The Pirambóia-Botucatu succession (Late Permian - Early Cretaceous, Paraná Basin, São Paulo and Paraná States): two contrasting eolian systems

THE PIRAMBÓIA-BOTUCATU SUCCESSION (LATE PERMIAN - EARLY CRETACEOUS, PARANÁ BASIN, SÃO PAULO AND PARANÁ STATES): TWO CONTRASTING EOLIAN SYSTEMS^*

LEANDRO M. DONATTI¹, ANDRÉ O. SAWAKUCHI², PAULO C. F. GIANNINI²AND LUIZ A. FERNANDES³

¹Programa de Pós-Graduação em Geologia Sedimentar, Instituto de Geociências, USP, São Paulo, SP.

²Instituto de Geociências, USP, São Paulo, SP.

³Departamento de Geologia, Universidade Federal do Paraná, Curitiba, PR.

Presented by ANTONIO C. ROCHA-CAMPOS

The Pirambóia-Botucatu succession (São Bento Group, Late Permian to Early Cretaceous of the Paraná Basin) was studied in outcrops in the States of São Paulo and Paraná. This succession comprises sandstones and sandy-siltstones of eolian depositional systems. The basal eolian sandstones interfinger with Permian coastal siltstones (Corumbataí and Teresina formations; Passa Dois Group). The top boundary is defined by an extensive supersurface (hundreds of kilometers) developed by lava flows of the Serra Geral Formation (Early Cretaceous). The sandstone succession is characterized by extra-erg and erg core deposits, corresponding to dune fields, wet and dry interdunes, oueds and alluvial plain deposits. The identified dune types are predominantly barchans and barchanoid chains. The upward succession may be subdivided into five main facies associations: (1) tidal plain with eolian sand sheets; (2) coastal dunes with frequently flooded interdune flats; (3) coastal dunes with rarely flooded interdune flats; (4) braided alluvial plain with eolian dunes; and (5) giant dunes with interdune depressions. Associations 1 to 4 correspond, in a broad sense, to the Pirambóia Formation and record a wet eolian system - an eolian depositional system whose phreatic level was close to the depositional surface ( Pirambóia wet eolian system). In association 5, sand dune facies prevail in a draa-erg context and the low-angle cross-bedded sandstones occur rarely, suggesting the existence of dry interdunes. This association belongs to Botucatu Formation ( Botucatu dry eolian system).

The higher phreatic level of the Pirambóia eolian system can be assigned to proximity of the coast, in an arid climate. The evidences for this interpretation include transitional contact between eolian and coastal systems, presence of high-strontium (up to 650 g/g) fibrous ooids in the Teresina subtidal deposits, and existence of palygorskite as cement in the eolian sandstones.

The Botucatu eolian system rests abruptly on the fluvio-eolian deposits of Pirambóia system, along a planar regional surface, probably erosional in character. The difference of age (more than 100 Ma) and the contrast between the Pirambóia (wet) and the Botucatu (dry) eolian systems are important criteria to define this regional surface as a remarkable unconformity. — ( December 8, 2000 )

Publication Dates

• Publication in this collection
  08 Oct 2001
• Date of issue
  Sept 2001