Abstract

MARCIAL, Enzo Rubén; ALBARRACIN, Virginia Helena  and  ESTEBAN, Susana Beatriz. PYRITE FRAMBOID AS INDICATOR OF REDOX CONDITIONS IN THE LAMPA-ZAR FORMATION (UPPER CAMBRIAN, SIERRA DE CAJAS, CORDILLERA ORIENTAL, ARGENTINA). Ser. correl. geol. [online]. 2023, vol.39, n.1, pp.11-20. ISSN 1666-9479.  http://dx.doi.org/10.5281/zenodo.7926836.

The aim of the present work is to define the oxygenation levels during the sedimentation of the Lampazar Formation using pyrite framboids present in dark shales. For this, the analysis of fine facies was carried out by microscopy of thin sections and using scanning electron microscope (SEM). As a result, four facies were recognized; facies 1 massive black shales; facies 2: dark gray shales with fine parallel lamination; facies 3: dark gray - greenish shales with thin siltstone levels and facies 4: fine sandstones with parallel to undulitic lamination alternated with yellowish - green shales. It is inter-preted that, throughout the sedimentation of the Lampazar Formation during the Upper Cambrian in the Sierra de Cajas, euxinic conditions prevailed on sea bottom waters (represented by facies 2), which through dilute bottom currents (facies 1 and 3) allowed oxygen to enter sporadically, which would ex-plain the presence of trilobite fauna on the seafloor. These events became more frequent towards the upper part of the Lampazar Formation (facies 4) indicating a somerization of the marine platform.

Keywords : Lampazar; Framboids; Redox; Oxygenation.

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