OCCURRENCES OF EVAPORITES IN THE IRATI SUBGROUP (LATE PERMIAN, PARANÁ BASIN)
J
ORGE HACHIRO
Instituto de Geociências, USP, São Paulo, SP.
Presented by ANTONIO C. ROCHA-CAMPOS
Evaporite deposits in the Paraná Basin are unusual and of limited occurrence. The Morro do Alto (lower) and Ipeúna (upper) members of the Assistência Formation (Irati Subgroup) include the most expressive evidence for Late Permian evaporitic sedimentation in this syneclise.
During the regressive event after sedimentation of the Taquaral Formation, the area north of the Ponta Grossa Arc (in São Paulo State) became a hypersaline residual sea, leading to calcium sulfate precipitation in a restricted stagnant paleoenvironment and dry climate.
The Taquaral-Assistência boundary is distinguished by the transition from non-bituminous shale to organic-rich bituminous shale. At this contact are evaporitic breccias that deform the basal beds of the overlying Assistência Formation.
In the upper part of the Bairrinho bed (Ipeúna Member, Assistência Formation), northeastern São Paulo, evaporite was deposited in another short transgressive-regressive cycle. Later this bed was deformed by salt mini-domes which were later replaced by chalcedony.
In the northern portion of the Paraná Basin (southern Goiás State), between the Assistência and Corumbataí formations, there are partially silicified strata with mesosaurid bones. This contact is marked by silicified mini-domes, horizons with radial-fibrous crystals and breccias like those found in the evaporitic deposits of São Paulo State. These silicified rocks occur above the last bituminous shale, thus denoting a third evaporitic acumulation at the top of the Irati Subgroup. (December 10, 1999)
Publication Dates
-
Publication in this collection
05 Jan 2001 -
Date of issue
Dec 2000
