United States Quaternary coastal sequences and molluscan racemization geochronology – What have they meant for each other over the past 45 years? |
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| Institution: | 1. Department of Geology, University of Tartu, Ravila 14A, 50411 Tartu, Estonia;2. Geology Department, Faculty of Science, Alexandria University, Alexandria 21568, Egypt;3. Department of Biological and Geological Sciences, Faculty of Education, Alexandria University, Alexandria 14037, Egypt;4. College of Science, King Saud University, Riyadh, Kingdom of Saudi Arabia;1. Department of Vascular and Endovascular Surgery, The Royal Oldham Hospital, Pennine Acute Hospitals NHS Trust, Manchester, UK;2. Department of Vascular and Endovascular Surgery, University Hospital of Alexandroupolis, Democritus University of Thrace, Alexandroupolis, Greece;3. Department of Surgery, University Hospital of Heraklion, University of Crete, Heraklion, Greece;1. Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Invalidenstraße 43, 10115 Berlin, Germany;2. Department of Geobiology, Geoscientific Centre of the University, Georg August University Göttingen, Goldschmidtstraße 3, 37077 Göttingen, Germany;1. Department of Geology, Faculty of Sciences, Minufiya University, El-Minufiya, Shibin El Kom, Egypt;2. Department of Palaeontology, Faculty of Mining and Geology, University of Belgrade, Kameni?ka 6, 11000 Belgrade, Serbia;3. GeoZentrum Nordbayern, Fachgruppe Paläoumwelt der Friedrich-Alexander-Universität, Erlangen-Nürnberg, Loewenichstr. 28, D-91054 Erlangen, Germany;4. Department of Mineralogy, Crystallography, Petrology and Geochemistry, Faculty of Mining and Geology, University of Belgrade, Dju?ina 7, 11000 Belgrade, Serbia |
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| Abstract: | The field of amino acid racemization (AAR) geochronology had its beginnings in the 1960's with the analysis of Quaternary mollusks of known relative age from United States Atlantic coast sites. Subsequent AAR studies of sites from Florida, California and then the entire western and eastern coasts of the U.S. have documented two important concepts: 1) in both uplifted marine terrace and subsurface sections, it can be demonstrated that D/L values increase with increasing geologic age; 2) D/L values in samples of equal age increase with decreasing latitude (increasing temperature). These two north–south coastlines with broad latitude ranges (Pacific sites span more than 20°, Atlantic sites more than 15°) provide an ideal, rare framework to test these principles, and the contrast in thermal histories of these two coasts (one maritime, the other more continental) adds additional insights into issues of aminozone correlation over latitude ranges as small as 2°. The trend of D/L values vs. latitude (isochrons) is established using calibrations based primarily on U–Th coral dating, the best of these calibrated trends seen for multiple sites on the Pacific coast. Pacific coast isochrons follow smooth trends and have been used to create and evaluate kinetic models using the modern latitudinal temperature gradient for comparison. Atlantic coast isochrons are more difficult to reconcile with the modern temperature gradient and available U–Th coral ages, suggesting either complex effective temperatures or unknown diagenetic effects on the AAR results. In addition to these studies that used local or regional field studies to test and evaluate AAR methods, relative or numerical ages based on AAR studies on both coasts have contributed to research on coastal uplift or subsidence rates, coastal stratigraphy and sea-level history, age mixing, and diagenesis of carbonate fossils. |
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