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Author: Rebecca Amy Macdonald
Publisher:
ISBN:
Category :
Languages : en
Pages : 600
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Late Quaternary histories are investigated here for sediment cores from Lakes Huron and Michigan, using the oxygen- and carbon-isotope compositions of biogenic carbonates and the oxygen- and hydrogen-isotope compositions of porewater. Age models for these cores are based on sedimentological information, and where possible, radiocarbon and pollen dates. The Michigan Basin cores provide a thick record of the late Pleistocene, whereas the Huron Basin cores primarily record Holocene deposition. Taken together, the histories recorded in biogenic carbonates from these sediments provide a clear account of lakewater isotopic changes - and their significance - over much of the history of the Great Lakes Basin. Biogenic carbonates, and ostracodes in particular, serve as excellent recorders of lakewater!18O values. Modern specimens from Lake Huron have been used to assess non-equilibrium oxygen- and carbon-isotope fractionation effects during shell formation within this setting. This information provides improved ability to calculate the oxygenisotopic compositions of paleolakewater using fossil biogenic carbonates from the cores. The fossil shell compositions indicate intervals characterized by low!18O meltwater originating from the retreating Laurentide Ice Sheet and/or associated proglacial lakes, and periods dominated by higher!18O water that are more reflective of regional precipitation, runoff and climatic conditions. Differences in the oxygen- and carbonisotope compositions of deep- versus shallower-water ostracode species in the Michigan Basin cores suggest isotopic stratification of its lakewater during the late Pleistocene. Results for previously unstudied parts of the Huron Basin suggest that sub-basins acquired different oxygen-isotope compositions during periods of very low lake levels, reflecting different water sources and/or different conditions at such times. Early Holocene influxes of glacial meltwater into the Huron Basin, and to a lesser extent the Michigan Basin, correlate with major global climate perturbations that were likely triggered by release of large volumes of glacial meltwater into the Arctic and/or North Atlantic Oceans. Porewater did not preserve original lakewater!18O and!D values. These compositions are largely controlled by downward diffusion of modern lakewater.
Author: Rebecca Amy Macdonald
Publisher:
ISBN:
Category :
Languages : en
Pages : 600
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Book Description
Late Quaternary histories are investigated here for sediment cores from Lakes Huron and Michigan, using the oxygen- and carbon-isotope compositions of biogenic carbonates and the oxygen- and hydrogen-isotope compositions of porewater. Age models for these cores are based on sedimentological information, and where possible, radiocarbon and pollen dates. The Michigan Basin cores provide a thick record of the late Pleistocene, whereas the Huron Basin cores primarily record Holocene deposition. Taken together, the histories recorded in biogenic carbonates from these sediments provide a clear account of lakewater isotopic changes - and their significance - over much of the history of the Great Lakes Basin. Biogenic carbonates, and ostracodes in particular, serve as excellent recorders of lakewater!18O values. Modern specimens from Lake Huron have been used to assess non-equilibrium oxygen- and carbon-isotope fractionation effects during shell formation within this setting. This information provides improved ability to calculate the oxygenisotopic compositions of paleolakewater using fossil biogenic carbonates from the cores. The fossil shell compositions indicate intervals characterized by low!18O meltwater originating from the retreating Laurentide Ice Sheet and/or associated proglacial lakes, and periods dominated by higher!18O water that are more reflective of regional precipitation, runoff and climatic conditions. Differences in the oxygen- and carbonisotope compositions of deep- versus shallower-water ostracode species in the Michigan Basin cores suggest isotopic stratification of its lakewater during the late Pleistocene. Results for previously unstudied parts of the Huron Basin suggest that sub-basins acquired different oxygen-isotope compositions during periods of very low lake levels, reflecting different water sources and/or different conditions at such times. Early Holocene influxes of glacial meltwater into the Huron Basin, and to a lesser extent the Michigan Basin, correlate with major global climate perturbations that were likely triggered by release of large volumes of glacial meltwater into the Arctic and/or North Atlantic Oceans. Porewater did not preserve original lakewater!18O and!D values. These compositions are largely controlled by downward diffusion of modern lakewater.
