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Only three sampled beds from the Walnut Creek Lower locality yielded diameter data. The two samples taken below the Lower Kellwasser horizon from the Angola Shale (WCL14--53 and WCL14--17) were not fossiliferous, and WCL14-0 was not able to be assessed. The WCL14-5 and the WCL14-21 beds show similar diameter frequency distributions, with most fossils falling between 35 μm and 110 μm, a pattern similar to beds sampled from the Upper Kellwasser. In contrast, the WCL14-13 shows a very different diameter frequency distribution. The population appears to be bimodal: while many fossils still fall between 35 μm and 110 μm in diameter, in this sample (and only this sample), fossils between 110 μm and 200 μm are most abundant. These large leiosphere specimens are beautifully preserved and have uniformly smooth, thin, walls, and a golden color. They very rarely show signs of pyrite framboids within the vesicles. While these characteristics are not unique to large specimens, large specimens are more likely than smaller specimens to have smooth, thin, walls and little pyritization. While specimens of this nature are not unique to WCL14-13, they are relatively rare in other beds.
All six beds sampled from Walnut Creek Upper were fossiliferous, although WCU14- -17 (below the Kellwasser horizon in the Angola Shale) was less fossiliferous and only 27 fossils were measured. Unlike the Walnut Creek Lower, all six beds from Walnut Creek Upper have very similar fossil diameter frequency distributions (Figure 4-7). Again, most fossils fall between 35 μm and 110 μm in diameter. The only apparent trend in the diameter frequency distributions between beds is a slight decrease of in diameter with increasing bed height. Fossils with diameters between 60 μm and 70 μm are most common in WCU14- 3, while in WCU14-130 fossils with diameters between 30 μm and 40 μm are more common. The average diameter of fossils in WCU14-130 is significantly less than fossils in WCU14-3 (two-sided t-test, p=0.003, 95% confidence that difference is between 5 and 22 μm).
Discussion
Figures:
- locality map
- strat section (some generalized with unites and Kellwassers) potentially in with the map?
- representative fossil images
- example of microbead slide?? (methods)
- Size/morphology graphs for all sections
- abundance data for all sections
- scaled TOC data for all sections