Middle Jurassic-Lower Cretaceous glendonites from the eastern Barents Shelf as a tool for paleoenvironmental and paleoclimatic reconstructions

Glendonites are carbonate pseudomorphs after ikaite which use as indicators of near-freezing temperatures. We describe the first glendonites of Middle-Late Jurassic to Early Cretaceous age from the Barents Shelf, including the first glendonites of Late Barremian-Early Aptian age ever discovered on Earth and provide the detailed mineralogical-geochemical and isotopic studies. Mesozoic glendonites are well-known across the Arctic realm, however the ikaite-calcite transformation and implication of glendonite findings are still debatable. Pseudomorphs are mainly composed of calcite. Cathodoluminescence and scanning electron microscopy studies reveal three types (I-III) of calcite: type I - elongated, rounded and irregular calcite; type II - blocky, fibrous and needlelike calcite/siderite; type III - blocky calcite in pores. Elemental analyses distinguish geochemical differences between the calcite types: type I comprises pure CaCO3; type II calcite contains Mg and P (in all studied samples), Fe (Bajocian-Callovian), S (Middle Volgian) or Sr (Upper Barremian-Lower Aptian); type III calcite is depleted in Mg, P and Fe. Concentrations of Mn, Fe, Sr and calculated Mn/Ca, Fe/Ca and Sr/Ca ratios are suggestive of diagenetic alteration. Bulk delta O-18 values range from 5.39 to 1.71 parts per thousand VPDB, supporting overprinting of primary values during burial diagenesis, while bulk delta C-13 values range from -33.3 to 22.6 parts per thousand VPDB, providing the influence of organic matter on ikaite-glendonite formation. However, Sr-87/Sr-86 values range from 0.7070 to 0.7110, mainly corresponding to Jurassic-Cretaceous seawater. Rare-earth elements characterize porewater REE-patterns, with slight middle REE-enrichment and depletion in light and heavy REE. Weak positive and negative Ce anomalies indicate fluctiating from anoxic to oxic conditions during ikaite-glendonite formation. Our new biostratigraphic data refine the ages of glendonite-bearing horizons in the Barents Shelf region, allowing a more definitive correlation with coeval glendonite occurrences across the Arctic realm and with global climatic changes during the Jurassic-Cretaceous.

Automated summary

This study describes glendonites of Middle-Late Jurassic to Early Cretaceous age from the Barents Shelf, including the first discovery of Late Barremian-Early Aptian age glendonites. The detailed mineralogical-geochemical and isotopic studies revealed differences in composition between different types of calcite in the pseudomorphs.