. Bulletins of American paleontology. max. = Srammatophom cf. oceanica var. macilenta T 1 1 r T 1 1 r 1995 1985 1976 1966 1956 Proportion Text-figure 7.—Relative abundances of select taxa from the Pass Key core 37. Relative abundances are standardized to the maximum abundance for each species. Values of 1 indicate a maximum abundance for that species. Samples are plotted by sample depth in centimeters. Dates (based on the average sedimentation rate derived from Pb-210 analyses) are shown on th
. Bulletins of American paleontology. max. = Srammatophom cf. oceanica var. macilenta T 1 1 r T 1 1 r 1995 1985 1976 1966 1956 Proportion Text-figure 7.—Relative abundances of select taxa from the Pass Key core 37. Relative abundances are standardized to the maximum abundance for each species. Values of 1 indicate a maximum abundance for that species. Samples are plotted by sample depth in centimeters. Dates (based on the average sedimentation rate derived from Pb-210 analyses) are shown on the right. (Text-fig 6). The sharp increase in C:P at the 88-90 cm sample interval also reflects the large amount of Cyclotella valves in this sample. Above 88 cm, the ratio declines. There is a general increase in the C:P ratio between 70 and 40 cm. The ratio declines slightly between 40 and 30 cm, and above 30 cm there is a gradual increase. Pass Key Core 37 Diatom Flora A total of 95 diatom species and varieties were iden- tified from Pass Key core 37. The five species with the highest mean percent abundances are Cyclotella cf. litoralis, Nitzschia granulata, Mastogloia crucicula, Cocconeis placentula cf. var. euglypta, and Fragilaria cf. tabulata var tabulata (Ag.) Lange-Bertalot. Select images of diatom taxa from PK 37 can be found in Pyle et al. (1998). The percent abundances of many of the more com- mon species show changes throughout the time period represented by the Pass Key core (Text-fig. 7). Nitz- schia granulata shows some of the largest changes in abundance (Text-fig. 7). This species is much more common deeper in the core, with percent abundances as high as 45% and 36% in the 64-66 cm and 50-52 cm samples, respectively. Above the 44-46 cm sam- ple, N. granulata is much less common, with percent abundances of 10% or less. Cyclotella cf. litoralis also shows changes in abundance, ranging from 12-18% in the deeper samples, and increasing to over 20% above the 44-46
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