José Tasso Felix Guimarães

Mid- and late-Holocene sedimentary process and palaeovegetation changes near the mouth of the Amazon River

The integration of sedimentary facies, pollen, spores, carbon and nitrogen isotopes records, C/N ratio and radiocarbon dates allowed the identification of changes in vegetation and the sources of organic matter accumulated on tidal flats near the mouth of the Amazon River during the mid and late Holocene. Data from the margin of Amazon River indicate marine influence related to mangrove presence over a tidal mud flat between 5560–5470 cal. yr BP and 5290–5150 cal. yr BP. Afterward, the mangrove area shrank following the return of more humid conditions and increase of Amazon River discharge. A common reworking process of the tidal flat through the lateral migration of a meandering creek occurred in the study site, with later development of transitional vegetation under freshwater influence. Following the natural vegetation succession under stable climate and hydrological conditions, the expansion of ‘várzea’ (flooded freshwater vegetation) forests occurred since 600–560 cal. yr BP until the present. Furthermore, regarding the tidal flats located west of the mouth of Amazon River, these stable conditions also allowed the mangrove maintenance over mudflats with deposition of marine organic matter during at least the last 2350–2300 cal. yr BP.

Four decades of land-cover, land-use and hydroclimatology changes in the Itacaiúnas River watershed, southeastern Amazon

Long-term human-induced impacts have significantly changed the Amazonian landscape. The most dramatic land cover and land use (LCLU) changes began in the early 1970s with the establishment of the Trans-Amazon Highway and large government projects associated with the expansion of agricultural settlement and cattle ranching, which cleared significant tropical forest cover in the areas of new and accelerated human development. Taking the changes in the LCLU over the past four decades as a basis, this study aims to determine the consequences of land cover (forest and savanna) and land use (pasturelands, mining and urban) changes on the hydroclimatology of the Itacaiúnas River watershed area of the located in the southeastern Amazon region. We analyzed a multi-decadal Landsat dataset from 1973, 1984, 1994, 2004 and 2013 and a 40-yr time series of water discharge from the Itacaiúnas River, as well as air temperature and relative humidity data over this drainage area for the same period. We employed standard Landsat image processing techniques in conjunction with a geographic object-based image analysis and multi-resolution classification approach. With the goal of detecting possible long-term trends, non-parametric Mann-Kendall test was applied, based on a Sen slope estimator on a 40-yr annual PREC, TMED and RH time series, considering the spatial average of the entire watershed. In the 1970s, the region was entirely covered by forest (99%) and savanna (∼0.3%). Four decades later, only ∼48% of the tropical forest remains, while pasturelands occupy approximately 50% of the watershed area. Moreover, in protected areas, nearly 97% of the tropical forest remains conserved, while the forest cover of non-protected areas is quite fragmented and, consequently, unevenly distributed, covering an area of only 30%. Based on observational data analysis, there is evidence that the conversion of forest cover to extensive and homogeneous pasturelands was accompanied by systematic modifications to the hydroclimatology cycle of the Itacaiúnas watershed, thus highlighting drier environmental conditions due to a rise in the regions air temperature, a decrease in the relative humidity, and an increase in river discharge.

Model of wetland development of the Amapá coast during the late Holocene

Os tipos de vegetacao atual, sequencias sedimentares, dados de polen e datacoes por radiocarbono obtidas em tres testemunhos de sedimento da planicie costeira de Calcoene foram utilizados para estabelecer uma historia paleoecologica durante o Holoceno superior das zonas umidas costeiras do Amapa conforme as mudancas no regime de inundacao, nivel do mar e clima. Baseado nestes tres registros, quatro fases de desenvolvimento da vegetacao sao apresentadas e provavelmente refletem a interacao entre o fluxo de energia na acumulacao do sedimento e a influencia das aguas salobras e doces na vegetacao. Este trabalho sugere alternâncias entre periodos caracterizados por influencias marinha e fluvial. O perfil longitudinal nao revelou a ocorrencia de manguezais nos sedimentos depositados por volta de 2100 anos A.P. Durante a segunda fase, a lama preencheu progressivamente as depressoes e canais de mare. Provavelmente, os manguezais iniciaram seu desenvolvimento nas margens dos canais, e os campos herbaceos nos setores elevados. A terceira fase e caracterizada por uma interrupcao no desenvolvimento dos manguezais e a expansao da vegetacao de varzea devido a uma diminuicao na influencia das aguas marinhas. A ultima fase e representada pela expansao de manguezais e varzeas. A correlacao entre os padroes atuais de distribuicao das unidades geobotânicas e a paleovegetacao indica que os manguezais e as florestas de varzea estao migrando sobre os campos herbaceos nos setores topograficamente mais elevados do litoral em estudo, o que pode estar relacionado a um aumento do nivel relativo do mar.

