The nature of inclusions in glendonites from the Paleocene Basilika Formation on Svalbard

Abstract

Glendonites are authigenic carbonate minerals formed after diagenetic transformation of the metastable hydrated carbonate mineral ikaite (CaCO3 • 6H2O). Since ikaite is only stable at low temperatures, glendonites are being used as proxies for cold climate conditions. Paradoxically, glendonites have been found in hothouse periods, such as the Eocene, Paleocene, Cretaceous, and Jurassic. In addition to low temperatures, other conditions are likely also important in driving ikaite precipitation and glendonite transformation, including elevated concentrations of P and Mg, and sulphate reduction coupled to methane oxidation. Here, we further examine the processes leading to ikaite transformation based on combined microscopic and organic geochemical analyses of glendonites from a drill core spanning the Paleocene Basilika Formation on Svalbard. Thin section analyses showed multiple growth generations of calcium carbonate in the glendonites, referred to as Type 1a, Type 1b, and Type 2. Biomarker analyses showed a strong presence of oil in both glendonites and surrounding sediments. Fluid inclusions mainly characterise carbonate generations Type 1a and 1b and can be shown to contain droplets of oil. Raman spectroscopy showed the principal calcium carbonate phase of glendonites to be calcite. In this work the presence of inclusions containing oil is used to evaluate ikaite-glendonite transformation mechanisms. Two new transformation mechanisms are proposed for the formation of the inclusion-rich type 1 generations. One mechanism involves calcium carbonate crystal nucleation on oil-water interfaces, the other involves interface-coupled dissolution-precipitation of ikaite to glendonite. Further research is warranted to determine the role of fluid inclusions in widespread ikaite formation.