U-Pb systematics of an Upper Carboniferous black shale from South Yorkshire, UK

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doi: 10.1016/S0009-2541(02)00383-2
Authors:Fisher, Q. J.; Cliff, R. A.; Dodson, M. H.
Author Affiliations:Primary:
University of Leeds, School of Earth Sciences, Leeds, United Kingdom
Volume Title:Chemical Geology
Source:Chemical Geology, 194(4), p.331-347. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0009-2541
Publication Date:2003
Note:In English. Includes appendix. 28 refs.; illus., incl. sect., 4 tables, sketch maps
Summary:Open-system behaviour of uraniferous shales, which has been known for many years, has discouraged attempts to use U-Pb geochronology to date sedimentary systems. Techniques now available can facilitate better understanding of their geochemical evolution and their possible use in geochronometry. For the U-rich Alton (G. listeri) Marine Band, a combined fission track mapping, electron optical and sequential chemical extraction study confirms that uranium is incorporated into francolite, an early diagenetic precipitate. U-Pb analyses of uranium-rich (>1000 ppm) francolite nodules are discordant and imply ages ∼50-150 Ma younger than the date of sedimentation. Pb isotopic analysis suggests that uranium daughters continually leaked from the francolite, 238U daughters being released more efficiently than those of 235U. Extrapolation of the U-Pb data to concordia produces an age consistent with the time of sedimentation. These features are also displayed by other uranium-rich shales such as the Swedish Kolm Measures, despite uranium being incorporated into different phases. Preferential loss of 238U daughters from fine-grained particles due to alpha recoil could explain the unusual U-Pb isotopic composition, in both examples. Further work would be justified to investigate the application of U-Pb isotopic analysis of such material to date sedimentary sequences. Abstract Copyright (2003) Elsevier, B.V.
Sections:Geochemistry
Subsections:Sedimentary rocks
Subjects:Absolute age; Backscattering; Black shale; Carboniferous; Clastic rocks; Coal Measures; Dates; Experimental studies; Fission-track dating; Leaching; Open systems; Paleozoic; Sample preparation; Sedimentary rocks; SEM data; Sequential extraction; TEM data; U/Pb; Upper Carboniferous; Uranium disequilibrium; Westphalian; England; Europe; Great Britain; Sheffield England; United Kingdom; Western Europe; Yorkshire England; Alton Marine Band; South Yorkshire England
Coordinates:N532000 N532500 W0012500 W0013500
Abstract Numbers:03M/2944
Record ID:2003027728
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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