1 Centro de Ciencias de la Tierra, UAEH, México

Centre for Geoscience and Engineering, Anna University, Chennai 600 025.

Soils around Chennai, Tamil Nadu are represented by ferricretes and red soils and these can be related to the underlying bedrock. In the present study, red soils and ferricretes have been studied from three different sites: Red hills, Vaipur and Pallavaram, which were formed over different parent rocks. Red soils and ferricretes around Vaipur and Red Hills are over the Upper Gondwana sandstone and shale while around Pallavaram; they are formed over the charnockites of the Precambrian age. In this paper micromorphology and geochemistry of ferricretes and red soils are presented.

Micro fabric elements in polished thin sections have provided a basis for the interpretation of processes involved in red soil and ferricrete formation. Micromorphology of red soils and ferricretes reveals high content of clay minerals and these are gibbsite, hematite, magnetite halloysite and smectite. Fe-oxide mineralogy is represented by hematite, gibbsite and magnetite. Pedogenesis has produced iron segregation that was formed into a great variability of colors, degree of opacification and both external and internal forms. Crack and fractures have been filled by iron oxide either by kaolinite or hematite. Some of the fractures are lined with black manganese oxide representing the final depositional phase. The complex process of groundwater fluctuation and pedogenesis has formed red soils and ferricretes of the study area. Based on geomorphology and occurrence of archaeological artifacts the soils were dated to Late Neogene-Early Quaternary period. Climatic conditions would have been wetter than today.

Laboratorio de Paleoetnobotánica y paleoambiente, Instituto de Investigaciones Antropológicas, UNAM

A rescue excavation was undertaken in 1997 close to the construction site of the Cuicuilco-Inbursa tower near the archaeological site of Cuiculco. Sediment samples were taken from an area under the lava flow that now covers most of the site. Botanical remains recovered from the sediment, including plant macrofossils and pollen, were analyzed in order to determine the vegetation characteristic of the zone prior to the eruption of Xitle (ca. 500 BC).

Forty-nine samples were processed using flotation for the recovery of macrobotanical evidence and Hydrofluoric acid and potassium hydroxide extraction for the recovery of pollen. Identifications of plant remains the presence of genera pertaining to the arboreal (Pinus, Querqus) and herbaceous (Amaranthus, Chenopodium, Solanum, Verbena) strata as well as lacustrine association (Cyperus).

Moscow Advanced Educational Inst., Starovatutinsky, 8, 129281 Moscow, Russia

In the central part of Moscow, above the surface of the initial soils (Albeluvisols, Podzols, Fluvisols), one can observe the cultural layer that was formed here in the 12-20th centuries. The thickness of this layer reaches 3 m on the elevated watersheds and up to 15 m in the depressions.

The accumulation of the cultural layer was a discontinuous process; often, active accumulation was interrupted. When the duration of these pauses in the sediment accumulation exceeded 10--20 years, thin (3-5 cm) soil humus horizons could develop under herbaceous vegetation and trees. Thicker soils (up to 20 cm of the humus layer) developed in the gardens.

The cultural layer contains mortar, bones and remains of timber debris, that is why it has an alkaline reaction and contains pedogenic carbonates, vivianite and organic matter. Carbonate has migrated into the underlying Podzoluvisol, and its reaction has changed from acidic to alkaline.

The horizons of the 17-19th centuries contain maximum concentration of such elements as lead, copper and arsenic (blue copperas that was used for pest control in gardens and orchards and in household). For example, arsenic in the horizons of the 18-19th centuries increases to 74 mg/kg (as compared to the background (clarke) value of 2 mg/kg). This increase resulted from the use of arsenic in the tanning and dyeing industries. These dies are bright and very stable; nowadays, their production is prohibited or severely restricted because of their harmful effect.

The content of pollutants at the depth of 1 m often exceeds the one in the surface layer. Deep layers with anomalously high concentrations of pollutants are extracted on the surface during excavation works, mix up with surface soils and enhance the degree of pollution of modern urban environment. The rise in the groundwater level has a destructive impact on the basement of buildings; this water gets saturated with various salts and toxic organic and inorganic compounds, which have a negative effect on green plantings and the biota as a whole.

Institute of Geography, Russian Academy of Sciences, Russia

The floodplains are characterised by high dynamics of all landscape elements, including soils. In the Holocene, the processes of river valley development, accumulation of alluvium, changes in flood levels and intensity resulted in periodical destruction and burying of older soils and development of new ones (Mandel, 1992).

In the floodplain of the middle Oka, some multilayered (from Neolithic to the Medieval period) settlements are found. Their cultural deposits are mostly correlative to buried soils (Alexandrovskiy et al., 1987). The soils were formed during the time when the plain was not flooded and the sedimentation of alluvium was interrupted. Four main buried soils dated by radiocarbon and archeological methods were identified from series of principal sections through the multilayered flood-plain settlements: S1 - Young alluvial soil of the floodplain, 300-100 BP; S2 - Early Iron age and Early Medieval cultural deposits, Luvisol, 2200-1000 BP; S3 - Bronze age, Fluvisol, 4000-2800 BP; S4 - Neolithic cultural deposit, Fluvisol, 6000-4500 BP.

When the Luvisol (S2) was formed, its profile developed downwards and illuvial Bt horizons were formed. The pedogenic processes reworked the underlying alluvial deposits, which caused their compaction and structural changes. The rates of alluvial accumulation calculated from the layer thickness and dating have considerably varied and notably lowered during the formation of the Luvisol (S2). The changes in hydrology of the floodplain led to multiple migrations of human settlements to the elevated positions and viceversa.

Because of progressive accumulation of alluvium many floodplains were not flooded any longer in the late and sometimes in the middle Holocene. As a consequence, soils of zonal types – Chernozems and Luvisols were formed on the floodplains. The periods of activation of alluvial sedimentation, which resulted in the burial of soils, are induced by climatic changes that occurred within the Holocene as well as increasing human impact. Deforestation and land cultivation in the river basins were enhanced in the last 700 – 900 years, causing an increase of intensity and level of floods. Because of this, on many floodplains of Central Russian Plain, Luvisols (Grey Forest Soils and Albeluvisols) were buried under recent alluvium, on top of which weakly developed Fluvisols are formed.

1Alfred-Wegener-Institut für Polar- und Meeresforschung, Telegrafenberg A43, 14473 Potsdam, Germany

Uludag University, Faculty of Agriculture, Department of Soil Science, 16059 Bursa / TURKEY

This study was undertaken as a preliminary investigation on the genesis of these soils in the Bursa region of Turkey. Terra Rossas occur in some parts of the region as isolated pockets. This soil type was formed on different parent materials under Mediterranean type of climate. These soils are under natural vegetation in the highest elevation of the region. The soils at the lower altitudes have been used traditionally on a variety of agronomic regimes such as cereals, vegetables, and orchards. At the Eastern side of the region, six soil profiles were selected for this research. The soils are formed on unconsolidated limestone and located at three different elevation. The physical, chemical, and morphological properties of the soils were examined and classified according to the systems of FAO/Unesco (1990), FitzPatrick (1988), and USDA Soil Taxonomy (1994). The objective of this study was to characterize six Terra Rossa profiles along an increasing vertical zonality, and to relate their properties to the pedogenic processes responsible for their formation.

The soils are shallow to deep, showing Ah-Bt horizons. They are alkaline in all profiles. Their texture varies from silty clay loam to clay. These soils show high clay content increasing with depth. The distribution of clay was increased gradually from the upper area to the lower one due to the geomorphological position of the profiles. The soils were allocated to the classes of Chromic Luvisols (FAO/Unesco, 1990), Argillos (FitzPatrick, 1988), and Typic Xeralfs (USDA Soil Taxonomy, 1994). The profile variation occurred according to their geomorphological location and pedogenetic process. Due to all results, it is concluded that the main process of soil formation is a periodic decalcification in these soils.

