Pedogenic Processes

Aeolian dust (windblown silt and clay) is an important component in arid-land ecosystems because it may contribute to soil formation and furnish essential nutrients. Few geologic surfaces, however, have been characterized with respect to dust-accumulation history and resultant nutrient enrichment. We have developed a combination of methods to identify the presence of aeolian dust in arid regions and to evaluate the roles of this dust in ecosystem processes. Unconsolidated sandy sediment on isolated surfaces in the Canyonlands region of the Colorado Plateau differs greatly in mineralogical and chemical composition from associated bedrock, mainly aeolian sandstone. Detrital magnetite in the surficial deposits produces moderately high values of magnetic susceptibility, but magnetite is absent in nearby bedrock. A component of the surficial deposits must be aeolian to account for the abundance of magnetite, which formed originally in far-distant igneous rocks. Particle-size analysis sug...

Although there is general consensus that a global greenhouse climate characterized the mid-Cretaceous, details of the climate state of the mid-Cretaceous Southern Hemisphere are less clearly understood. In particular, continental paleoclimate reconstructions are scarce and exclusively derived from paleontological records. Using paleosol-derived climofunction studies of the mid-to Upper Cretaceous Mata Amarilla Formation, southern Patagonia, Argentina, we present a reconstruction of the mid-Cretaceous climate of southern South America. Our results indicate that at ~60º south paleolatitude during the Cenomanian-Santonian stages, the climate was subtropical temperate-warm (12ºC ± 2.1ºC) and humid (1404 ± 108 mm/yr) with marked rainfall seasonality. These results are consistent with both previous estimations from the fossil floras of the Mata Amarilla Formation and other units of the Southern Hemisphere, and with the previous observations of the displacement of tropical and subtropical floras towards the poles in both hemispheres. The data presented here show a more marked seasonality and slightly lower mean annual precipitation and mean annual temperature values than those recorded at the same paleolatitudes in the Northern Hemisphere.

Factors governing the spatiotemporal soil development on a deglaciated area of Pindari Glacier in the Indian Central Himalaya were investigated over a timespan of 170 years. Glacier retreat exposed sediments to weathering, decarbonation, illuviation, acidification and melanisation. The spatiotemporal scales of soil transformation in this proglacial environment are significantly greater than in other chronosequences in the alpine environment. The accumulation of SOC and N in the oldest moraine is reflected in high accumulation rates of 52.6 g C m-2 year-1 and 4.8 g N m-2 year-1 in the 20-cm deep soil layer. Reference data from the topsoil of the rhododendron woodlands indicate that the oldest moraine topsoil is close to reaching some sort of a steady state. At least 100 years was required to stabilise the soil cover in most of the proglacial area. The results highlight the importance of rapid glacier retreat as well as inhibited weathering due to plant succession in soil formation, under impact of local climate characterized by high precipitation, temperatures and moisture delivery.

The isotopic ratios '3C/1zC and '80/'60 of cellulose from tamarix trees which were used by the Roman army as a groundwork of the siege-rampart of Masada (AD 70-73) were compared with ratios measured in present-day tam&x trees growing in the Masada region and in central Israel. The ancient tamarix cellulose is depicted in both 13C and 180 compared to cellulose from trees growing in the Masada region today. Similar trends were observed on comparing modern tamarix trees growing in the Negev Desert with those growing in the temperate climate of central Israel. Considering the factors that can contribute to the observed changes in isotopic composition, we conclude that the ancient trees enjoyed less arid environmental conditions during their growth compared to contemporary trees in this desert region. This report demonstrates the potential in using combined '*O and 13C analyses of archeological plant material as independent indication of regional climatic change in desert areas (where conventional isotopic analyses, such as in tree rings, are impractical).

A catenary sequence of soils formed on reworked loess under semiarid climatic conditions was studied. Four soil profiles located on the piedmont of Sierra Chica de Córdoba, central Argentina, were described, classified and geochemically analyzed. All soils, developed on summit, shoulder, backslope, and toeslope positions, were classified as Mollisols. Decarbonatation-carbonatation, melanization, and argilluviation are the main pedogenic processes recognized in these soils, which appear to control the differentiation of genetic horizons along the catena. Different geochemical approaches indicate that there are not substantial variations in the chemical composition of the studied soils along the catena, with the exception of the soil in the toeslope position, which exhibits slightly differences. In general, all profiles show weak depletions of mobile elements (Ca, Na, Mg, Sr, U) in the upper continental crust UCC-normalized diagrams which are attributed to a slight chemical alteration. Other elements, such as Fe, Cr, Co and Ni, also exhibit depletions compared to UCC, which can be explained by the alteration of ferromagnesian silicates, but can also be an inherited feature from the parent material. The significant enrichment in As compared to UCC, evident in all profiles along the catena, is also a typical feature of the pampean plains' loess of Argentina. So, the chemical differences in the profile located on the toeslope are mainly attributed to the supply of materials from local sources, i.e., crystalline basement and sedimentary rocks, due to its position in the catena. Statistical correlations and multivariate cluster analyses reinforce the assumption that the geochemistry of the studied soils is inherited from the parent material. In addition, chemical indices (CIA, ICV), elemental ratios (Ba/Sr, Rb/Sr) and the A-CN-K ternary diagram indicate an incipient degree of chemical alteration for these soils, compatible with the weathering regime prevailing in the region. Thus, the differentiation of genetic horizons along the catena is the result of weak weathering and pedogenic processes, which have not been strong enough to mask the chemical imprint of the parent material.

