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

Thomas, Christopher W ; Graham, Colin M ; Ellam, Robert M ; Fallick, Anthony E

Journal of the Geological Society, 2004-03, Vol.161 (2), p.229-242 [Periódico revisado por pares]

London: Geological Society of London

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Título:
87Sr/86Sr chemostratigraphy of Neoproterozoic Dalradian limestones of Scotland and Ireland; constraints on depositional ages and time scales
Autor: Thomas, Christopher W ; Graham, Colin M ; Ellam, Robert M ; Fallick, Anthony E
Assuntos: alkaline earth metals ; Appin Group ; Argyll Group ; calcite ; carbonates ; chemostratigraphy ; Dalradian ; diagenesis ; Donegal Ireland ; Earth sciences ; Earth, ocean, space ; Europe ; Exact sciences and technology ; Geochemistry ; Grampian Highlands ; Great Britain ; Ireland ; Islay Group ; Isotope geochemistry ; Isotope geochemistry. Geochronology ; isotope ratios ; isotopes ; metalimestone ; metals ; metamorphic rocks ; metamorphism ; metasedimentary rocks ; Neoproterozoic ; O-18/O-16 ; oxygen ; paleo-oceanography ; Precambrian ; Proterozoic ; Scotland ; Scottish Highlands ; secular variations ; Soil and rock geochemistry ; Sr-87/Sr-86 ; stable isotopes ; Stratigraphy ; strontium ; time scales ; trace elements ; United Kingdom ; upper Precambrian ; water-rock interaction ; Western Europe
É parte de: Journal of the Geological Society, 2004-03, Vol.161 (2), p.229-242
Descrição: 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.
Editor: London: Geological Society of London
Idioma: Inglês

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

Thomas, Christopher W ; Graham, Colin M ; Ellam, Robert M ; Fallick, Anthony E

London: Geological Society of London

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