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Abstract Detail

The Devonian Period: a time of major plant diversification: a symposium in honor of Patricia G. Gensel and her contributions to Devonian paleobotany.

Stein Jr, William [1].

Composition and structure of the Earth’s oldest forests.

The origin of tree-size plants in the Middle Devonian signaled a fundamental change in Earth’s terrestrial ecosystems with multiple consequences on atmospheric CO2 levels, climate, sedimentation patterns, global nutrient cycling, and possibly mass extinction. Perhaps the most famous fossil locality documenting an in situ forest of this age is the “oldest known petrified forest” at Gilboa in the Catskill Mountains of NY (Goldring 1927). At this site, hundreds of tree bases of Eospermatopteris, now known to be large pseudosporochnaleans (Cladoxylopsida), were found in rooted in life position. Recently, we had the opportunity to examine a portion of the original site previously inaccessible for nearly 90 years. A fossil soil (palosol) comprised of a gleyed fine sandstone is still intact and provides well-preserved evidence of relative sizes and positions of trees in this ancient forest. Instead of a monospecific stand, it was a surprise to find a mixed forest comprised of dominant Eospermatopteris plus two other tree-sized plants. These included the earliest known arborescent lycopsid in North America, and very large scrambling to ascendant plants identified as aneurophytaleans (Progymnospermopsida). Probably due to the presence of wood, the aneurophytaleans were the only plants preserved at the site showing both abundant compression carbon and partial preservation in pyrite. The association of typical aneurophytalean (probably Tetraxylopteris) aerial shoot systems with large scrambling main stems represents a significant amplification in the reconstruction of these forms heretofore considered ‘shrubs’. General features of the site suggest that the famous forest surface was one of several rooting horizons each on the upper surface of recurring meter-thick sandstone units showing no direct evidence of marine influence. This, and the plants themselves, suggests an ephemeral forest in a disturbed wetland environment associated with periodic and probably catastrophic terrestrial flooding bringing in large quantities of sand. Although the original Gilboa site is no longer available for study, ongoing work at a nearby site provides additional and contrasting information on floral composition of the Gilboa-age Catskill forest. In addition to Eospermatopteris, large radiating root systems likely belonging to a very early Archaeopteris are found in a mixed assemblage. The paleosol suggests a more aerated environment than at Gilboa. This occurrence also includes well-articulated placoderms and chondrichthyans suggesting marine overwash into an adjacent lowland terrestrial environment perhaps killing the trees and preserving the paleosol.

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1 - State University of New York, Biological Sciences, Binghamton, NY, 13902-6000, USA

Earliest Forest.

Presentation Type: Symposium or Colloquium Presentation
Session: SY10
Location: Prince of Wales/Riverside Hilton
Date: Wednesday, July 31st, 2013
Time: 10:15 AM
Number: SY10006
Abstract ID:242
Candidate for Awards:None

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