Paleopedology Symposia during the XVII INQUA Congress,

Cairns, Australia, 28 July - 3 August 2007

(full list of Symposia of INQUA Commission on Terrestrial Processes, Deposits and History (INQUA TERPRO) is available at the Congress web site).

Timescales of soil formation. Conveners: Daniela Sauer (Germany), Edoardo Costantini (Italy)

Studies on soil development may enable us to estimate the age of land surfaces and - in combination with other proxies - to reconstruct changing paleoenvironments. An estimation of soil formation time is also needed to evaluate the tolerable soil erosion rate for different environments. Therefore, we should aim at continuously increasing our understanding of pedogenic processes, their rates, and the ways in which they are influenced by soil forming factors, including man, in order to build a reliable basis for the correct and efficient use of the potential of the soil archive. One important step in this direction was the conference "Global Soil Change: Time-Scales and Rates of Pedogenic Processes" in May 2005 in Mexico.

With the session Timescales of soil formation we intend to continue on this way.

Focuses of the session will be:

• Studies of soil chronosequences in different environments and materials (e.g. moraines, fluvial and marine terraces, beach ridges and sand dunes, volcanic ashes)
• Soil development as a tool for landscape history reconstruction (e.g. for relative chronologies of tectonic activity, sealevel changes, sand dune development, glacier retreats)
• Soil properties and indices which are suitable for estimating landsurface ages (pedo-dating)
• Studies of polygenetic soils, interpretation of soil characteristics indicating certain (changing) paleoenvironments
• Studies on the influence of soil forming factors, including man, on the rate of pedogenesis

Besides this list, other kinds of contributions on how to read the story written in a soil profile, i. e. how to use the soil archive correctly and efficiently for paleoenvironmental reconstruction are welcome.

Pedogenic analysis of aeolian deposits: Conveners: Martin Iriondo (Argentina), Birgit Terhorst (Germany)

Pedogenesis on aeolian sediments is a classical issue in research of continental Quaternary. Particularly, loess-paleosol sequences have been studied since several decades in middle latitudes of Asia, Europe and the Americas. Those sequences provide imprtant information for the reconstruction of Quaternary environments and processes. Different proxies, both classical and new, are applied in such investigations and new results frequently appear.

We pretend to add broader fields in the classical relation aeolians-pedogenesis. In first place, pedogenetic processes on Aeolian sands are scarce, and such systems deserve to be studied with the same methods and tools than the loess-paleosol profiles. Interesting results
can undoubtedly appear in important regions of several countries of the world.

Moreover, different types of fine aeolian deposits (non-classical varieties of loess) have been described in some areas, especially in low latitudes of the Earth: volcanic-related loess, tropical loess and others. In most cases, such sediments are intercalated with paleosols.

Reconstructing Quaternary environments in drylands is generally complicated by the scarcity of paleoecological indicators and dating materials. In such areas recent advancements have demonstrated that pedogenic carbonate can serve as a good paleoenvironmental and chronological proxy. Thus for example, stable isotopic composition soil accumulation of secondary carbonate can reflect changes in vegetation (δ¹³C), and help detecting modification of precipitation sources and rainfall regime using stable oxygen isotopes (δ¹⁸O). The recognition based on micromorphological observations of accretionary stages, i.e. expressed by polyphased laminae, provides the relative chronological frame to interpret the changes of geochemical and mineralogical properties in terms of relative climatic shifts. Several dating techniques such as ¹⁴C, Th/U, luminescence and measuring the thickness of secondary carbonate coatings on stones can serve as a basis for numerical age-determination of pedogenic carbonate.

Despite the methodological progress in understanding the nature of secondary carbonate accumulations in soils over the last two decades, their use in Quaternary studies has been relatively limited. This is most probably due to conventional view on the uncertainties involved into interpretation of pedogenic carbonate as a paleoclimatic record or a chronological marker.

The aim of the symposium, therefore will be to highlight recent advances in paleoenvironmental and geochronological applications of pedogenic carbonate and thus to contribute to a broader use of this tool in Quaternary research. The symposium will focus on summarising the potential and limitations of pedogenic carbonate as a proxy with special emphasis on (1) Use of secondary soil carbonates as high-resolution terrestrial archives of climate , (2) chronometric methods –scope and limitations and (3) analysis of factors complicating interpretation of the record in pedogenic carbonate (diagenetic alteration a.o.), (4) role of these carbonates as long term sources and sinks of CO₂ and implications for global carbon cycle.

We expect to bring out the publication as a special issue.