Magnetostratigraphy of the Quebrada La Porcelana section, Sierra de Ramos, Salta Province, Argentina: age limits for the Neogene Orلn Group and uplift of the southern Sierras Subandinas

We present a magnetostratigraphic investigation of Neogene Orán Group strata at Quebrada La Porcelana. The area is located in the southern Sierras Subandinas of northwestern Argentina within the zone of ‘normal’ subduction. The oldest datable Neogene strata were deposited ∼8.1 Ma at the base of the Terciário Subandino. We estimate that the youngest strata are considerably younger than 1 m.y. The basal age is millions of years younger than lateral correlative units farther to the south in the Transition Zone. These chronostratigraphic results suggest that foreland thrusting was initiated much later in northernmost Argentina than it was in the Transition Zone. ta suggest that generation and migration of hydrocarbons from the Los Monos source horizon began about 3.8 Ma. Growth strata deposition began at ∼4.2 Ma, suggesting that trapping structures were available in the region when migration began.