Detrital provenance of the Upper Triassic siliciclastic rocks from southwest Iberia: a review

Abstract

In southwestern Iberia the Upper Triassic successions of Lusitanian, Alentejo and Algarve basins records the fragmentation of Pangaea in Permian–Triassic during which the paleogeography of Iberia was dominated by a series of coalescing, alluvial–deltaic wedges and axial braided rivers. In this study, we discuss the potential sediment sources of the Lusitanian, Alentejo and Algarve basins based on detrital zircon-age spectra, suggesting that Iberia occupied a central position Iberia in Pangaea during late Triassic. Conventional sedimentary petrography and paleocurrent measurements of previous works was combined with recently published detrital zircon U–Pb geochronology of the Upper Triassic siliciclastic rocks of southwest Iberia to shed light on the detrital provenance record. Zircon age populations found in the Upper Triassic strata of the Lusitanian, Alentejo and Algarve basins is dominated by Neoproterozoic (33–76%) and Paleoproterozoic (12–15%) grains. The most important differences are the dominance of Devonian–Carboniferous (33%) zircon in the Alentejo basin and the greater representativeness of Permian–Carboniferous (6%) zircon in the Lusitanian basin. The deposition in these Upper Triassic basins of Portugal is marked by variability in sedimentary sources, involving the denudation and local-scale directions of sediment transport from the Iberian basement with possible additional supplies derived from outside present-day Iberia. The Upper Triassic successions evolved separately with the detrital transport being probably controlled by local drainage systems, and occupying a central position in Pangaea just before the opening of the Central Atlantic Ocean.