Author: Allan Frank Schneider
Publisher: Geological Society of America
ISBN: 0813722519
Category : Science
Languages : en
Pages : 133
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Author: Jerry T. Wickham
Publisher: Forgotten Books
ISBN: 9780331374384
Category :
Languages : en
Pages : 32
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Excerpt from Late Quaternary Sediments of Lake Michigan The maps revealed that the glaciolacustrine Equality Formation is dis continuous in Lake Michigan; however, in an area southwest of Grand Haven, Michigan, it displays a thickening that probably represents an offshore exten sion of the Allendale Delta of the glacial Grand River. The two lower members of the overlying Lake Michigan Formation are thickest in the deepwater basins of Lake Michigan. These lower members are composed of an extremely fine grained red glaciolacustrine clay deposited from suspension. In contrast, the upper three units of the Lake Michigan Formation are thickest in a belt along the eastern side of the lake and consist of gray clay resulting from erosion within the Lake Michigan drainage basin by waves and streams. A large influx of sediments from streams in western Michigan and possible redistribution of shoreline erosion debris by lake currents causes the accumulation of gray clay to be greatest on the eastern side of the lake. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.
Author: Ronald B. Davis
Publisher: Springer Science & Business Media
ISBN: 9400926553
Category : Science
Languages : en
Pages : 255
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stable or falling water levels, and permit differen tiation between gradual and sudden transgression The level of Lake Ontario was long assumed to of the shoreline. Vegetational succession reflects have risen at an exponentially decreasing rate shoreline transgression and increasing water solely in response to differential isostatic rebound depth as upland species are replaced by emergent of the St. Lawrence outlet since the Admiralty aquatic marsh species. If transgression continues, Phase (or Early Lake Ontario) 11 500 years B. P. these are in turn replaced by floating and sub (Muller & Prest, 1985). Recent work indicates merged aquatic species, commonly found in water that the Holocene water level history of Lake to 4 m depth in Ontario lakes, below which there Ontario is more complex than the simple rebound is a sharp decline in species richness and biomass model suggests. Sutton et al. (1972) and (Crowder et al. , 1977). This depth varies with Anderson & Lewis (1982, 1985) indicate that physical limnological conditions in each basin. periods of accelerated water level rise followed by Because aquatic pollen and plant macrofossils are temporary stabilization occurred around 5000 to locally deposited, an abundance of emergent 4000 B. P. The accelerated water level rise, called aquatic fossils reflects sedimentation in the littoral the 'Nipissing Flood', was attributed to the cap zone, the part of the basin shallow enough to ture of Upper Great Lakes drainage. support rooted vegetation.
Author: Geological Association of Canada
Publisher: [St. John's, Nfld.] : Geological Association of Canada ; [Toronto, Ont., Canada : GAC Publications
ISBN:
Category : Science
Languages : en
Pages : 280
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Author: John C (John Carr) 1912- Ayers
Publisher: Hassell Street Press
ISBN: 9781014501004
Category :
Languages : en
Pages : 60
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Book Description
This work has been selected by scholars as being culturally important and is part of the knowledge base of civilization as we know it. This work is in the public domain in the United States of America, and possibly other nations. Within the United States, you may freely copy and distribute this work, as no entity (individual or corporate) has a copyright on the body of the work. Scholars believe, and we concur, that this work is important enough to be preserved, reproduced, and made generally available to the public. To ensure a quality reading experience, this work has been proofread and republished using a format that seamlessly blends the original graphical elements with text in an easy-to-read typeface. We appreciate your support of the preservation process, and thank you for being an important part of keeping this knowledge alive and relevant.
Author:
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 1506
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Author: Geological Association of Canada
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 274
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Author: Frank Leverett
Publisher: Franklin Classics
ISBN: 9780343567989
Category :
Languages : en
Pages : 590
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Book Description
This work has been selected by scholars as being culturally important and is part of the knowledge base of civilization as we know it. This work is in the public domain in the United States of America, and possibly other nations. Within the United States, you may freely copy and distribute this work, as no entity (individual or corporate) has a copyright on the body of the work. Scholars believe, and we concur, that this work is important enough to be preserved, reproduced, and made generally available to the public. To ensure a quality reading experience, this work has been proofread and republished using a format that seamlessly blends the original graphical elements with text in an easy-to-read typeface. We appreciate your support of the preservation process, and thank you for being an important part of keeping this knowledge alive and relevant.
Author: Frank Bursley Taylor
Publisher: Franklin Classics
ISBN: 9780341916383
Category :
Languages : en
Pages : 582
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Book Description
This work has been selected by scholars as being culturally important and is part of the knowledge base of civilization as we know it. This work is in the public domain in the United States of America, and possibly other nations. Within the United States, you may freely copy and distribute this work, as no entity (individual or corporate) has a copyright on the body of the work. Scholars believe, and we concur, that this work is important enough to be preserved, reproduced, and made generally available to the public. To ensure a quality reading experience, this work has been proofread and republished using a format that seamlessly blends the original graphical elements with text in an easy-to-read typeface. We appreciate your support of the preservation process, and thank you for being an important part of keeping this knowledge alive and relevant.
