Ikaite versus seep-related carbonate precipitation in the Late Jurassic–Early Cretaceous of West Spitsbergen: evidence for cold versus warm climates?

Glendonites and seep-related carbonate bodies from the Jurassic/Cretaceous boundary interval of West Spitsbergen were studied using mineralogical, isotopic, and geochemical methods. The stratigraphic distribution of seep-related carbonate bodies and glendonites (pseudomorphs after ikaite, Ca(CO₃)·6H₂O) reveals that although they can be occasionally found close to each other, their formation differs through time. Seep carbonates are found in the Oxfordian, Kimmeridgian, Volgian, and Ryazanian deposits, while glendonites appear in the Valanginian–Hauterivian and Middle Aptian–Lower Albian deposits of West Spitsbergen. Furthermore, numerous appearances of seep carbonates correlate with warming and shelf dysoxic–anoxic events in the Arctic, while glendonite occurrences correlate with cooling events. The δ¹³C values obtained for seep-related carbonates and glendonite samples reflect mixed sources including thermogenic and biogenic methane, oil fractions, decomposing organic matter, and dissolved inorganic carbon. We assume the precipitation of seep carbonates was caused by methanogenesis and anaerobic oxidation of organic matter promoting dense communities of benthic organisms and carbonate precipitation in warm climatic condition. At the end of the Ryazanian, shallowing of the basin coupled with climate cooling led to decrease in methanogenesis and anaerobic decomposition of methane and organic matter. Locally, in areas of anaerobic organic matter oxidation under low bottom temperatures, ikaite crystallized.

Graphical abstract