STRATIGRAPHIC ARCHITECTURE AND PROVENANCE OF THE CRETACEOUS CERRO BARCINO FORMATION, PATAGONIAN BROKEN FORELAND BASIN, SOUTHERN ARGENTINA

The Las Plumas and Cerro Castaño members of the Cerro Barcino Formation comprise an anomalously coarse-grained interval within the widespread and dominantly fine-grained Cretaceous Chubut Group of the Patagonian broken foreland basin, Chubut Province, Argentina. The coarse-grained character and distal position of this stratigraphic interval may signal a change from a continuous to broken foreland basin setting. To address this hypothesis, we assess the provenance and depositional history of the upper Lower Cretaceous Las Plumas-Cerro Castaño succession. We employ a multifaceted provenance approach including detrital zircon U-Pb geochronology, conglomerate clast counts, and sandstone petrography. Detailed unit descriptions, correlated stratigraphic sections, and detrital zircon U-Pb maximum depositional ages are used to refine the regional chronostratigraphic framework. Our results indicate maximum depositional ages of 107.4 ± 0.86 Ma (Albian) for the Cerro Castaño Member and 107.6 ± 1.2 Ma (Albian) and 96.2 ± 1.5 Ma (Cenomanian) for the Las Plumas Member. Provenance results indicate a polarity reversal from a west-derived Andean sediment source (<145 Ma) during deposition of the Cerro Castaño Member to east-derived intrabasinal basement-uplift sources (~188-177 Ma and >300 Ma) during deposition of the Las Plumas Member. This switch in dominant detrital age populations is accompanied by a change in depositional environment from fine-grained fluvial-lacustrine to conglomeratic braided fluvial conditions. We conclude this late-Early Cretaceous shift in sedimentary provenance signals foreland basin partitioning by basement-involved uplift during earliest Andean shortening.