Sediment cores from twelve lakes in lower Michigan and one in southern Ontario were examined in search of annual laminations containing authigenic carbonate minerals. Nine lakes contained some degree of such laminations, but lamination quality and mineral abundance varied considerably due to localized hydro logic effects. The exceptional nature of sediment records from three lakes made them subject to detailed study. All three were supersaturated with respect to calcite in their epilimnetic waters, though carbonate minerals were not detected in surface sediments of the lake with undersaturated hypolimnetic waters. Empirical and model evidence suggests that calcite dissolution in hypolimnetic waters acts as a primary control on sediment calcite abundance. The Holocene varves of Derby Lake, MI, record high- and low-frequency variability in sediment calcite and organic carbon abundance through the Holocene to 8700 calendar years before present. These data exhibit many low-carbonate intervals that generally persist for less than a century in but increase in frequency through the latter part of the record. Some intervals occur in concordance with known Holocene paleoclimatic events, including the globally recognized 8200 cal yr BP event. In sediments that have accumulated since 1890 AD, periods of high carbonate abundance correspond to intervals of below-normal temperature and aboveaverage precipitation. This climatic regime favors limnologic conditions conducive to calcite preservation. Authigenic siderite occurs in isolated intervals of high abundance (up to 80%) in the Holocene varves of Otter Lake, MI. Iron concentrations at present are an order of magnitude lower than required for siderite saturation. The stable-isotopic composition of siderite carbon in high-abundance intervals is enriched several per mille relative to lake inorganic carbon values, which may indicate a dissolved inorganic carbon input from methanogenic sediments. Siderite likely precipitated at or near the lake bottom during periods of enhanced iron supply and incomplete lake circulation. Geochemical indicators of human disturbance occur in sediments of Crawford Lake, Ontario coincident with periods of documented Iroquois and European activity in the watershed. Elemental indicators of landscape erosion and chronology are sensitive enough to detect a three-decade abandonment of an Iroquois village near the turn of the 15th century.
A Dissertation submitted to the faculty of the Graduate School of the University of Minnesota by Chad Andrew Wittkop in partial fulfillment of the requirements for the degree of Doctor of Philosophy, October 2004.
Wittkop, Chad Andrew.
Paleoenvironmental Reconstruction Using Laminated Sediments Containing Authigenic Carbonate Minerals: Case Studies from the Great Lakes Region of North America.
Retrieved from the University of Minnesota Digital Conservancy,
Content distributed via the University of Minnesota's Digital Conservancy may be subject to additional license and use restrictions applied by the depositor.