Uludag University, Faculty of Agriculture, Department of Soil Science, 16059 Bursa / TURKEY

Cambisols occur in large areas of northwestern Turkey under natural vegetation. This soil group developed on various type of parent materials and geomorphic surfaces. This research was carried out as a preliminary investigation on the genesis of the most extensive soils under natural vegetation in northwestern Turkey. Six soil profiles were selected in this study. These soils are developed on schist parent material of Paleocene under dense cover which lies 200-450 m above sea level. Their characterization included field morphology, physico-chemical routine analysis and clay mineralogy.

The soils are shallow, showing Ah-Bw-C horizons. The texture of the soils varies from sandy clay loam to clay loam. Soil pH is slightly acidic in all the studied profiles. The obtained data indicate that analyzed soils were characterized by downward movement of clay, iron, formation of a cambic horizon and leaching of bases. According to the clay mineralogy, illite is the dominant mineral throughout all profiles. Kaolinite and chlorite-smectite are the minor minerals and gibbsite and plagioclases are present in trace amounts in all horizons of the profiles. All studied soils were classified as Eutric Cambisols (FAO/Unesco, 1990), Altosols (FitzPatrick, 1988), and Typic Xerochrepts (USDA Soil Taxonomy, 1994).

According to overall soil properties, it is concluded that at present the main process of soil formation is faunal mixing of organic and mineral material to form well structured fine granular upper horizons in the soils. Much of the variation among the soils can be related to the geomorphological position of the profiles and the geomorphological history of the region.

1Institute for Rock Magnetism and Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, USA

For case (a), two hypotheses have been offered: (i) lower values of X in paleosols due to decreased delivery of lithogenic coarse magnetite during glacial climate as in Siberia and Alaska and (ii) lower values caused by oxidation of magnetite to hematite, as seen in loess of Buenos Aires province, Argentina. Through a multi-magnetic proxy approach, we show that even in Alaska neoformed magnetite is present and can provide information about paleohumidity and cyclic reductive/oxidative history. Iron diagenesis, and not fluctuating delivery of lithogenic coarse magnetite, may be the dominant control on magnetically depleted paleosols. For case (b), we provide examples of possible anthropogenic enhancement superimposed on natural enhancement at the Cahokia archaeological site in Illinois, at archaeological sites in the Red River Valley in Minnesota and North Dakota, and in Amazonian dark earths (terra preta do Índio). In addition, we describe results of controlled in vitro production of nanophase magnetite from iron hydroxide precursors by IRB. We hope that their magnetic signatures can thus help recognize and quantify past microbial activity. In short, careful multi-magnetic proxies and supporting soil morphological and chemical data can yield a comprehensive picture of past environmental conditions.

119899, Department of Soil Science, Moscow State University, Vorob'evi Gori, Moscow, Russia

The morphological features of biogenic silica derived from plants and soil animals have been analysed. Biogenic silica of diatoms (Bacillariophyta), testate amoeba (Protozoa: Testacea), freshwater sponge (Spongia) etc is a basis of the systematics of these organisms (Round, 1973; Ogden, Hedley, 1980). The morphology of pancirery, shells and spinules is an important systematic criteria, since it is genetically determined (is controled by the genome). Morphological features of biogenic silica in lower plants and protozoa as well as the composition of their communities are also determined by the ecological conditions of their habitats. The well established systematics and ecology of silica-accumulating organisms are the basis for the development of such paleoecological methods as diatom analysis and rhyzopod analysis (Battarbee, 1986; Tolonen, 1986).

A possibility to use biogenic silica forms for paleoreconstuction of pedogenic factors has been supported by the example of burried soils of Dnepr river flood valley (archaeological complex “Gnezdovo”, Smolensk district, Russia). Sponge diatoms and spicules were also counted in 16 soil samples. The morphological diversity and amount of phytoliths have been determined as well as species composition and population density of shell amoebaes.

Several periods of alluvial soil development were recognised during the last two thousand years from the data on biogenic silica forms. The distribution of .diatoms and spicules along the soil profile was found to be similar. Decrease of diatom population density came together with the reduction of the amount of sponge spicules or their absense. Four periods of increasing hydromorphism appeared while diatom population density reached 100000 ind/g of dry soil.

As usual, an increase of the amount complied with appearence of phytoliths of hydrofilic plants - sedges and reed - in the soil samples. Pecularities of shell amoebae’s species composition made possible to specify the hydromorphic periods of soil formation.

Geograph. Institut Universität Kiel, D-24098 Kiel, Germany

Unidad de Ciencias de la Tierra (UNICIT), Instituto de Geología, UNAM, Querétaro, México. freyre@servidor.unam.mx

Ground Penetrating Radar (GPR) profiles, or radargrams, were collected in the lacustrine deposits of Chalco, in Mexico, with a ZOND 12c equipment (Radar Systems, Inc.) using the 900 and 300 MHz antennas. The aim of this work was to assess the application of this non-destructive tool to the identification of paleosols in volcanic-lacustrine basin sequences.

At GPR frequencies, the dielectric constant variations of soils and granular materials are related to specific interactions between the electromagnetic waves and water molecules filling voids. Therefore, water content, physico-chemical characteristics of pore water; solid-liquid-air proportion and, soil structure control radar wave behavior and are related with physical aspects of soils and sedimentary materials. As a matter of fact, the GPR method has a low detection capacity in saturated clayey materials due mainly to their high water retention capacity and low electrical resistivity. However, when a high dielectric contrast is present, for example between clay and sandy materials, the capacity of detection improves considerably with increasing salinity of pore water and textural contrasts.

The Chalco sequence is characterized by soils and saturated layers of plastic clay (with saline pore water) alternating with volcanic ashes and pyroclastic sand. In order to quantify physical variations that can produce electric contrast to be recorded in a radargram, core samples of the Chalco site were analyzed at the Geomechanical Laboratory of the UNICIT (UNAM). In the field, parallel vertical GPR profiles were obtained in two perpendicular directions in order to identify the spatial variations of the recorded reflectors. The surveying was based on detailed observations of the physical variations of the soil profiles. Analysis of radargrams supported by punctual determinations of water content, electrical conductivity, granular size and, textural changes demonstrated a relation between the electromagnetic recorded response and the physical properties of the clayey-sandy lacustrine sequence.

Results presented show the stratigraphic, textural and structural features recognized in the radargrams. The best definition in the stratigraphical and structural features was obtained with the 300 MHz antenna, whereas soil characteristics were best recorded using the 900 MHz antenna. Two of the principal stratigraphic targets with contrasting electrical properties were a paleosol located between 0.45 and 0.80 m depths and a sand layer located between 2.55 and 2.85 m depths. The structural and textural heterogeneities such as fractures, sand lenses, and concretions within a brownish silty clay at 1.3 m depth presented a specific radar signature.

We can state that comparisons of profiles from a lacustrine sequence permitted lateral and vertical stratigraphic monitoring of paleosols and permit a field characterization of the soil morphology and depositional conditions of sedimentary materials.

The twelve soils studied developed on acid rocks and on slope, alluvial and colluvial deposits, were dated in a time span ranging from Lower Pleistocene to Holocene.

Illite and kaolinite were found to be the most quantitatively important phyllosilicate, while vermiculite, hydroxy interlayered vermiculite (HIV), illite-HIV and illite-chlorite mixed layers, and chlorite content were related to different degrees of soil weathering. Comparing soils of different ages, the most characteristic clay mineralogy transformation with time was a progressive increase of kaolinite and vermiculite, as well as a decrease of illite.

The most outstanding pedological processes, i.e. crystalline free iron content, clay illuviation, glossic horizon and fragipan formation, were all found to be related to kaolinite content.

Clay mineralogy examination of the soil horizons also permitted a differentiation of so-called “lithological discontinuities”, which had been recognized during the field survey, into lithological and chronological discontinuities of the soil profiles.

