CLIMATICALLY INDUCED FLORISTIC CHANGES ACROSS THE EOCENE-OLIGOCENE TRANSITION IN THE NORTHERN HIGH-LATITUDES, YUKON-TERRITORY, CANADA

Global temperature decline associated with the Eocene-Oligocene transi tion resulted in extinctions of plants and animals in both marine and nonmarine environments. The extensive stratigraphic exposures, well-pr eserved palynological assemblages, and interbedded coal seams of the n onmarine Amphitheatre Formation, Burwash Basin, Yukon Territory, provi de a comprehensive record of this transition. The formation spans a pa leoclimatically significant interval otherwise poorly represented in h igh-latitude deposits of the northwestern Cordillera. Palynological da ta constrained by the chronologic and stratigraphic framework establis hed for the Amphitheatre Formation indicate that the global temperatur e decline resulted in a shift from warm temperate, angiosperm-dominate d to cooler temperate, gymnosperm-dominated (mainly coniferous) forest types. This turnover is seen in the increase in the percentage of gym nosperm compared to angiosperm pollen upsection. The effect of climate change is also recorded in the systematic composition of the angiospe rm pollen spectra. The highly diverse palynoflora of the lower Amphith eatre Formation is dominated by angiosperm pollen characteristic of pl ants favoring warm temperate climates, and consistently includes polle n of broad-leaved evergreen taxa. In contrast, the angiosperms most co nspicuous in the low-diversity palynoflora of the upper Amphitheatre F ormation are characteristic of plants favoring a cooler temperate clim atic setting. Petrographic compositional changes in the coals document the same plant community changes. The floristic data also indicate th at, at high latitudes, there may have been a change to a wetter and le ss seasonal climate during the overall global cooling trend.