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Weathering in a regolith on the Werenskioldbreen forefield (SW Spitsbergen) : modelling of pore water chemistry

Kwaśniak-Kominek M., Manecki M., Rzepa G., Płonka A. M., Górniak D.

Annales Societatis Geologorum Poloniae

2016

Vol. 86, No. 3

249--264

The mineral framework and pore waters of glacial sediments exposed in the foreland of Weren- skioldbreen in SW Spitsbergen were sampled and analyzed to model the evolution of pore water chemistry, representing the advancement of weathering in a chronosequence. Three samples were taken at distances representing snapshots of approximately 5, 45 and 70 years of exposure. Complementary mineralogical analyses of the mineral framework and chemical analyses of pore waters, coupled with thermodynamic modelling of mineral-water interactions were applied. Recently uncovered sediments of the bottom moraine underwent very little weathering underneath the glacier cover; both the sediments and pore waters in the forefield of the Werenskioldbreen represent a very immature system. Poorly sorted sediments were deposited by the glacier and not reworked by fluvioglacial waters. The ratio of ‘amorphous iron’ to ‘free iron’ Feo/Fed increases with distance from the glacier terminus from 0.30 through 0.36 to 0.49, typical for fresh glacial till. The increase in saturation with CO2 (from p(CO2) –3.8 to –2.4) and the concentration of all major ions in pore waters (from 123 to 748 mg/L total dissolved solids, TDS) was observed in this young chronosequence. The waters evolved from carbonate- dominated to sulphate-dominated, indicating that with progress in weathering the dominating processes are equilibration with carbonates, oxidation of sulphides and the influence of gypsum precipitation by seasonal freeze-thaw cycles. Mass balance calculations and inverse modelling of the composition of pore waters, verified by microscopic observations of alteration on the surfaces of mineral grains, allowed thermodynamic confirmation of the fact that the relative significance of carbonate weathering decreases and that of sulphate increases down the chronosequence. The participation of silicate minerals in weathering is low, indicating a relatively immature stage of weathering within this particular chronosequence. It is significant that the morphology of etch pits and the formation of secondary phases apparent on mineral surfaces were identical, regardless of the distance from the glacier terminus. This might indicate that the mechanisms of particular weathering processes at the mineral-water interface are the same at the initial as well as at the more mature stages and do not change at least within ca. 70 years of exposure.

Radiocarbon-dated Late Pleistocene and Early Holocene Marine Shells at Werenskioldbreen, South Spitsbergen

Birkenmajer K., Olsson I.

Bulletin of the Polish Academy of Sciences. Earth Sciences

1998

Vol. 46, nr 1

21-34

Fragmented bivalve (mainly Mya truncata) and Balanus shells were collected at 21-35 m a.s.l. from terminal/marginal moraine, and at 46-65 m a.s.l. from morainic dirt cones and eskers at Werenskioldbreen, south Spitsbergen. They yielded radiocarbon ages of 26,600 š 1400 years B.P. (Late Pleistocene = Vistulian Glaciation), and 10,660 š 220 - 10.500 š 160 years B.P. (Pleistocene/Holocene transition: Younger Dryas/Preboreal), respectively. In 1974, the source marine deposit, probably shell-bearing clays, was hidden under glacier ice. Formation of this deposit could be simultaneous with raised marine abrasion terraces at 36-40 m and 24-32 m a.s.l., respectively.