A catenary sequence of soils formed on reworked loess under semiarid climatic conditions was studied. Four soil profiles located on the piedmont of Sierra Chica de Córdoba, central Argentina, were described, classified and geochemically analyzed. All soils, developed on summit, shoulder, backslope, and toeslope positions, were classified as Mollisols. Decarbonatation-carbonatation, melanization, and argilluviation are the main pedogenic processes recognized in these soils, which appear to control the differentiation of genetic horizons along the catena. Different geochemical approaches indicate that there are not substantial variations in the chemical composition of the studied soils along the catena, with the exception of the soil in the toeslope position, which exhibits slightly differences. In general, all profiles show weak depletions of mobile elements (Ca, Na, Mg, Sr, U) in the upper continental crust UCC-normalized diagrams which are attributed to a slight chemical alteration. Other elements, such as Fe, Cr, Co and Ni, also exhibit depletions compared to UCC, which can be explained by the alteration of ferromagnesian silicates, but can also be an inherited feature from the parent material. The significant enrichment in As compared to UCC, evident in all profiles along the catena, is also a typical feature of the pampean plains' loess of Argentina. So, the chemical differences in the profile located on the toeslope are mainly attributed to the supply of materials from local sources, i.e., crystalline basement and sedimentary rocks, due to its position in the catena. Statistical correlations and multivariate cluster analyses reinforce the assumption that the geochemistry of the studied soils is inherited from the parent material. In addition, chemical indices (CIA, ICV), elemental ratios (Ba/Sr, Rb/Sr) and the A-CN-K ternary diagram indicate an incipient degree of chemical alteration for these soils, compatible with the weathering regime prevailing in the region. Thus, the differentiation of genetic horizons along the catena is the result of weak weathering and pedogenic processes, which have not been strong enough to mask the chemical imprint of the parent material.

Although there is general consensus that a global greenhouse climate characterized the mid-Cretaceous, details of the climate state of the mid-Cretaceous Southern Hemisphere are less clearly understood. In particular, continental paleoclimate reconstructions are scarce and exclusively derived from paleontological records. Using paleosol-derived climofunction studies of the mid-to Upper Cretaceous Mata Amarilla Formation, southern Patagonia, Argentina, we present a reconstruction of the mid-Cretaceous climate of southern South America. Our results indicate that at ~60º south paleolatitude during the Cenomanian-Santonian stages, the climate was subtropical temperate-warm (12ºC ± 2.1ºC) and humid (1404 ± 108 mm/yr) with marked rainfall seasonality. These results are consistent with both previous estimations from the fossil floras of the Mata Amarilla Formation and other units of the Southern Hemisphere, and with the previous observations of the displacement of tropical and subtropical floras towards the poles in both hemispheres. The data presented here show a more marked seasonality and slightly lower mean annual precipitation and mean annual temperature values than those recorded at the same paleolatitudes in the Northern Hemisphere.

Although there is general consensus that a global greenhouse climate characterized the mid-Cretaceous, details of the climate state of the mid-Cretaceous Southern Hemisphere are less clearly understood. In particular, continental paleoclimate reconstructions are scarce and exclusively derived from paleontological records. Using paleosol-derived climofunction studies of the mid-to Upper Cretaceous Mata Amarilla Formation, southern Patagonia, Argentina, we present a reconstruction of the mid-Cretaceous climate of southern South America. Our results indicate that at ~60º south paleolatitude during the Cenomanian-Santonian stages, the climate was subtropical temperate-warm (12ºC ± 2.1ºC) and humid (1404 ± 108 mm/yr) with marked rainfall seasonality. These results are consistent with both previous estimations from the fossil floras of the Mata Amarilla Formation and other units of the Southern Hemisphere, and with the previous observations of the displacement of tropical and subtropical floras towards the poles in both hemispheres. The data presented here show a more marked seasonality and slightly lower mean annual precipitation and mean annual temperature values than those recorded at the same paleolatitudes in the Northern Hemisphere.

Although there is general consensus that a global greenhouse climate characterized the mid-Cretaceous, details of the climate state of the mid-Cretaceous Southern Hemisphere are less clearly understood. In particular, continental paleoclimate reconstructions are scarce and exclusively derived from paleontological records. Using paleosol-derived climofunction studies of the mid-to Upper Cretaceous Mata Amarilla Formation, southern Patagonia, Argentina, we present a reconstruction of the mid-Cretaceous climate of southern South America. Our results indicate that at ~60º south paleolatitude during the Cenomanian-Santonian stages, the climate was subtropical temperate-warm (12ºC ± 2.1ºC) and humid (1404 ± 108 mm/yr) with marked rainfall seasonality. These results are consistent with both previous estimations from the fossil floras of the Mata Amarilla Formation and other units of the Southern Hemisphere, and with the previous observations of the displacement of tropical and subtropical floras towards the poles in both hemispheres. The data presented here show a more marked seasonality and slightly lower mean annual precipitation and mean annual temperature values than those recorded at the same paleolatitudes in the Northern Hemisphere.

The type of stratum in dryland ephemeral channel beds (wadis) determines its hydrological characteristics, which impact vegetation productivity. The objective of this study was to assess some key properties of a cemented, fine-grained bed stratum, previously characterized as a fluvio-pedogenic unit (FPU), as well as those of the overlying non-cohesive gravel bed stratum, known as a fluvially active unit (FAU). While the latter is an outcome of regular fluvial processes of recurring scour and fill, the former is characterized by horizonation, calcium carbonate deposition, oxidation, and accumulation of fine-grained material, defining it more as a soil or pseudo soil than as a sediment. The study was conducted in the hyper-arid southern Negev and Arava Valley of Israel, where the FAU and the underlying FPU were investigated, focusing on geo-ecological functioning. The results revealed considerable differences between the two types of strata. The contents of hygroscopic moisture, total organic carbon, and calcium carbonate were fourfold, 57%, and 36% greater, respectively, in the FPU than these in the FAU. Above all, the fine particle contents, including the clay and silt fractions, were almost eightfold and almost sixfold greater, respectively, for the FPU than those for the FAU, characterizing the former as loamy fine sand and the latter as fine sand. Altogether, these properties determine the stratum's field capacity and permanent wilting point, which were 73% and 50% greater, respectively, in the FPU than those in the FAU. In turn, the last two properties determine the available water capacity, which was almost twofold greater under the FPU than that under the FAU. Considering the (i) FPU's mean thickness of 0.6 m; (ii) FPU's horizonation into A, B, and C horizons; and (iii) a 70-90% decrease in available water capacity between FPU's A and B horizons, as well as between its B and C horizons, then the total available water capacity throughout this stratum's thickness is 20-87% greater under the FPU than that under the FAU. In addition, the FPU's cemented nature seems to provide a safe stratum that remains stable during floods, sustaining the establishment and growth of deep-rooted perennial vegetation. It is concluded that the FUP's properties have positive implications for vegetation growth and survival under the harsh climatic conditions across the region.

