Abstract Detail

The Miocene vegetation and environment of Western North America

Dillhoff, Richard [1], Dillhoff, Thomas [2], Jijina, Anthony [3], Sherrod, Brian [4], Stromberg, Caroline [5].

­­­The Vasa Park flora, King County, Washington, USA – a window into the Late Miocene of the Pacific Northwest.

A Late Miocene flora (11.4 from Bellevue, Washington is described using macro and micro fossils to summarize the flora, estimate climate and vegetation coverage.  Genera recognized from macrofossils include pteridophytes (Equisetum, Woodwardia and Allantodiopsis, an apparent relict from the Eocene Puget Group flora); rare Cupressaceous conifers and common angiosperms (Platanus, Cercidiphyllum, Ulmus, Fagus, Hydrangea, Alnus, Acer and Persea).  Including unidentified morphotypes, the macroflora records a bryophyte, six pteridophytes, one gymnosperm and twenty four angiosperms.  Well preserved fossil pollen from the same sediments reveals a much richer regional flora.  Although TCT Cupressaceous pollen is the most common element, a diverse record of Pinaceae is revealed by the palynoflora including Abies, Picea, Pinus, Pseudotsuga/Larix and Tsuga.  In contrast, the Pinaceae is totally absent from the macrofossil record. Additional angiosperm genera identified from pollen include Liquidambar, Ilex, cf. Sarcobatus, Carya, Juglans, Nyssa, Fraxinus and Salix.  Significant rare elements in the pollen flora include representatives of the Poaceae and Asteraceae.  In total the palynomorph assemblage documents more than twice the diversity found in the macroflora.  Coexistence analysis based on the pollen assemblage estimates Mean Annual Temperature (MAT) of 11.6-16.6°C.  Together, the macroflora and palynofloras suggest that Pacific Northwest plant communities—and climates—had not changed substantially since the Middle Miocene. Phytoliths recovered from the sediments suggest a closed canopy forest with warm-adapted grasses of the PACMAD clade in the understory or in forest gaps.  Geological and botanical evidence indicate that the fossils are preserved in flood overbank deposits associated with widespread Late Miocene conglomerates found throughout Western Washington. Keywords: Miocene, Geology, Paleobotany, Palynology, Phytoliths.

1 - 1307 212TH AVE NE, SAMMAMISH, WA, 98074, USA, 425/868-0468
2 - 10521 37th St SE, Lake Stevens, WA, 98258, USA, 425-335-4573
3 - University of Washington, Biology, Box 351800, 24 Kincaid Hall, Seattle, Wa, 98195, USA
4 - USGS at University of Washington, Dept of Earth and Sapce Sciences, Box 35130, Seattle, Wa, 98195, USA
5 - University Of Washington, Department Of Paleobotany, 24 Kincaid Hall, Box 351800, Seattle, WA, 98195-1800, USA, 206-619-2152

Keywords:
Miocene
Paleobotany
Palynology
Phytoliths.

Presentation Type: Symposium or Colloquium Presentation
Session: C2
Location: Salmon/Boise Centre
Date: Tuesday, July 29th, 2014
Time: 4:15 PM
Number: C2012
Abstract ID:51
Candidate for Awards:None