Continental carbonate facies of a Neoproterozoic panglaciation, north‐east Svalbard
Abstract 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 glac...
Published in: | Sedimentology |
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Main Authors: | , , , , , , , , , , , , |
Other Authors: | , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
Wiley
2016
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Subjects: | |
Online Access: | http://dx.doi.org/10.1111/sed.12252 https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fsed.12252 https://onlinelibrary.wiley.com/doi/pdf/10.1111/sed.12252 |
Summary: | Abstract 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 ... |
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