A catenary sequence of soils formed on reworked loess under semiarid climatic conditions was studied. Four soil profiles located on the piedmont of Sierra Chica de Córdoba, central Argentina, were described, classified and geochemically analyzed. All soils, developed on summit, shoulder, backslope, and toeslope positions, were classified as Mollisols. Decarbonatation-carbonatation, melanization, and argilluviation are the main pedogenic processes recognized in these soils, which appear to control the differentiation of genetic horizons along the catena. Different geochemical approaches indicate that there are not substantial variations in the chemical composition of the studied soils along the catena, with the exception of the soil in the toeslope position, which exhibits slightly differences. In general, all profiles show weak depletions of mobile elements (Ca, Na, Mg, Sr, U) in the upper continental crust UCC-normalized diagrams which are attributed to a slight chemical alteration. Other elements, such as Fe, Cr, Co and Ni, also exhibit depletions compared to UCC, which can be explained by the alteration of ferromagnesian silicates, but can also be an inherited feature from the parent material. The significant enrichment in As compared to UCC, evident in all profiles along the catena, is also a typical feature of the pampean plains' loess of Argentina. So, the chemical differences in the profile located on the toeslope are mainly attributed to the supply of materials from local sources, i.e., crystalline basement and sedimentary rocks, due to its position in the catena. Statistical correlations and multivariate cluster analyses reinforce the assumption that the geochemistry of the studied soils is inherited from the parent material. In addition, chemical indices (CIA, ICV), elemental ratios (Ba/Sr, Rb/Sr) and the A-CN-K ternary diagram indicate an incipient degree of chemical alteration for these soils, compatible with the weathering regime prevailing in the region. Thus, the differentiation of genetic horizons along the catena is the result of weak weathering and pedogenic processes, which have not been strong enough to mask the chemical imprint of the parent material.

Factors governing the spatiotemporal soil development on a deglaciated area of Pindari Glacier in the Indian Central Himalaya were investigated over a timespan of 170 years. Glacier retreat exposed sediments to weathering, decarbonation, illuviation, acidification and melanisation. The spatiotemporal scales of soil transformation in this proglacial environment are significantly greater than in other chronosequences in the alpine environment. The accumulation of SOC and N in the oldest moraine is reflected in high accumulation rates of 52.6 g C m-2 year-1 and 4.8 g N m-2 year-1 in the 20-cm deep soil layer. Reference data from the topsoil of the rhododendron woodlands indicate that the oldest moraine topsoil is close to reaching some sort of a steady state. At least 100 years was required to stabilise the soil cover in most of the proglacial area. The results highlight the importance of rapid glacier retreat as well as inhibited weathering due to plant succession in soil formation, under impact of local climate characterized by high precipitation, temperatures and moisture delivery.

The isotopic ratios '3C/1zC and '80/'60 of cellulose from tamarix trees which were used by the Roman army as a groundwork of the siege-rampart of Masada (AD 70-73) were compared with ratios measured in present-day tam&x trees growing in the Masada region and in central Israel. The ancient tamarix cellulose is depicted in both 13C and 180 compared to cellulose from trees growing in the Masada region today. Similar trends were observed on comparing modern tamarix trees growing in the Negev Desert with those growing in the temperate climate of central Israel. Considering the factors that can contribute to the observed changes in isotopic composition, we conclude that the ancient trees enjoyed less arid environmental conditions during their growth compared to contemporary trees in this desert region. This report demonstrates the potential in using combined '*O and 13C analyses of archeological plant material as independent indication of regional climatic change in desert areas (where conventional isotopic analyses, such as in tree rings, are impractical).

Pedogenic (secondary) carbonate is mostly CaCO₃ or calcium carbonate. Pedogenic carbonation occurs when rainwater mixes with carbon dioxide in the atmosphere. Together they form a diluted carbonic acid or H₂CO₃ in the soil. That weak acidic mixture dissolves other minerals in the soil and yields water-soluble calcium carbonate, bicarbonate, and other salts capable of precipitating onto other rocks and minerals when groundwater conditions permit it.

Agricultural terraces are the most widespread archaeological landforms worldwide. Despite their far-reaching
prevalence in many inhabited parts of the world, archaeological soils in terraces (hereafter ‘terrace soils’) are
scarcely studied and their nature is poorly defined. This study aims to depict a space–time framework for the
development of calcareous soils in archaeological stone-wall bench terraces and suggest modifications to their
soil classification and mapping. To do so, we examined soils at the forefront of five terraces in Catalonia (Spain),
that had been previously dated with optically stimulated luminescence to periods from Medieval-Late Middle
Ages (1200 ± 60 CE) to Modern (1810 ± 15 CE). Local soils surrounding the terraces are Entisols and Inceptisols
in the relatively drier areas and Mollisols in the moister areas. Methods applied are field survey, standard
physico-chemical analyses, and soil micromorphology. CaCO3 content, P, OM and CEC show irregularly trending
values throughout the profiles. Micromorphology shows abundant content of charred components throughout
the profiles and slight discontinuous carbonate recrystallization, mostly biogenic. Based on these observations,
the main parent material was determined to be local soil that was redeposited by the workforce as fill material for
terracing. We further interpret that pedogenesis mainly involved structure development under the influence of
anthroturbation and bioturbation, inheritance of ex situ aggregates from parent soil, reaggregation with little
occurrence of organic matter, and low levels of lessivage and CaCO3 redistribution. We found that pedogenesis in
these terraces started in a chaotic manner, considerably faster than pedogenesis in natural soils, primarily
influenced by the act of terracing, the maturity of its inherited parent soil material, and relatively large depth.
Therefore, early stages of terrace soil development can differ greatly from known soil models, questioning
paradigms of pedogenic ‘time zero’ and ‘maturity’ in terrace soil. We suggest four terrace fill settings for terrace
material and propose a model for the state of entropy and development of terrace soils. We classify the studied
soils as Archaeo-Anthroportic Xerorthents, (Anthrosols (Calcaric, Escalic)), and Archaeo-Anthroportic Typic
Haploxerolls (Anthrosols (Calcaric, Escalic, Relocatic, Anthromollic)), both overlying buried Inceptisols (Cambisols). Our primary conclusion is that terrace soils should be separately classified and mapped by treating
terracescapes as distinct morpho-stratigraphic units in which age is the same as the age of their geomorphic
surface. This study advances the pedological understanding of archaeological stone-wall bench terraces and
identifies gaps in the understanding of terrace soils

The dry climate of Israel and the karstic nature of its rocks have always imposed human innovation for utilisation of water resources and agriculture. Large perennial karst springs are available only in the lowlands, but sophisticated water supply systems were built both in the lowland and highland regions. Marl layers interbedded within carbonates give rise to local perched springs and allow terrace construction. Deforestation has taken place for some 4000 years, causing intense soil erosion, but terraces have reduced this impact.

