Characterization and stratigraphic review of the upper Jurassic – Lower Cretaceous Mendoza Group in the Blanco river valley (∼33°SL)

Abstract

The Jurassic-Cretaceous Mendoza Group is one of the most distinctive lithostratigraphic units of the widely surveyed Neuquén basin. This work focuses on its development in the Aconcagua basin, which crops out at the Aconcagua fold-and-thrust belt in the Principal Cordillera, and contrasts with its evolution in the main Neuquén basin by remarkable differences. By logging a series of stratigraphic sections, we performed a detailed revision of the Mendoza Group's stratigraphy and contact relations along the Blanco River valley (∼33°S). We reassigned several outcrops to the Mendoza Group based on our field observations and recent research, updating the current geological map of the study area. We identified an irregular development of the lower contact relation with the Auquilco Formation that denotes the existence of a paleo-topography at the time of deposition of the upper beds of the Mendoza Group. Moreover, we dismissed previous proposals of a lateral interfingering relation with the Juncal Formation, and in place, we describe an angular unconformity with an overlying Upper Miocene volcanic unit. Additional insight from the redefinition of the upper contact is brought by the characterization of an erosive surface at the top of the Mendoza Group, and the identification of a period of subaerial platform exposition and erosion. A previous paleogeographical model shows a good fit with the observed facies along the Blanco River valley and can be extended towards southern latitudes. Differences in the development of the Mendoza Group in the Aconcagua basin and the main Neuquén basin have been acknowledged, and a potential origin of this unusual behavior has been explored in the reactivation of an Early Jurassic structural high.