here, which involved measuring the
14C activity o
f specimens collected live in two geologic settings that maximize the potential
for ingestion o
f old carbon: (1) alluvium dominated by Paleozoic carbonate rocks, and (2) adjacent to extant springs with highly
14C-de
ficient water present at the sur
face. We
found that several minute taxa, including
Vallonia, incorporate signi
ficant and variable amounts o
f old carbon (
![](/images/glyphs/BQ1.GIF)
2 to >30%) during shell
formation. The
14C activities o
f the land snails
Pupilla blandi and
Euconulus fulvus, however, are indistinguishable
from the
14C activity o
f live plants. The
14C activity o
f the semi-aquatic gastropod
Catinella sp. (Family:
Succineidae) deviates
from modern values in the presence o
f 14C-de
ficient water by an amount equivalent to
![](/images/glyphs/BQ1.GIF)
10%o
f the local carbon-reservoir e
ffect. These results imply that at least some minute gastropods can provide reliable
14C ages even when
14C-de
ficient carbon is readily available. To demonstrate an application o
f our
findings, we
14C-dated shells
from
P. muscorum,
E. fulvus, and
Succinea sp. (Family:
Succineidae) recovered
from the Coro Marl, a late Pleistocene spring-
fed marsh deposit exposed at the
Murray Springs Paleoindian site in the San Pedro Valley o
f southern Arizona, USA. Radiocarbon ages obtained
from the minute gastropods show that the unit was deposited between
![](/images/glyphs/BQ1.GIF)
25 000 and 13 000
14C years ago. The marl is situated >15 m above the modern water table at Murray Springs, and is similarly positioned in discontinuous outcrops along a
![](/images/glyphs/BQ1.GIF)
150-km stretch o
f the San Pedro Valley. Thus, the
14C ages o
f minute gastropods presented here may be used to in
fer the timing o
f high water-table levels throughout the valley.