Morphological and vegetation changes on tidal flats of the Amazon Coast during the last 5000 cal. yr BP

The analysis of morphology, sedimentary facies, palynology, carbon and nitrogen isotopes, C/N ratio and radiocarbon data from tidal flats sediments influenced by the Amazon River indicates that vegetation development during the last 5000 cal. yr BP was controlled by morphological changes associated with marine and fluvial process. The proximal portion of the tidal flat corresponds to abandoned channels surrounded by terrestrial vegetation since 5280–5160 cal. yr BP. During the last 2840–2750 cal. yr BP, autochthonous organic material became prevalent as well as the increase in contribution of terrestrial organic matter mainly from ‘várzea’ vegetation. Herbaceous plants already colonized the tidal flat before 3170–2970 cal. yr BP, and after 2630–2310 cal. yr BP and 1350–1290 cal. yr BP they were replaced by mangrove vegetation following the development of secondary channels connected to the sea with brackish water influence. Furthermore, the erosion of the herbaceous field to form chenier ridges/tidal mixed flat after 3170–2970 cal. yr BP and before 220–140 cal. yr BP in the distal portion of the tidal flat suggests an overall interpretation of a retrogradation cycle. This process was driven by a relative sea-level rise influenced by the increase of Amazon discharge during the late Holocene.

PALYNOLOGY OF THE MIDDLE MIOCENE–PLIOCENE NOVO REMANSO FORMATION, CENTRAL AMAZONIA, BRAZIL

Abstract. In order to reassess and amend previously published palynological data drawn from the Novo Remanso Formation, central Amazonia, we revisited the organic-rich samples from their work using systematic and quantitative biostratigraphic analyses, with possible implications in the biodiversity and paleoecological studies of Late Neogene deposits of Amazonia. In the study area, the Novo Remanso Formation is characterized by sandstones and mudstones deposited in a meandering river environment. The palynological assemblage comprises 46 morphotypes, including 21 species of pollen and 25 species of spores. Polypodiisporites usmensis, Retitrescolpites? irregularis and Mauritiidites franciscoi var. franciscoi, typical of lowland freshwater forests and shallow water lakes dominate the assemblage. Also, lower frequencies of Grimsdalea magnaclavata co-occur with Psilatricolporites crassoexinatus, Proteacidites triangulatus, Bombacacidites simpliciriloensis, Pteridaceoisporis gemmatus and Cingulatisporites laevigatus. Based on quantitative biostratigraphic techniques, the Novo Remanso Formation Is assigned a middle Miocene—Pliocene age In our study area. The presence of Elaterosporites klaszii (Albian-Cenomanian) In the Novo Remanso deposits strongly indicates Cretaceous rocks in the source-area, whereas absence of Andine palynomorphs may be indicative of a nearby source area for the deposits during the deposition of the Novo Remanso Formation.

Fossil Fungi from Miocene Sedimentary Rocks of the Central and Coastal Amazon Region, North Brazil

