Moldes de Cristais de Gipsita como Pseudofósseis no Arenito Botucatu, RS

LUIZ FERNANDO DE ROS, MARGOT GUERRA SOMMER, LUIZ JOSÉ TOMAZELLI

Resumo


Sedimentary features in eolian sandstones with plane-parallel lamination of the Botucatu Formation, situated in a quarry in Novo Hamburgo (RS), southern Brazil, were preciously interpreted as possible plant imprints. They show very variable shapes, comprising: a) small, isolated, lenticular or lamellar molds with oblique borders; b) aggregated molds, comprising divergent or intercepting, rarely radiated geometry; c) large, lenticular or lamellar molds with small molds transversally to their margins; d) rounded or oval-shaped molds, some with small molds along their margins. The shapes and distribution of these imprints indicate their origin from the dissolution isolated and aggregated gypsum (CaSO42H2O) crystals, an evaporitic mineral common in desertic environments. The gypsum was precipitated as large crystals (“selenitic gypsum”) within eolian sheet sands shortly after their deposition. Gypsum dissolution was promoted by the later percolation of meteoric groundwaters throughout the sandstones, leaving molds delineated by iron and manganese oxides. Therefore, the studied imprints represent pseudofossils, without any relationship with plants.



Palavras-chave


pseudofossils; gypsum molds; eolian sandstones

Texto completo:

PDF/A


DOI: https://doi.org/10.22456/1807-9806.21161

Apontamentos

  • Não há apontamentos.







Instituto de Geociências, Universidade Federal do Rio Grande do Sul
Av. Bento Gonçalves, 9500 - Prédio 43113
91.540-000, Porto Alegre, RS, Brasil
E-mail: pesqgeoc@ufrgs.br