Browsing by Author "Aksola, Aleksanteri Mitja"

The research material consists of 21 dolomite samples taken from the Kalvberget formation in western Sweden. δ13C and δ18O values were analysed from these samples, as well as trace elements and REE composition. Analysis was performed using IRMS, XRD and ICP-MS methods. Main function of trace elemental analysis was to conclude if the isotopical values represented primary marine values or if these values were changed during metamorphical processes. Main question in this thesis was to find out if these samples represented Neoproterozoic cap carbonates and how these samples fit in the global Neoproterozoic δ13C graph. The samples had undergone a green schist-amphibolite facies metamorphosis. The samples were gathered around the Kalvberget formation, representing approx. 30 m of the outcrop. Samples represented thickness of 15 m from the outcrop. Samples K1-K6 had metamorphosed more clearly than samples K7-K21. This was found out from the trace elemental composition. Samples K1-K6 had reacted with silicates, thus changing their primary composition of δ13C and δ18O towards a more negative value. δ13C values of samples K1-K6 were between -3,07 ... -3,34‰ and δ18O values were between -12,04 ... -12,59‰. Samples K7-K21 had δ13C values between +2,07 ... +4,42‰ and δ18O values between -5,94 ... -8,59‰. Indication of metamorphosis affecting the isotopic values in samples K1-K6 led to removal of these samples from the isotopic examination. Samples K7-K21 thus represent primary marine values better. Samples K7-K21 had signs of δ18O values changing because of the interaction with fluids, but the δ13C values represented almost constant values. REE composition showed some signs of detrital matter in the silicate rich samples. Part of the samples were left out from the REE composition examination, as they represented more PAAS content and not primary marine values. Because silicate concentration clearly affected the REE concentrations, all samples with less than 85% carbonate were left out from the REE examination. With these restrictions only samples K7, K11-K16, K18 and K20 were left from examination. REE plots of these samples resembled modern seawater REE plots, although the samples were depleted in HREE compared to modern seawater. From the Ce/Ce* anomaly it was concluded that these samples formed in anoxic environment. Mean value for Ce/Ce* anomaly was 0,94, which differed greatly from modern values. Samples K7-K21 were plotted in global Neoproterozoic δ13C plot. In the plot they placed between the Marinoan and Sturtian iceages 700 – 650 Ma. Conclusion from these results is that these samples do not represent typical cap carbonates formed in Neoproterozoic glaciations, but they are carbonate sediments formed in marine environment between the iceages.