THE DEVONIAN IN THE NORTHERN PARANÁ BASIN: PROVENANCE ANALYSIS, REGIONAL VARIATION, CAUSES, AND CORRELATIONS

Three major second-order sea-level variations have been registered during the Devonian in SW Gondwana. The intracratonic Paraná Basin of 1.5 x 10⁶ km² extent, exhibits a well-developed Devonian stratigraphic interval. The mostly arenitic, basal Furnas Formation is related with a period of rising sea-level, and the shales of the overlying Ponta Grossa Formation represent the maximum flood surface of the first transgression. The Tibagi Member of the lower São Domingos Formation sandstones are related with a fall of the sea level related to the second event, whereas the third event is well represented by the shales of the upper São Domingos Formation. Considering the present geographic configuration of South America as a proxy for the Devonian paleogeography of the Paraná Basin, and in order to track the sediment sources, provenance analysis by U-Pb on 601 detrital zircons and Sr-Nd whole-rock analyses were applied to the Devonian sequence of the Northern Paraná Basin. Two samples from the Ponta Grossa Formation, two from the Tibagi Member, and one sample from the upper Sao Domingos Formation were analyzed by LA-MC-ICP-M at the Laboratory of Isotopic Geochemistry at the University of Ouro Preto, Brazil.

All units show provenance from proximal, intermediate and distal sources. Proximal source is represented by the Goiás Magmatic Arc (~630 Ma), intermediate sources are represented by the Serra da Mesa (~1770 and 2100 Ma) and Paranoá (~2100 Ma) groups, and the Goiás Block (~2420 Ma), and distal/very distal sources are represented by the Sunsas-Aguapeí Belt (~900-1200 Ma). The main provenance differences between these three Devonian units are a peak at ~2604 Ma only observed for the upper part of the São Domingos Formation and a peak at ~435 Ma observed only for the Ponta Grossa and São Domingos formations. As the upper part of the São Domingos Formation represents the third transgressive event, this peak can be related with provenance from very distal sources, like the Trairas Group (with a diagnostic peak at ~2600 Ma) that would be the basement of the Brasilia Belt to the east. The peak at ~435 Ma for the Ponta Grossa Formation, Tibagi Member, and São Domingos Formation can be explained as having been derived directly from very distal sources, like the Famatinian magmatic arc located to the west in the Andean region. The MultiDirectional Scaling plot (MDS) indicates that there are differences in provenance when the northern and southern part of the Paraná Basin are considered and that the Devonian interval of the northern sector appears similar in provenance to the typical Tarija Basin provenance. Also, the Famatinian ages could be related directly with provenance from the reworked section in the Tarija Basin, located to the west, and which was probably connected to the Paraná Basin at that time.

The εNd_{(380 Ma)} values for this sample suite do not vary much and only range from -12.4 to -10.6. In the Age (Ga) versus εNd diagram a general increase of older crustal sources is observed towards the top of the sequence. ⁸⁷Sr/⁸⁶Sr₍₃₈₀₎ ratios and T_DM values show a decrease when there are contributions from younger sources, as is the case of the Ponta Grossa Formation and the upper part of the São Domingos Formation, with presence of material from younger sources associated with the Famatinian Magmatic Arc. Thus, the distal/very distal sources can be related here to the first transgression, represented by the Ponta Grossa Formation, and then again to the second transgression corresponding to the upper part of the São Domingos Formation.

Taking all these observations together, this work encompasses a combination of provenance analysis that allows to consider proximal versus distal sources with the actual paleographic configuration as a proxy for the paleogeography during deposition in the Devonian. This approach is also promising for application to Phanerozoic sequences of other intracontinental basins.