The São Jerônimo da Serra Site, Rio do Rasto Formation (Middle/Upper Permian), Paraná Basin, Brazil: faciological and taphonomic context

In this paper we characterize pecopterids found in deposits of the Passa Dois Group (Upper Permian of the Paraná Basin) in a new outcrop, on the side of the BR-153 road, located at the municipality of Aceguá, Rio Grande do Sul State, Brazil. Pecopterids are common in the Permian paleophytogeogragic realms, signaling interglacial phases of the Late Paleozoic. Pecopteris are one of the floral elements of the Permian Glossopteris flora and become extinct in the Permo-Triassic boundary. Mudstone strata levels bearing phytofossils with different preservation qualities allowed the recognition of Pecopteris sp. and cf. Scolecopteris sp. floral elements. Taphonomic and depositional processes that conditioned the preservation of phytofossils are suggested accordingly the specimens described. Phytofossil specimen described support and highlight polymorphic nature of Gondwanan pecopterids. These new findings demonstrate potential for further paleobotanical studies in the upper portion of the Passa Dois Group and strength the notion of Permian strata for the Teresina Formation.

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Middle–Late Permian magnetostratigraphy and the onset of the Illawarra Reversals in the northeastern Parana Basin, South America

Geophysical Journal International ◽

10.1093/gji/ggab011 ◽

2021 ◽

Vol 225 (2) ◽

pp. 860-871

Author(s):

Marcela Aragão ◽

Giancarlo Scardia

Keyword(s):

Sediment Accumulation ◽

Magnetic Polarity ◽

Large Igneous Province ◽

Upper Permian ◽

Late Permian ◽

Reverse Polarity ◽

Karoo Basin ◽

Paraná Basin ◽

Dual Polarity ◽

Parana Basin

SUMMARY Recent compilations of the Illawarra Reversals show remarkable differences in the onset age (265 Ma versus 269 Ma) and the magnetic polarity pattern, hampering the establishment of a reference geomagnetic timescale for the Middle–Late Permian. The Parana Basin hosts a 7-km-thick, discontinuous sedimentary succession spanning the Palaeozoic to the Mesozoic, including the Gondwana 1 supersequence which extends from Late Carboniferous to the Triassic or Jurassic. We provide the magnetostratigraphy of the middle and upper Permian part of this sequence of a ca. 300-m-long core, pertaining to the Passa Dois Group and the Piramboia Formation. Sample demagnetization of NRM revealed two magnetic overprints ascribed to the Brunhes chron and to the emplacement of Parana Large Igneous Province in the Early Cretaceous, respectively. Stable, dual polarity characteristic components (ChRM) were isolated at temperatures higher than 450 °C and interpreted as a primary detrital magnetic remanence (DRM), acquired during or soon after sediment deposition. Available U-Pb dating on volcanic zircons from the literature provided independent chronologic constraints for our magnetostratigraphy. A total of 8 reverse polarity intervals were identified, the lowermost of which (up to 110 m thick) correlates to the Kiaman Superchron. The overlying Illawarra is dominated by a reverse polarity magnetization with thin (4–5 m thick) normal polarity intervals. This pattern agrees with the Illawarra sequence from the Karoo Basin and other proposed timescales for the Permian. The onset of the Illawarra reversals is interpolated to ca. 270 Ma, close to the age of 269 Ma from the Karoo Basin. Combined magnetostratigraphy and geochronology yielded sediment accumulation rates of ca. 8 m Myr–1 for the Passa Dois Group in the northeastern (marginal) sector of the Parana Basin, indicating that Serra Alta and Teresina Formations span 279–274 Ma and 274–254 Ma, respectively.

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