Abstract Detail

The Miocene vegetation and environment of Western North America

PIGG , KATHLEEN B [1], DeVore, Melanie L. [2].

Yakima Canyon reconsidered.

The pemineralized middle Miocene (15.6 mya) Yakima Canyon flora of the Columbia River Basalts resembles a modern bald cypress swamp of southeastern North America. Taxodium fossils are dominant and include wood, stems, roots, pollen and seed cones, cone scales, and seeds containing embryos. Nyssa endocarps are also common and similar to those of the tupelo gum, N. sylvatica of southeastern North America in having a single locule, veins within grooves, a triangular germination valve and an apical prominence.  Fossil rhizomes, fronds and chain-like sori are assignable to the extant Virginia chain fern, Woodwardia virginica. Other ferns include Osmunda wehrii of subgenus Osmunda and the onocleoid Wessiea yakimaensis. Remains of Pinus foisyi include stems, leaves, and pollen cones and among the earliest asymmetric seed cones. Acorns of Quercus hiholensis have embryo and involucre structures that identify them with extant, annually fruiting white oaks. Infructesences and seeds of Liquidambar changii resemble the Asian L. acalycina. The family Lythraceae is represented by an extinct taxon Shirleya grahamae, which is known from fruits and more recently discovered flowers. This plant bears a strong resemblance to the extant crepe myrtle Lagerstroemia but anatomical features suggest adaptation for a marginal aquatic habitat. Lythraceous seeds similar to Decodon are also occasionally recovered. Other elements include quite common Paliurus (Rhamnaceae) endocarps; occasional vitaceous seeds and small vines; Melia (Meliaceae) endocarps that are very similar to their modern Asian relatives; a tiny Platanus staminate inflorescence; and Typha-like foliage. Prunus and Cornus endocarps and a variety of yet unidentified seeds and twigs are also present.  Galls, fungal hyphae and various damage patterns occur in Taxodium branches and within Q. hiholensis acorns.Lepidopterid coprolites have also been found. Some interesting questions that arise about the flora: 1) Why is Paliurus among the most commonly preserved endocarp?  Why are Paliurus endocarps found in the fossil recod but rarely leaves, while Zizyphus leaves are well known but fruits are rare? 2) Why don't we find Melia more often in comparison to the more common Cedrela? 3) Why is there no Ginkgo? Its last North American occurrence is in the nearby Vantage woods. 4) Why are there not more diverse dicot woods? Is it because of taphonomic bias? 5) How does the Yakima assemblage compare with a strikingly similar permineralized flora of eastern Hungary studied by Peter Huber, and the Shimokawa flora of Hokkaido, Japan?

1 - Arizona State University, SCHOOL OF LIFE SCIENCES FACULTY & ADMIN, BOX 874501, Tempe, AZ, 85287-4501, USA
2 - Dept Of Biology & Env. Science, GC & SU Campus Box 81, MILLEDGEVILLE, GA, 31061-0001, USA

Keywords:
Miocene
permineralization
Taxodium swamp
Woodwardia virginica
Lythraceae
Liquidambar
Washington State.

Presentation Type: Symposium or Colloquium Presentation
Session: C2
Location: Salmon/Boise Centre
Date: Tuesday, July 29th, 2014
Time: 4:00 PM
Number: C2011
Abstract ID:334
Candidate for Awards:None