A chronologic framework for Cenozoic megafossil floras of northwestern North America and its relation to marine geochronology

Abstract

Collection and analysis of fossil plants in several stratigraphic sections have produced a chronologic framework for plant-bearing rocks of the northwesternNorth American province. The geographic extent of this province varied during the Cenozoic, but the stage framework can generally be applied to the region west of the Rocky Mountains (including Alaska) during the Paleogene and Miocene. The occurrence of some plant megafossils in dominantly marine sections of Paleogene age provides only a general concept of relation to the marine geochronology. Numerous Neogene floras have been radiometrically dated and can thus be more accurately related to the marine geochronology. The changes in the floral assemblages are largely the result of major climatic changes. If these changes are assumed to represent secular phenomena, the provincial chronology can also be related to the Cenozoic terminology in those Northern Hemisphere regions where paleobotanical data indicate that a similar series of climatic changes occurred. Inferences based on a combination of radiometric ages, correlations of West Coast benthic foraminiferal stages to the planktonic chronologies, and marine-nonmarine correlations of West Coast units indicate that the Eocene/Oligocene boundary may be as young as 32 m.y.

Stratigraphic Occurrence and Correlation of Early Tertiary Vertebrate Faunas, Trans-Pecos Texas: Agua Fria–Green Valley Areas

“…In addition there are problems of a lack of samples at desirable geographic and stratigraphic locations, lack of agreement on correlation from deep-sea cores to stratotypes, and lack of agreement on which zonal boundaries represent epoch/series boundaries. The younger date, 32-33 m.y., has been used by Armentrout (1981) and Wolfe (1981) for the correlation of chronostratigraphic units in Oregon and Washington and by Harris (1982) and Powell and Baum (1982) on glauconite from the Atlantic coastal plain. It is beyond the scope of this work, however, to do more than point out the discrepancy.…”

Mammal and Bird Tracks from the Eocene Puget Group, Northwest Washington, USA

“…The median age would be equivalent to the early Uintan Land Mammal Stage, but the ±4.2 Ma uncertainty spans a range of late Bridgerian to late Uintan. Because of the questionable reliability of radiometric dates in a region where local igneous activity may have partially annealed fission tracks, we prefer the older age estimate based on plant fossils (Wolfe, 1968(Wolfe, , 1981. This age range corresponds to the time when early Eocene tectonic activity resulted in the formation of sedimentary basins at many other locations in Washington and British Columbia (Johnson, 1985).…”

The Seldovian Regional Stage in Alaska and Its Analogs in the Soviet Far East

“…In his opinion, it corresponds to N5-N12 in the zonal scale [23]. Wolfe [48] half of the Hemingfordian and lower half of the Barstovian in the North American scale of stages based on mammals, a large part of the Newportian in the molluscan scale, and the upper half of the "Saucesian" and "Relizian" in the benthic foraminiferal scale, and, finally, in the standard scale of Mediterranean stages, to the upper half of the Burdigalian, the Langhian, and the lower part of the Serravalian.…”

“…The Seldovian was recently considered by Wolfe [48] to be a provincial stage of the whole northwestern part of North America, west of the Rocky Mountains and north of central California (approximately 38° N), including Alaska. In his opinion, it corresponds to N5-N12 in the zonal scale [23].…”

“…1, Section HI). Paleontological characterizations of these sections, and of the reference section at Seldovia Point, have been published by Wolfe [45][46][47][48] and by Wolfe and Tanai [50].…”