A Bacia de Itaboraí é considerada o primeiro segmento do Rifte Continental do Sudeste do Brasil a se abrir, durante o Paleoceno. Há referências à existência de calcretes na bacia, entretanto, até o momento, não foram realizados estudos específicos sobre os calcretes e sobre sua ocorrência, e ainda há um número reduzido de trabalhos envolvendo a caracterização petrográfica dos depósitos sedimentares da bacia. Apresenta-se aqui uma caracterização, macromorfológica e micromorfológica dos calcretes vadosos que constituem o preenchimento inicial da bacia e que são encontrados nas suas bordas norte e oeste. Foram descritos e interpretados os aspectos composicionais, texturais e de fábrica de 27 seções delgadas preparadas de amostras de calcretes. Os calcretes pedogenéticos mostram diferentes fácies (pulverulento, nodular, maciço, placoso, laminar incipiente e brechado), que foram atribuídas a estágios morfogenéticos distintos. As principais fei- ções micromorfológicas incluem: nódulos, gr...

A Bacia de Itaboraí é considerada o primeiro segmento do Rifte Continental do Sudeste do Brasil a se abrir, durante o Paleoceno. Há referências à existência de calcretes na bacia, entretanto, até o momento, não foram realizados estudos específicos sobre os calcretes e sobre sua ocorrência, e ainda há um número reduzido de trabalhos envolvendo a caracterização petrográfica dos depósitos sedimentares da bacia. Apresenta-se aqui uma caracterização, macromorfológica e micromorfológica dos calcretes vadosos que constituem o preenchimento inicial da bacia e que são encontrados nas suas bordas norte e oeste. Foram descritos e interpretados os aspectos composicionais, texturais e de fábrica de 27 seções delgadas preparadas de amostras de calcretes. Os calcretes pedogenéticos mostram diferentes fácies (pulverulento, nodular, maciço, placoso, laminar incipiente e brechado), que foram atribuídas a estágios morfogenéticos distintos. As principais fei- ções micromorfológicas incluem: nódulos, gr...

Resumo A micromorfologia é uma técnica de estudo de amostras não deformadas de solos e de rochas que permite, com a ajuda de técnicas microscópicas e ultramicroscópicas, identifi car os constituintes elementares e as diversas associações destes (esqueleto, plasma, nódulos, poros), além de permitir precisar suas relações mútuas no espaço e, muitas vezes, no tempo. Para o preparo de uma lâmina é necessário a coleta do material em campo, impregnação com resina para seu endurecimento e a posterior laminação. Com as respectivas lâminas prontas realiza-se a descrição micromorfológica de cada amostra coletada. O presente estudo tem como objetivo contribuir, através da análise micromorfológica, no entendimento das características geológicas e geotécnicas de um perfi l de alteração de um cambissolo. A análise dos dados micromorfológicos permitiu auxiliar o entendimento do sistema de percolação de água nos diversos horizontes estudados. O horizonte C é o destacadamente mais arenoso entre os materiais analisados e a condutividade hidráulica é semelhante ao dos demais horizontes estudados. Pode-se justifi car esse fato pela análise das laminas de micromorfologia, onde se verifi cou que os poros deste horizonte não são conectados, difi cultando a circulação da água livremente. Com isso, pode-se concluir que a micromorfologia pode ser uma ferramenta importante para a compreensão de características geológico-geotécnicas de solos.

A Bacia de Itaboraí é considerada o primeiro segmento do Rifte Continental do Sudeste do Brasil a se abrir, durante o Paleoceno. Há referências à existência de calcretes na bacia, entretanto, até o momento, não foram realizados estudos específicos sobre os calcretes e sobre sua ocorrência, e ainda há um número reduzido de trabalhos envolvendo a caracterização petrográfica dos depósitos sedimentares da bacia. Apresenta-se aqui uma caracterização, macromorfológica e micromorfológica dos calcretes vadosos que constituem o preenchimento inicial da bacia e que são encontrados nas suas bordas norte e oeste. Foram descritos e interpretados os aspectos composicionais, texturais e de fábrica de 27 seções delgadas preparadas de amostras de calcretes. Os calcretes pedogenéticos mostram diferentes fácies (pulverulento, nodular, maciço, placoso, laminar incipiente e brechado), que foram atribuídas a estágios morfogenéticos distintos. As principais fei- ções micromorfológicas incluem: nódulos, gr...

A Bacia de Itaboraí é considerada o primeiro segmento do Rifte Continental do Sudeste do Brasil a se abrir, durante o Paleoceno. Há referências à existência de calcretes na bacia, entretanto, até o momento, não foram realizados estudos específicos sobre os calcretes e sobre sua ocorrência, e ainda há um número reduzido de trabalhos envolvendo a caracterização petrográfica dos depósitos sedimentares da bacia. Apresenta-se aqui uma caracterização, macromorfológica e micromorfológica dos calcretes vadosos que constituem o preenchimento inicial da bacia e que são encontrados nas suas bordas norte e oeste. Foram descritos e interpretados os aspectos composicionais, texturais e de fábrica de 27 seções delgadas preparadas de amostras de calcretes. Os calcretes pedogenéticos mostram diferentes fácies (pulverulento, nodular, maciço, placoso, laminar incipiente e brechado), que foram atribuídas a estágios morfogenéticos distintos. As principais fei- ções micromorfológicas incluem: nódulos, gr...

A Bacia de Itaboraí é considerada o primeiro segmento do Rifte Continental do Sudeste do Brasil a se abrir, durante o Paleoceno. Há referências à existência de calcretes na bacia, entretanto, até o momento, não foram realizados estudos específicos sobre os calcretes e sobre sua ocorrência, e ainda há um número reduzido de trabalhos envolvendo a caracterização petrográfica dos depósitos sedimentares da bacia. Apresenta-se aqui uma caracterização, macromorfológica e micromorfológica dos calcretes vadosos que constituem o preenchimento inicial da bacia e que são encontrados nas suas bordas norte e oeste. Foram descritos e interpretados os aspectos composicionais, texturais e de fábrica de 27 seções delgadas preparadas de amostras de calcretes. Os calcretes pedogenéticos mostram diferentes fácies (pulverulento, nodular, maciço, placoso, laminar incipiente e brechado), que foram atribuídas a estágios morfogenéticos distintos. As principais fei- ções micromorfológicas incluem: nódulos, gr...

