Abstracts of Symposium 55 and some papers from other related Symposia.

Soil Age Relationdhips and Age Correlations: Examples from the Chromosequence in the Ljubljana Basin, Slovenia

Natasha J. VIDIC, Agronomy Dep., Univ. Lj., Jamnikarjeva 101, 61000 Ljubljana, Slovenia

Chronosequence studies have gained importance because of the potential use of soil development for the estimations of soil age. which is especially relevant because of the lack, of datable materials and dating methods for Quaternary. Indices, such as eluvial-illuvial coefficients (EICs¹) and soil development indices (SDIs²), eliminate the differences in PM and theoretically offer the means to correlate soil development between different areas. Soil stratigraphy in the Ljubljana Basin was determined by ¹⁰Be and paleomagnetic analyses³ and enabled the solution of chronofunctions for the post-incisive chronosequence developed on Quaternary outwash deposits (5 ka to 1.8 Ma). The development of most of the soil properties increases with logarithm of time suggesting that the rates of development decrease with time The EICs chronofunctions could not be solved because of the High intrinsic variability of studied soils. and were not suitable for local or regional age correlations. The comparison of rates of soil development (derived from the chronofunctions of SDIs) between the Ljubljana Basis chronosequence (humid climate) and chronosequences in California (xeric), Pennsylvania (humid) and New Mexico (aridic), however, has shown, that in contrast with findings of Harden and Taylor⁴, rates of soil development differ in areas with different climate and seem to increase with the increasing rate of precipitation. Similar climate between the compared areas is therefore a prerequisite for any soil based age correlations. Within the chronosequence, the development of several time-dependent soil properties can he used to discriminate between soil members: alone, however each of them has a limited ability to do so, because the confidence intervals for deposits overlap. Total texture and weighted means of soil development based on the best four properties can be used to distinguish between groups of soils: 5-62 ka, 450 ka and 980 ka -1.8 Ma. and relative abundances of total Al and Fe to distinguish between soils of 980 ka and 1.8 Ma. The described soil properties could, therefore. when combined, be used to discriminate between 5- 62 ka 450 ka, 980 ka and 1.8 Ma soils. The inability of soil properties to discriminate between all soil members is ascribes to high intrinsic variability of soils, a low number of replicates on each deposit. and a slow rate of development that causes small differences between the soils of advanced ages. Sampling of additional replicate soil profiles would narrow the confidence intervals. allow more precise solutions of chronofunctions, and possibly increase the ability to discriminate between the soils on different deposits. Additional sampling, however, would not reduce the variability introduced into the chronofunctions by age uncertainties, because the slopes of chronofunctions may change if age estimates change. For the studied chronosequence, the changes in age estimates within the established uncertainty intervals caused differences in rates up to 20% for semi-logarithmic chronofunctions, and up to 180% for linear chronofunctions. Age predictions based on the rates of soil development derived from soil chronofunctions. therefore will have to wait until better age control and larger numbers of replicates are available.

1) Muir, J W., Logan J., 1982 J. Soil Sci 33, 295-308
2) Harden. J.W., 1982, Geoderma 28, 1-28
3) Pavich, M.J, and Vidic, N., 1993, Geophysical Monograph 78, 263-275
4) Harden. J.W. and Taylor. E.T., 1983, Quat. Res 20, 342-395

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