Institute of Geography, Russian Academy of Sciences, Staromonetny, 29, Moscow, 109017, Russia, paleo@online.ru

The central East European Plain is the northest region of the World with Middle Pleistocene paleosols preserved up to now. Those occur in the loess-soil-cryogenic series below the Dnieper (Saale, stage 6) loess overlain by the Mezin soils complex (Eemian, stage 5e). In the region, two interglacial soils developed between the Dnieper and Oka glaciations under conditions of boreal and subboreal climate are known as Upper Kamenka and Inzhavino (or Lower Kamenka) soils. The soils are dated to the interval 250 to 450 ka BP.

The paleosols have been repeatedly eroded over the territory and can be found at the present time but just in a few sections. Those sections have been studied by using a range of techniques. Carbonates, organic matter, micromorphology, R₂O₃ and clay differentiation along the soils profile were observed. It seems, that the lower paleosol (Inzhavino) is present in several sections as pedosediment.

Its stratigraphic position is defined as occurring between the Upper Kamenka soil and deposits dated to the Oka glacial epoch. Such a case is of special interest, because it provides a possibility to appraise the pedosediments as a source of data on the soil formation, during the ancient warm stages. In the reconstructions, it was assumed that the paleosol properties, as recorded in the fossil soil profile, reflect primarily climate and environment of the optimum interglacial.

Pedosediments occur generally in small paleo-depressions or on paleo-slopes. At present, those landforms are buried, and only a portion of paleo-catena can be seen in the exposures. Therefore, it had to be also assumed that any given pedosediment contained the material derived from a single paleosol and was removed only from the eluvial part of the mentioned landscape. To make a conclusion as to the provenance of the pedosediment material, the organic matter composition and properties were studied together with a micromorphological analysis.

When analyzing specific properties of organic matter, only conservative characteristics were used, such as humus group composition, humic acids to fulvoacids ratio, humification degree (Cha/Ctot) and optical properties of humic acids. Where possible, the most humified layers were sampled and analyzed. The analyses have shown that in case two nearby sections were studied, one with the Inzhavino paleosol, and the other with a stratigraphically analogous pedosediment, the organic matter of the two formation is similar. In the micromorphological studies of the pedosediments, our primary attention was paid to the nature of microaggregates, composition and structure of the clay coatings, and to b-fabric types. There are also iron and carbonate neoformations.

It has been shown that aggregates from illuvial horizons are well-preserved in pedosediments; they include clay coatings as papules and fragments of channel-like voids. There are characteristic deformations of microaggregates that resulted from redeposition. The presence of speckled and striated b-fabric types, suggests that argillification in situ, is present in the original paleosol formation.

As an example, a number of sections from the Oka drainage basin are considered; the Inzhavino paleosol features, an eluvial-illuvial profile there and developed with participation of surficial gleying processes.

1Departamento de Edafología, Institututo de Geología, UNAM, Mexico

1Instituto de Geología, UNAM, México

The whole Russian Plain was inhabited by man in the second part of the Holocene. Because of that, the imprints of human activity can be found in the Holocene soils (including buried paleosols) in all landscape zones. In some cases, the soil features produced by human activity can be mistaken for climatic signals that cause interpretation problems. We studied the soils in the vicinities of ancient settlements and sequences of buried paleosols at small valleys (balkas) in humid and semihumid zones of Russian Plain, to determine the type and degree of anthropogenic environmental change and its influence on further soil evolution.

Radiocarbon dating and traditional soil analyses were used. The main method was biomorphical. The biomorph analysis is the study of the macro and micro remains of biota (biomorphs), in the context of the conditions of their origin. Each of the biomorphs (phytoliths, pollen, diatoms, sponge spicules and others) characterizes the specific conditions of the origin and evolution of a soil profile. Multiple biomorph analysis that includes the study of as many different biomorphs as possible allow to obtain additional information on the genesis and evolution of a soil. Data on these studies complement each other; their integrated analyses make it possible to reveal an unambiguous picture of the event sequence in the development of a particular soil object. The application of biomorph analysis permit to: (a) distinguish the origin of some soil-forming rocks, especially those of hydromorphic nature; (b) identify such events as erosion and accumulation and to judge the thickness of eroded or deposited layers; (c) diagnose the anthropogenic impacts on soils, even when there are no evident morphological traces of these impacts; (d) reveal the composition of local and regional plant communities; (f) identify and diagnose the buried character of soil horizons. By using biomorph analysis, it is possible to obtain new, previously unavailable information and to elucidate some controversial questions on soil genesis and evolution. All these adventages of biomorph analysis lead us to consider this method very promising in the study of soil and to recommend it for wider application during the study of soils, natural and anthropogenic deposits.

Our results have shown considerable human impact on surrounding landscapes and soils in all studied sites. In humid zone the soils on the sandy parent material were studied near the bronze age settlement in Ryazan oblast. Forest cleaning which caused the formation of humus-rich neutral meadow soil was documented. About 500 ye. after the settlement was abandoned, the zonal type of vegetation – pine forest – was restored in the area. The upper part of the profile was transformed in the Podzol direction, whereas the lower part of the meadow soil humus horizon persisted at 35-45 cm, forming the so called “second humus horizon”.

Sequences of buried soils in balkas near ancient settlements in a semihumid zone (Tula oblast), also indicate man-induced deforestation. Forest cleaning and subsequent cultivation caused strong erosion, resulting in the burial of soils in balkas under colluvium, derived from humus horizons of the watersheds. When land –settlements- was under no activity havin low human impact, colluviation ceased, forests were restored and soil formation features, typical for forest pedogenesis, proceeded.

We conclude, that in the second part of the Holocene human activity was one of the main factors of soil evolution. At least in the areas around the settlements, its influence was more pronounced than global climatic change.

The micromorphological soil studies and the Quaternary-geological field investigations carried out between the years 1997 and 2000 established the existence of a whole cratena of fossil and subfossil soils, which starts with syrosems (raw soils) and rankers and ends with earthified rotlehms (red plastosols, ultisols). The best developed and most intensive soils occur upon the pumice and andesite substratum, whereas those upon volcanic cinders and tuffs are less expressive. The same is true for non-volcanic sediments, like for example sub-fossil soils within the fluvial overbank deposits.

Marshy soils and equivalent redeposited soil sediments are present in the mangrove strips along the Pacific coast (e.g. in the vicinity of Leon town and the Cosiquina volcano). Frequent admixture of fresh unweathered volcanic material indicates frequent repetitions of intensive volcanic activities. The proximity of an active volcano is indicated by the presence of volcanic edaphoids, originated from pumices of volcanothermic processes. The identified soil types developed upon the volcanic rocks -volcanic ashes, tuffs, cinders and pumices correspond to Andosols (cf. Soil Taxonomy, 1975). The individual identified soils differ strongly and, therefore, also the relevant time interval needed for their development is different. While the raw soils and rankers developed a relatively short time (approx. decades) the development of plastosols lasted probably for thousands of years or more. Of course more exact time estimations are not possible due to the lack of concrete data.

University of Regensburg

In the basin of Puebla-Tlaxcala in central Mexico, there has been a pronounced relationship between climate change, geomorphology and soil erosion on the one hand and the development of the ancient civilisations on the other hand (HEINE 1978, 1983, 1988; COOK 1986). There is no direct relationship between climate and the development of civilisation. Changes in settlement patterns and other human activities (land-use) have been influenced mostly by human, not natural factors. Soil erosion in the Puebla-Tlaxcala basin has been almost exclusively a result of human activity. Various phases of increased soil erosion occurred during times of population growth, increased settlement of previously uninhabited upper slopes of the volcanoes as well as intensification of agriculture. As early as 2000 years ago during the Tezoquipan phase, large areas had been eroded all the way to resistant indurated horizons (tepetate and caliche). Geomorphologic, sedimentologic and paleopedologic evidence shows that 2000 years ago, larger areas of central Mexico were devastated by erosion than at present. During the Tenanyecac phase (AD 100 - 650), isolated farms were abandoned in favour of villages. While villages increased in size, there was an overall decrease in population. Areas with pronounced soil erosion experienced especially large decreases in population. It appears that people moved to the villages. In comparison the number and location of villages in the basins, where soil erosion was not widespread, has remained relatively constant since about 600 B.C. After the Tenanyecac phase, population increased during the Texcalac phase, resulting in renewed cultivation of slopes prone to erosion. When population decreased during the following Tlaxcala phase, soil erosion also became less pronounced. After the conquest of Mexico by Spaniards in AD 1521, disease caused significant reduction in population over a short period of time. Simultaneously, erosion decreased because large areas of arable land were not cultivated. Since then, erosion has increased, especially after AD 1900.

