Resumo

LOPEZ DE AZAREVICH, Vanina; AYENDEZ, Martín; AZAREVICH, Miguel  e  DE PAUL CAMACHO, Marianela. Estudio geológico del Manto Ferrífero II de la Formación Lipeón (Silúrico), noroeste argentino: consideraciones paleoambientales y genéticas. Ser. correl. geol. [online]. 2015, vol.31, n.2. ISSN 1666-9479.

The ferriferous basin of Northwest Argentina (NOA) includes 2 litoestratigraphic units: Zapla Formation (Ordovician-Silurian) and Lipeón Formation (Silurian). This last is a sedimentary sequence compound by medium oolite-sandstones interlayered with micaceous limolites, which were deposited in a shallow marine environment. This sequence hosts a Fe-mineralization of the Minnette Type, with 3 Ferriferous Horizons (I-II-III). In the Unchimé District (Salta province) outcrops the Ferriferous Horizon II (20-45 % Fe), conformed by Ferich minerals with minor Mn contents: chamosite, hematite, limonite and siderite. Hematite and chamosite are dominant, and are found in the cement or recovering oolites, which develops from sub-angular grains of quartz or chamosite, lithic or shell´s fragments and even around previous oolites. Distribution of some trace elements indicates that Fe origin was by continental meteorization. Oscillation of Fe vs Mn along profiles shows that sedimentation in the Silurian basin was conditioned by periodic oscillation of the sea level, which produced oxidant and reducing conditions that favored concentration of Fe as hematite (Fe³⁺), and Mn and Fe as chamosite (Fe²⁺), respectively. Evidences support the interpretation of a marine environment among shoreface and transitional to offishore, sub-mitted to the action of oscillatory process by waves, along a platform locates at 30º-45º latitude and humid climate. Interlayering of sandy (Fe-oolitic) and limolite banks, at that paleolatitud, and the paleoclimatic conditions installed by that epoch (postglacial), it can be recognized slightly periodicity as related to a climatic seasonality, which would be linked to generation of such short transgressive/regressive cycles.

Palavras-chave : Silurian. Ferriferous. Oolites. Fe-Mn. Nortwest Argentina.

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