A record of Permian subaqueous vent activity in southeastern Brazil.
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.
Yamamoto
Jorge Kazuo
JK
Institute of Geosciences, University of São Paulo, Rua do Lago, 562, CEP 05508-080, São Paulo, Brazil. jkyamamo@usp.br
Fairchild
Thomas Rich
TR
Boggiani
Paulo Cesar
PC
Montanheiro
Tarcísio Jose
TJ
de Araújo
Carlos César
CC
Kiyohara
Pedro Kunihiko
PK
de Matos
Sergio Luis Fabris
SL
Soares
Paulo César
PC
D000818:Animals; D001938:Brazil; D019015:Geologic Sediments / Q000737:chemistry*; D049690:History, Ancient; D045482:Hot Springs / Q000737:chemistry*; D008974:Mollusca / Q000737:chemistry; D009792:Oceans and Seas; D012825:Silicon / Q000032:analysis / Q000737:chemistry
D012825:Silicon