A Bacia de Itaboraí é considerada o primeiro segmento do Rifte Continental do Sudeste do Brasil a se abrir, durante o Paleoceno. Há referências à existência de calcretes na bacia, entretanto, até o momento, não foram realizados estudos específicos sobre os calcretes e sobre sua ocorrência, e ainda há um número reduzido de trabalhos envolvendo a caracterização petrográfica dos depósitos sedimentares da bacia. Apresenta-se aqui uma caracterização, macromorfológica e micromorfológica dos calcretes vadosos que constituem o preenchimento inicial da bacia e que são encontrados nas suas bordas norte e oeste. Foram descritos e interpretados os aspectos composicionais, texturais e de fábrica de 27 seções delgadas preparadas de amostras de calcretes. Os calcretes pedogenéticos mostram diferentes fácies (pulverulento, nodular, maciço, placoso, laminar incipiente e brechado), que foram atribuídas a estágios morfogenéticos distintos. As principais fei- ções micromorfológicas incluem: nódulos, gr...

Dealing with the sediment problems associated with floods poses difficult challenges to planners and managers of desert towns. Infrequent but powerful floods from even small catchments generally contain 5-10% of sediment by weight, most of it bed material. As shown by several case studies, corroborated by a simulated flash flood experiment, this sediment is capable of disrupting drainage regulators such as check dams and diversions. Based on the experience of Eilat in southern Israel, and its hyperarid surroundings, several options for dealing with the flooding/sediment hazard are evaluated. Minimal intervention with the dimensions and pathways of the natural drainage system, coupled with effective zoning regulations, should be the preferred choice in protecting desert towns.

The installation of a fully automatic sediment monitoring station in an ephemeral channel allows the bed load and suspended sediment yields of a dryland stream to be assessed independently using measurements of bed load discharge and suspended sediment concentration obtained during flash floods. The suspended sediment yield of 433 t km"2 year"1 is relatively high, even by global standards. The bed load yield (391 km"2 year"1) is also high but it represents, nevertheless, only 8% of the total sediment yield of 472 t km"2 year"1. The balance between the bed load and suspended load reflects the specific environmental characteristics of the drainage basin. In particular, given that the floods are generated almost entirely by overland flow, the high suspended sediment yield indicates a substantial wash load that results from the plentiful supply of fine material on the sparsely vegetated slopes of the water catchment.

Within the hyper-arid to semiarid areas of Israel three experimental drainage basins varying in area, climate, monitoring duration and type have been being research-monitored. Lessons derived from a large number of published and ongoing research projects on these experimental basins focus on runoff and sediment in drylands. The effect of the spatial distribution of rainfall on runoff generation becomes increasingly important with aridity. Rainfall angle on hillslopes and storm intensity and direction derived from rainfall recorders and radar backscatter are crucial for explanation of runoff response. Runoff hydrographs have more bores, shorter-duration peaks, briefer recessions, longer dry periods, and are more variable in flood volume and flood peaks with increased aridity. Suspended-sediment fluxes, yields and concentrations are high in the semiarid realm, reaching maxima at the beginning of a flood season and after long, dry spells. Bedload fluxes are exceptionally high from dryl...

Within the hyper-arid to semiarid areas of Israel three experimental drainage basins varying in area, climate, monitoring duration and type have been being research-monitored. Lessons derived from a large number of published and ongoing research projects on these experimental basins focus on runoff and sediment in drylands. The effect of the spatial distribution of rainfall on runoff generation becomes increasingly important with aridity. Rainfall angle on hillslopes and storm intensity and direction derived from rainfall recorders and radar backscatter are crucial for explanation of runoff response. Runoff hydrographs have more bores, shorter-duration peaks, briefer recessions, longer dry periods, and are more variable in flood volume and flood peaks with increased aridity. Suspended-sediment fluxes, yields and concentrations are high in the semiarid realm, reaching maxima at the beginning of a flood season and after long, dry spells. Bedload fluxes are exceptionally high from dryland basins where hillslopes are minimally vegetated and where bedload transport takes place in channels lacking an armor layer. The bedload/ suspended-sediment load ratio increases with aridity and may rise to 70%. The depth of channel bed activity is indicated by a fluvio-pedogenic unit. Hillslope to channel connectivity is high in drylands. In the hyperarid region the finer suspended-sediment is derived from hillslopes while the sandy fraction derives from the channel bed.

Pedogenic features considered to be produced by subsurface flow were observed on the hillslopes of a zero-order basin in the Judean desert where the mean annual rainfall is 230 mm. The basin, some 5000 m' in area, is composed of soft chalk covered by soil material, with slope gradients ranging from 30-60 per cent. A comparison of carbonate, gypsum, and soluble salts distribution within the soil, and also their characteristics in this study area, to the same variables in other arid environments, allows one to determine and analyse pedogenic indicators of subsurface flow. In particular gypsic crusts, which exhibit specific characteristics not observed in other areas where pedogenic features are controlled by vertical limited leaching, highlight the existence of lateral subsurface flow. The spatial distribution of these pedogenic indicators within the basin and in the soil was analysed in terms of soil water regime, soil thickness, and the permeability of the soil and bedrock.

Factors governing the spatiotemporal soil development on a deglaciated area of Pindari Glacier in the Indian Central Himalaya were investigated over a timespan of 170 years. Glacier retreat exposed sediments to weathering, decarbonation, illuviation, acidification and melanisation. The spatiotemporal scales of soil transformation in this proglacial environment are significantly greater than in other chronosequences in the alpine environment. The accumulation of SOC and N in the oldest moraine is reflected in high accumulation rates of 52.6 g C m-2 year-1 and 4.8 g N m-2 year-1 in the 20-cm deep soil layer. Reference data from the topsoil of the rhododendron woodlands indicate that the oldest moraine topsoil is close to reaching some sort of a steady state. At least 100 years was required to stabilise the soil cover in most of the proglacial area. The results highlight the importance of rapid glacier retreat as well as inhibited weathering due to plant succession in soil formation, under impact of local climate characterized by high precipitation, temperatures and moisture delivery.

