engleski

Depositional environments and diagenesis of Quaternary carbonate tills in Rujno paleoglacier, Velebit Mountain, Croatia

Establishing chronologies of paleoglaciers in carbonate regions is complex due to multiple processes that alter the till geochemical, sedimentological and morphological properties. Here we presented a study of the depositional environments and the diagesesis of three different tills from a carbonate region. One of the tills was characterized as a lodgement till and the other two as melt out tills. The lodgement till has a limited permeability and the primary properties of the sediment are preserved. On the other hand, the melt out tills have a significant permeability and water percolation caused significant dissolution of some carbonate pebbles, although calcite cements have also been identified. There is a large spatial variability in the dissolution and cementation processes in relation to the distribution of clay and silt fraction that prevents the water flow. A substantial increase of organic matter took place in the melt out tills due to the rootlets propagation through porosity. On the contrary, the limited porosity of the lodgement till prevents the penetration of roots aside from weathered till sectors. The study of the morphostratigraphy, sedimentology and diagenesis of these tills has highlighted different potential problems that may arise at the time of establishing their chronology. Thus, erosion processes in some tills and the weathering rates of these carbonates anticipate accuracy problems in case of the use of 36Cl dating method. The U-Th method in calcite cements is not recommended since the water percolation implies an open system of these tills. Finally, the increase of organic matter prevents to identify primary organic particles that could be used for radiocarbon analyses. This research has identified potential problems prior to apply any dating method. We recommend carrying out similar studies in carbonate regions before conducting paleoglacier chronologies in order to identify and minimize their inaccuracy.

Paleoglacier ; Till ; Carbonate diagenesis ; Velebit Mt. ; Croatia

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