engleski

Carbonate till diagenesis - implications for accuracy of glacial chronologies: example from Southern Velebit Mountain (Croatia)

The morphostratigraphical record of paleoglaciers is an important paleoclimatological and paleoenvironmental archive in Quaternary studies. In the Mediterranean region, most of the glaciers during this period were hosted in carbonate mountains, where establishing a glacial chronology is complex. Diagenetical processes such as cementation, dissolution and increase of organic content, together with the carbonate nature of the deposits, prevents the application of most of available absolute dating method to accurately date carbonate tills. As well, processes such as percolation of water through sediment, propagation of rootlets and carbonate corrosion/surface denudation are impediments to obtain suitable glacial chronologies. Radiocarbon analyses of calcite cements are known to be inaccurate due to dead-carbon contribution from dissolved carbonate bedrock. U-series dating of carbonate cements is not applicable since: (1) cements generally have several phases of growth ranging from the time of deposition to present and (2) more importantly, a closed carbonate system is unlikely to be preserved, implying isotopic leaching. Due to lack of significant amounts of quartz and feldspars in the bedrock carbonates OSL dating is not applicable to carbonate tills. Exposure dating could be applicable to some till boulders by in situ produced cosmogenic nuclides using 36Cl, but surface weathering and denudation rate must be taken into account. For this reason, 36Cl burial dating is likely to be the best option to reproduce accurate chronologies. Here we show a study of a carbonate tills from southern part of Velebit Mt. were we evaluate their depositional environments and the diagenetical processes that affect them.

paleoglacier ; till ; carbonate diagenesis ; Velebit Mt. ; Croatia

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