Resumo - A Bacia de Itaboraí é considerada o primeiro segmento do Rifte Continental do Sudeste do Brasil a se abrir, durante o Paleoceno. Há referências à existência de calcretes na bacia, entretanto, até o momento, não foram realizados estudos específicos sobre os calcretes e sobre sua ocorrência, e ainda há um número reduzido de trabalhos envolvendo a caracterização petrográfica dos depósitos sedimentares da bacia. Apresenta-se aqui uma caracterização, macromorfológica e micromorfológica dos calcretes vadosos que constituem o preenchimento inicial da bacia e que são encontrados nas suas bordas norte e oeste. Foram descritos e interpretados os aspectos composicionais, texturais e de fábrica de 27 seções delgadas preparadas de amostras de calcretes. Os calcretes pedogenéticos mostram diferentes fácies (pulverulento, nodular, maciço, placoso, laminar incipiente e brechado), que foram atribuídas a estágios morfogenéticos distintos. As principais feições micromorfológicas incluem: nódu...

Pedogenic features considered to be produced by subsurface flow were observed on the hillslopes of a zero-order basin in the Judean desert where the mean annual rainfall is 230 mm. The basin, some 5000 m' in area, is composed of soft chalk covered by soil material, with slope gradients ranging from 30-60 per cent. A comparison of carbonate, gypsum, and soluble salts distribution within the soil, and also their characteristics in this study area, to the same variables in other arid environments, allows one to determine and analyse pedogenic indicators of subsurface flow. In particular gypsic crusts, which exhibit specific characteristics not observed in other areas where pedogenic features are controlled by vertical limited leaching, highlight the existence of lateral subsurface flow. The spatial distribution of these pedogenic indicators within the basin and in the soil was analysed in terms of soil water regime, soil thickness, and the permeability of the soil and bedrock.

Arid regions are expected to undergo significant changes under a scenario of climate warming, but there is considerable variability and uncertainty in these estimates between different scenarios. The complexities of precipitation changes, vegetation-climate feedbacks and direct physiological effects of CO 2 on vegetation present particular challenges for climate change modelling of arid regions. Great uncertainties exist in the prediction of arid ecosystem responses to elevated CO 2 and global warming. Palaeodata provide important information about the past frequency, intensity and subregional patterns of change in the world's deserts that cannot always be captured by the climatic models. However, it is important to bear in mind that the global mechanisms of Quaternary climatic variability were different from present-day trends, and any direct analogies between the past and present should be treated with great caution. Although palaeodata provide valuable information about possible past changes in the vegetation-climate system, it is unlikely that the history of the world's deserts is a key for their future.

Advanced techniques were applied to determine the spatial distributed parameter values of a non-calibrated rainfall-runoff model in a large arid catchment. Channel dimensions and infiltration characteristics were determined by air-photo analysis and verified by careful fieldwork. A GPS device was used for positioning during field surveys and channel transmission losses were studied by artificial tracers. During one high intensity event (October 1991) rainfall radar yielded the spatial pattern of rainfall intensities, while during another (October 1979) the input rainfall was traced back by the model using a physically-based description of convective arid rainfall. Due to its physical basis, the model could combine different sources of information: basin characteristics determined by field surveys and remote sensing, results of existing experiments, and general scientific experience. Compared with calibrated conceptual models, this resulted in a higher flexibility facilitating applications to basins or events with poor data records, urgently needed for many parts of the arid zone.

Stratigraphic studies conducted on the alluvial fill of several ephemeral stream channels in the southern Arava Valley, Dead Sea Rift, indicate the existence of a calcic 'soil' developed 50-100 cm beneath the channel surfaces. This anomalous calcic 'soil' does not fall within the categories of any standard soil or paleosol definition and thus has been termed ''Fluvial Pedogenic Unit'' (FPU). The FPU occurs at the lower limit of the contemporary scour-and-fill processes in the aerated zone and it defines the maximum scour-and-fill during floods. The FPU is also found in late Pleistocene and Holocene terraces, termed paleo-FPU, indicating that the hydrological regime of past floods was similar to the present one.

There is no major chemical variation in the late Quaternary calcic nodules formed within vertisols in the foot-hill regions, and hardpan calcretes (greater than 200 ka) formed over the Precambrian substrate that occur as duricrust horizons in the plains around Coimbatore region, Tamil Nadu, India. The bulk chemistry of calcic nodules and the hardpan calcretes show very little variability in CaO, SiO 2 , Al 2 O 3 and Fe 2 O 3 content. The trend of trace metal content in calcic nodules and in the hardpan calcrete is Mn > Zn > Ni > Cr > Pb > Co > Cu and Zn > Mn > Ni > Co > Pb > Cu > Cr respectively. PAAS-normalised REE data of the calcretes (calcic nodules and the hardpan) demonstrate a positive Euanomaly. This could be attributed to feldspar, apatite mineral alteration and soil digenetic processes, differential weathering leaving behind plagioclase phenocrysts and apatite grains which are enriched in Eu. The stable isotope values of the calcic nodules do not exhibit a wide range (d 18 O À3.39 to À5.84& and d 13 C À3.01 to À6.64&), compared to the hardpan calcretes (d 18 O À2.91 to À12.98&) and d 13 C (À0.05 to À7.4&). The palaeoenvironment during the formation of the calcretes nodules was dominated by the C4 plants with sparse vegetation cover and that the parent material/bedrock supported a thin veneer of soil column with sparse vegetation cover as present day. Calcic nodule accumulations in the soils has resulted from differential weathering and chemical histories within the soil profiles while the hardpan calcretes formed by complex pedogenic and chemical e groundwater processes in arid e semi-arid conditions over along geological period. During the late MIS3 to the LGM period the south west monsoon was weak with mean annual rainfall (MAR) between 300 and 500 mm/yr, the sea level was low and the rainfall at the time of carbonate formation would have remained damp enough to allow silicate weathering of the soil sediments.

