Coupled U–Pb and Lu–Hf zircon data of the marine Pilmatué Member, Agrio Formation: Implications for sedimentary provenance and source areas across the Early Cretaceous in the Neuquén Basin, Argentina

Abstract

The Lower Cretaceous Neuquén Basin is characterized by an almost complete stratigraphic record with marine and continental successions that have been addressed from the perspective of compositional and provenance analyses. However, determination of source areas through geological time is still a matter of debate. This work focuses in the upper Valanginian–lower Hauterivian Pilmatué Member (Agrio Formation of the Mendoza Group), a marine unit that represents shallow to offshore settings mainly composed of mudstones. In order to study the provenance and source areas, outcrop samples were examined through petrography, X-ray diffraction, and U–Pb/Lu–Hf zircon analyses. Sandstone deposits are scarce in the unit and show high compositional maturity related to fine-grained sediments preserved during transport until their final deposition. In the Pilmatué Member, the clay fraction is dominated by detrital illite and chlorite derived from the erosion of plutonic/metasedimentary basement rocks likely subjected to arid–semi-arid climate in the hinterland. Four main U–Pb age populations were determined: (1) Mesoproterozoic–Neoproterozoic, (2) Cambrian–Ordovician, (3) Permian–Triassic, and (4) Early–Middle Jurassic, which indicate an important denudation of old igneous-metamorphic basement rocks not recorded in the underlying Upper Jurassic and Lower Cretaceous units. A detailed compilation of the limited U–Pb/Lu–Hf zircon data from Upper Jurassic and Lower Cretaceous units reinforce the ideas that hinterland source regions located adjacent to the basin boundaries were the main source of clastic detritus. Since U–Pb ages show little variations across late Valanginian–Albian times, sediment transfer zones seem to have been stable during the closure of the back-arc basin stage.