LONG-DISTANCE FLUVIAL SAND ROUTES IN JURASSIC OF WESTERN GONDWANA: FLUVIAL-AEOLIAN STRATA OF PIRAMBÓIA FORMATION

Pirambóia Formation is a fluvial-aeolian strata deposited in West Gondwana, currently central Brazil. The unit is composed mostly by sandstones formed in fluvial-aeolian environments. Its sedimentary facies record cycles of fluvial strata - as bars, sheet flows, and ripples and aeolian strata - as dunes, interdunes, and sandsheets. Based on 552 zircons from 6 samples, the detrital zircon age spectra display Neoproterozoic as the main contribution (500 – 650 Ma), with secondary contributions of Tonian-Stenian (900-1200), Permian (250-290 Ma) and Paleoproterozoic (1.8 Ga). In detail, a small fraction of grains from 165-185 Ma provides novel ages as maximum depositional age for the unit. The ²⁰⁶Pb/²³⁸U calculated maximum depositional age for Pirambóia Formation is 171 ± 5 Ma (2σ). This novel age is the first to constrain the unit to Middle Jurassic, providing the most reliable absolute age for the Piramboia Formation. The eHf found a mean value of -11, and 1284 Ma T_DM age. In order to pinpoint the sources of the Jurassic contribution, we compile 1615 U-Pb ages and 402 Lu-Hf ratios from zircon grains Southern Gondwana Jurassic volcanics, including Chon Aike volcanism (South Argentina), Karoo volcanism (South Africa) and Vestjfalia intrusion (Antarctica/East Africa). The U-Pb and Lu-Hf signatures display a consistent contribution from Vestjfalia Mountains, in NW Antarctica. Such sourcing points to sedimentary route system across from southeast to Northwest Gondwana. Considering the well-established wind-pattern in the region (NE trade winds) the sedimentary route are envisaged to be controlled by a > 1000 km transcontinental river systems across the many intracratonic basins in Gondwana. This behaviour is displayed in the sedimentary register including the Jurassic in north America and Ordovician in NE Brasil. Overall, the detrital zircon signature display consistent recycling of Parana Basin underlying strata, with minor contributions from this long-distance sources. In addition, the novel Jurassic age constrain the unit age, clearing the previous unclear ages that have been described as Permian, Triassic and Jurassic.