There is no major chemical variation in the late Quaternary calcic nodules formed within vertisols in the foot-hill regions, and hardpan calcretes (greater than 200 ka) formed over the Precambrian substrate that occur as duricrust horizons in the plains around Coimbatore region, Tamil Nadu, India. The bulk chemistry of calcic nodules and the hardpan calcretes show very little variability in CaO, SiO 2 , Al 2 O 3 and Fe 2 O 3 content. The trend of trace metal content in calcic nodules and in the hardpan calcrete is Mn > Zn > Ni > Cr > Pb > Co > Cu and Zn > Mn > Ni > Co > Pb > Cu > Cr respectively. PAAS-normalised REE data of the calcretes (calcic nodules and the hardpan) demonstrate a positive Euanomaly. This could be attributed to feldspar, apatite mineral alteration and soil digenetic processes, differential weathering leaving behind plagioclase phenocrysts and apatite grains which are enriched in Eu. The stable isotope values of the calcic nodules do not exhibit a wide range (d 18 O À3.39 to À5.84& and d 13 C À3.01 to À6.64&), compared to the hardpan calcretes (d 18 O À2.91 to À12.98&) and d 13 C (À0.05 to À7.4&). The palaeoenvironment during the formation of the calcretes nodules was dominated by the C4 plants with sparse vegetation cover and that the parent material/bedrock supported a thin veneer of soil column with sparse vegetation cover as present day. Calcic nodule accumulations in the soils has resulted from differential weathering and chemical histories within the soil profiles while the hardpan calcretes formed by complex pedogenic and chemical e groundwater processes in arid e semi-arid conditions over along geological period. During the late MIS3 to the LGM period the south west monsoon was weak with mean annual rainfall (MAR) between 300 and 500 mm/yr, the sea level was low and the rainfall at the time of carbonate formation would have remained damp enough to allow silicate weathering of the soil sediments.

Resumo - A Bacia de Itaboraí é considerada o primeiro segmento do Rifte Continental do Sudeste do Brasil a se abrir, durante o Paleoceno. Há referências à existência de calcretes na bacia, entretanto, até o momento, não foram realizados estudos específicos sobre os calcretes e sobre sua ocorrência, e ainda há um número reduzido de trabalhos envolvendo a caracterização petrográfica dos depósitos sedimentares da bacia. Apresenta-se aqui uma caracterização, macromorfológica e micromorfológica dos calcretes vadosos que constituem o preenchimento inicial da bacia e que são encontrados nas suas bordas norte e oeste. Foram descritos e interpretados os aspectos composicionais, texturais e de fábrica de 27 seções delgadas preparadas de amostras de calcretes. Os calcretes pedogenéticos mostram diferentes fácies (pulverulento, nodular, maciço, placoso, laminar incipiente e brechado), que foram atribuídas a estágios morfogenéticos distintos. As principais feições micromorfológicas incluem: nódulos, gretas de contração, rizólitos, argilas infiltradas, grãos corroídos e fraturados, micas expandidas, e agregados argilosos. Os calcretes pedogenéticos se desenvolveram em depósitos aluviais intemperizados, em períodos de estabilidade tectônica e são característicos de ambientes continentais áridos a semiáridos. Ocorrem intercalados a travertinos, crostas carbonáticas de origem hidrotermal, cuja deposição é condicionada pela movimentação de falhas ativas e favorecida em períodos de clima úmido. Os resultados indicam que processos pedogenéticos e hidrotermais foram extremamente atuantes durante o início do preenchimento da Bacia de Itaboraí, e sua caracterização é importante para a compreensão da evolução inicial do Rift Continental do Sudeste do Brasil.
Palavras-chave: carbonatos terrestres, fácies pedogenéticas, pedogênese, micromorfologia.
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Abstract - Pedogenetic calcretes from the Itaboraí Basin, Rio de Janeiro State, Brasil. The Itaboraí Basin, located in Rio de Janeiro State, Brazil, is considered the first segment from the Southeastern Brazil Continental Rift opened, during the Paleocene. The occurrence of calcretes was previously reported in the literature, although studies dealing specifically with such calcretes and their distribution were not performed. Furthermore, there is limited research involving the petrographic characterization of the sedimentary deposits of the basin. This study developed a characterization on both macro and micro scale of the vadose calcretes that occur along the northern and western margins of the basin and constitute its initial infilling. The compositional, textural and fabric features of 27 thin sections prepared from calcrete samples were described and interpreted. The pedogenetic calcretes were separated in different facies (chalky, nodular, massive, platy, incipient laminar and brecciated), and classified according to morphogenetic stages. The main microscopic features include nodules, contraction cracks, vadose pisoliths, rhizocretions, infiltrated clays, corroded grains, expanded micas and clay aggregates. The pedogenetic calcretes were developed on weathered alluvial deposits during tectonic stability periods. They are typically generated on continental environments under arid to semiarid climates and occur intercalated with travertines (carbonate crusts of hydrothermal origin), which deposition is favored by fault activity during humid climate periods. The results indicate both pedogenetic and hydrothermal processes have been extremely active and have played important role during the early evolution of Itaboraí Basin. Thus, the characterization of such processes is essential to the understanding of the initial evolution of Southeastern Brazil Continental Rift.
Keywords: terrestrial carbonates, pedogenetic facies, pedogenesis, micromorphology.

The hydrodynamic characteristics af tne Lower Esino Basin have been studied with typical hydrogeological methods which al10w the recognition cf che main elements (gro:undwater f10\ol, water types, etc.). Grounduater belongs to che calcium-bicarbonate, bicarbonate-calcium types, sometimes enriched with Na, Cl, Hg, 504 and chiaride sodium and calclum-chloridesodium waters. The aquifer 19 situated in an area which has been subject to recent tectanie movements that a1so affect the alluvial deposits. The fracture network has been identified Erom 'geomorphologic analysis that a150 shows some paleothalwegs corresponding to the main groundwater flow. The main faults correspond to areas where bicarbonate calcium water strongly enriched with Cl, Hg, Na and 504 and chloride sodium and calcium-sodium waters are presento The chemlcal characteristics do not correspond to particular rock types and demonstrate thae these waters come Erom Lower Pliocene sandstone saturated with fossil salt water.

The isotopic ratios '3C/1zC and '80/'60 of cellulose from tamarix trees which were used by the Roman army as a groundwork of the siege-rampart of Masada (AD 70-73) were compared with ratios measured in present-day tam&x trees growing in the Masada region and in central Israel. The ancient tamarix cellulose is depicted in both 13C and 180 compared to cellulose from trees growing in the Masada region today. Similar trends were observed on comparing modern tamarix trees growing in the Negev Desert with those growing in the temperate climate of central Israel. Considering the factors that can contribute to the observed changes in isotopic composition, we conclude that the ancient trees enjoyed less arid environmental conditions during their growth compared to contemporary trees in this desert region. This report demonstrates the potential in using combined '*O and 13C analyses of archeological plant material as independent indication of regional climatic change in desert areas (where conventional isotopic analyses, such as in tree rings, are impractical). DENIRO M. J. and EPSTEIN S. (I 979) Relationship between the oxygen isotope ratios of terrestrial plant cellulose, carbon dioxide, and water. Seienee 204, 5 l-53. EDWARDS T. W. D. and BUHAY W. M. (1994) Paleoclimatic significance of oxygen and hydrogen isotope correlation in tree rings. Paleogeogr. Paleoclimatol. Paleoecol. (in press). EDWARDS T. W. D. and FRITZ P. ( 1986) Assessing meteoric water composition and relative humidity form '*O and %I in wood cellulose: paleoclimatic implications for southern Ontario, Canada. Appl. Geochem. 1, 715-723.

