THE PROPERTIES, GENESIS AND ENVIRONMENTAL SIGNIFICANCE OF CALCITIC PENDENTS FROM THE HIGH ARCTIC (SPITSBERGEN)

Calcitic pendents occurring beneath coarse clasts were investigated from a well drained profile, near Ny-Alesund (Spitsbergen), developed on fluvio-glacial deposits with a few carbonate rock fragments. Micromorphological study was combined with mineralogical, geochemical and isotopic investigations to determine the relationships of calcitic pendent characteristics to soil conditions. Calcitic pendents are observed at all depths beneath clasts and display a succession of five types of laminae with strongly differentiated overall characteristics. The number of laminae and their specific attributes are nearly unchanged with depth and with the petrographic nature of the host clast. Each lamina consists of weakly differentiated micro-laminae that are grouped into six morphological facies. Precipitation of pedogenic carbonates is shown to be currently active throughout the profile, induced by supersaturation of solutes with respect to calcite during the initial stage of freezing. This process would form beneath clasts the calcitic pendents that are suggested to successively grow at all depths, following the gradual progression of the frost front. Carbonate dissolution appears to mainly affect the fine soil mass from the surface down to the permafrost level, controlled by summer biological activity. Differences of isotopic values of the whole calcitic pendents from those that would precipitate in equilibrium with present-day soil conditions are explained by changes in soil conditions during the accretionary process. C-14 values suggest that accretion of the pendents integrates phases which occurred during earlier episodes than the Holocene. The complex layering of calcitic pendents provides a sequential record of evolving soil-forming conditions during a time period possibly longer than the last glacial cycle. Previous conditions are interpreted in relation to present conditions of precipitation. The succession of micro-laminae is thought to reflect minor climatic fluctuations and marked changes between adjacent laminae are thought to indicate significant climatic changes.