It appears that cyclical political developments (cf. MARCUS 1992) are responsible for a large part of the observed cycles of soil erosion: The phase of reduced soil erosion between AD 100 - 650 (cf. FOWLER 1987) coincides with a decrease in influence of Teotihuacán on neighbouring regions. At the same time Teotihuacán itself experienced the highest population density of its history. Considering this evidence, it is no surprise that phases of soil erosion in central Mexico are asynchronous both in time and space.

References

Cook, A.G. (1986): El control de la erosión en Tlaxcala: Un problema secular. - Erdkunde 40: 251-262.

Fowler, M.L. (1987): Early Water Management at Amalucan, State of Puebla, Mexico. - Nat. Geogr. Res. 3: 52-68.

Heine, K. (1978): Mensch und geomorphodynamische Prozesse in Raum und Zeit im randtropischen Hochbecken von Puebla/Tlaxcala, Mexiko. 41. dt. Geogr.-Tag Mainz, Tagungsber. u. wiss. Abh., Wiesbaden: 390-406.

Heine, K. (1983): Bodenabtrag in Zentralmexiko: Messungen - Extrapolationen - geomorphologisch-sedimentologische Befunde. - Geogr. Ztschr. 71: 28-40.

Heine, K. (1988): Klimagang, Geomorphodynamik und Kulturentwicklung in Zentralmexiko. - Jb. Geogr. Ges. Hannover 1988: 189-211.

Marcus, J. (1992): Political Fluctuations in Mesoamerica. Dynamic Cycles of Mesoamerican States. - Nat. Geogr. Res. & Expl. 8: 392-411.

Department of Soil, Water & Environment, University of Dhaka, Dhaka-1000, Bangladesh

The Gangetic flood plain in Bangladesh covers an area of 3 million hectares of the Bengal delta. The sediment of this floodplain has around 40 percent weatherable minerals. From the estimated 2.5 billion tons of sediments carried out to Bangladesh by the rivers a portion is deposited on the various floodplains during the monsoon season facilitating the formation of Paleosols in some selected locations. Results of six soil series from the Gangetie flood plain having buried soils in their profiles are reported in this paper. These soils are seasonally flooded and remain inundated for different periods.

Morphologically, the paleosols are identified by the presence of relatively darker horizons than those occurring above them in the profile. Therefore, color is an important indicator for paleosol identification. The organic matter in the surface horizon is high, but it is higher in some subsoil horizons. Texture of the surface soil varies from silty clay loam to clay. Paleosol particle size distribution shows an abrupt variation in some profiles while in some others, it is uniform. The present clay contents show a variation from 31 to 81%. The pH values in the surface horizons are higher and range from 5.2 to 7.8. The cation exchange capacities of soils range from 13.1 to 47.6 cmol/kg. Clay mineralogy is dominated by 2:1 expanding lattice minerals followed by mica and kaolinite. These soils have been classified as Thapto-Histic Haplaquepts. Rice is the major crop in all these soils yielding two tons per hectare.

Departamento de Paleontología, Instituto de Geología, UNAM; México

The presence of the Paleogene bauxites in the Yenisey River Basin (Siberia), which is characterized at the present time by the cold-temperate climate, is obviously linked to the fact that during the last 65 Ma the paleogeography of Eurasia and, in consequence Earth’s climate system, has experienced continuous change. On the basis of dinoflagellate cyst analyses, four new paleogeographical reconstructions are proposed for the late Paleocene- early Eocene of Western Siberia. The maximum flooding of Siberian Sea connected to the Arctic Basin and the Tethys corresponds to the latest Thanetian-Ypresian. It is suggested that the first major regression of Siberian Sea from the north due to the separation from the Arctic Basin occurred during the Lutetian. The last marine regression occurred at the end of Eocene: from the Oligocene no communication existed between the Arctic Basin and the Tethys via Siberian Sea and Turgay Strait. At the same time the palynological data suggest that the climate of Western Siberia was close to subtropical with dominance of evergreen taxa during the late Paleocene-early Eocene; towards to the end of Eocene the climate became progressively colder. The time of this cooling corresponds to the complete disappearance of Siberian Sea. The impact of important paleogeographical changes such as disappearance of Siberian Sea and Turgay Strait on the climate, biodiversity and pedogenesis of Eurasia during the Cenozoic is discussed.

The sediments with loessic characteristics of the pampean plain are called “loess y limos pampeanos” (pampean loess and silts) (Frenguelli, 1955) to separate those of purely eolian origin from the reworked by water. The term “loessoide” (loess like) is used by the same author to designate the second ones.

In the continental border of La Plata River, mainly loess-like sediments of the Late and Middle Pleistocene outcrop at approximately 20 Km from the coast. In the same direction they underlie at 2–5 m depth to the Holocene sediments (Imbellone, 1996) deposited by the regressive events in the successive lowering of sea level during the latest 6.000 years. At Parana River bluffs loess like sediments are exposed.

The object of this work is to describe the field, sedimentological and mineralogical characteristics, as well as the intensity of the paleopedogenic processes in the area. To integrate previous and new information, four big quarries with loess-like sediments are described laterally.

Successions are at about 15 m.a.s.l. with partially continuous development of pedological features from the macroscopic point of view. The buried paleosols are superposed, welded with different pedogenesis degree, indicated by macro and micromorphological features of illuviation and hydromorphism. In some cases these features would have been formed simultaneously with the deposition of the aeolian dust trapped by grass vegetation and reworked by water. The pedogenesis degree would depend on the relationship between the intensity of the accretion and reworked process and pedogenesis. Pedogenesis affected partially or totally the sedimentary units.

Two units of rich volcanic glass loess-like deposits were detected at San Pedro quarry (Cumba and imbellone, 1999). Previous (Riggi et al, 1986; Teruggi e Imbellone, 1988) and new information reveals the same situation near La Plata city. The upper one is found between 2 and 3 m deep, with 20 to 30% of volcanic glass and in cases constitute the parent material of the present soil. The deeper unit is at 7 –10 m depth, with 60 to 70% volcanic glass. Micromorphological observations confirm the presence of scarce to abundant clasts of previous illuvial horizons and loess embedded in the majority of sediment matrix.

Pedological processes are more developed at the deeper part of the successions indicated by strong structure degree and abundant, laminated and complex textural and amorphous features. The loess-like units and the associate lower paleosols could be informal stratigraphic correlation units for the continental deposits of the area.

References

Cumba, A. and P.A. Imbellone, P. 1999. Indices pedoestratigráficos en sucesiones costeras de la zona de San Pedro. Provincia de Buenos Aires. 245-249. 5ª Jornadas Geológicas Bonaerenses. Mar del Plata. Argentina.

Frenguelli, J. 1955. Loess y limos pampeanos. Serie técnica y didáctica Nº 7. Universidad Nacional de La Plata. 88p.

Imbellone, P.A. 1996. Redistribución de carbonato de calcio en sucesiones cuaternarias de la llanura costera bonaerense. A.A.S.Revista 3: 63-76.

Riggi, J.C., F.Francisco, O.R.Martínez and N.Porro. 1986. Geología de los “Sedimentos pampeanos” en el Partido de La Plata. Asociación Geológica Argentina, Revista XLI: 316-333.

