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LATE QUATERNARY VEGETATION HISTORY OF SOUTHWESTERN YUKON TERRITORY

VERMAIRE, JESSE C  University of New Brunswick.
Cwynar, Les C  University of New Brunswick.

Late Quaternary vegetation and climate history of the southwestern Yukon is of interest to paleoecologists

as this region remained unglaciated during the last glacial period and formed the southeastern corner of the Bering land bridge (Beringia). Rampton (1971) cored Antifreeze Pond (AP), southwestern Yukon Territory, Canada, from which he obtained 7 14C bulk sediment dates and analysed the pollen. The basal dates indicate that the AP sediment record spans 30, 000 14C yr. B.P.. If this chronology is correct, AP is one of only two known lakes in the Yukon Territory with a sediment record extending into the middle Wisconsinan, a period poorly understood in southeastern Beringia. This chronology has been questioned due to a date reversal near the base of the core and the possibility of old carbon within the lake. A new core from AP has been obtained and 23 samples of terrestrial plant macrofossils have been submitted for AMS 14C dating.

Pollen, stomates, and plant macrofossil analyses of a 5 m long sediment core from AP provides a vegetation history of southwestern Yukon Territory. The use of a multi-proxy approach will provide both a regional and local signal of past vegetation. Preliminary evidence suggests that during the late Quaternary southwestern Yukon Territory underwent five major environmental shifts. The early vegetation history was

dominated by sedges (Cyperaceae) and grasses (Gramineae) along with Artemisia , Thalictrum, and Pediastrum. This period is interrupted by an interstadial inferred by an increase in Picea, Alnus, and Salix pollen along with macrofossils of Ranunculus aquatilis, Potamogeton, Chara, Sphagnum, and statoblasts of the bryozoan Cristatella mucedo. Also, conifer stomates are present during this period suggesting that southeastern Beringia may have been lightly forested. This may represent an

eastern expansion of Picea woodland into southwestern Yukon Territory during the middle Wisconsinan. Although this has been previously hypothesized, the pollen data from this region have been inconclusive. Following the interstadial is an environment again dominated by Cyperaceae and Gramineae. Few plant macrofossils, diatoms, and chironomids were recovered during this period, which may represent a hiatus in the lacustrine record. Approximately 13,000 yr. B.P., Salix pollen increases coeval to a rise in Hippuris, Eleocharis, Ranunculus

aquatilis and Potamogeton macrofossils. This period is also marked by a rapid sedimentation rate. The characteristic boreal forest vegetation, with increased Picea, Betula, Alnus, and Salix and a decrease in herbaceous pollen, developed approximately 9,000 yr. B. P. in southeastern Beringia.

REFERENCES
Rampton, V., 1971, Late Quaternary vegetational and climatic history of the Snag-Klutlan area, southwestern Yukon Territory, Canada: Geological Society of America Bulletin, v. 82, p. 959-978.


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