Geobiological and diagenetic insights from Malvinokaffric devonian biota (Chapada Group, Paraná Basin, Brazil) : paleobiological and paleoenvironmental implications.
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2017
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This study tests the presence of differential preservation in the Devonian Malvinokaffric fauna from the
Chapada Group (Parana´ Basin, Brazil). Results of EDXRF, EDS, Raman Spectroscopy, and petrographic analyses
show differential preservation of shells that were originally calcite as hematite and goethite fossils, while organisms
with original calcium phosphate shells tend to be preserved inside phosphatic concretions. Both preservation types are
commonly associated with pseudoframboids, while calcium sulfate minerals are commonly associated with hematized
fossils. From this evidence, a diagenetic model for these fossils is proposed. The model includes an early diagenetic
phase (characterized by anaerobic sulfate reduction and precipitation of pyrite and carbonate-fluorapatite) and a
second, near-surface chemical weathering phase (characterized by the oxidation of pyrite and precipitation of iron
oxyhydroxides and calcium sulfates). Acidic conditions in both phases may account for the dissolution of less stable
minerals compared to calcium phosphate. It is considered that this model may assist in understanding other similarly
preserved biotas, as well as enhancing understanding of the taphonomic overprint that may occur within this
important and endemic Devonian biota.
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KERBER, B. B. et al. Geobiological and diagenetic insights from Malvinokaffric devonian biota (Chapada Group, Paraná Basin, Brazil): paleobiological and paleoenvironmental implications. Palaios, Tulsa, v. 32, p. 238-249, 2017. Disponível em: <http://palaios.geoscienceworld.org/content/32/4/238>. Acesso em: 25 ago. 2017.