TheMarinoan glaciation (Neoproterozoic) in northeast Svalbard

Two separate and distinct diamictite-rich units occur in the mixed carbonate-siliciclastic PolarisbreenGroup, which comprises the top kilometer of47 km of Neoproterozoic strata in the northeast of the Svalbard archipelago.The platformal succession accumulated on the windward, tropical to subtropical margin of Laurentia.The older PetrovbreenMember is a thin glacimarine diamictite that lacks a cap carbonate. It contains locally derived clasts and overlies a regional karstic disconformity that was directly preceded by a large (410%) negative dC anomaly in the underlying shallow-marine carbonates.This anomaly is homologous to anomalies in Australia, Canada and Namibia that precede theMarinoan glaciation.The younger and thickerWilsonbreen Formation comprises terrestrial ice-contact deposits. It contains abundant extrabasinal clasts and is draped by a transgressive cap dolostone 3^18m thick.The cap dolostone is replete with sedimentary features strongly associatedwith post-Marinoan caps globally, and its isotopic pro¢le is virtually identical to that of otherMarinoan cap dolostones. From the inter-regional perspective, the two diamictite-rich units in thePolarisbreenGroup should represent the ¢rst and ¢nal phases of theMarinoan glaciation. Above the Petrovbreen diamictite are 200m of ¢nely laminated, dark olive-coloured rhythmites (MacDonaldryggenMember) interpreted here to represent suspension deposits beneath shorefast, multi-annual sea ice (sikussak).Above the suspension deposits and below theWilsonbreen diamictites is ao30-m-thick regressive sequence (SlangenMember) composed of dolomite grainstone and evaporitic supratidal microbialaminite.We interpret this sabkha-like lagoonal sequence as an oasis deposit that precipitatedwhen local marine ice melted away under greenhouse forcing, but while the tropical ocean remained covered due to in£ow of sea glaciers from higher latitudes. It appears that the PolarisbreenGroup presents an unusually complete record of theMarinoan snowball glaciation.