Two Pollen Diagrams from Southeastern Minnesota: Problems in the Regional Late-Glacial and Postglacial Vegetational History

Abstract

Research Article| November 01, 1963 Two Pollen Diagrams from Southeastern Minnesota: Problems in the Regional Late-Glacial and Postglacial Vegetational History H. E WRIGHT, JR.; H. E WRIGHT, JR. School of Earth Sciences, University of Minnesota, Minneapolis, Minn Search for other works by this author on: GSW Google Scholar THOMAS C WINTER; THOMAS C WINTER U. S. Geological Survey, St. Paul, Minn Search for other works by this author on: GSW Google Scholar HARVEY L PATTEN HARVEY L PATTEN Shell Oil Co., Houston, Texas Search for other works by this author on: GSW Google Scholar Author and Article Information H. E WRIGHT, JR. School of Earth Sciences, University of Minnesota, Minneapolis, Minn THOMAS C WINTER U. S. Geological Survey, St. Paul, Minn HARVEY L PATTEN Shell Oil Co., Houston, Texas Publisher: Geological Society of America Received: 31 May 1962 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1963, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1963) 74 (11): 1371–1396. https://doi.org/10.1130/0016-7606(1963)74[1371:TPDFSM]2.0.CO;2 Article history Received: 31 May 1962 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation H. E WRIGHT, THOMAS C WINTER, HARVEY L PATTEN; Two Pollen Diagrams from Southeastern Minnesota: Problems in the Regional Late-Glacial and Postglacial Vegetational History. GSA Bulletin 1963;; 74 (11): 1371–1396. doi: https://doi.org/10.1130/0016-7606(1963)74[1371:TPDFSM]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Kirchner Marsh and Lake Carlson are located 3 miles apart in Dakota County about 15 miles south of Minneapolis in the St. Croix moraine, which was formed by the Superior lobe during the Cary phase of the Wisconsin glaciation. During the Mankato phase that followed, the Des Moines lobe advanced to within a few miles of the sites. The region today is in a mixed-oak forest, with a maple-basswood forest 15 miles to the west and a re-entrant of the prairie on the sand plain south of the moraine. The general limit of coniferous trees is about 50 miles northeast of the sites, although outliers, especially of Pinus strobus, may be found along the Mississippi Valley a few miles to the east.One sediment core 12–13 m long from each site was analyzed for pollen content at 5–25-cm intervals. Diagrams based on percentage of total pollen (trees, shrubs, wind-pollinated herbs) show essentially identical sequences at the two sites, starting with the late-glacial phase of ice retreat. The diagrams have been subdivided into pollen zones according to the A-B-C sequence introduced by Deevey for New England.The late-glacial pollen record starts at Kirchner Marsh with a short Picea-Cyperaceae-Gramineae phase (Zone K), believed to represent a spruce parkland. Its C-14 date of 13,270 BP and the stratigraphy indicate a pre-Two Creeks and post-Cary correlation. Apparently the Kirchner site did not become established as a lake until this time owing to persistence of dead ice in the moraine. The absence of pollen of specific tundra indicators and the presence of pollen of such thermophilous plants as Fraxinus, Quercus, Corylus, Ambrosia, Humulus, and Typha latifolia imply that the climate was cool rather than cold.Zone A-a, which follows, correlates with the Two Creeks interstade. It is marked by the dominance of Picea, with appreciable percentages of Fraxinus and Ambrosia and with minor amounts of other thermophilous plants and the normal boreal associates of spruce like Betula, Larix, and Salix. Zone A-b, starting 12,050 C-14 years ago, correlates with the Valders ice advance. It is represented at both Kirchner and Carlson and shows the withdrawal of Fraxinus and Ambrosia and the slight rise of Artemisia.Except for the absence of pine in the late-glacial assemblage the vegetation implied by these three zones seems to have its closest modern counterpart in the southern fringe of the Boreal Forest of the Riding Mountain region of southwest Manitoba. It is concluded that pine did not migrate southward with the spruce during the Wisconsin glaciation, at least in the western Great Lakes region, and was thus eliminated from this region. During the late-glacial phases of ice retreat, herbs and spruce pioneered on the deglaciated terrain; pine did not follow until the destruction of the spruce forest at the end of the late-glacial phase.Zone B introduces postglacial time. It represents the time of rapid vegetational succession following the deterioration of the spruce forest. Simultaneous maxima of Betula, Alnus, Fraxinus, and Abies occurred 10,230 years ago at Kirchner Marsh. These were followed rapidly by a Pinus maximum and then a rise of Ulmus, Quercus, and other deciduous types, dated as 9300 years ago at the correlative site of Madelia. This succession may represent differential rates of migration from refuges south and east of Minnesota.Deciduous trees dominate the C Zones. Zone C-a shows Ulmus and Ostrya/Carpinus followed by Quercus; it probably represents principally a mesic maple-basswood forest changing to oak. Zone C-b represents the advance of prairie into the region at the expense of the oak woodland or savanna. The large and abrupt fluctuations in the curves for Ambrosia-type and Chenopodiineae, especially at the Carlson site, may record encroachment of annual weeds onto intermittently dried lake bottoms. C-14 dates place Zone C-b between 7100 and 5100 years ago. In Zone C-c the Quercus again dominates until the abrupt increase in Ambrosia-type and Chenopodiineae that marks the time of forest clearance and land settlement 50–75 years ago. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.