Origin of “cannon−ball ” concretions in the Carolinefjellet Formation (Lower Cretaceous), Spitsbergen
ABSTRACT: Ball−shaped concretions (“cannon balls”) commonly occur in a marine, or− ganic carbon−rich sedimentary sequence (Innkjegla Member) of the Carolinefjellet Forma− tion (Aptian–Albian) in Spitsbergen. The sedimentologic, petrographic and geochemical investigation of these concretions in the K...
| Main Authors: | , , |
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.500.8536 http://www.polish.polar.pan.pl/ppr24/ppr24-217.pdf |
| Summary: | ABSTRACT: Ball−shaped concretions (“cannon balls”) commonly occur in a marine, or− ganic carbon−rich sedimentary sequence (Innkjegla Member) of the Carolinefjellet Forma− tion (Aptian–Albian) in Spitsbergen. The sedimentologic, petrographic and geochemical investigation of these concretions in the Kapp Morton section at Van Mijenfjorden gives in− sight into their origin and diagenetic evolution. The concretion bodies commenced to form in subsurface environment in the upper part of the sulphate reduction (SR) diagenetic zone. They resulted from pervasive cementation of uncompacted sediment enriched in frambo− idal pyrite by non−ferroan (up to 2 mol % FeCO3) calcite microspar at local sites of enhanced decomposition of organic matter. Bacterial oxidation of organic matter provided most of carbon dioxide necessary for concretionary calcite precipitation (13CCaCO3 –21 ‰ VPDB). Perfect ball−like shapes of the concretions originated at this stage, reflecting isotropic per− meability of uncompacted sediment. The concretion bodies cracked under continuous burial as a result of amplification of stress around concretions in a more plastic sediment. The crack systems were filled by non−ferroan (up to 5 mol % FeCO3) calcite spar and blocky pyrite in deeper parts of the SR−zone. This cementation was associated with impregnation |
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