Abstract
Late-glacial and early postglacial pollen stratigraphy is described for a gyttja and peat section overlying Mankato drift, in the center of the Des Moines glacial lobe near Madelia. Five pollen zones are distinguished; the oldest may represent pioneer vegetation shortly after the retreat of the ice. The transition from zone I to II is likely to be the beginning of the Two Creeks interstadial. The Two Creeks vegetation shows up in the pollen diagram as a spruce-ash forest. During zone III, the Valders stadial, a shrub forest with birch, alder, spruce, and Artemesia seems to have been present. The postglacial starts with a rapid decline of spruce and a strong rise of birch (zone IV) followed by elm and oak (zone V). The diagram is controlled by 2 radiocarbon dates: the transition from zone I to 11 is dated at 12,650+ or -350 B.P. (W-824); the top of zone IV at 9300+ or -350 B.P. (W-825). The locality lies less than 200 mi. outside the presumed margin of the Valders ice. It is therefore worth noting that the Valders readvance did not produce tundra or park tundra at the site but merely increased the proportion of shrubs in the forest.
This article requires a subscription to view the full text. If you have a subscription you may use the login form below to view the article. Access to this article can also be purchased.
