Abstract
Basal Ediacaran barite, which has mass-anomalous depleted 17O, supporting Snowball Earth models, likely grew in shallow-marine settings, but sedimentological constraints lack details. Environmental conditions in the Varanger Palaeovalley during the basal Ediacaran are well preserved in the Nyborg Formation, where barite forms < 15 mm high synsyn-sedimentary crystal fans on Archean basement or thin intervening sediments. Sedimentary evidence suggests crystal fans formed in low-energy, very shallow-marine to subaerial facies. Rare earth element and yttrium signatures in associated carbonates suggest non-saline growth environments. Post-depositional fluid-flow replaced crystal fan barite with silica (now quartz) and redeposited barite as: <1 × 0.2 mm “dispersed” grains in sediments below fans; <5 mm grains replacing calcite filling desiccation cracks; <1 mm grains in basement fissures; <3 µm grains replacing matrix calcite; irregular grains in detrital sheet-silicate + calcite grains. Caledonian dissolution-reprecipitation reworked barite into brittle fractures and stylolites. Barite Δ17O values are amongst the most negative (-0.9 – -1.25 ‰) and δ18O values the lowest recorded (9.9 – 16.9 ‰) anywhere, consistent with a high latitude Baltica at ∼ 635 Ma. δ34S values (17.7 – 24.5 ‰) lie within the known range for basal Ediacaran barite.
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