Traverse's 2007 Paleopalynology (2nd Ed.) contains a chapter solely dedicated to reworked palynomorphs. If I understood correctly, spores or pollen found in rocks of older age can be released and subsequently redeposited in younger rocks. One major hint is that they can be more thermally mature/carbonised than the assemblage, and may not be as well-preserved.
However, when dealing with such scenarios, determining the last appearance of a certain morphotaxa becomes tricky. This issue is further complicated by the fact that it can be hard to distinguish reworked taxa from background levels of rare morphotaxa that may persist over time. In one core that I am analysing there is even a secondary acme of a morphospecies in strata that are almost a million years apart!
Should these potentially reworked specimens therefore be included in a biostratigraphic range chart, ignored, or singled out?
Hola Marcos
i'm no palynologist but faced this problem several times while trying to date some sedimentary levels. For example with Triassic palynomorphs within a Bathonian level. I am affraid there is no rule, and that only experience can help.
marc
Hi Marcos,
I believe it will depend on what are the main aims of your study. For example, if you can check the provenance of the rocks based on the reworked specimens, then you may want to consider them. Why not use a part of the biostrat scheme only for reworked?!
Cheers
I would include reworked specimens, even if you are certain they are reworked. In some cases, for example Classopollis spp. in Paleocene strata from western North America, there is disagreement about whether the genus survived the K/Pg extinction. I've worked industry wells as a nannofossil micropaleontologist and palynologist and sometimes there would be uncertainty about whether the LAD/top of a species is a reworked specimen or not; in that case, I would make a text comment saying something like "T Coccolithus miopelagicus? Possibly reworked." Experience and familiarity with the assemblages will help with figuring this out; for example, reworking of rare Cretaceous nannos in an otherwise typically Miocene assemblage is obvious.
Hi Marcos. This is an eternal issue for palynologists and other biostratigraphers. My general opinion is that reworked taxa should be shown in charts, and properly annotated (usually Rw). But if the reworked taxa are irrelevant to your study, you may want to exclude them from the charts, but should in any case refer to them when describing the assemblages in the text.
It depends on your objective and what you want to show with your data.
All the best
Gil
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