Teruggi, M.E. and P.A. Imbellone. 1988. Paleosuelos loéssicos superpuestos en el Pleistoceno superior- Holoceno de la región de La Plata. Ciencia del Suelo 5: 175-188.

CONICET – Facultad de Ing. y Ciencias Hídricas, UNL; C.C. 217 (3000) Santa Fe, Argentina

In the Uruguay river basin (285,000 km²) a generalized pedogenesis occurred during the Climatic Optimum of the Holocene, approximately between 8,500 and 3,500 years before Present. This period of 5,000 years was characterized by a humid and warm climate.

In terms of factors of soil formation an interesting pattern appears. The climate was relatively homogeneous on the whole basin. The age is the same in all cases and the influence of relief and vegetation was modest. Therefore those factors can be considered as basically uniform. On the contrary, the parent materials form a complex mosaic. The granulometric and mineralogical characteristics of the parent materials dominate the nature of the hypsithermal pedogenesis even at the higher level of the soil classification.

Several cases of this regional pattern can be cited. Moderately to well developed B horizons of six buried soils have been registered in the region. Each of them cover a significant area.

A buried soil belonging to the Ultisol Order was developed on the Oberá Formation (the Late Pleistocene tropical loess) in the north of the region (in Misiones province, Argentina; and Rio Grande do Sul state, Brazil). A well developed Argillisol –Alfisol- was generated on the lower fluvial terrace of the Uruguay (the Concordia Formation, Lower Holocene in age) and tributaries in the middle-lower basin (in E Corrientes and W Entre Ríos provinces, Argentina; SW Rio Grande do Sul state and W Uruguay). Some profiles are pedocomplexes with clear evidence that the soil formation was interrupted by the accumulation of andean volcanic ashes.

On a Late Pleistocene-Lower Holocene paludal unit (the Tapebicuá Formation, in E Corrientes province) a distinct buried soil with an argillic yellowish brown horizon was developed. A moderately developed Gleysol appears on the lower terrace of the tributaries in SW Rio Grande do Sul state (the Touro Passo Formation, Lower Holocene in age). A conspicuous Vertisol covers the southwestern of the river basin (in Entre Ríos province). The parent material of this buried soil is a clayey playa unit (Hernandarias Formation, Lower Pleistocene in age).

On the Late Pleistocene loess at the exteme south of the basin (in SE Entre Ríos province and W Uruguay), appears a moderately developed Argillisol, which is the typical occurrence in the Pampa region.

The hypsithermal soil was truncated by aeolian erosion in most of the region. Later, it was covered by a thin loessic layer (the San Guillermo Formation, sedimented during the Upper Holocene). Both, the remaining B- and C horizons and the loess layer, are affected by the current incipient pedogenesis under a humid subtropical/tropical climate, which began 200 years ago. The only exception to this influence is represented by the Ultisol, which is covered by 2 – 4 m of red fine aeolian sediments (Upper Holocene in age), and consequently isolated from the present dynamic.

Bronger, A. 1991. Advances in Soil Science 15: 41-90.

Johnson, W.C. and K.L. Willey. 2000. Quaternary International 67: 89-106.

Kuzila, M.S. 1995. Geoderma 65: 45-57.

Mason, J.A. and M.S. Kuzila. 2000. Quaternary International 67: 119-131.

Institute of Physical, Chemical and Biological Problems of Soil Science of RAS, Pushchino, Moscow region, 142290, Russia.

Reconstruction of paleoenvironmental conditions based on the study of paleosols buried under archaeological monuments (kurgans) may be problematic due to various reasons. In the Southern Pre-Ural, the soil cover is characterized by a high complexity and a spatial variability caused by variegated lithological and geomorphological factors, microrelief in particular. Parent rocks of the region are characterized by irregular alternation of layers with different texture. Besides, they contain carbonates. The activity of soil burrowing animals in the dry steppe zone is very high, especially inside of artificial ground archaeological objects (kurgans). All these factors complicate a paleoclimatic reconstruction based on a study of paleosols buried under the kurgans in the dry steppe zone of the Southern Pre-Ural. Continuous recent cultivation leveled microrelief, partly destroyed kurgans and sometimes affected the upper part of buried soils. This further complicates the study of variability related to microrelief both in paleosols and modern soils.

The main aim of this work is the study of soil property variation, both in the modern Dark Kastanozems and in the paleosols buried under kurgans of the Early Nomads on the Southern Pre-Ural, Russia, using statistical methods and application of the results to paleoenvironmental reconstruction.

The key site for our study was a burial ground Pokrovka 10 located in the south of the Orenburg region. Two studied chronosequences consisted of the paleosols buried under the Savromatian (2500-2600 yr BP), the Late Sarmatian (1700-1800 yr BP) kurgans and the modern Dark Kastanozems were located on top and slope of mezokatena.

A considerable spatial variability of soil features has been revealed both for the modern Dark Kastanozems and the paleosols. Because of this, the thickness and depth of soil horizons, the degree of humus horizon tonguing, the content of carbonate CO₂ and pH was impossible to use for a comparative study of soils in chronosequences to reconstruct conditions of paleoenvironment. The thickness and the depth of soil horizons are related to interstratification of parent rocks, activity of burrowing animals and the depth of plowing rather than with evolution of pedogenesis. The degree of humus horizon tonguing is connected with a location of soil in mezocatena and not with change of climatic conditions in time. The content of carbonate CO₂ and pH is determined by carbonate content in parent rocks. Morphology of pedogenic carbonates in Bk horizons, depth and quantity of gypsum and humus content proved to be more reliable for paleoenvironmental reconstruction.

In paleosols buried at the Late Sarmatian Time (the end of II - III centuries AD), the size and quantity of carbonate accumulations in Bk horizon were the greatest in the chronosequences, with considerable heterogeneity of size and quantity. Furthermore, the depth and content of gypsum were similar in the Late Sarmatian paleosols and the modern Dark Kastanozems. The features of the modern Dark Kastanozems and the Savromatian paleosols were nearly similar.

Based on these observations we tried to reconstruct environmental conditions in the Early Nomads Age on the Southern Pre-Ural.We concluded that in the Savromatian Time the environment was practically the same as compared with nowadays. An arid climatic episode (probably, short but abrupt and intensive) was likely to precede the time of burials of the Late Sarmatian paleosols. By the beginning of the Late Sarmatian Time, the more humid and mild climatic conditions settled.

Moscow State University, Russia; natalia_kovaleva@mail.ru

The soil cover of the extensive territory of Tian-Shan is represented by the polygenetic present-day and burial in loess soils of Late Pleistocene and Holocene age. Its specific properties are due to the action of elementary current and relic soil processes, which could either coincide or alternate under the influence of glacier and climatic fluctuations.

The profiles of the Holocene polygenetic soils, which were formed on moraines of the glacieres during the last 13000 years, are clearly differentiated in the Late Holocene upper part (3010+ 120 years) and buried Middle Holocene (5500+ 90 years) lower part by the morphology, values of the humification index (1.90 % and 10.88 %), optical density of humic acids (0.14 and 0.24), the ratio Cha/Cfa (1.05 and 2.52), the content of aromatic carbon (30 % and 36 %), (acid/aldegid)_v ratio (>2 and <1). These properties indicate the humid moderate climate of the Late Holocene and automorphic conditions of the soil formation in the Middle Holocene. The form of evolution is “superposed” with the elements of the “inheriting” one. Thus,

Climatic changes in the Holocene in the mountaine regions of the Central Asia seem to coincide in Eastern Europe, Northwestern Caucasus and correspond to the global climate changes.

References:

Williams, M.A.J., Dunkerley, D.L., De Dekker, P. Kershaw A.P. and Chappel, J., 1998. Quternary Environments. (Second Eddition) Edward Arnold, London.

