SUMMARYPeatlands are soil environments that store carbon and large amounts of water, due to their composition (90 % water), low hydraulic conductivity and a spongelike behavior. It is estimated that peat bogs cover approximately 4.2 % of the Earth's surface and stock 28.4 % of the soil carbon of the planet. Approximately 612 000 ha of peatlands have been mapped in Brazil, but the peat bogs in the Serra do Espinhaço Meridional (SdEM) were not included. The objective of this study was to map the peat bogs of the northern part of the SdEM and estimate the organic matter pools and water volume they stock. The peat bogs were pre-identified and mapped by GIS and remote sensing techniques, using ArcGIS 9.3, ENVI 4.5 and GPS Track Maker Pro software and the maps validated in the field. Six peat bogs were mapped in detail (1:20,000 and 1:5,000) by transects spaced 100 m and each transect were determined every 20 m, the UTM (Universal Transverse Mercator) coordinates, depth and samples collected for characterization and determination of organic matter, according to the Brazilian System of Soil Classification. In the northern part of SdEM, 14,287.55 ha of peatlands were mapped, distributed over 1,180,109 ha, representing 1.

The Upper Cretaceous Bauru Group in south‐east Brazil consists of alluvial strata whose characteristics and distribution indicate a fluvial system developed in a semi‐arid to arid climate. Sections exposed within a 90 000 km2 study area in Minas Gerais State (in south‐eastern Brazil) were evaluated using facies and palaeosol analysis to formulate depositional and pedogenic models that may account for geomorphic and climate features. From east to west, the study succession records a gradual decrease in grain size, an increase in the width/thickness ratio in channels, a decrease in the lateral and vertical connectivity of channel deposits, and an increase in overbank deposits. The fluvial architecture indicates a braided channel belt, ephemeral ribbon–channels, and an unconfined fluvial facies from east to west in the study area. The lateral and vertical distribution of facies, stratigraphic architecture and palaeocurrent data suggest proximal, medial and distal portions of a progradational distributive fluvial system. The sedimentary dynamics were marked by the building and abandonment of channels related to processes of aggradation, vegetation growth and palaeosol generation. Macromorphological and micromorphological analyses have identified pedological and mineralogical features that indicate an arid to semi‐arid climate with a provenance from the north‐eastern part of the basin (Alto Paranaiba Uplift). From the proximal to the distal portions of the distributive fluvial system, the palaeosol development is different. In the proximal portion, the palaeosols are absent or poorly developed, allowing a possible general comparison with the present soil order: Inceptisols and Aridisols. In the medial portion of the fluvial system, the palaeosols are well‐developed and characterized by Bt, Btk, C and Ck horizons (Alfisols, Aridisols, Inceptisols and Entisols). Poorly drained to well‐drained palaeosols from the base to the top in the distal plain (Aridisols and Inceptisols) are associated with geomorphic and hydromorphic changes in the fluvial system due to progradational evolution. The genetic relationship between the fluvial architecture and the palaeosols enhances the understanding that the sedimentation and pedogenesis that occurs in different portions of the distributive fluvial system are related to the tectonic and climatic evolution of the basin.

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Disponível on-line no endereço www.igc.usp.br/geologiausp -273 -Resumo O aquífero associado à Formação Alter do Chão (FAC) -subsistema aquífero Alter do Chão (AAC) -é o mais conhecido da região amazônica. Estudos recentes indicam sua possível conexão com o subsistema aquífero cretáceo Tikuna, que possui continuidade por todas as bacias amazônicas, ambos integrando o grande Sistema Aquífero Amazônico (SAA). O objetivo do presente trabalho foi o aperfeiçoamento do modelo conceitual de funcionamento do AAC a oeste de Manaus. A metodologia incluiu medidas do nível d'água, de parâmetros físico-químicos in situ em poços e amostragem para análises químicas e isotópicas das águas subterrâneas. Realizou-se o levantamento das características geológicas e limites do aquífero, baseado em dados de poços de petróleo e de abastecimento de água existentes. Os resultados revelaram que as águas do AAC a oeste de Manaus possuem duas origens principais: 1) origem meteórica, pouco mineralizadas, situadas nas camadas aquíferas superiores, em um sistema livre, com recarga local; 2) origem remota, mais mineralizadas, com maior tempo de residência no aquífero, armazenadas nas camadas mais profundas em um sistema provavelmente confinado, originadas possivelmente em áreas de recarga do bordo oeste do SAA. As análises isotópicas calibradas sugerem uma idade média de 21.380 anos para águas subterrâneas mais mineralizadas e profundas dos municípios de Manacapuru e Careiro. Essa água é, provavelmente, resultado de uma mescla de águas mais antigas com águas de recarga mais recente. Por conta dessa diferenciação hidrogeoquímica, correlacionada com a geologia local, o AAC foi subdividido em uma porção superior, livre e menos mineralizada, e outra inferior, mais antiga e mineralizada, ambas misturadas a leste do Arco de Purus, com progressiva diluição pela chuva.Palavras-chave: Aquífero Alter do Chão; Hidrogeologia; Hidrogeoquímica; Região Metropolitana de Manaus. AbstractThe aquifer associated with the Alter do Chão Formation (ACF) -Alter do Chão Aquifer subsystem (ACA) -is the best known in the Amazon region. Recent studies have indicated its possible connection with the Cretaceous Tikuna Subsystem, which is continuous throughout the Amazon basins, both parts of the great Amazon Aquifer System (AAS). The aim of the article was to generate new insights on the ACA functioning, in the west of Manaus. The methodology included measurements of water level and in situ physical-chemical parameters in wells, along with groundwater sampling for chemical and isotopic analysis. Geological characteristics and aquifer boundaries were estimated with data from existing oil and water wells. Results show that ACA waters in western Manaus have two main origins: 1) meteoric origin, with poorly mineralized waters, situated in the upper aquifer layers in an unconfined system with local recharge; 2) remote origin, more mineralized, with longer residence time in the aquifer, stored in the deeper layers, probably in a confined system. Its origin is presumably in the rec...