Weathering of Precambrian basement and formation of sedimentary particles in Scania

Abstract

This study describes weathering pattern in saprolites of the Vånga Granite along various profiles at Ivö Klack, Scania (southern Sweden) and provides a model against which paleo-chemical weathering of ancient profiles (e.g. Utsira High) can be compared. These weathering profiles have been analyzed combining field data with XRD, thin sections and SEM analyses. Special emphasis has been on secondary minerals formation associated with paleoclimate, composition of primary minerals and its distribution in parent rock. Intrusive origin is attributed to the Vånga Granite which has composition between monzogranite and syenogranite (plotted on Streckeisen diagram). Sericite needles identified on plagioclase grains approve post-magmatic alteration of fresh granite. Two weathering profiles namely; profile-1 and profile-2, have been investigated in detail to give a representative overview on weathering processes prevailed at the locality. Two weathering stages (initial and advanced stage of weathering) have been designated to weathering profiles based on XRD% of three minerals (kaolinite, plagioclase and K-feldspar). Chemical weathering reactions largely include transformation of feldspars and phyllosilicates to kaolinite, smectite, illite and vermiculite. Plagioclase, especially anorthite content, and biotite are readily affected by weathering whereas K-feldspar stands out as more resistant mineral phase. During initial stage of weathering, pore waters achieve equilibrium with K-feldspar, kaolinite and illite. As weathering proceeds (upon total consumption of plagioclase) formation of kaolinite increases greatly due to dissolution of potassic phases. Three clay mineral phases (smectite, illite and kaolinite) are observed in both weathering profiles. In most weathered samples from both weathering profiles kaolinite˃˃ illite ˃ smectite. Deep kaolinite weathering and argillization at the study area started in humid tropical climate of the Rhaetian. Weathering of bedrock continued in humid tropical to sub-tropical climate from the Late Triassic to Late Cretaceous until Campanian Sea transgressed the area. Further, saprolites were covered and preserved with Late Cretaceous carbonates until quarrying of limestone and kaolinite in late 19th century. Keywords: Scania, Ivö Klack, weathering profiles, weathering stages, chemical weathering, secondary minerals, kaolinite weathering, XRD, clay mineralogy.