New Spruce (Picea spp.) Macrofossils from Yukon Territory: Implications for Late Pleistocene Refugia in Eastern Beringia

New radiocarbon-dated plant macrofossils provide evidence for black spruce (Picea mariana) and white spruce (Picea glauca) within the unglaciated Yukon Territory at the onset of glacial conditions during the Marine Isotope Stage 3/2 transition, between about 26 000 and 24500 14C yr BP. These data indicate that spruce trees were able to reproduce sexually and grow to maturity within a glacial environment characterized by widespread steppe-tundra vegetation, loess aggradation, and icewedge formation. These trees may have been restricted to rare valley-bottom habitats that provided adequate shelter and moisture similar to those at the present latitudinal tree line. Previously published hypotheses suggest that low Picea frequencies in regional Beringian pollen data point to the local persistence of spruce trees through the last glaciation. Although our data provide evidence for local spruce trees at the onset of the last glaciation, the available macrofossil record is inconclusive regarding the survival of spruce through the Last Glacial Maximum in Eastern Beringia. These new plant macrofossil data require palynologists to reexamine the relationship between Picea pollen frequency and local trees and highlight the importance of integrated pollen- and macrofossil-based paleoecological reconstructions.De nouveaux macrofossiles de plantes datés au C14 attestent de la présence d’épinette noire (Picea mariana) et d’épinette blanche (Picea glauca) dans le territoire non glaciaire du Yukon au début des conditions glaciaires, pendant la transition Marine Isotope Stage 3/2, et s’étendant entre environ 26 000 et 24 500 années avant le présent, daté au C14. Selon ces données, les épinettes étaient capables de se reproduire par voie sexuée et de croître jusqu’à maturité dans un milieu glaciaire caractérisé par une végétation à forte densité de steppe et de toundra, par l’aggradation de loess et par une formation de glace fossile. Il se peut que ces arbres se limitaient à de rares habitats au fond de vallées, habitats qui leur procuraient un abri adéquat et un degré d’humidité similaires à ceux qui existent dans la limite actuelle transversale de végétation des arbres. D’après des hypothèses déjà publiées, la faible fréquence de Picea dans les données régionales de pollen bérégien laissent supposer la persistance locale des épinettes pendant la dernière glaciation. Bien que nos données fournissent la preuve de l’existence d’épinettes locales au début de la dernière glaciation, les données macrofossiles disponibles ne sont pas concluantes en ce qui a trait à la survie de l’épinette pendant le dernier maximum glaciaire dans la Béringie de l’Est. Ces nouvelles données macrofossiles de plantes impliquent que les palynologues doivent réexaminer la relation entre la fréquence du pollen de Picea et les arbres locaux, et font ressortir l’importance des reconstructions paléoécologiques intégrées du pollen et des macrofossiles

Upper Pleistocene Stratigraphy, Paleoecology, and Archaeology of the Northern Yukon Interior, Eastern Beringia. I. Bonnet Plume Basin

New stratigraphic and chronometric data show that Bonnet Plume Basin, in northeastern Yukon Territory, was glaciated in late Wisconsinan time rather than during an earlier advance of Laurentide ice. This conclusion has important ramifications not only for the interpretation of all-time glacial limits farther north along the Richardson Mountains but also for non-glaciated basins in the Porcupine drainage to the northwest. The late Wisconsinan glacial episode in Bonnet Plume Basin is here named the Hungry Creek advance after the principal Quaternary section in the basin. Sediments beneath the till at Hungry Creek have produced well-produced pollen, plant macrofossils, insects, and a few vertebrate remains. The plant and invertebrate fossils provide a detailed, if temporally restricted, record of a portion of the mid-Wisconsinan interstadial, while the vertebrate fossils include the oldest Yukon specimen of the Yukon wild ass. Some of the mid-Wisconsinan sediments have also yielded distinctive chert flakes that represent either a previously unreported product of natural fracturing or a by-product of stone tool manufacture by human residents of Bonnet Plume Basin. In addition to presenting new data on these diverse but interrelated topics, this paper serves as an introduction to a series of reports that will treat in turn the Upper Pleistocene record of Bluefish, Old Crow, and Bell basins, respectively.&nbsp

Late Tertiary and Early Pleistocene Paleosols in Northwestern Canada

Late Tertiary paleosols occurring in the unglaciated portion of the Yukon Territory of northwestern Canada have either Podzolic or Luvisolic soil development. The early Pleistocene paleosols in this area also display Luvisolic soil development in addition to cryogenic soil properties resulting from frost action. Most of these latter paleosols have deeply weathered sola and they usually have rubified argillic horizons. These soil properties suggest that the climate during the late Tertiary and early Pleistocene was warmer than at present. The cryogenic soil properties found in the early Pleistocene paleosols suggest that these soils were exposed to cold climates during subsequent glacial periods.Key words: paleosols, late Tertiary, early Pleistocene, northwestern Canada, soil environments, soil developmentMots clés: paléosols, Tertiaire tardif, Pléistocène précoce, nord-ouest canadien, environnements pédologiques, formation des sol

Tundra and boreal forest of interior Alaska during terminal MIS 6 and MIS 5e

Two sites within the boreal forest of interiorAlaska shed light on the climate and vegetation of terminalmarine isotope stage (MIS) 6 (ca. 140–130 kyr ago) andMIS 5e (125–116 kyr ago). The Birch Creek and Koyukuklocalities are river-cut exposures with sediments datingfrom the penultimate glaciation (at least) to the present.Plant macrofossils, pollen, and beetles were analyzed atthese sites. Terminal MIS 6-aged samples indicate a coolerthan modern climate and the presence of shrub tundra.During MIS 5e, boreal forest grew at the sites and temperatureswere similar to modern times. However, theforest may also have been more mesic than today, asindicated by relatively abundant ferns. Winters may havebeen warmer than today, as suggested by beetle-basedclimatic reconstructions as well as the presence of twoextralimital taxa that today live in regions where wintertemperatures are up to 15 ?C warmer than at the sitelocalitie