Continental carbonate facies of a Neoproterozoic panglaciation, north-east Svalbard
The Marinoan panglaciation (ca 650 to 635 Ma) is represented in north-east Svalbard by the 130 to 175 m thick Wilsonbreen Formation which contains syn-glacial carbonates in its upper 100 m. These sediments are now known to have been deposited under a CO 2 -rich atmosphere, late in the glaciation, an...
Published in: | Sedimentology |
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Main Authors: | , , , , , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
2016
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Subjects: | |
Online Access: | https://risweb.st-andrews.ac.uk/portal/en/researchoutput/continental-carbonate-facies-of-a-neoproterozoic-panglaciation-northeast-svalbard(98dc5e8c-5383-4879-b856-9a061e588f10).html https://doi.org/10.1111/sed.12252 https://research-repository.st-andrews.ac.uk/bitstream/10023/10231/1/Benn_2016_Sedimentology_Continental_AAM.pdf |
Summary: | The Marinoan panglaciation (ca 650 to 635 Ma) is represented in north-east Svalbard by the 130 to 175 m thick Wilsonbreen Formation which contains syn-glacial carbonates in its upper 100 m. These sediments are now known to have been deposited under a CO 2 -rich atmosphere, late in the glaciation, and global climate models facilitate testing of proposed analogues. Precipitated carbonates occur in four of the seven facies associations identified: Fluvial Channel (including stromatolitic and intraclastic limestones in ephemeral stream deposits); Dolomitic Floodplain (dolomite-cemented sand and siltstones, and microbial dolomites); Calcareous Lake Margin (intraclastic dolomite and wave-rippled or aeolian siliciclastic facies); and Calcareous Lake (slump-folded and locally re-sedimented rhythmic/stromatolitic limestones and dolomites associated with ice-rafted sediment). There is no strong cyclicity, and modern analogues suggest that sudden changes in lake level may exert a strong control on facies geometry. Both calcite and dolomite in stromatolites and rhythmites display either primary or early diagenetic replacive growth. Oxygen isotope values (−12 to +15‰ VPDB ) broadly covary with δ 13 C. High δ 13 C values of +3·5 to +4·5‰ correspond to equilibration with an atmosphere dominated by volcanically degassed CO 2 with δ 13 C of −6 to −7‰. Limestones have consistently negative δ 18 O values, while rhythmic and playa dolomites preserve intermediate compositions, and dolocretes possess slightly negative to strongly positive δ 18 O signatures, reflecting significant evaporation under hyperarid conditions. Inferred meltwater compositions (−8 to −15·5‰) could reflect smaller Rayleigh fractionation related to more limited cooling than in modern polar regions. A common pseudomorph morphology is interpreted as a replacement of ikaite (CaCO 3 ·H 2 O), which may also have been the precursor for widespread replacive calcite mosaics. Local dolomitization of lacustrine facies is interpreted to reflect microenvironments with ... |
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