Effects of glacial transport and neomorphism on Precambrian dolomite crystal sizes (original) (raw)

Nature volume 304, pages 714–716 (1983)Cite this article

Abstract

Late Precambrian glacial rocks are notable for their association with dolostones1 and this has been regarded as a palaeoclimatological paradox2–5. However, little detailed work has been carried out to determine the mode of origin of the dolomite. In north-east Spitsbergen (Svalbard), the Vendian6,7 succession contains two glacial stratigraphical units8,9 which are dolomitic and are underlain and overlain by dolostones. Evidence from sedimentary structures and gross textures indicates that dolomite within the glacial units is detrital whereas at other levels it is a precipitate10. Accordingly, dolomite crystal sizes were analysed to determine whether evidence of glacial erosion and transport (rock flour) has been preserved. Allowing for the effects of later crystal enlargement (aggrading neomorphism), which vary within and between samples, the results show a markedly higher proportion of very fine crystals in the inferred detrital dolostones compared with the precipitated dolostones. The very fine crystals are interpreted as relics of rock flour, the preservation of which demonstrates a novel means of testing the origin of dolostones associated with glacial sequences. Inorganic precipitation of dolomite during glaciation or secondary dolomitization of till are not required to explain the dolomite–tillite association, but pronounced climatic changes at the onset and close of glacial periods are indicated.

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  1. Department of Geological Sciences, University of Birmingham, PO Box 363, Birmingham, B15 2TT, UK
    Ian J. Fairchild

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Fairchild, I. Effects of glacial transport and neomorphism on Precambrian dolomite crystal sizes.Nature 304, 714–716 (1983). https://doi.org/10.1038/304714a0

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