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

Particular Types of Secondary CaCO₃ Accumulations as Indicator of the Environment in Upper Pleistocene Loess Paleosoils of Europe

Judit BESZE-DEAK^a, Eric VERRECCHIA^b, Roger LANGOHR^a
a - Soil Science Unit, Univ. Gent, Krijgslaan281/S8, B-9000, Gent, Belgium.
b - URA 157 CNRS, Universite de Bourgogne, 6Bd. Gabriel, 21000 Fijon, France.

The link between various morphological types of secondary CaCO₃ and their paleoenvironment has been studied in 14 well known loess paleosoil sites of the Last Interglacial and Glacial periods from West and east Europe. Macro-, meso- and micromorphological and SEM observations combined with laboratory analyses were performed on selected samples. The focus of this study is on microschale CaCO₃ accumulations: Calcified root cells (CRC) are branching structures consisting of bright sparitic crystals, visible with the hand lens. They represent in situ redistribution of CaCO₃ due to biomineralization of root parenchyma cells. They seem to be related to a period of loess deposition on a patchy, possibly grass vegetation, most probably in a climate with a pronounced dry season. Local abundance of the CRC may indicate a longer stability of the soil surface. CaCO₃ hypocoatings are micritic impregnations of the soil matrix around the pores, mostly visible at the macro level. They seem to be related to the precipitation from soil solution due to root section. Needle-fiber calcite (NFC) randomly accumulates in larger pores, best observable under the microscope. It is related to biomineralization inside the mycelia bundles. NFC was observed often associated with hypocoatings. Its absence is some of the humiferous soil sedimentary complexes studied indicates an extremely dry environment during the deposition and evolution of these complexes. Powdery coatings have been recorded at macro and meso levels in the clay accumulation horizon of a Last Interglacial soil. Observation at the ultramicroscale (SEM) showed that they consist of needles. They are interpreted at the combined result of biomineralization and physico-chemical precipitation related to the evolution of the environment after the burial by the new calcareous sediments. Biospherolits are pure calcite nodules, mostly episoidal and observable only under the microscope. They are related to biomineralization which take place in the calciogeneous glands of earthworms, living in soils where there is available Ca in the system. Their absence in the buried loess and soils is probably related with the moisture stress during the upbuilding of the loess.

All these CaCO₃ accumulations are related to the biological activity and the understanding of their presence or absence in potentially of great value in the reconstruction of the paleoenvironment. In order to better understand their relationship with the environment the presence/absence of these various types of secondary carbonates must be recorded more systematically and more precisely.

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