IMPORTANT OUTCOMES FROM STUDIES OF THE SUCCOR CREEK FLORA OF THE MIDDLE MIOCENE SUCKER CREEK FORMATION, IDAHO/OREGON

Ongoing research by this author over the last 25 years has led to the discovery of 25 new taxa and a re-interpretation of the 15 Ma Succor Creek paleoflora of the Sucker Creek Formation, southwestern ID and eastern OR. The study area is about 50 km N-S by 10 km E-W and centered on the ID/OR state line. Fossil material is found in a series of intra- and inter-caldera volcanic deposits exposed along the westward-flowing and then north-flowing Succor Creek. These volcanoes appear to be part of several larger (tectonic?) NW-SE trending structures (i.e., Olympic-Wallawa Lineament). Over 100 fossil-bearing sites have been sampled. At least 150 species are now recognized in the paleoflora (compared to 67 in the most recent previous study). This includes 22 gymnosperm taxa (compared to 8 in past studies). In contrast to previous studies, there is a remarkable level of parity between the palynologic and megafossil taxonomic representation in the flora. Over 600 taxonomic revisions are proposed. Distinct “Swamp/Wetland”, “Floodplain/Slope”, “Drier Slope”, and “Relative Upland” paleofloral assemblages are now recognized. An early paleosuccessional component and a summer rain-requiring component are also inferred throughout these assemblages. New conifer-rich megafossil discoveries confirm what pollen previously suggested, a paleoelevational gradient (from lower and wetter in the north to higher and drier in the south). This is consistent with a hot spot to the south that “migrated” in a southwest to northeast direction about 15 million years ago. This also suggests that paleopalynology can serve as a good predictive tool for vegetation beyond the immediate range, but that its “effective sampling range” (ESR) is only a few km (not 10’s of km) away. Conversely, the ESR for megafossils in volcanic regimes may be on the order of only 5-6 km, not 15-20 as previously suggested. Revised stratigraphic correlation eliminates duplicated sections from the Devil’s Gate region, but correlation from there southward to two isolated groups of sections (Rockville-Short Cut and Coal Mine Basin-“South Bend”) is pending.