Abstract Samples from outcrops of the Miocene Solimões and Barreiras formations from the central and coastal Amazon regions of Brazil were analyzed palynologically. Assemblages of fossil fungi were identified, and are described herein, and their relevance to paleoenvironmental and paleoclimatic studies in tropical regions discussed. The fungal assemblage comprises four spore groups, 19 species belonging to 12 genera. Additionally, two new species are proposed. The samples from the Solimões Formation contain the following taxa: Mediaverrunites elsikii, Mediaverrunites mulleri, Monoporisporites sp., Fusiformisporites crabbii, and Multicellites cingulatus. The presence of these suggests river channel margins colonized by freshwater vegetation, where seasonal fluctuations of water table and rainfall produce wetter substrates. The samples from the Barreiras Formation showed higher species and generic diversity than those from the Solimões Formation with Hypoxylonites minutus, Hypoxylonsporites ater, Hypoxylonites sp., the new species Inapertisporites multiporus n. sp., Pluricellaesporites regularis, Lacrimasporonites levis, Monoporisporites annulatus, Spirotremesporites simplex, Dyadosporites novus, Dyadosporites sp., and Multicellaesporites attenuates. All of these correspond to parasitic fungi from a range of from tropical wetlands. Spegazzinites sp. and Dicellaesporites aculeolatus, good indicators of marine influence and mangrove presence, were also identified in the samples from the Barreiras Formation. Furthermore, the fungal spore taxa Inapertisporites multiporus, Mediaverrunites elsikii, Mediaverrunites mulleri, Pluricellaesporites regularis, and Spirotremesporites simplex serve as stratigraphic indicators when combined with miospore index taxa such as Crassoretitriletes vanraadshooveni, Grimsdalea magnaclavata and Fenestrites longispinosus indicating a Miocene age for these sediments in the Amazon region.

Mineralogia e geoquímica de perfis de solo com Terra Preta Arqueológica de Bom Jesus do Tocantins, sudeste da Amazônia

A comparacao de dados morfologicos, mineralogicos e quimicos de solo com horizontes antropicos - Terra Preta Arqueologica (TPA) com Argissolos adjacentes permitiu identificar os principais processos responsaveis pela formacao da TPA em um sitio arqueologico no Municipio de Bom Jesus do Tocantins, sudeste do Estado do Para. A similaridade entre os dados dos horizontes subsuperficiais do solo com TPA e solos adjacentes indica que o horizonte antropico do solo TPA foi provavelmente desenvolvido a partir de um horizonte similar aos Argissolos adjacentes com posterior transformacao pedogenetica atraves da introducao de materiais orgânicos e inorgânicos por antigas colonizacoes humanas, resultando no espessamento do horizonte superficial e em concentracoes maiores de CaO e P2O5 (teores totais), Zn (teor traco), P e Zn disponivel (teores disponiveis), alem de Ca e Mg trocaveis (teores trocaveis) em relacao aos Argissolos adjacentes. Alem disso, essa intervencao antropica antiga tambem provocou modificacoes no horizonte subsuperficial do Argissolo com TPA, como concentracoes altas de P2O5 e principalmente P disponivel. O Soil Taxonomy e o Sistema Brasileiro de Classificacao de Solos (SiBCS) sao adequados para a identificacao de solo com horizonte antropico (p.exe. TPA), uma vez que priorizam nas ordens do solo os principais processos pedogeneticos atuantes na formacao do solo, relacionados aos horizontes subsuperficiais, alem das transformacoes pedogeneticas posteriores no horizonte superficial. Contudo, este trabalho recomenda o acrescimo de alguns atributos diagnosticos como quantidade de artefatos cerâmicos e liticos, P2O5, P e Zn disponiveis, C orgânico, Ca2++ Mg2+ (teores trocaveis), CTC e indice de saturacao por bases no horizonte superficial para o agrupamento e distincao dos diversos tipos de solos antropicos antigos da Amazonia.

Modern pollen rain as a background for palaeoenvironmental studies in the Serra dos Carajás, southeastern Amazonia

