Report on the VI International Symposium and Field Workshop on Paleopedology, Mexico City, Mexico, 7-16 October 2001.

The YI ISFWP was very well organized by our colleagues of the Universitad Nacional Autonoma de México (E. Solleiro, S. Sedov, K. Oleschko, A.M. Soler, D. Flores, J. Gama-Castro, S. Palacios, E. Ballejo, L. Flores, G. Werner and T. Poetsch) and was attended by 46 people coming from 10 countries. The local state governor, MVZ Alfonso Sánchez Anaya, welcomed the participants to the meeting with a very interesting speech. He mentioned the importance of basic and applied researches on soils, and expressed the expectation that policy makers rely on soil scientists, who should provide for the useful information to solve the peculiar agricultural and environmental problems of the area.

During the three days of conference, 30 oral and 11 poster papers were presented about: i) Paleosol-sedimentary sequences (loess, alluvial, lacustrine, volcanic, etc.) as a record of the Pleistocene and Holocene environmental change; ii) Magnetic properties of Quaternary and pre-Quaternary paleosols and sediments as paleoclimatic indicators; iii) Paleopedology and archaeology and dating of paleosols. Paleopedological evidences of ancient man-induced environmental change. Applied Paleopedology. Biomorphs (pollen, phytoliths, macroremains) in paleosols: research and interpretation problems; iv) Polygenetic models of pedogenesis in relation to Quaternary and Pre-Quaternary climatic change.

Comparing with the previous Symposia (held in Germany 1997, China 1998, Russia 2000) the following new tendencies are notable: 1) traditional topic of study and interpretation of loess-paleosol sequences was enriched with the presentations on loess profiles from South America, until now much less studied compared with the sequences of Eurasia and North America (H. Veit, A. Schellenberger, D. Krhling). These presentations, besides the field and analytical results, presented an accurate correlation with other regional Quaternary records and with existing paleoclimate models. Regarding the Eurasian loess, the detailed stratigraphic schemes and far distance correlation of the sequences were discussed by A. Bronger and S. Markovic. A specific Holocene loess from the North American Great Plains was considered in the presentation of P. Jacobs. Only the presentation from R. Mailänder dealt with the paleosols of the Pleistocene periglacial area of Europe, the topic being discussed extensively at the previous meetings. 2) A completely new item, presented for the first time in the ISFWP, were the results from tephra-paleosol sequences of Mesoamerica (P. Havlicek, E. Solleiro, S.Sedov) and from the buried paleosols in alluvial sediments of Argentina (M. Iriondo, A. Cumba). 3) The studies of magnetic properties of paleosols were represented by a set of lectures on the different magnetic characteristics of the Mexican paleosols and modern soils (J. Urrutia, B. Ortega, A.M. Soler). The completely different pattern from that of the soils of the standard zonal sequence was shown, that requires more research to be explained.

Besides papers focused to new paleopedology frontiers, a set of presentations were devoted to classical studies about: 1) mineralogical characteristics of paleosols to be interpreted as an indicator of modern versus ancient weathering and mineral neoformation (Th. Poetsch, E. Costantini, K. Oleschko, P. Krasilnikov). 2) Archaeological paleopedology and paleosol indicators of past human impact on the environment, especially in the area of pre-hispanic civilizations of America (E. McClung and K. Heine). 3) Applied topics of paleopedology (S. Palacios, D. Flores, Y. Ramos). 4) Paleogeographical interpretation of pre-Quaternary paleosols (E. Yakimenko and A. Iakovleva).

The organization committee provided for a pre-meeting, a middle meeting, a post meeting and a post-post meeting field trip. The first one was related to the research obtained from the tephra-paleosol sequences of the Nevado de Toluca volcano, during the mid one we were shown the very peculiar saline soils of the Mexico city lacustrine basin, formed on volcanic ashes, and the archeological remains of the Aztec and pre-Aztec civilizations. The post conference tour was conduced in the region of Tlaxcala state and several modern soils and paleosols formed on volcanic ashes were presented. Many of the soils of the area are characterized by the presence of particularly impressive indurated horizons, all named “tepetates”, which are very common all along the Andes chain and present peculiar management problems. In spite of being called with the same name, different kind of properties and possible origins were recognized during the field trip.

The post-post-conference field trip was in the El Eden Reserve, in the state of Quintana Roo (Mexico), on the Peninsula of Yucatan. The region has been disturbed by human impact, hurricanes and forest fires. Notwithstanding, it was amazing to notice how the ecosystem recovered very fast in a time span of 10 – 20 years. It can be supposed that human impact and natural disasters are responsible for a weak development of soils in the El Eden Reserve. Soils are very shallow and don't exceed 40 cm of thickness, although pedogenesis takes place under a humid tropical climate. Another problem is, that the risk of soil erosion caused by deforestation is extraordinary high. Furthermore, it has been discussed how a numerous ancient Maya civilization could sustain for centuries in such a "poor and sensible soil environment". A solution for this mystery could be seen in the use of fertilizer in the Mayan civilization, that is the use of periphyton, which is a biocoenosis of algae, fungi and bacteria. Further information about the research station of El Eden can be found on the web: http://www.ucr.edu/pril/peten/images/el_eden/Home.html.