Stable isotopes of oxygen and hydrogen in meteoric water during the Cryogenian Period

Skelton, A., Löwhagen, L., Fairchild, I. J., Boyce, A. , Mörth, C.-M., Siegmund, H., Webster, D. and Spencer, A. M. (2019) Stable isotopes of oxygen and hydrogen in meteoric water during the Cryogenian Period. Precambrian Research, 320, pp. 253-260. (doi: 10.1016/j.precamres.2018.11.006)

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We measured δ18O and δ2H values of muscovite and carbonate mineral separates from metamorphosed carbonate-bearing mudstone layers in late Tonian to early Cryogenian strata, including Sturtian glacial deposits, which were deposited in a coastal setting at an approximate paleolatitude of 30-35°S and now crop out on Islay and the Garvellach Islands, Scotland. From these values, we calculated δ18O and δ2H values of meteoric water that equilibrated with clay at diagenetic conditions which we infer were reached shortly after deposition (i.e. before the end of the Cryogenian Period) because sediment accumulation was rapid due to fast subsidence at that time. This calculation required removal of the effects of exchange with reservoir rocks, metamorphic volatilization and mixing with metamorphic fluids on δ18O and δ2H values. The values we calculated for meteoric water fall within the 2σ ranges δ18O = -1 to -4 ‰ and δ2H = 0 to -23 ‰, respectively. These ranges are similar to present day values at equivalent latitudes. This finding is consistent with sediment accumulation in the Cryogenian Period having occurred in a climate similar to present day (Ice Age) conditions. This conclusion is not at odds with the Snowball Earth hypothesis because one of its predictions is that sediment accumulation occurred as the climate warmed at the end of panglaciation, a prediction supported by sedimentological evidence of multiple glacial advances and retreats in our study area and elsewhere.

Item Type:Articles
Additional Information:The Swedish Research Council and the Bolin Centre for Climate Research are acknowledged for financial support.
Glasgow Author(s) Enlighten ID:Boyce, Professor Adrian
Authors: Skelton, A., Löwhagen, L., Fairchild, I. J., Boyce, A., Mörth, C.-M., Siegmund, H., Webster, D., and Spencer, A. M.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Precambrian Research
ISSN (Online):1872-7433
Published Online:12 November 2018
Copyright Holders:Copyright © 2018 Elsevier B.V.
First Published:First published in Precambrian Research 320:253-260
Publisher Policy:Reproduced in accordance with the publisher copyright policy

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