Lineaforma

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Lineaforma shows up relatively infrequently in early Mesoproterozoic assemblages, having been found only in one basin in northern Russia and another basin in Australia. It is relatively easily identified- as its name implies, it is characterized by the presence of fine striations or lines along its length, as well as relatively large size (i.e., wider than about 30-40 micrometers).

I recently discovered Lineaforma in both the Chamberlain and Greyson Formations of the Belt Supergroup of Montana. The image above includes specimens from the Chamberlain Formation, where they make up a pretty large fraction of all of the recovered assemblages from the unit. In the Greyson Formation, by contrast, I only found a couple of specimens amongst all of the assemblages despite a very intense search.  On the basis of this difference in relative abundance, and the presence of other fossils such as Coniunctiophycus, Symplassosphaeridium and Synsphaeridium, I have argued that the fossil may helpfully indicate the relationship of the host deposits to distance from the ancient shoreline. The taxon may have more detailed biostratigraphic and biochronological applications, but it must first be found in more basins to ascertain whether it truly represents a narrow slice of time or a narrow range of environments before its utility can be confirmed.

You can read more about this fascinating fossil in my recently published paper, Paleoenvironmental Indications of an Expanded Microfossil Assemblage from the Chamberlain Formation, Belt Supergroup, in GSA Special Paper volume 522.

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