* This work was made in the Soil Science and Soil Geography department of the Bayreuth University (BRD) under the guidance of Prof. W.Zech during the DAAD sholarship

1Institute of Geography, Staromonetny 29, Moscow, 109017, Russia

Institute of biology, Karelian Research Centre, Petrozavodsk, Russia

Soil formation in Eastern Fennoscandia is generally believed to start after the last deglaciation approximately 12000 y.b.p., or even later, 9500 y.b.p., when higher vegetation has occupied the region. No research was done on the effect of pre-glacial weathering and Early Holocene geomorphologic processes on soil formation in the region. In fact, the parent material is usually considered as a kind of tabula rasa, unweathered and undisturbed before modern soil formation has started. In fact, this is not completely true. Most glacial tills and glaciofluvial sediments have undergone pre-glacial weathering before their re-deposition. Thus, the mineralogical composition of the parent material reflects the soil conditions of the latest inter-glacial period. Another consideration is that Early Holocene processes could contribute to the modern soil morphology. This period was characterized by less humid and much cooler climatic conditions than now in Eastern Fennoscandia. Thus, geomorphologic processes connected with cryogenic sediment disturbances were widespread, and it is possible now to detect their traces.

A key to the reconstruction of pre-glacial weathering environments is in the mineralogical composition of soil parent material. According to the results obtained both by our group and other investigators, the predominant layer silicates in the glacial sediments are micas, chlorites, and mixed-layered products of their transformation. No kaolinite, smectite, or vermiculite minerals were detected as pure minerals in these sediments. The presence of nontronite in some profiles was ascribed to hydrothermal alteration of parent rocks. The only sample from alluvial sands from the very north of the region contained significant amount of kaolinite. The phenomena can be assigned to hydrothermal processes, and to the presence of residues of weathering crusts at the mountainous north of the region, where glacial erosion processes were less intensive. One of the possible explanations for the difference in clay mineralogy of sediments in Eastern Fennoscandia and West European plain (where much more weathered clay minerals are abundant) is that the uppermost soil horizons containing the most weathered clay material were eroded at the first stages of the last glaciation, and distributed over north of the West European plain. In any case, there is still a striking difference in clay mineralogical composition of the latest glaciation and previous ones. This points on the relatively weak development of weathering processes.

Early Holocene processes affected the modern soil cover both due to the changes of sea level, and to thermocarst processes. Intensive sea level transgression have lead to the formation of salt-containing sea clays and sands. Later on sea level regression exposed these sediments to modern soil formation. The soils formed on sea clays are characterized by neutral or alcaline reaction at 0.5 m depth, and exhibit some properties of Solonetz. Thawing of giant ice lenses in glaciofluvial sands have lead to the formation of shell-holes in the surface, where erosion and creeps are abundant. Soil erosion intensifies after forest fires: most accumulated material on the soil surface contains coal particles. Creeps occur on the steep slopes of the shell-holes, leading to the formation of polygenetic, “many-storied” soil profiles. No distinct differences were detected in the morphology and properties of modern and buried soils; varying climatic conditions of the Holocene seem to have a small effect on Podzol formation on glaciofluvial sands.

CONICET – Facultad de Ing. y Ciencias Hídricas, UNL; C.C. 217 (3000) Santa Fe, Argentina

The southwest of Entre Ríos province covers an area of 14,000 km² (31°45´- 33°15´ S and 58°15´ - 60° 45´ W) and it is situated at the northeastern of the Pampean Loessic Belt. The stratigraphic column of the area is formed by two well defined aeolian sedimentation cycles. Pedogenic processes were active throughout both cycles.

The older cycle is Lower Pleistocene in age (Matuyama epoch), it lies on miocene marine sediments. The second cycle occurred during the Late Pleistocene and the Holocene (Brunhes epoch). Several episodes of pedogenesis and local erosive discordances were registered in both major sedimentation cycles, particularly in the older one. The long sedimentation hiatus, which covers all the Middle Pleistocene and a half of the Upper Pleistocene, constitutes a remarkable regional feature.

Sedimentary cycle 1 was defined as Punta Gorda Group. It is composed of three units:

a) The Puerto Alvear Formation is a silty unit (thickness 9 m) accumulated as infilling of an abandoned belt of the Paraná river. It presents a close net formed by CaCO3 platy precipitates of groundwater origin. Numerous vertical large and botrioidal concretions indicate a remobilisation of the carbonate. An internal unconformity separate both members of the unit; in some places the top of the lower member are the Bw- and C horizons of a weakly developed palaeosol.

b) The La Juanita Formation lays discordantly on the Puerto Alvear Fm, with a thickness of 3 m. It is composed of brown to olive silt sedimented in a non-permanent swamp environment.

c) The Punta Gorda Formation is a loessic (6 m thick) unit with several interbedded paleosols and frequent local internal unconformities. At the type locality, the lower section of this unit is a clayey silt paludal deposit. It is covered by a Ckm horizon of a soil, represented by vertical cilindric welded concretions. The central section is formed by a brown loess with a net of diagenetic CaCO3 precipitates. Three weakly to moderately developed paleosols (B- and Ck horizons) have been recorded at a typical site. These soils are laterally discontinuous as a result of uneven erosional contacts with the overlying loess, they also are recalcified from this material. The upper section begins with a Ckm horizon of another eroded paleosoil, covered by 1m thick paludal deposit.

Sedimentary cycle 2 is represented by the Pampean loess. This cycle begins in the area with a yellowish brown sandy silt (2-3 m thick) named Tezanos Pinto Formation. lt was acumulated during the Last Glacial Maximum. A moderately developed buried soil appears on top of the loess. It is represented by the Bt- and C horizons, generated during the Hypsithermal Period. The sedimentary sequence ends with a thin loessic unit (the San Guillermo Formation) accumulated on the partially eroded palaeosol during the Upper Holocene.

Important similarities were found between the sedimentary cycles 1 and 2. Both cycles were dominated by aeolian deposition. The main source of sediments has been the Andean region, which produced fine materials originated by nival processes and volcanic eruptions. The contribution of fine sediments from the Brazilian shield and associated areas in the northeast of the studied area is scarce. These materials were conveyed by the Paraná and Uruguay rivers.

Similar sedimentary macrosistems can be postulated for both cycles. The younger cycle is reasonably well know and can serve as a model to design a scenario for the older one. Sedimentological and pedogenetic processes in the cycle 1 indicate a more dynamic environment during the Lower Quaternary than at the Upper Quaternary.

Institute of Geography of Siberian Branch of Russian Academy of Sciences, Irkutsk.

The spotty (polygonal) soil cover structure of paleocryogenic nature is typical of the southern part of East Siberia. Microrelief, unaltered by cultivation is presented by the alternation of hillocks up to 1-2 meters high and 20-30 meters in diameter separated by the shallow depressions. According to a common view, the formation of microrelief is associated with the climatic warming at the beginning of Holocene when polygonal frozen fractures formed in more severe climate conditions of Pleistocene, had been transformed into shallow depressions. At the bottom of depressions relic almost black humus horizons are situated below modern humus horizons. According to radiocarbon dating they were formed during the Holocene optimum (6,6-4,7 thousand years ago for fractions I and II of humic acids respectively). According to G.A. Vorobieva (1984), the maximum humus accumulation is characteristic of the interval 6,5-4,0 thousand years ago.

The boundary of humus horizon in many sections corresponds to the textural change. Modern soil formation is taking place in the superficial layer, that is heavier in texture and was deposited during the final phase of eolian activity. The differences in the thickness of this layer may serve to measure the degree of deflation.

Because soil cover was damaged by deflation, deluvial drift and other reasons, simple genetic interpretation is not always possible. Soil profiles are characterized by bimodal distribution of humus content: its second maximum belongs to the relict horizon. Relic humus horizons differ considerably from modern ones, indicating the difference in climatic conditions of their formation. Relic humus horizons are characterized by high ratio of Chumic acid/Cfulvic acid (2,0 – 4,0); maximum optical density indexes of humic acids and very low content of nonhydrolysed residue. Though palynological analysis confirms the similarity of the spore and pollen spectrum of relict soil and spectrum of up-to-date vegetable cover.

