. Bulletins of American paleontology. . Text-figure 14.—A06 Cladium and Nymphaceae sclereids (a); A23 Cladium and Nymphaceae sclereids (b). 64-57 cm is marl; 57-25 cm is fibrous peat. Marl at cm yielded a radiocarbon date of c. 1960 yr B. P. The upper part of Zone 2 has no radiocarbon dates, but the change in pollen spectra between Zone 2 and 1 suggests that there is a hiatus: however, the charcoal profile does not show a sharp increase at the top of Zone 2. This zone is characterized by cheno- am dominance (Text-fig. 13a), ca. 60% of the pollen spectrum throughout the zone. At the beg
. Bulletins of American paleontology. . Text-figure 14.—A06 Cladium and Nymphaceae sclereids (a); A23 Cladium and Nymphaceae sclereids (b). 64-57 cm is marl; 57-25 cm is fibrous peat. Marl at cm yielded a radiocarbon date of c. 1960 yr B. P. The upper part of Zone 2 has no radiocarbon dates, but the change in pollen spectra between Zone 2 and 1 suggests that there is a hiatus: however, the charcoal profile does not show a sharp increase at the top of Zone 2. This zone is characterized by cheno- am dominance (Text-fig. 13a), ca. 60% of the pollen spectrum throughout the zone. At the beginning of Zone 2 slough-marsh and upland pollen groups occur at lower percentages than in preceding Zone 1, but by the end of Zone 2 the slough-marsh component in- creases to ca. 20% of the total pollen, while the upland component remains at less than 10%. Ferns occur at low frequency and the mangrove component makes a small contribution in the middle of Zone 2. Cladium sclereid concentrations rise gradually to a peak at 50- 45 cm (Text-fig. 14a). decline and then rise to a higher peak at 32-25 cm. Nymphaceae sclereid concentra- tions rise faster than Cladium sclereids and reach a peak at 57-50 cm, decline slightly, rise to a second higher peak at 45-39 cm, and then decline again. The high percentage of cheno-am pollen may be an indi- cator of rapidly fluctuating water levels and/or variable hydroperiod. Cheno-ams are early successional weeds which can take advantage of briefly available habitats such as areas alternating between inundation and des- sication over short time intervals. In late Zone 2 at 50-25 cm the slough and marsh pollen group per- centages rise and both Nymphaea pollen and Nym- phaceae sclereid concentrations increase. This suggests a longer hydroperiod during this interval. Zone 3, 25-0 cm is stratigraphically fibrous peat. A radiocarbon date on sediment from 25-20 cm yielded a modern (<~100 years old) date. Zone 3 cheno-am pollen spectra show a sharp d
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