The clay in pollen zone 9 did not contain any diatoms. The first diatom to appear above trace levels was Opeophora martyi, a halophilic thick walled benthic species. This would indicate waters with low salinity and suggests the water was not completely fresh. Halophilic species were dominant in pollen zone 6, but other species began to be abundant. The eurytopic and alkaliphilic species indicate fresh water was floating on denser brackish water below it. By the end of pollen zone 6, only one halophilic taxa was abundantly present, Gyrosigma attenuatum, which can also live in fresh water. This reduction in halophilic species is believed to be due to a deepening of the fresh water, which would exceed the depth in which light could reach, and therefore affecting the photosynthesis process, or by a decline in salinity below tolerable limits.
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Epithemia
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