Título:	Role of kaolinite epigenesis in ferruginous oolitic micronodule formation in Plinthosols from Central Brazil.
Autoria:	CAMPOS, D. S. de VIDOCA, T. T. BRIZZI, R. R. BRITO, H. D. RAMOS, M. R. ALMEIDA, R. E. M. de VIDAL-TORRADO, P.
Afiliação:	DANIELA SCHIEVANO DE CAMPOS, UNIVERSIDADE DE SÃO PAULO THIAGO TAVARES VIDOCA, UNIVERSIDADE DE SÃO PAULO RAPHAEL RODRIGUES BRIZZI, UNIVERSIDADE DE SÃO PAULO HERMES DIAS BRITO, UNIVERSIDADE ESTADUAL PAULISTA "JÚLIO DE MESQUITA FILHO" MICHELE RIBEIRO RAMOS, UNIVERSIDADE DE SÃO PAULO RODRIGO ESTEVAM MUNHOZ DE ALMEIDA, CNPASA PABLO VIDAL-TORRADO, UNIVERSIDADE DE SÃO PAULO.
Ano de publicação:	2026
Referência:	Catena, v. 273, 110397, 2026.
Conteúdo:	Extensive areas of Petric and Pisoplinthic Plinthosols comprise ancient flat and stepped surfaces in the state of Tocantins, in the north-central region of Brazil. Some of these petroplinthites are derived from siltstones and sandstones of the Pimenteiras Formation (Devonian), and have been extensively investigated from pedogenetic, macro- and micromorphological perspectives. Ferruginous oolitic micronodules were identified on thin sections, always associated with alteromorphic siltstone nodules. Furthermore, the evolutionary stages of these micronodules were observed, indicating a completely pedogenetic origin. Although the formation of ooid nodules is classically associated with sedimentary and diagenetic processes, the evolution of the ferruginous oolitic micronodules identified here required detailed investigations to understand the subsequent processes. For this purpose, thin sections were prepared and systematically described using an optical microscope, and areas with the presence of oolitic micronodules were selected and subsequently analyzed using SEM-EDS. Thus, the association of ooids with the siltstones of the Pimenteiras Formation is attributed to the common presence of very fine micas, and the consequent transformation of illite crystals into kaolinite. The cyclicity between reductive and oxidative periods, inherent to the ferrolysis process, induced the epigenetic replacement of kaolinite by hematite, forming ferruginous booklets. Subsequently, the centripetal reorganization of hematite, combined with the confined space of the matrix, resulted in the formation of oval oolitic micronodules. This finding demonstrates that these relict soils retain characteristics whose identification and elucidation remain a challenge for scientific research.
Palavras-chave:	Plintossolo Caulinita Ferrólise Cortificação centrípeta Petroplintita Duricrustas Pisolito
ISSN:	0341-8162.
Digital Object Identifier:	https://doi.org/10.1016/j.catena.2026.110397
Tipo do material:	Artigo de periódico
Acesso:	openAccess
Aparece nas coleções:	Artigo em periódico indexado (CNPASA)