The Klondike goldfields and Pleistocene environments of Beringia

Abstract

The Klondike goldfields of Yukon, Canada, contain a key record of Pleistocene Beringia, the region of Alaska, Siberia, and Yukon that remained largely unglaciated during the late Cenozoic. A concentration of mining exposures, with relict permafrost that is locally more than 700,000 years old, provides exceptional preservation of paleoenvironmental archives and a new perspective on the nature of paleoenvironments during the Pleistocene. A critical feature is the stratigraphic association of distal tephra beds with these paleoenvironmental archives, which facilitates their regional correlation and, in many cases, provides independent ages for the paleoenvironmental assemblages. Paleoenvironmental analyses of fossil arctic ground-squirrel middens and buried vegetation indicate the presence of cryoxerophilous (?steppe-tundra?) vegetation growing on well-drained substrates with deep active layers (seasonal thaw depths) during cold intervals of the Pleistocene. Studies of full-glacial paleosols and cryostratigraphic relations of associated ground ice indicate the importance of active loess deposition and surface vegetation cover in maintaining the functionally distinct mammoth-steppe biome, which supported grazing mega-fauna populations, including mammoth, horse, and bison.Peer reviewe

PERMAFROST AND PERIGLACIAL FEATURES | Yedoma: Late Pleistocene Ice-Rich Syngenetic Permafrost of Beringia

“…Upland silts mantle hilltop exposures and are commonly found on alluvial terraces or sheltered behind bedrock obstacles, and have been unambiguously interpreted as loess (Muhs et al, 2008;Péwé, 1975). However, it should be noted that these upland silt deposits are not ice-rich and differ significantly from Yedoma deposits as described in valleybottom settings (e.g., Bray et al, 2006;Froese et al, 2009;Péwé, 1975).…”

“…In North America, syngenetic ice-rich silt deposits, thought to be broad equivalents to the Siberian examples, occur in lower segments of the Arctic Foothills, in the northern part of Seward Peninsula, in numerous areas in Interior Alaska (Kanevskiy et al, 2011), and the Klondike region of Yukon Territory (Froese et al, 2009). The Klondike sites, by virtue of the gold-mining activities, have created excellent exposures for study ( Figure 2).…”

“…For example, in eastern Beringia, plant macrofossils from Arctic ground squirrel (Spermophilus parryii) nests, seed caches, and burrows are dominated by grasses, dryland sedges, sage, and a wide variety of flowering forbs (e.g., Zazula et al, 2007). Together, these plants indicate open grass-and forb-rich steppe tundra in eastern Beringia, developed on largely well-drained substrates during MIS 2 (Froese et al, 2009).…”

“…Perhaps their most distinctive property, however, is the pungent odor they give off from the incompletely decomposed organic matter that is exposed as they thaw. Although these deposits are largely of late Pleistocene age, the presence of distal, dateable volcanic ash (tephra) within some of them indicates a middle Pleistocene age (Froese et al, 2008(Froese et al, , 2009Reyes et al, 2010).…”

“…These deposits are often referred to as 'Ice Complex' (in Russian: ledovyi kompleks) or 'Yedoma' in Siberia, while in North America, other terms such as 'muck' or retransported silt could be partially considered as equivalent terms (Froese et al, 2009;Péwé, 1975;Shur et al, 2004). Solov'ev (1959) first defined Ice Complex as frozen deposits of various age, composition, genesis, and thickness, with numerous ice wedges.…”