A record of Permian subaqueous vent activity in southeastern Brazil

Abstract

The remarkable occurrence of more than 4,500 conical siliceous mounds in an area of less than 1.5 square kilometres has been reported in the Paraná basin, near Anhembi, São Paulo, in southeastern Brazil. These structures, which are up to two metres high, are thought to have been formed at the margin of a very shallow, broad but waning internal sea, and it was originally suggested that they are stromatolites. Yet their restricted occurrence, unusual abundance and nearly pure siliceous composition have never been satisfactorily explained by this hypothesis. Here we report field and laboratory observations on their shape, construction, composition and mineralogy. On the basis of our data we suggest that the conical mounds are the result of subaqueous Late Permian vent activity in southwestern Gondwana. The present siliceous cone field differs considerably from other Palaeozoic siliceous hot spring deposits, such as those at Rhynie, Scotland, and the Drummond basin, Australia, and therefore represents an unusual occurrence of vent activity.

A Formação Serra Alta, Permiano, no centro-leste do Estado de São Paulo, Bacia do Paraná, Brasil

“…No entanto, evidencias de hidrotermalismo e a presença de estruturas de deformacionais como sismitos e falhas sin-sedimentares nas formações Teresina, Rio do Rasto, Corumbataí e Piramboia indicam que a bacia estava sujeita a esforços tectônicos oriundos das margens de Gondwana (Riccomini et al 1992;Rostirolla et al 2000;Yamamoto et al 2005;Warren 2005). Diques clásticos que seccionam depósitos da Formação Serra Alta nas cercanias das cidades de Piracicaba (SP) confirmam a hipótese de que essa unidade se depositou sob influência de tectonismo ativo (Fig.…”

Biogenic Iron-Rich Filaments in the Quartz Veins in the Uppermost Ediacaran Qigebulake Formation, Aksu Area, Northwestern Tarim Basin, China: Implications for Iron Oxidizers in Subseafloor Hydrothermal Systems

“…This suggestion is evidenced by the specific vertical stacking occurrence that the quartz veins terminate immediately under the overlying bedded chert successions without upward penetration. Moreover, the characteristic textural and compositional features of these veins, which are analogous to the hydrothermal silica-barium deposits on the modern oceanic seafloor (Herzig et al, 1988;Urabe and Kusakabe, 1990;Stüben et al, 1994;Bogdanov et al, 1997;Bohrmann et al, 1999;Halbach et al, 2002;Hein et al, 2008) and ancient examples (Nijman et al, 1999;Yamamoto et al, 2005;Kiyokawa et al, 2006;Van Kranendonk, 2006;Chen et al, 2009;Wang et al, 2012), also suggest a subseafloor hydrothermal origin. In this case, the low-temperature, silicarich hydrothermal fluids were vented diffusively into the earliest Cambrian bottom seawater, promoting widespread deposition of the overlying bedded cherts in the basal Cambrian Yurtus Formation.…”

Origin of John’s Stone: A quartzitic boulder from the site of the 1908 Tunguska (Siberia) explosion

“…Composition and textures of JR are similar to those of Permian siliceous mounds from southeastern Brazil, generated probably by subaqueous hydrothermal venting (Yamamoto et al, 2005), as well as to siliceous mounds formed by hydrothermal activity in shallow water at Yellowstone (Guidry and Chafets, 2003). Pokrovskii et al (2001) reported at several sites in the Tunguska region, including one less than 20 km from the TE epicenter, carbonate-magnetite deposits formed allegedly by hydrothermal alteration of Permian-Triassic Trap basalts.…”