10.6084/m9.figshare.3454967.v1 John Parnell John Parnell Darren Mark Darren Mark Anthony E. Fallick Anthony E. Fallick Adrian Boyce Adrian Boyce Scott Thackrey Scott Thackrey The age of the Mesoproterozoic Stoer Group sedimentary and impact deposits, NW Scotland Geological Society of London 2016 ejecta blanket Mesoproterozoic Stoer Group impact ejecta deposit impact deposits Stac Fada Member lake water palaeomagnetic data 1180 Ma Fluid inclusion analysis degassing structures Ar NW Scotland Geology 2016-06-21 12:28:36 Dataset https://geolsoc.figshare.com/articles/dataset/The_age_of_the_Mesoproterozoic_Stoer_Group_sedimentary_and_impact_deposits_NW_Scotland/3454967 <p>The Mesoproterozoic Stoer Group of the ‘Torridonian' has been dated at 1177 ± 5 Ma (2σ), based on <sup>40</sup>Ar/<sup>39</sup>Ar dating of authigenic K-feldspars precipitated in degassing structures within the Stac Fada Member, interpreted previously as an impact ejecta deposit. Fluid inclusion analysis of the K-feldspar shows that it precipitated from hot fluids, and so must immediately post-date emplacement of the ejecta blanket. The oxygen isotopic composition of K-feldspar is remarkably constant at 9.7 ± 0.2‰ (V-SMOW) and is consistent with derivation from evaporated lake water. The new age supports previous determinations of 1199 ± 70 Ma from Pb–Pb dating of limestone and 1180 Ma from palaeomagnetic data, but provides much higher precision. </p>