The heterogeneity of soil cover should be taken into account while mapping. One should distinguish between polygenetic accumulative and degraded soils. The necessary information can be derived from aerial photographs at 1:25000 scale and larger. During the mapping and agrochemical survey, it is necessary to reflect the properties of each component and the area occupied with an approximate estimation. It is reasonable to regard soil cover as “spotty-residual hillocky microstructure”. In such a definition, the morphological properties, antropogenic impact, relief and soil transformation are reflected.

Soil cover structure should also be presented on the soil maps at smaller scale, as well as ecological, landscape and agricultural maps. It is partly carried out on the maps of the ecological atlas of the Irkutsk region prepared for publication; the distribution of buried humus horizons is shown by special marks, and the soil cover heterogeneity is determined as a factor which limits soil fertility.

Results of pollen analyses from Valle El Marrano (located at 3850 m in the NW side of Iztaccihuatl volcano, southeastern Basin of Mexico) in combination with glacial chronology and tephrochronology provide information of Holocene vegetation and climatic changes. Glacial advances occurred between 12 to 10 ka (Mipulco-1) and from 8.4 to 7.4 ka (Mipulco-2) according to the ³⁶Cl chronology. A moraine depression was formed by 10 ka after a Milpulco-1 glacier receded. Swampy conditions established there and sediments began to accumulate. A 460 -cm core was recovered from this moraine depression. The sequence elapses the last 10,000 years according to the ¹⁴C dates. The sediments are mainly sandy loams derived in part from colluvially reworked tephras. Two paleosols are intercalated, one beneath a distinctive 5000 ¹⁴C yr pumice layer and the second one beneath an ash with an age of 8780 ¹⁴C yr BP. The pollen record of the Valle El Marrano shows the colonization by the elements of the alpine grasslands after the retirement of the glacier, i.e. during the earliest Holocene. Following the Mipulco-2 glacial advance a sudden change in vegetal communities is documented; the site is invaded by pine forest at ca. 6000 yr. BP and after this event the alpine grasslands return. For the last 4000 years the expansion of the Pinus harttwegii forests is recorded.

1Instituto de Investigaciones Antropológicas, UNAM

Institute of Geography, University of Berne, Switzerland

How are modern soils and their parent materials influenced by Pleistocene processes? We contribute to the knowledge about colluvial sediments and palaeosols by presenting results from the central Swiss Plateau. We studied soil evolution and the stratification of soil parent materials on glacial deposits varying from Late Glacial to pre-Würmian in age. Soils of all studied sites are developed from colluvial layers called cover-beds. By relating them to underlying deposits we find a regular spatial distribution of soils and cover-bed types. A surficial layer (Upper Layer) having relatively constant thickness (around 50 cm independent of relief position) covers Pleistocene sediments of any age. Probably it was formed mainly by cryoturbation/solifluction either during a short phase of the Younger Dryas or during the Oldest Dryas. Layers that originate mainly from aeolian processes (Intermediate Layers) are restricted to areas outside the recessional moraines of the Berne-Stade. Hence they were formed merely up to the late Pleniglacial. They frequently consist of two distinct layers with the lower one displaying slightly stronger clay cutans than the upper one. These findings may indicate that the lower Intermediate Layer contains the relics of a palaeosol. That in turn would be an interesting finding, because it would point to clay illuviation during the late Pleniglacial.

Outside the glaciation of the Last Glacial Maximum (LGM) cover-beds in places overlie pre-LGM palaeosol relics. These are preserved even on higher relief positions. That suggests low periglacial erosion during the Pleniglacial. The palaeosol relics also occur on till of the so-called Older Wangen-Stade which is generally thought to represent the LGM. Eventually the distribution of soil types and their ecological characteristics are influenced considerably by cover-beds and palaeosols. As these beds reflect distinct phases of the Pleistocene, colluvial sediments provide a major tool for linking modern landscape characteristics to the Late Quaternary climate evolution.

Mineral and rock weathering statistics based on visual information are strongly biased and depend on the researcher’s experience and on the available image resolution. High-resolution images are needed for the precise estimation of the frequency and size of grain surface features. Due to these problems the commonly used qualitative or semi-quantitative classification schemes are unreliable, of low inter-observer reproducibility, and scale dependent. Geotechnical properties of minerals, are controlled by the density and arrangement of weathering features within the mineral, but the quantitative relationships between weathering feature pattern and weathering grade are still not established. The weathering patterns are considered the clues to landform evolution, soil formation analysis, studies on paleoweathering, analysis of solute concentration dynamics in ecosystems.

We used a novel fractal approach to design an unbiased and robust quantitative weathering assessment scheme, which is universal, objective, precise and scale independent. To justify the fractal approach, a strong statistical self-similarity over four decades of length scales was documented for both the weathering and fresh features of two common silica minerals of contrasting origin: quartz and biogenic A-opal (phytolith).

One of the main problems limiting the general applicability of fractals is the subjective, operator dependent thresholding applied to the digital images. In the present research, the spectral attributes of weathering features were used as the basic parameters for weathering classifiers design. The gray-tone microscopic images of mineral were firstly transformed into measure images by means of the Local Fractal Analysis (LFA) algorithm. LFA drastically reduced thresholding bias and robust measures of weathering features (color and discoloration, fracture state and change therein, the location and extent of weathering products) and fresh solid matrix features could be established. The local fractal dimension proved to be especially suitable to detect edges of the textural and structural features, independently of scale and illumination. Four fractal weathering classifiers (C) were proposed and used in the present research: Mineral weathering signature (C1); heterogeneity of the weathering and fresh features patterns (C2); Rugosity of the interfaces (C3), Continuity and tortuosity of the patterns (C4).

Keywords: weathering, fractal, self-similarity, thresholding, quartz, phytolith

Institute of Geography, University of Hamburg

In the Central Highlands of Mexico, a tropical climatic area with one rainy season, volcanic soils of the stratigraphical unit T-2 (13,000 – 21,000 B.P.) and their palaeosols, up to the present soil surface, were studied micromorphologically and microscopically. A profile, bordering a “barranca”, was chosen, situated at 2600 m above sea level, south of the village of Tlalpan (northwest of Apizaco).

Here, the parent material is a sequence of relocated, “epiclastic” volcanic tuffs. They contain shells of Diatoms and Silicoflagellates, thus proving a relocation within a water body.

Three palaeosols are separating four strata of such tuffs. The material contains negligible quantities of carbonates and iron oxides only, so the silica-gel components are not masked optically by these substances.

Undisturbed samples were taken from the profile in a close sequence and thin sections produced by them. Large-scale thin sections (47 x 47 mm) were made to gain a general view and to prove the representative of the detailed sections. Standard-sized thin sections, only 5 – 10 µm thin, were produced. These especially thin sections facilitate the evidence of silica-gel and allow to show detailed objects in a way rich in contrast.

There is microscopical evidence for silica-gel-derived formations throughout the profile in considerable quantities. Opals (phytoliths, shells of diatoms and silicoflagellates) are remarkable among them. Even more interesting from the point of view of soil mineralogy, are opaline deposits like micro-crusts, -flocks, and –lamellae. The lamellae are to be found both as separate components of the soil structure, and integrated into, or attached to the margin of, clay cutans. If connected to clay cutans, they follow their micro-lamination. On the other hand, the silica-gel is quite frequently, integrated sub-microscopically into the clay without forming its own micro-lamellae. In this case, very characteristic bodies of sub-microscopically mixed material develop. Samples with a different degree of hardening were compared micromorphologically. The basis of the profile´s most hardened layer, forming itself the basis of the T-2 unit, is characterized by a lack of microscopical coarse pores, which allow downward water percolation. Here, we will have to think of a production of silica in situ, rather than a downward transportation from the profile´s upper strata. The mineralogical results were checked and corroborated by chemical analyses, carried out by means of a microprobe.