An unusual 240 mm rainstorm and consequent major flood (peak discharge 110 m3s-1) with an estimated recurrence interval of about 50 years occurred on Dec. 31, 1998 in Nahal Me'arot, an ungauged 25 km2 coastal ephemeral stream in Mt. Carmel, NW Israel. The flood caused morphological modifications along the channel, including intensive stripping of the channel bed and floodplain along several segments and deposition of large gravel bars downstream of these segments. One of such segments served as a study reach; composed of a massive, coarse, 200 m long gravel-bar formed downstream of a segment (150 m long) that was deeply scoured. The bar’s stratigraphy consisted of a very coarse gravel lag, well sorted on the surface overlying much finer sediment characterized by sandy layers mixed with gravel among different types of facies. The difference between its volume and the scoured reach upstream was only 20% (1270 m3 compared to 1010 m3) signifying that scour and aggradation occurred i...

The impact of large twentieth century floods on the riparian vegetation and channel morphology of the relatively wide anabranching and braided Nahal Arava, southern Israel, was documented as part of developing tools to (a) identify recent large floods, (b) determine these flood's respective magnitudes in alluvial ungauged streams, and (c) determine long-term upper bounds to flood stages and magnitudes. Along most of its course Nahal Paran, a major tributary that impacts the morphology, floods and sediments of Nahal Arava at the study reach, is a coarse-gravel, braided ephemeral stream. Downstream of the Arava-Paran confluence, aeolian and fluvial sand delivered from eastern Arava valley alters the channel morphology. The sand has accreted up to 2.5 m above the distinct current channels, facilitating the recording of large floods. This sand enhances the establishment of denser riparian vegetation (mainly Tamarix nilotica and Haloxylon persicum) that interacts with floods and affects stream morphology. A temporal association was found between specific floods recorded upstream and tree-ring ages of re-growth of flooddamaged tamarix trees ('Sigafoos trees') in the past 30 years. This association can be utilized for developing a twentieth century flood chronology in hyperarid ungauged basins in the region. The minimum magnitude of the largest flood that covered the entire channel width, estimated from flood deposits, is approximately 1700-1800 m 3 s − 1 . This is a larger magnitude than the largest gauged flood of 1150 m 3 s − 1 that occurred in 1970 about 30 km upstream in Nahal Paran. Our estimation agrees with flood magnitude estimated from the regional envelope curve of the largest floods. Based on Holocene alluvial stratigraphy and OSL dating in the study reach we also conclude that flood stages did not reach the late Holocene (∼ 2.2 ka) surface and therefore we estimate a non-exceedance upper bound of ∼ 2000 m 3 s − 1 flood magnitudes for Nahal Arava during that interval. This study Available online at www.sciencedirect.com Geomorphology 95 274 -294 www.elsevier.com/locate/geomorph ⁎ Corresponding author. Tel.: +972 2 6584210; fax: +972 2 5662581.

Schick proposed a conceptual model for the geomorphic response to Pleistocene to Holocene climate change, based on the hyperarid Nahal Yael watershed in the southern Negev Desert. In this model, the change from semiarid late Pleistocene to hyperarid early Holo cene climates reduced vegetation cover, increased the yield of sediment from slopes, and accelerated aggradation of terraces and alluvial fans. The model is now over 30 yr old, and during this time, chronologic, paleoenvironmental, and hydrogeomorphic research has advanced. Here, we reevaluate the model using data acquired in Nahal Yael over the 30 yr since the original model was proposed. Recent studies indicate that the late Pleistocene climate was hyperarid, and a transition from semiarid to hyperarid climates did not occur. The revised chronology reveals a major 35-20 ka episode of accelerated late Pleistocene sediment production on slopes (with lower rates probably already at ca. 50 ka) due to increased frequency of wetting-drying cycles caused by frequent extreme storms and fl oods between 35 and 27 ka. Without lag time, these sediments were transported and aggraded in depositional landscape components (fl uvial terraces and alluvial fans). This intensifi ed sediment production and delivery phase is unrelated to the Pleistocene-Holocene transition. The depositional landforms were rapidly incised between 20 and 18 ka. Since and/or soon after this Last Glacial Maximum (LGM) incision, most material leaving the basin originated from sediments stored in depositional landforms and was not produced from bedrock.

The isotopic ratios '3C/1zC and '80/'60 of cellulose from tamarix trees which were used by the Roman army as a groundwork of the siege-rampart of Masada (AD 70-73) were compared with ratios measured in present-day tam&x trees growing in the Masada region and in central Israel. The ancient tamarix cellulose is depicted in both 13C and 180 compared to cellulose from trees growing in the Masada region today. Similar trends were observed on comparing modern tamarix trees growing in the Negev Desert with those growing in the temperate climate of central Israel. Considering the factors that can contribute to the observed changes in isotopic composition, we conclude that the ancient trees enjoyed less arid environmental conditions during their growth compared to contemporary trees in this desert region. This report demonstrates the potential in using combined '*O and 13C analyses of archeological plant material as independent indication of regional climatic change in desert areas (where conventional isotopic analyses, such as in tree rings, are impractical). DENIRO M. J. and EPSTEIN S. (I 979) Relationship between the oxygen isotope ratios of terrestrial plant cellulose, carbon dioxide, and water. Seienee 204, 5 l-53. EDWARDS T. W. D. and BUHAY W. M. (1994) Paleoclimatic significance of oxygen and hydrogen isotope correlation in tree rings. Paleogeogr. Paleoclimatol. Paleoecol. (in press). EDWARDS T. W. D. and FRITZ P. ( 1986) Assessing meteoric water composition and relative humidity form '*O and %I in wood cellulose: paleoclimatic implications for southern Ontario, Canada. Appl. Geochem. 1, 715-723.