PROVENANCE HISTORY OF SANDSTONES OF THE PARNAÍBA (CRATONIC) BASIN THROUGH A MULTIDISCIPLINARY APPROACH

Our database of ~4,200 U–Pb detrital zircon ages of Silurian–Triassic sandstones of the Parnaíba Basin (NE South America) points to a strong similarity characterized by three major age populations: Palaeoproterozoic, Stenian–Tonian and late Neoproterozoic, which comprise 80-90% of the ages identified in a total of one hundred samples collected along the entire sedimentary column. Differences in provenance patterns are highlighted by variations in the relative abundances of each zircon age population within the stratigraphic units, as well as the presence of specific heavy minerals. Definition of almost identical detrital zircon spectra requires the consideration of at least two alternative (but not exclusive) hypotheses to explain the basin filling: long–term denudation of common source areas and/or intrabasinal recycling. If crystalline terranes played the primary role in terms of sediment production and delivery during the sedimentary filling of the basin, the similarity between the spectra would imply a long–term (~230 Mya) maintenance of palaeodrainage pathways from common and roughly unchanging (zircon–rich) source areas, a model not fully supported by other geological evidences. For example, the fluvial systems that promoted sediment dispersion changed significantly after the glacial events that affected this part of the Gondwana supercontinent. Intrabasinal recycling, in turn, is a very hard hypothesis to be tested given the limitation in differentiating how much detritus originated from first–order sedimentary cycles and how much originated from the recycling of older deposits within the basin. A preliminary study applying optically stimulated luminescence (OSL) signals from quartz and feldspar grains extracted from the Parnaíba sandstones has shown promising results in differentiating the target stratigraphic units. For example, the OSL sensitivity of quartz is related with sedimentary reworking and correlates with sediment accumulation rate in the Parnaíba Basin. The progress of this study might certainly help our understanding on the importance of ‘autophagy’ process and external detrital inputs (either by tectonic activity or climate changes) in the formation of such large cratonic basin.