The posters complete the oral contributions, especially they enriched this symposium with various case studies, moreover some important new trends in soil genesis become apparent through posters. Posters have been regrouped in six items.

General discussions on concepts, processes. Only one poster, the P. Buurman’s, is fully devoted to general discussions. However many others tackle with concepts and processes, e.g. the A. Chernyachovsky et al.’s. P. Buurman discusses some of the crucial problems faced by paleopedology. He first considers that “errors in recognition of genetic features and reconstruction of soil forming processes are usually due to insufficient knowledge of these processes. ” Consequently he suggests that “ soil genesis in recent soils should be documented in more detail, especially for the kind of environments in which paleosols are frequently found ”. Then he considers that “ interpretation of paleosols through modern landscape/climate equivalents is hampered by the difference in the kind of information that is gathered on modern soils and on paleosols. In addition, even in modern soils it is difficult to reconstruct the climatic and time factors that were instrumental in their formation. Without adequate data on modern counterparts, paleosols cannot be interpreted properly ”. To improve paleosol interpretation, he proposes : (1) to investigate paleosols and recent soils in catenas, (2) to collect data on under various climates, preferably in alluvial soils, (3) to promote co-operation between soil geneticists and geomorphologists. P. Buurman’s insistence to interpret paleosols by comparing them with modern analogs must be considered sceptically. Everyone will agree that elementary soil forming processes are undoubtedly unchanging through time, however combination of these processes in the past should have been different from the present ones. For instance, posters dealing with abrupt events show clearly that this combination was different at some periods.

Others important problems of soil genesis through time, such as the fast decreasing rate of soil development with depth, are incidentally discussed in various posters. A. Alexandre et al., demonstrate this assumption on the basis of phytolith investigations while D. Schwartz and A. Mariotti reach an equivalent result by comparing d¹³C in sub-surface and deep horizons. A. Alexandrovskiy using classical methods reaches an equivalent conclusion. These results lead to the conclusion that sub-surface horizons are renewed almost permanently, in other words their life time is short, while deep horizons can be stable for longer periods. Moreover D. Schwartz and A. Mariotti show that a plant association is registered in deep horizons only if it is stable for more than a few centuries. This result could lead to a more general conclusion which can be, the registration of environmental events which is almost daily at the soil surface, e.g. the surface crusting, becomes with depth less accurate, only some long term events are register while others, even long term are missing because their records do not penetrate in depth.

A new research, the impact of wild fires and to a less extent of man induced fires on soil development is emerging (M.A. Courty et al. oral presentation and A. Alexandre et al. poster).

More classical investigations (detailed physical, chemical, mineralogical, and micromorphological analyses, combined with 14C dates of buried organic materials and completed in a few soils, by 14C dating of several soil horizons in order to evaluate features between adjacent horizon) by P. Zdruli and H. Eswaran on incipient soils of Albania enabled also to achieve precise rates of soil processes. These scientists show that pedogenic calcitic nodules and coatings form rather rapidly within 500 to 1,000 years, a mollic epipedon in less than 1,000 years while an argillic horizon seems to form in about 2,000 to 8,000 years. K. Dalsgaard and B.V. Odgaard demonstrate the possibilities of the AMS 14C dating technique combined with pollen analysis and general soil analysis for dating sequences of buried podzols in windblown sand. A. Gennadyiev gives trends and rate of soil formation in the Russian plain from the southern taiga to the Caspian semi-desertic lowlands during the Late Holocene.

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Age of soils in previous studies according to P. Zdruli and H. Eswaran, were approached from a geomorphic point of view. They conclude that “ age relationships may be valid on old stable landscapes, however recent sediments demonstrate that many processes are rapid and some of the features observed require a short time frame of less than a few thousands years to form ”.

Research in soils for signatures of past events. The range of markers of past environmental events in soils used by pedologists has been considerably widened and diversified in recent years. The macro- and micromorphological soil analysis continue to be in favour as well as interpretation of mineral soil constituents. However a great attention is presently paid to bio-tracers and to stable isotopes. Nevertheless we should regret that researches in soils on signatures of past events are performed in extended order while we need integrated investigations for understanding the soil complexity

Pedogenic carbonates. The carbonate profile is a good sensitive record of past environments. O. Khokhova et al. have compared carbonate profiles in Chernozems of northern Caucasus in irrigated soils, in virgin soils and in soils buried under funeral mounds using differential thermal analysis, X-ray diffraction, isotopic composition. Some interesting results are presented, such as the values of ë ¹³C which are lighter in the soils buried between 5000 and 3800-4000 BP than in latter soils.

Magnetic susceptibility in soils. Magnetic susceptibility is presently commonly used in paleopedology as well as in soils. Unfortunately in the symposium, we do not have any general presentation of the possibilities and limits of the magnetic susceptibility . The poster of R. Naidu and R. Fitzpatrick concerns only magnetic susceptibility changes in soils during long-term farming.

Elemental analysis. Microprobe (e.g. X-rays, SIMS, PIXE) elemental analysis are commonly utilised, however detected elements are rarely used as indicators. H. Dybkowska and H. Jaworska have attempted to elucidate the nature, origin and distribution of titanium in Alfisols of different age, formed from glacial deposits (Poland).