Several alternative interpretations of the pollen records of lake sediments in the Amazonia may arise due to a lack of understanding of the modern environments, mainly related to pollen–vegetation relationship. Therefore, in this work, we studied the modern pollen rain in sediments of the Amendoim Lake, plateaus of the Serra Sul dos Carajás, southeastern Amazonia. This study indicates the predominance of pollen grains from forest formation (ombrophilous forests and capão florestal) over montane savanna in the lake sediments, despite the fact that montane savanna occupies ~90% of the drainage basin. Additionally, these sediments reflect stronger signal of pollen from ombrophilous forests that occur in the slopes of the plateau. Important components of montane savanna such as Vellozia and Cereus were not observed in the modern pollen rain, which may be related to their shorter flowering periods restricted to the beginning of wetter conditions. The absence of Sacoglottis, Trichilia, Clusia, Emmotum, Guapira and Simarouba in the pollen rain is likely associated with different pollination strategy. The occurrence of windblown pollen of Alchornea, Pseudolmedia, Ilex and Cecropia, which are found from low to highlands of the Carajás region, reinforces a regional vegetation signal in sediments. Several plants from the studied site have been improperly described, according to taxonomy and ecology. For example, the current occurrence of Ilex and Styrax in the study site clearly suggests that they cannot be used as indicators of colder palaeoclimate conditions, as previously described. In addition, Poaceae can be found in drier to wetter substrate conditions, and abundance of their pollen grains in lakes can significantly vary according to relief morphology and cannot indicate palaeovegetation openness. Therefore, this work is a good background for further palaeobotany studies for this region.

Holocene history of a lake filling and vegetation dynamics of the Serra Sul dos Carajás, southeast Amazonia

Down-core changes in sedimentary facies, elemental geochemistry, pollen, spore, δ13C, δ15N and radiocarbon records from a filled lake, named R4, of the Serra Sul dos Carajás were used to study the relationship between the paleomorphological and paleoecological processes and their significance for Holocene paleoclimatology of the southeast Amazonia. The sediment deposition of the R4 lake started around 9500 cal yr BP. Increase of detrital components from 9500 to 7000 cal yr BP suggests high weathering of surrounding catchment rocks and soils, and deposition into the lake basin under mudflows. At that time, montane savanna and forest formation were already established suggesting predominance of wet climate. However, from 7000 to 3000 cal yr BP, a decline of detrital input occurred. Also, forest formation and pteridophytes were declined, while palms and macrophytes were remained relatively stable, indicating that water levels of the lake is likely dropped allowing the development of plants adapted to subaerial condition under drier climate conditions. After 3000 cal yr BP, eutrophication and low accommodation space lead to high lake productivity and the final stage of the lake filling respectively, and forest formation may has acquired its current structure, which suggests return of wetter climate conditions.

Mineralogical and geochemical influences on sediment color of Amazon wetlands analyzed by visible spectrophotometry

Com base em dados sedimentologicos e geoquimicos, este trabalho relaciona medicoes espectrofotometricas com a composicao do sedimento, e sua aplicacao em estudos paleoecologicos das areas alagaveis da Amazonia. Os dados CIELAB estao diretamente relacionados a composicao mineralogica e quimica dos sedimentos, especialmente quartzo, oxihidroxidos e sulfetos de ferro, e carbono orgânico total. Conteudos de carbono orgânico total entre 0,4-1%, 1-2%, 3-5% e 15-40% foram relacionados a dados de L* (luminosidade) de 27, 26-15, 7-10 e 7 ou menos, respectivamente. Os valores CIELAB de um deposito com turfa em Maraba, Para, foram proporcionais a variacoes no conteudo de quartzo e carbono orgânico total, mas mudancas nas zonas de cores similares, principalmente nos valores de +a* (vermelho) e +b* (amarelo), ao longo de outros depositos em Calcoene, Amapa e Soure, Para, indicam uma relacao muito proxima entre os conteudos de carbono orgânico total, oxihidroxidos e sulfetos de ferro. Alem disso, o diagrama Q7/4 (razao entre valores percentuais de refletância em 700 nm e 400 nm, juntamente com dados de L*) indicou sedimentos ricos em ferro para a facies lama bioturbada no deposito do Amapa, facies lama bioturbada e areia bioturbada do deposito de Soure, e das facies areia com laminacao cruzada e areia macica do deposito de Maraba. Ainda, sedimentos ricos em carbono orgânico foram encontrados na lama bioturbada no deposito do Amapa, facies heterolitica lenticular e lama bioturbada do deposito de Soure, e das facies lama laminado e turfa do deposito de Maraba. Na area de Maraba, os dados sugerem uma influencia autoctone com formacao de turfa. As areas de zonas umidas costeiras no Marajo e Amapa representam o desenvolvimento tipico de planicies de mare com formacao de sulfetos e oxihidroxidos de ferro durante alternâncias entre inundacao e exposicao.