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Fields, Patrick F [1], Ertter, Barbara [2].

Update on the Ponderosa Flora, an early middle Miocene Megafossil and Palynologic Assemblage from Payette Lake, Valley County, Idaho.

Patrick F. Fields*, O.J. Smith Museum of Natural History, College of Idaho, Caldwell, ID 83605 and 5349 North Canal Road, Dimondale, MI 48821 ( and Barbara J. Ertter, O.J. Smith Museum of Natural History, College of Idaho, Caldwell, ID 83605.   The 1977 discovery and 2014 rediscovery of the Ponderosa middle Miocene flora, near Payette Lake, Valley County, ID was first reported to the paleobotanical world (MPC) in 2017.   At that time about 45 megafossil taxa were recognized from finer layers within a coarse micaceous sandstone, that also contains woody and charcoal fragments, and cuticle in some of the specimens.   The flora as presently understood consists of approximately 75 identified taxa in 53 genera (13 of which are also represented by pollen, and 3 represented so far by pollen only). There are also numerous as-yet unidentified leaves, seeds, and palynomorphs. The recognized taxa consist of at least 56 dicotyledonous angiosperm species, 3 monocots, at least 9 gymnosperms, and one lower vascular plant.   Of note are the presence of Amentotaxus, abundant Zizyphoides leaves and Nordenskioldia fruit (perhaps conspecific organs; collectively representing a southern-most extension from the Latah-type floras to the north), Sequoia (a northern-most extension from the floras encircling the Western Snake River Plain), the first Miocene record of North American Cotinus fossils, possibly Platanus bark, at least two distinctly identifiable taxa of uncertain affinity, and the occurrence of four relatively rare taxa for the Miocene of the inland Pacific NW: Cercidiphyllum, Ginkgo, Metasequoia, and Sequoia.   As previously reported, the flora suggests lacustrine/riparian and overbank/floodplain floral paleoenvironments, to which we can now add a lessor component of more paleo-upland, conifer rich elements.   In light of the recent revisions to isotopic dating of the Columbia River Basalts, and the fact that the Ponderosa assemblage occurs immediately below an early flow of the Grande Ronde Basalts, the flora is now interpreted to be about 16.7-16.5 MA, and falls within the mid-Miocene Climatic Optimum interval.   Acknowledgement is due to Drs. Christopher Davidson for discovery and collecting, and William C. Rember for preliminary  palynologic identifications and geologic interpretations.

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1 - self, 5349 N Canal, Dimondale, MI, 48821-8712, USA
2 - Boise State University, Snake River Plains Herbaria, , Boise, Idaho, 83725, USA

Latah Flora.

Presentation Type: Oral Paper
Session: PL7, Paleobotany: Mesozoic/Cenozoic Paleobotany
Location: /
Date: Thursday, July 22nd, 2021
Time: 2:00 PM(EDT)
Number: PL7007
Abstract ID:1060
Candidate for Awards:None

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