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Abstract Detail

The Miocene vegetation and environment of Western North America

Reinink-Smith, Linda [1].

Comparison Of Late Miocene Floras Of Alaska With Those Of Washington And Oregon.

During the Late Miocene (Homerian) interval the forests of southern Alaska were broadly similar with those of southern Washington and northwestern Oregon. At 70° N paleo-latitude in the Cook Inlet area was a mixed conifer hardwood forest with much in common with the present forests of southern New York State, namely a flora rich in Quercus, Juglans, Carya, Ulmus and Pinus cf strobus. The mean annual temperature was ~10 to 11° C, ca. 5°C warmer than today. Annual precipitation was between 800-1000 mm, with most falling in summer. In Washington/Oregon areas the floras of the late Miocene, Wilkes Formation and Faraday Dam floras have a similarity quotient of .75 with the Cook Inlet area as shown by Sörensen’s similarity coefficient (range: 0-1). The mean annual temperature of the Washington Late Miocene floras is estimated at about 12-13 °C. Presently, western Washington is at ~11.54° C with dry summers (annual precipitation of 952 mm). This means that the mixed hardwood and conifer forest belt of Alaska extended from ~70° N at least down to 43° N, near the Oregon/Washington border (Wilkes and Faraday floras). The floras share ~60% of the genera. Some typical examples are genera of the Fagaceae, Ulmaceae, Nyssaceae. The Homerian flora (Late Miocene) of Cook Inlet also shows great similarity with the Late Miocene flora of Chukotka, Siberia. Hence the same forest zone spanned the Pacific Rim during the Miocene. But the forests were not unchanging. The advance of an Asian population across the Bering Land Bridge in the Clamgulchian time marked a biogeographical change in alders (Subgenus Alnus) from mainly 4-pored in the Miocene to 5-pored in the Miocene/Pliocene. They entered into Alaska and later became practically dominant among the alder taxa in the Alaska province.

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1 - Kuwait University, Department of Earth and Environmental Sciences, P.O. Box 5969, Safat, 13060, Kuwait

pollen flora.

Presentation Type: Array
Session: C2
Location: Salmon/Boise Centre
Date: Tuesday, July 29th, 2014
Time: 4:45 PM
Number: C2014
Abstract ID:477
Candidate for Awards:None

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