Associated terrestrial and marine fossils in the late-glacial Presumpscot Formation, southern Maine, USA, and the marine reservoir effect on radiocarbon ages |
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| Authors: | Woodrow B Thompson Carol B Griggs Norton G Miller Robert E Nelson Thomas K Weddle Taylor M Kilian |
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| Institution: | a Maine Geological Survey, 22 State House Station, Augusta, ME 04333-0022, USA;b Tree-Ring Laboratory, Cornell University, B48 Goldwin Smith Hall, Ithaca, NY 14853, USA;c Biological Survey, New York State Museum, 3140 Cultural Education Center, Albany, NY 12230, USA;d Department of Geology, Colby College, 5804 Mayflower Hill, Waterville, ME 04901-8858, USA;e Department of Geology and Geophysics, Yale University, New Haven, CT 06511, USA |
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| Abstract: | Excavations in the late-glacial Presumpscot Formation at Portland, Maine, uncovered tree remains and other terrestrial organics associated with marine invertebrate shells in a landslide deposit. Buds of Populus balsamifera (balsam poplar) occurred with twigs of Picea glauca (white spruce) in the Presumpscot clay. Tree rings in Picea logs indicate that the trees all died during winter dormancy in the same year. Ring widths show patterns of variation indicating responses to environmental changes. Fossil mosses and insects represent a variety of species and wet to dry microsites. The late-glacial environment at the site was similar to that of today's Maine coast. Radiocarbon ages of 14 tree samples are 11,907 ± 31 to 11,650 ± 50 14C yr BP. Wiggle matching of dated tree-ring segments to radiocarbon calibration data sets dates the landslide occurrence at ca. 13,520 + 95/?20 cal yr BP. Ages of shells juxtaposed with the logs are 12,850 ± 65 14C yr BP (Mytilus edulis) and 12,800 ± 55 14C yr BP (Balanus sp.), indicating a marine reservoir age of about 1000 yr. Using this value to correct previously published radiocarbon ages reduces the discrepancy between the Maine deglaciation chronology and the varve-based chronology elsewhere in New England. |
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| Keywords: | Presumpscot Formation Maine Late Pleistocene AMS and β -decay radiocarbon ages Radiocarbon age calibrations Marine reservoir effect Dendrochronology Marine bivalves and barnacles Fossil mosses and insects Plant macrofossils Pollen Landslides |
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