87Sr/86Sr chemostratigraphy of Neoproterozoic Dalradian limestones of Scotland and Ireland; constraints on depositional ages and time scales

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doi: 10.1144/0016-764903-001
Authors:Thomas, Christopher W.; Graham, Colin M.; Ellam, Robert M.; Fallick, Anthony E.
Author Affiliations:Primary:
British Geological Survey, Edinburgh, United Kingdom
University of Edinburgh, United Kingdom
SUERC, United Kingdom
Volume Title:Journal of the Geological Society of London
Source:Journal of the Geological Society of London, 161(2), p.229-242. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0016-7649
Publication Date:2004
Note:In English. 90 refs.; illus., incl. geol. sketch map
Summary:New calcite 87Sr/86Sr data for 47 limestones from the metamorphosed and deformed Neoproterozoic-Cambrian Dalradian Supergroup of Scotland and Ireland are used to identify secular trends in seawater 87Sr/86Sr through the Dalradian succession and to constrain its depositional age. Dalradian limestones commonly have Sr >1000 ppm, indicating primary aragonite and marine diagenesis. Low Mn, Mn/Sr <0.6, δ18O and trace element data indicate that many 87Sr/86Sr ratios are unaltered since diagenesis despite greenschist- to amphibolite-facies metamorphism, consistent with the documented behaviour of Sr and O during metamorphic fluid-rock interaction. Thus, the 87Sr/86Sr data are interpreted largely to reflect 87Sr/86Sr of coeval seawater. Currently available data show that Neoproterozoic seawater 87Sr/86Sr rose from c. 0.7052 at 850-900 Ma to c. 0.7085 or higher in the latest Neoproterozoic. Temporal changes at c. 800 Ma and c. 600 Ma bracket the range in 87Sr/86Sr values of calcite in Grampian, Appin and lowest Argyll Group (c. 0.7064-0.7072) and middle and uppermost Argyll Group (c. 0.7082-0.7095) limestones, consistent with a rise in seawater 87Sr/86Sr around 600 Ma. 87Sr/86Sr data are consistent with the sedimentary affinity of the Islay Subgroup with the underlying Appin Group, and with a possible time interval between deposition of Islay and Easdale Subgroup rocks. They indicate that the Dalradian, as a whole, is younger than c. 800 Ma.
Sections:Age determination; Geochemistry; Petrology
Subsections:Sedimentary petrology; Sedimentary rocks
Subjects:Alkaline earth metals; Calcite; Carbonates; Chemostratigraphy; Dalradian; Diagenesis; Geochemistry; Isotope ratios; Isotopes; Metalimestone; Metals; Metamorphic rocks; Metamorphism; Metasedimentary rocks; Neoproterozoic; O-18/O-16; Oxygen; Paleo-oceanography; Precambrian; Proterozoic; Secular variations; Sr-87/Sr-86; Stable isotopes; Strontium; Time scales; Trace elements; Upper Precambrian; Water-rock interaction; Donegal Ireland; Europe; Grampian Highlands; Great Britain; Ireland; Scotland; Scottish Highlands; United Kingdom; Western Europe; Appin Group; Argyll Group; Islay Group
Coordinates:N551500 N574500 W0014500 W0055000
N542800 N552300 W0065600 W0084800
Abstract Numbers:04M/1346
Record ID:2004029048
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from The Geological Society, London, London, United Kingdom
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