Signatures of abrupt events in soils. Paleoclimatologists consider, based on recent results obtained from ice cores and deep sea cores that many of the climatic fluctuations occurred abruptly (e.g. contributions to the PAGES Open Science Meeting, London 1998). How these climatic abrupt events were registered in soils ? to which facies or microfacies could they correspond ? Pedologists as well as paleopedologists have not yet tackled this problem from a general view point. Five case study posters are proposed on signatures of abrupt events in soils. G. Corti describes signatures of catastrophic paleo-events detected in profiles of Vallombrosa forest (Florence, Italy). J.Wattez et al. refer to an extraordinary event which took place at 3900 yr. B.P., signatures of which are a peculiar petrographic assemblage and specific micro-fabrics. B. Buck has investigated a regional aeolian erosional event dated of the Mid-Holocene characterised by a surficial lag composed of coarser materials, including stage II calcitic nodules of the underlying soil. This author also mentions another less prominent desertification event which occurred in the late Holocene. Black nodules which are ferruginized charcoal, are sometimes found under podzolic soils of Komi Republic (North East Russia). A. Golyeva demonstrates that these charcoal were produced during great wood fires, which occurred around 7000 yr. BP. She concludes that these charcoal corresponds to some natural catastrophe. P. R. Owens et al. describe the morphology of liquefaction features due to the passage of earthquake shear waves and discuss some the impacts on soil development. More attention should be paid by pedologists and paleopedologists on the impact of earthquakes on soils.

Registration of Holocene soil development. Exhibited posters show clearly that the Holocene soil development was quite complex, in relation with climatic fluctuations and was non linear as believed earlier. A. Alexandrovskiy observed on the foothills of Northwest Caucasus development of Chernozems from 5.5 to 3.5 ka BP which were later replaced by Luvisols in relation with a broad leaf forest extension. The leaching of calcite took place at the beginning of the forest stage, within the first hundreds years. Afterwards, the illuviation process started. A. Gennadiyev investigated trends and rate of soil formation in central and southern Russian plain during Late Holocene. He proposes a fundamental mathematical equation of soil evolution. A. Yamkish et al. compared fulvic versus humic acids in Holocene paleosols in the Yenisei valley (Central Siberia). N. Kovaleva describes two humus horizons in chernozem like soils on the subalpine meadows of Tian-Shan (Kirkizia); the age of the lower one is 5560 BP± 120 while the upper one is 3010 BP± 90. L. Reintam and T. Moora have investigated changes in pedogenesis during the Holocene on deposits of the Baltic transgressions in areas of ancient human settlements in West Estonia. R. Ortiz et al. on consolidated material in the Sierra de Carrascoy (SE Spain) have evidenced processes of paleo-rubification and clay accumulation prior to erosion and humification, bioturbation and recarbonatation.

Registration of long term soil exposure and of Pleistocene climatic changes. The complexity of soils, exposed for long periods, e.i. from one glacial cycle to eventually the whole Pleistocene, and even longer periods, is presently well recognised. This complexity results of the superimposition of varied, acting at different time scales, soil forming processes and erosional-sedimentary phenomenon.

The weathering of the parental rock is a long term process and is considered to be only time dependent. A. Chernyachovsky et al. which have compared the weathering mantle on high marine terraces of the Black Sea shores with the one on volcanic islands and ash covered high atolls of Tonga islands, show that the dominant factor of weathering is the parental rock while the weathering mantle diversity results on one hand, of the heterogeneity of the parental rock and on the other hand, of erosional events and phases.

M. Cooper et al. restrict themselves on some features of an Oxisol-Alfisol soil sequence in Piracicaba (SP), Brazil. The transformation of the oxic microfabric into an argillic one occurred, according to M. Cooper et al., during two stages, a first characterised by a dry climate then a second which resulted from the change to the present more humid climate with a well-defined dry season.

Past and modern impacts of human activities on soils. Investigations on man impact on soils have developed considerably in recent years. This impact can be direct through cultivation and irrigation or indirect through a change in vegetation induced by Man. K. Dalsgaard and B.V. Odgaard have studied in Denmark the relationships between the man-made Calluna vulgaris heath and the podzolisation.

M. Pieters et al. which have excavated a deserted Late Medieval fishermen's village in the polder area of Raversijde (Ostend, Belgium) emphasise on the complexity of the soil cover in the village and its vicinity which is mainly the result of the intense human interference in this very dynamic coastal environment.

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Man induced Chernozem alterations have been intensively studied in Russia. E. Riazonova et al. in the Rostov region studied the effects of irrigation which have resulted in an increase of soluble salts, in an alkalinization and in losses of soil structure in consequence of a mineralised of water used for irrigation and near the surface ground water. However E. Kovalyova et al. show no essential changes of the humic components in steppe soils, irrigated by weakly saline water over periods of: 0-5-10-13 and 20 years.

N. Karavaeva has investigated Podzoluvisol continuously ploughed since the 14^th century in the south of the taiga zone near the city of Novgorod (north-western Russia). The humus-accumulative, highly biogenic P horizon has replaced the initial eluvial horizon, eluvial character of which has been however increased, and transitional horizons while the Bt boundary is lowered, e.i. clays are translocated at a greater depth.. All the labile properties have been modified. Z. Klimowicz and S. Uziak have investigated the impact of cultivation on soils on loess and on rendzinas in the Lublin area (Poland). They ascertain an increase of the mosaic of the soil cover, an increase on slopes of soil erosion, and other minor changes. L. Kolesnichenko et al. have established a data-base (280 sites) of physical and chemical properties of cultivated soils in Western Siberia. They ascertain a decrease in the humus content in the sub-surface horizons as well as a decrease in exchange capacity, exchangeable cations, including potassium. F. Kozlovski has modelled long-term transformation of plough soils in the Russian plains