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To obtain more accurate reconstructions of past salinities and climate it is necessary to merge regional datasets of saline lake diatoms and water chemistry; a prerequisite of which is to standardize taxonomic practice. To illustrate this process, an investigation of the identity of a small Cyclotella species, frequently observed in the diatom community of saline lakes, is described. This taxon, which has been referred to in earlier literature as Cyclotella caspia, is of interest because it is present in fossil African assemblages, yet is absent from the modem flora of this region. Uncertainties over its correct identification prevented material in a North American dataset from being used as an analogue in salinity reconstructions. LM and SEM investigations reveal that there are no significant differences between Recent North American and Holocene sub-fossil North American and African material which suggests that the salinity optimum calculated from the North American water chemistry data can be used for ...

Diatom assemblages are documented from diatomite layers of two Miocene fluvio-lacustrine units from the basins of the western Cordillera of northern Peru: the Namora formation and the Cajabamba formation. Emphasis is given to taxa of particular stratigraphic interest such as Mesodictyon sp., Cyclotella stelligera Cleve & Grunow, and Aulacoseira agassizii (Ostenfeld) Simonsen and their ultra- structure is investigated with the SEM. The diatom assemblages indicate for the Namora formation the occurrence of swampy conditions with very dilute, low alkalinity water. The diatom assemblages of the Cajabamba formation reflect the occurrence of fresh, slightly alkaline, eutrophic lakes with deep water in some samples, and swampy conditions with relatively high salt content in other samples. The Namora formation is late Miocene in age based on the diatom assemblages and radiometric analyses (7.2 ± 0.6 Ma). The diatom layers of the Cajabamba formation are dated as late middle to early late Miocene (ca. 11–8 Ma) base...