The study area is situated near the village of Schatthausen, 10 km south of Heidelberg in SW-Germany. Thick deposits of Quaternary calcareous loess are widespread in the region, derived from the nearby Rhine Valley. The studied loess/ palaeosol sequence of Schatthausen was formed during the last glacial/interglacial cycle.

Paleosols and sediments were studied by pedological and isotopic methods. Particular emphasis was placed on the isotopic geochemistry of soil organic matter (¹³C) and carbonate material (¹³C, ¹⁸O). Additionally, radiocarbon age of 5 carbonate samples was determined.

The sequence consists of an interglacial Eemian soil, several interstadial paleosols in its basal parts and weak Tundra Gleys and calcaric loess in the upper parts. The ¹³C values (-25,4 to -22,8) indicate a soil organic matter origin predominantly from C3 vegetation with small positive shifts during the phases of loess accumulation. This result is in agreement with previous research in the region. The stable carbon isotope ratios of secondary carbonate accumulations, such as calcified root cells and the so-called "loesskindl" (¹³C = ca. -9.2) differ from the ratios on disseminated calcite in matrix (¹⁸O = ca. -6.5 and ca. -6.0 respectively).

Two facts testify a development, at least partially, of the calcified root cells, during the Holocene: First, it can be observed that the combination of the stable carbon and oxygen isotope ratios correlates with the values for pedogenic carbonate in recent environments of the region according to the model calculations. Second, 3 uncalibrated radiocarbon dates for the calcified root cells from the upper part of the sequence fall within the Early to Mid-Holocene.

On the other hand, the radiocarbon dating of terrestrial mollusc shells and worm calcite show Late Pleistocene ages in the same part of the sequence. The last two dates, as well as a number of radiocarbon dates on shell carbonate in loess in other works indicate that the loess-paleosol sequences remained an essentially closed isotopic system during the Holocene and the diagenetic alteration of the carbon isotopic ratios in carbonate was, if at all, minimal.

Sedimentation Conditions and Mineral Magnetic Properties of Quaternary Deposits From Laguna de Santa Rosa, Iturbide-Linares, Northeastern Mexico

1Facultad de Ciencias Forestales, Universidad Autonoma de Nuevo Leon (UANL), Linares 67700, Nuevo Leon, MEXICO

1Centro Regional del INAH de Tlaxcala, México

Department of Biology and Soil Science, St. Petersburg State University, St. Petersburg, Russia

In summer 2000 the soil cover structure (SCS) and parent rocks of the North-West edge of the Sheksnin-Kostroma interfluve (Vologodskaya region) were investigated. This territory is located in the extraglacial zone of the Valday (Würm) Glacation where there is an absence of pronounced morphology of end-moraine formations. The area is presented with the series of terraces and terraced surfaces of different ages, rising as ledges from the Rybinsk water storage reservoir (110 m a.e.) to the western branches of Danilovskaya upland (219 m a.e.).

Close attention was paid to the study of the SCS of the upper Pleistocene terraced surface (155 – 160 m a.e.) which occupied a large part of the area of interest. Soil forming rocks that occur in this territory belong to noncalcareous loesslike loams (NLL) underlain by moraine loams, sometimes at a depth of 1,0 m. These rocks alternate with sporadic outcrops of layered sands. The elevated levels of topography within this surface (up to 170 m a.e.) are covered by moraine loams. The Holocene automorphic and semihydromorphic Sod-Podzolic soils are developed on all these rocks. The organized heterochronous sequence complex including the Bryansk buried soil was studied in the quarry within this area (2.3 km to the North-East of the Rybinsk water reservoir; 58°49' N , 38°19' E; 155 m a.e.).

This profile with a 2.0 m thickness consists of the following horizons: B1-B2-IIBt-B3t-B4tg-[AG]-[G], the upper (0 – 25 cm) horizons of the sequence being representative of NLL. The upper and lower intermediate layers consist of red brownish clayey Valday moraine with distinct large prismatic structures. Well preserved Bryansk Sod-Glay soil formed in Moscovian moraine was found at the bottom of the sequence (at a depth of 104 – 150 cm). The thickness of the [AG] horizon varies from 14 to 25 cm. The profile of paleosol is cracked and turbated by cryogenic deformations.

The radiocarbon data from humic acids obtained for [AG] horizon 33200 ± 2000 BP (ЛУ-4600) permit to attribute the paleosol to the early of Bryansk Interstadial. The [AG] horizon is brown-black with a reddish hue, clayey (the content of <0,01 mm fraction is 54 %) in texture and has a cedemented nutty-platy structure which is compact and porous. In this horizon discontinuous brown-reddish and iron-gray films on ped faces, rusty spots, gleyed smudges and the inclusion of small boulders, grusses and coals have been noticed.

The humus content in the upper (0 – 15 cm) horizon is 0,8 %, in upper and lower intermediate layers vary from 0.3 to 0.4 % and in [AG] horizon the content of humus reaches 1.0 %. The layers of this studied sequence are leached of carbonates: pH_water varies from 5.0 to 5.6 within the whole profile.

The analysis of the results leads to the following conclusions.

The NLL of investigated and close areas has definitely subaqueous genesis. The data obtained show that the highstand (>160 m a.e.) of wide extraglacial lakes existed here during the maximum advancement of the Valday glaciation. Our research has shown that the glacier tongue could go forward along Mologo-Sheksnin lowland covering close terrased surfaces by low-powered sedimentary mantle. Thus, it is accepted that the Valday glacial boundary within the investigated area might soon be drawn a little further south.

Institute of Geography, University of Berne, Switzerland (schello@giub.unibe.ch)

Stratigraphic studies on loess deposits in the intramontane basin Valle de Tafí (27°S, 66°W) revealed up to 32 intercalated paleosols. TL/IRSL dating of the sediments provided strong evidence for a mid-Pleistocene age of the profiles. Independent age control was derived from paleomagnetic studies. Here we focus on the 50 m thick loess-paleosol sequence Las Carreras, where the Matuyama-Brunhes boundary (MBB) and Jaramillo subchron were detected (cf. Schellenberger et al., this volume). Because no erosional unconformities could be observed throughout the whole section, we suppose that the sequence provides a detailed and complete paleoclimatic archive of at least 1.1 Ma.

A number of 19 paleosols (mainly represented by well-developed Bt horizons, partly showing prismatic structures with organo-argillic coatings) were identified within the Brunhes chron. Between the MBB and the Jaramillo subchron the sequence contains 8 paleosols showing weak clay illuviation. The Jaramillo subchron is represented by two soil formations. The average pedogenesis cycles are about 41 ka, 16 ka and 45 ka, respectively. Due to the lack of TL/IRSL data from Las Carreras so far, a periodicity synchronous to the orbitally driven obliquity and precession cycles remains speculative.

Paleopedological and sedimentological characteristics indicate a shift to arid conditions within the Jaramillo subchron that persisted until approximately 700 ka BP, when more humid conditions were established. The analogy with the mid-Pleistocene climate transition as it is reported elsewhere (e.g. Schmieder et al., 2000) is striking.

Thus, the Las Carreras loess-paleosol sequence reflects a pattern of distinct paleogeoecological changes, especially of effective moisture, in a very sensitive transition area between Gran Chaco and Prepuna. The sequence can be used to extend our knowledge about dynamics and intensity of the subtropical circulation patterns in the north-eastern part of the Arid Diagonal of South America back into the early Pleistocene.

Reference

Schmieder, F., von Dobeneck, T. & U. Bleil (2000): The Mid-Pleistocene climate transition as documented in the deep South Atlantic Ocean: initiation, interim state and terminal event. - Earth and Planetary Science Letters 179: 539-549.