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“PACKRATS” OF BERINGIA: PALEOECOLOGY OF SMALL MAMMAL MIDDENS IN CENTRAL YUKON.
ZAZULA, GRANT D Department of Biological Sciences, Simon Fraser University.
Mathewes, Rolf W Department of Biological Sciences, Simon Fraser University.
Froese, Duane G Department of Earth and Atmospheric Sciences, University of Alberta.
Storer, John E Yukon Heritage Resources, Government of Yukon Territory.
Westgate, John A Department of Geology, University of Toronto.
Sanborn, Paul T Ecosystem Science and Management Program, University of Northern British Columbia.
Perennially frozen loess exposures in the Klondike goldfields of west-central Yukon (Fig. 1) are important archives of Pleistocene terrestrial environments (Kotler and Burn, 2000; Zazula et al., 2003; Schweger, 2003). Ages from distal tephra beds (Westgate et al, 2001; Froese et al., 2002) mark accelerated loess deposition at multiple sites during Marine Isotope Stage (MIS) 2 (ca. 25,000 to 14,000 yr BP) and 6 (ca. 190,000 – 130,000 yr BP). Burrows and hibernacula containing nests and seed caches from Arctic ground squirrels (Spermophilus parryi) and microtine rodents are common within these frozen loess sequences (Fig. 2, 3). The middens provide a site-specific record of local full-glacial vegetation in valley-bottom and valley margin settings in eastern Beringia. Preliminary macrofossil analyses indicate a locally diverse, herb-dominated flora during MIS 2 including Poa sp., Elymus sp., Festuca sp., Deschampsia caespitosa, Hierochloë hirta ssp. arctica, Carex spp., Allium schoenoprasum, Astragalus sp. Ranunculus sp., Potentilla sp., Draba sp., Cardamine sp., Lepidium cf. densiflorum, Papaver cf. mcconnellii, Androsace septentrionalis, Cerastium sp., Minuartia sp., Silene cf. taimyrensis, Penstemon gormanii, Erigeron sp., Artemisia frigida and Taraxacum ceratophorum (Fig. 4). This assemblage suggests open, pioneer-type vegetation that grew on well-drained, actively accreting loess and colluvial substrates subjected to continuous disturbance from cryo- and bioturbation. The presence of burrow systems and nesting sites indicates that active layers were thicker during Pleistocene glacials than at present, especially on north-facing slopes. Although these paleoecological records are biased by small mammal behavior (e.g., McLean, 1985), they represent important paleobotanical archives of vegetation which may have also been available to Beringian megaherbivores as forage.
Froese, D.G., Duk-Rodkin, A., Bond, J.D. (Eds.), 2001, Field guide to Quaternary research in central and western Yukon Territory. Occasional Papers in Earth Sciences No. 2, Heritage Branch, Government of Yukon. 104 pp.
Froese, D.G., Westgate, J.A., Preece, S., Storer, J.E., 2002, Age and significance of the late Pleistocene Dawson tephra in eastern Beringia. Quaternary Science Reviews v.21, p. 2137-2142.
Kotler, E., Burn, C.R., 2000, Cryostratigraphy of the Klondike “muck” deposits, west-central Yukon Territory. Canadian Journal of Earth Sciences v.37, p. 849-861.
McLean, I.G. 1985. Seasonal patterns and sexual differences in the feeding ecology of arctic ground squirrels (Spermophilus parryi plesius). Canadian Journal of Zoology v. 63, p. 198-1301.
Schweger, C.E., 2003, Paleoecology of two marine oxygen isotope stage 7 sites correlated by the Sheep Creek tephra, northwestern North America. 2003. Quaternary Research v. 60, p. 44-49.
Westgate, J.A., Preece, S.J., Froese, D.G., Walter, R.C., Sandhu, A.S., Schweger, C.E. 2001. Dating Early and Middle (Reid) Pleistocene glaciations in central Yukon by Tephrochronology. Quaternary Research v. 56, p. 335-348.
Zazula, G.D., Froese, D.G, Schweger, C.E., Mathewes, R.W., Beaudoin, A.B., Telka, A.M.,Harington, C.R., Westgate, J.A., 2003, Ice age steppe vegetation in east Beringia. Nature v. 423, p.603.
Figure 1. Map of Eastern Beringia with Klondike goldfields inset.
Figure 2. Arctic ground squirrel nest in Dawson Tephra (24,000 14C yr BP) at Quartz Creek (after Froese et al., 2002 QSR).
Figure 3. Nest in MIS 6 loess at Dominion Creek.
Figure 4. Selected plant macrofossils from MIS 2 aged small mammal middens associated with Dawson Tephra: a) Elymus sp. floret; b) Hierochloë hirta ssp. arctica spikelet; c) Carex sp. achene; d) Deschampsia caespitosa floret; e) Cardamine sp. silique; f) Draba sp. silicle; g) Lepidium densiflorum silique; h) Ranunculus sp. seed; i) Potentilla sp. achene; j) Cerastium sp. seed; k) Papaver cf. mcconnellii capsule; l) Silene cf. taimyrensis capsule; m) fossil Silene cf. taimyrensis seed (left) and modern Silene taimyrensis seed (right); n) Androsace septentrionalis seed; o) Artemisia frigida leaves
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