All slides were examined for diatom biostratigraphic data on an Olympus CH-2 microscope at a magnification of 400x. Species identification was confirmed at 600x and 1000x. Each slide was scanned through four traverses across the cover glass (22 mm x 40 mm) to ascertain the presence or absence of diatoms. Observation of no identifiable diatoms or diatom fragments constituted a barren (B) assignment to the sample. Samples containing identifiable valves or fragments of valves were then further examined to document species occurrence and estimate the relative abundance (see Tables T1, T2, T3, T4). The following convention was used to report the overall diatom abundance observed at 400x on each slide:
1 specimen observed per traverse.
Abundance estimates were derived from examination of the smear or strewn slides to achieve an unbiased analysis of the sediment. Ten transects were completed for each slide examined. Sieved slide examination allowed the inclusion of many rare species that statistically would have otherwise been likely to remain unobserved.
