Sedimentology and porewater isotope chemistry of Quaternary deposits from the St. Clair delta, Walpole Island, Ontario, Canada.

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Walpole Island is part of a large freshwater delta complex located at the St. Clair River mouth in southwestern Ontario. Petrographic study of 3 continuously sampled sediment cores taken along a 14 km north-south transect of the island show that the stratigraphy of Walpole Island Quaternary sediments reflects a general retreat of the Laurentide Ice Sheet northwards from the area. From top to bottom, the stratigraphy is as follows: (a) Nipissing to Modern Great Lakes stage sandy deltaic sediments; (b) an Early Holocene green accretion gley found only in the middle core; (c) Two Creeks Interstade, Greatlakean Stade, and Early Holocene non-rhythmically stratified lacustrine clayey silt; (d) Early Mackinaw Interstade to Early Two Creeks Interstade varved glaciolacustrine clayey silt; (e) Port Bruce Stade Rannoch Till; a waterlain, carbonate-rich clayey silt till containing numerous inclusions of Erie Interstade glaciolacustrine sediments and bedrock clasts; and (f) a coarser, sandy lodgment facies of the Rannoch Till. Porewater $\rm\delta\sp{18}O,\ \delta D\ and\ \delta\sp{13}C\sb{DIC}$ value profiles for cores located in the north and middle of Walpole Island indicate that older ($>$10000 y.b.p.), deeper, glacigenic porewaters have mixed with, and have been displaced by younger ($<$10000 y.b.p.) surficial waters. Porewater $\rm\delta\sp{18}O,\ \delta D\ and\ \delta\sp{13}C\sb{DIC}$ value profiles for the core from the southern portion of Walpole Island indicate that modern St. Clair River water has penetrated the length of the 20 m core via fractures, effectively displacing all glacigenic porewater. Fracturing and faulting or slumping are clearly visible throughout the southern core, which is located on the trend of the Electric Fault. (Abstract shortened by UMI.)Dept. of Earth Sciences. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1995 .C85. Source: Masters Abstracts International, Volume: 34-06, page: 2323. Thesis (M.Sc.)--University of Windsor (Canada), 1995.