The Salamanca Formation of the San Jorge Basin (Patagonia, Argentina) preserves critical records of Southern Hemisphere Paleo cene biotas, but its age remains poorly resolved, with estimates ranging from Late Cretaceous to middle Paleocene. We report a multidisciplinary geochronologic study of the Salamanca Formation and overlying Río Chico Group in the western part of the basin. New constraints include (1) an 40 Ar/ 39 Ar age determination of 67.31 ± 0.55 Ma from a basalt fl ow underlying the Salamanca Formation, (2) micropaleontological results indicating an early Danian age for the base of the Salamanca Formation, (3) laser ablation HR-MC-ICP-MS (high resolutionmulti collector-inductively coupled plasmamass spectrometry) U-Pb ages and a high-resolution TIMS (thermal ionization mass spectrometry) age of 61.984 ± 0.041(0.074) [0.100] Ma for zircons from volcanic ash beds in the Peñas Coloradas Formation (Río Chico Group), and (4) paleomagnetic results indicating that the Salamanca Formation in this area is entirely of normal polarity, with reversals occurring in the Río Chico Group. Placing these new age constraints in the context of a sequence stratigraphic model for the basin, we correlate the Salamanca Formation in the study area to Chrons C29n and C28n, with the Banco Negro Inferior (BNI), a mature widespread fossiliferous paleosol unit at the top of the Salamanca Formation, corresponding to the top of Chron C28n. The diverse paleo botanical assemblages from this area are here assigned to C28n (64.67-63.49 Ma), ~2-3 million years older than previously thought, adding to growing evidence for rapid Southern Hemisphere fl oral recovery after the Cretaceous-Paleogene extinction. Important Peligran and "Carodnia" zone vertebrate fossil assemblages from coastal BNI and Peñas Coloradas exposures are likely older than previously thought and correlate to the early Torrejonian and early Tiffanian North American Land Mammal Ages, respectively.

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Sand samples collected from cores recovered at Sites C0004, C0006, C0007, and C0008, Integrated Ocean Drilling Program Expedition 316, are dominantly feldspathic litharenites containing between 18% and 40% detrital quartz within the total quartz, feldspar, lithic (QtFL) fraction. The lithic component includes a mix of volcanic, sedimentary, metamorphic, and plutonic fragments. The feldspar component is dominated by Ca-plagioclase. A grain-size control on modal composition is apparent, notably a greater concentration of feldspar grains in the finer samples. No significant stratigraphic or geographic trends in modal grain composition are observed within this sample set.