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Abstract Detail

Paleobotanical Section

Smith, Robin [1], Basinger, James [1], Greenwood, David [2].

Forest dynamics, climate, and disturbance in the greenhouse world of the early Eocene: evidence from the Okanagan Highlands, British Columbia.

Fossil floras of early Eocene Okanagan Highlands sites in British Columbia and Washington provide a rich resource for studying the evolution of North American temperate forest communities. These floras reflect upland microthermal forest communities in contrast to coeval mesothermal forests in lowland western North American sites. The Falkland site, in south-central B.C., consists of an isolated outcrop of thinly bedded lacustrine shale radiometrically dated to 50.61 ± 0.16 Ma, near the end of the Early Eocene Climatic Optimum (EECO, 50-52 Ma), the warmest period of the Cenozoic. The site has been sampled using an unbiased census approach, yielding >1700 compression fossils from 15 quarries in three correlative rock units. 61 dicot leaf morphotypes have been identified to date for the site, with diversity for individual units ranging from 25 to 46 dicot morphotypes. Based on leaf physiognomy, paleoclimate is characterized as microthermal and mesic. Analysis of the three units indicates a decrease in mean annual temperature over time, a trend consistent with the site falling at the end of the EECO. Concurrent with change in climate, statistical analysis of morphotypes across the three units suggests an increase in plant diversity, and an abrupt shift to increasing dominance of angiosperms relative to gymnosperms in the youngest (and coolest) unit following a major volcanic environmental disturbance. Changes in plant community structure cannot be attributed solely to this disturbance, as earlier volcanic events were not followed by changes of similar magnitude in the fossil flora. Trends observed in the three units indicate that climatic thresholds may have played an important role in mediating the impact of disturbance events on the development of this predominantly deciduous upland forest. This study demonstrates the value of fine-scale, census-style sampling, as significant floristic and climatic transitions would have been masked in whole-site analysis of the Falkland flora.

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1 - University of Saskatchewan, Department of Geological Sciences, 114 Science Place, Saskatoon, Saskatchewan, S7N 5E2, Canada
2 - Brandon University, Department of Biology, 270 18th Street, Brandon, Manitoba, R7A 6A9, Canada

Okanagan Highlands
Early Eocene Climatic Optimum
leaf physiognomy

Presentation Type: Oral Paper:Papers for Sections
Session: 17
Location: 169/Law
Date: Monday, July 28th, 2008
Time: 1:45 PM
Number: 17002
Abstract ID:387

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