THE DEVONIAN INTERVAL OF THE PARANÁ BASIN: IS THERE A RELATIONSHIP BETWEEN SEA-LEVEL VARIATION AND U-Pb PROVENANCE ANALYSIS?

WILSON LÓPEZ ABANTO; ARNOLD GARCIA ZAVALETA ; JOYCE SOUZA RIBEIRO ; NATALIA HAUSER; WOLF UWE REIMOLD; CRISTIANO CARVALHO LANA ; PAMELA ALEJANDRA APARICIO GONZÁLEZ

Santiago de Chile

Congreso; XII South American Symposium on Isotope Gology; 2022

Universidad del Desarrollo Chile

The Paraná basin of 1.5 x 106 km2 size is a typical intracratonic basin located on the Brazilian platform. This basin registered sedimentation from the Ordovician to the Upper Cretaceous. The Devonian interval has been well constrained by sedimentological, geochemical and paleontological studies. Three important though second-order sea-level variations, related to tectonics and eustasy, occurred in SW Gondwana and are also recognized in the Paraná basin. The first of these events was transgressive and has been related with the Precordilleran I orogeny. In the Paraná basin, the Furnas Formation is related with a sea-level rise, and the shales of the Ponta Grossa Formation represent the maximum flood surface for this first transgression. The second sea-level variation was regressive and has been related with both the Precordilleran II orogeny and a decrease of sea-level. The sandstone of the Tibagi Member of the São Domingos Formation has been related to the fall of the sea-level during this second event in the Devonian. The third event, well recognized in several basins of SW Gondwana, was again transgressive and is related with a global high sea-level stand. This event has been related with the shales of the upper part of the São Domingos Formation. As there is a well constrained relationship between stratigraphy and sea-level variations for the Paraná basin during Devonian time, the present work was designed to analyze variations in U-Pb zircon provenance possibly related to sea-level variation. Five samples from the northern part of the Paraná basin, including two from the Ponta Grossa Fm., two from the Tibagi Member, and one from the São Domingos Formation, were analyzed by LA-MC-ICP-MS (Neptune Plus Thermo Finnigan instrument coupled with a Photon-Machines 193 nm laser system) at the Laboratory of Isotope Geochemistry at the University of Ouro Preto, Brazil. For our discussion, we take into consideration: 1) paleocurrent data that indicate that the main provenance for the northern part of the Paraná basin was from the ENE-W, and subordinately from the E; and 2) we assume that the present paleogeographic configuration of the basin is a proxy for the paleogeography during the Devonian. This allows us to classify the probable sources as proximal, intermediate and distal: The Goiás Magmatic Arc (~630 Ma) would represent a proximal source, the Serra da Mesa, Paranoá Group and Goiás Block (~1770 Ma and 2100 Ma for the Serra da Mesa, and only ~2100 Ma for the Paranoá Group, and ~2420 Ma for the Goiás Block) would represent intermediate sources; and the Trairas Group (~1520 and 2604 Ma), the Sunsas-Aguapeí Belt (~900-1200 Ma), and the Famatinian magmatism (~435 Ma) might represent distal/very distal sources, respectively. The concordant U-Pb data from our samples (470 analyses) indicate provenance from these proximal, intermediate, and distal (and very distal) sources, for all three units analyzed. The zircon age populations exhibit a main peak of zircon ages at ~630 Ma, minor peaks at ~1770 and ~2100 Ma, a range of ages between 900 and 1200 Ma, a peak at ~2420 Ma, and a minor peak at ~435 Ma. The main difference between the provenance patterns of the three units is an age peak at ~2604 Ma, which is only observed in the upper part of the São Domingos Formation and can probably be related with the Trairas Group. As the upper part of the São Domingos Formation registered the 3rd transgressive event, this peak is related with a very distal source, such as the Trairas Group, which would represent the basement for the Brasilia Belt to the NE, today ~500 km from the basin. The peak at ~435 Ma that was observed in the Ponta Grossa (4 % of zircons), Tibagi (3 % of zircons), and São Domingos formations (6 % of zircons) but not in the underlying Furnas Formation, can be explained as direct provenance from the Famatinian Magmatic Arc, located at ~1100 km distance. Alternatively, zircons with these ages could be derived from reworking of the deposits of the Tarija Basin, which is located some 650 km to the west and possibly was connected to the Paraná Basin in Devonian time. We can conclude, using the Paraná Basin as an example, that U-Pb provenance analysis can be applied well to the study of sea-level variation in a basin, if there is a well-constrained paleogeography and if sea-level variation is well defined in stratigraphy.