U–Pb detrital zircon ages in the Lajas Formation at Portada Covunco: Maximum depositional age and provenance implications for the Neuquén Basin, Argentina

Abstract

The Lajas Formation of the Neuquén Basin (Argentina) was deposited mainly during the Middle Jurassic but with a highly diachronic pattern. The exact time elapsed in the deposition of this unit remains controversial and depends on the location within the basin. Particularly in the Portada Covunco locality, north of the Huincul High, the debate on the age of the Lajas Formation persists. The age of the unit has been assigned by sequence stratigraphy, palynological, and magnetostratigraphic studies. Moreover, previous studies suggest that the Lajas Formation in this locality is composed of two depositional sequences (Sq1 and Sq2) with a change in the composition of the sandstone, indicating different areas of sedimentary supply. The new U–Pb data (LA-ICP-MS) in the detrital zircons allows us to define a maximum depositional age of approximately 163 Ma for Sq1 and 162 Ma for Sq2, suggesting a Callovian age for the Lajas Formation in the studied area. Furthermore, we propose that the provenance pattern in Sq1 was dominated by U–Pb ages of detrital zircons from the Permian–Triassic (peak at 264, 244 and 215 Ma), indicating derivation predominantly from the North Patagonian Massif magmatic units; while Sq2 shows a provenance pattern of detrital zircons associated with the uplift and exhumation of units located to the southwest margin of the basin during the end of the Middle Jurassic. Interestingly, it is not possible to rule out that the Huincul High may be related to the change in the sedimentary supply area; the probable uplift of the Huincul High has resulted in an effective physical barrier that limited sediment input from the extreme southeast during the deposition of Sq2.