DEGEO - Departamento de Geologia

URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8

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20202

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Autor: search.filters.author.Varajão, Angélica Fortes Drummond ChicarinoAssunto: search.filters.subject.Volcanic islands

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    Non-allophanic Andosols of Trindade Island, south Atlantic : a new soil order in Brazil.
    (2020) Mateus, Ana Carolina Campos; Varajão, Angélica Fortes Drummond Chicarino; Oliveira, Fábio Soares de; Petit, Sabine; Schaefer, Carlos Ernesto Gonçalves Reynaud
    The pedological studies carried out so far in Trindade Island (TI) have obtained patchy evidences of allophane, without detailed mineralogical and micromorphological studies to confirm the occurrence of Andosols in TI. Therefore, in this study, the mineralogical, micromorphological, physical and chemical characterization of four soil profiles from Vulcão do Paredão (P1) and Morro Vermelho formations (P2, P3, and P4) were carried on the latest volcanic events in Brazil from Trindade Island (TI) with the aim of to evaluate the presence of Andosols in this oceanic island. Profiles P1 and P2 are developed on pyroclastic bombs, and show, respectively, A-Bi- C and decapitated A-C horizons, whereas P3 and P4 are developed on lapillitic and bomb pyroclasts, show A-C horizons. The soil profiles have a reddish and brownish clayey matrix, are highly friable and show a plastic consistency. Their microstructures are granular, single grain and intergrain microaggregate, in which aggregates display an undifferentiated b-fabric. The mineralogical constituents of the bulk fraction are biotite, hematite, magnetite, ilmenite, pyroxene, olivine, halloysite, goethite, anatase, and rutile. The clay fraction is marked by the presence of halloysite, ferrihydrite, and little amounts of allophane. All soils presented andic properties and can be classified as non-allophanic Andosols. In addition, micromorphological features closely resemble those reported in Andosols from other volcanic islands from elsewhere. The predominance of halloysite in the clay fraction formed by alteration of sideromelane, suggests that allophane would be an intermediate phase of this rapid transformation favored by the wet climate conditions of the highest parts of TI.
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    Phosphatized volcanic soils of Fernando de Noronha Island, Brazil : paleoclimates and landscape evolution.
    (2020) Silveira, Jonas Carvalho; Oliveira, Fabio Soares; Schaefer, Carlos Ernesto Gonçalves Reynaud; Varajão, Angélica Fortes Drummond Chicarino; Varajão, Cesar Augusto Chicarino; Senra, Eduardo Osório
    Volcanic oceanic islands host soils that may hold important paleo-environmental proxies, based on vegetation and faunal evidences coupled with pedological and geomorphological indicators. In this regard, the main Brazilian oceanic island of Fernando de Noronha (FNI) still lacks a deeper and more complete analysis of its climatic history and soil evolution. We select and collect representative FNI soils to interpret their chemical, physical and mineralogical properties and to explain their changing pedogenesis and geomorphic balance, aiming at revealing the environmental and landscape evolutionary history of this island. Ten soil pedons on phonolites, ankaratrites and the associated pyroclastic rocks were collected in June/2018. Six profiles were classified as Inceptisols, one as Entisol, one as Mollisol, one as Vertisol and another as the first Oxisol ever described in a Brazilian oceanic island. The pH ranged between 5.0 and 6.0 in the more developed, dystrophic and Al-saturated soils, whereas alkaline pHs were found in the eutrophic and Na-rich pedons. For the latter group, chemical and physical attributes are closely associated with the parent material composition, whereas in the former, present day soil features overprint paleoweathered regoliths and former pedogenetic processes. High concentrations of available phosphorus (P) were observed in all soils and horizons, even at depths greater than 150 cm, and P forms were detected as amorphous or poorly-crystalline phosphates (Al, Fe, Na, Ca and K). High- and low-activity clay minerals coexist, combined with gibbsite and unstable primary minerals, indicating the polygenetic nature of FNI soils. A combined pedogeomorphological analysis indicated the existence of a high paleoweathered plateau with relict soils, and erosional surfaces hosting younger soils. Results showed the succession of at least three distinct main paleoclimates since the Pliocene and a post-magmatic model for landscape evolution. The unreported, widespread and intense phosphatization of all soils and paleosurfaces is attributed to a past large population of birds nesting all over the island, corroborating old historical records of the island’s early occupation. Report the occurrence of Brazil’s first ornithogenic Oxisol with more than 500 mg/ kg of bioavailable P.