Gênese e evolução de espeleotemas em cavidade natural N4E-29 ao longo de formações ferríferas bandadas, Serra Norte de Carajás-PA

Abstract

Serra dos Carajás, study area, cavities developed along Unidade Espeleológica de Carajás (UEC) on jaspilites of Carajás formation and lateritic cover up. Weathering processes through physicalchemical reactions by water percolation in relatively soluble rocks provide speleothems generation in iron systems. In this context, it is observed interaction between chemical precipitation and biological action. Chemical precipitation generates crystalline deposits inside these caves called generically as speleothems. Biological action caused by presence of photo dependent microorganisms (bacteria, lichens and mosses) composing crusts speleothems type. In N4E-29 cavity occur Pure Acicular Coralloid speleothem of Goethite and White and Yellow Crusts. Coralloid is a catch-all term for varieties of nodular, globular, botrioidal, coral-like morphology speleothems. Precipitation of Pure Coralloids studied in the cavity occurs under aphotic system by a ferric hydroxide gel that precipitates in acicular habit (Coralloid Standard 1) or acicular / radial habit (Coralloid Standard 2). Biological action of photo dependent microorganisms that compose crusts speleothems in White / Yellow color may interfere with the Coralloids crystallinity if they were precipitated in euphotic system. Issues such as rich source of iron (III), alkaline conditions (11 <pH <13.5) and temperature between 30 and 70 ° C are needed for a good crystallinity during precipitation of Goethite.