Abstract
The fault‐bounded Cianzo basin represents a Cenozoic depocenter between the Puna plateau and Eastern Cordillera of northern Argentina. Analysis of fold‐thrust relationships, nonmarine sedimentation, and detrital provenance at 23–24°S helps constrain the origin, interconnectedness, and subsequent uplift and exhumation of the Cianzo basin, a potential analog for intermontane hinterland basins in the Andes. Structural mapping reveals a plunging syncline within the >6000‐m‐thick, upward coarsening Cenozoic clastic succession in the shared footwall of the N‐striking, E‐directed Cianzo thrust fault and transverse, NE‐striking Hornocal fault. Growth strata within upper Miocene levels indicate syncontractional accumulation adjacent to the Hornocal fault. Measured stratigraphic sections show upsection changes from (1) paleosol‐rich, distal‐fluvial sandstones (∼400 m Paleocene‐Eocene Santa Bárbara Subgroup) to (2) braided fluvial sandstones and mudstones (∼1400 m upper Eocene‐Oligocene Casa Grande Formation) to (3) distributary fluvial megafan sandstones and conglomerates (∼3300 m upper Oligocene‐Miocene Río Grande Formation) to (4) alluvial fan conglomerates (∼1600 m upper Miocene Pisungo Formation). The 40Ar/39Ar geochronological results for interbedded tuffs indicate continuous Río Grande deposition from at least 16.34 ± 0.71 to 9.69 ± 0.05 Ma. Sandstone petrographic results define distinct upsection trends in lithic and feldspar content, potentially distinguishing the Western Cordillera magmatic arc from Puna‐Eastern Cordillera thrust‐belt sources. In addition to growth stratal relationships and 40Ar/39Ar ages, conglomerate clast compositions reflect distinct lithologic differences, constraining activation of the Cianzo thrust and coeval reverse slip on the reactivated (inverted) Hornocal fault. Finally, detrital zircon U‐Pb ages, paleocurrents, and facies patterns distinguish local from distal sources, revealing a systematic forelandward (eastward) advance of Eocene through upper Miocene fold‐thrust deformation.
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