Late E ocene– P liocene basin evolution in the E astern C ordillera of northwestern A rgentina (25°–26° S ): regional implications for A ndean orogenic wedge development

Important aspects of the A ndean foreland basin in A rgentina remain poorly constrained, such as the effect of deformation on deposition, in which foreland basin depozones C enozoic sedimentary units were deposited, how sediment sources and drainages evolved in response to tectonics, and the thickness of sediment accumulation. Zircon U‐Pb geochronological data from E ocene– P liocene sedimentary strata in the E astern C ordillera of northwestern A rgentina ( P ucará– A ngastaco and L a V iña areas) provide an E ocene ( ca . 38 Ma) maximum depositional age for the Q uebrada de los C olorados F ormation. Sedimentological and provenance data reveal a basin history that is best explained within the context of an evolving foreland basin system affected by inherited palaeotopography. The Q uebrada de los C olorados F ormation represents deposition in the distal to proximal foredeep depozone. Development of an angular unconformity at ca . 14 Ma and the coarse‐grained, proximal character of the overlying A ngastaco F ormation (lower to upper M iocene) suggest deposition in a wedge‐top depozone. Axial drainage during deposition of the P alo P intado F ormation (upper M iocene) suggests a fluvial‐lacustrine intramontane setting. By ca . 4 Ma, during deposition of the S an F elipe F ormation, the A ngastaco area had become structurally isolated by the uplift of the S ierra de los C olorados R ange to the east. Overall, the E astern C ordillera sedimentary record is consistent with a continuous foreland basin system that migrated through the region from late E ocene through middle M iocene time. By middle M iocene time, the region lay within the topographically complex wedge‐top depozone, influenced by thick‐skinned deformation and re‐activation of C retaceous rift structures. The association of the E ocene Q uebrada del los C olorados F ormation with a foredeep depozone implies that more distal foreland deposits should be represented by pre‐ E ocene strata ( S anta B arbara S ubgroup) within the region.