Our test involved a series of 9 matched sets, each pair comprised of a 14C date obtained from fossil seeds of a submerged aquatic plant vs. an age from terrestrial plant macrofossils for the same stratigraphic level of a lake-sediment core, and comparison of the paired results using a T-test as well as a graphical approach (plotted normal probability density functions). Consistently, the aquatic macrofossils provided erroneously older ages (“bad dates”), the offset ranging from 445 to 2225 14C years, with a greater disparity with depth. The exception was during the “radiocarbon plateau,” at about 10,000 14C yr BP, when the difference was insignificant. Based on these results, we recommend that 1) all fossil seeds considered for 14C dating be identified to the genus or species level and 2) that macrofossils of submerged aquatic plants not be submitted for dating.
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