New age constraints for the Salamanca Formation and lower Rio Chico Group in the western San Jorge Basin, Patagonia, Argentina: Implications for Cretaceous-Paleogene extinction recovery and land mammal age correlations

作者：Clyde William C^*; Wilf Peter; Iglesias Ari; Slingerland Rudy L; Barnum Timothy; Bijl Peter K; Bralower Timothy J; Brinkhuis Henk; Comer Emily E; Huber Brian T; Ibanez Mejia Mauricio; Jicha Brian R; Krause J Marcelo; Schueth Jonathan D; Singer Bradley S; Raigemborn Maria Sol; Schmitz Mark D; Sluijs Appy; Zamaloa Maria del Carmen

来源：Geological Society of America Bulletin, 2014, 126(3-4): 289-306.

DOI：10.1130/B30915.1

The Salamanca Formation of the San Jorge Basin (Patagonia, Argentina) preserves critical records of Southern Hemisphere Paleocene biotas, but its age remains poorly resolved, with estimates ranging from Late Cretaceous to middle Paleocene. We report a multi-disciplinary geochronologic study of the Salamanca Formation and overlying Rio Chico Group in the western part of the basin. New constraints include (1) an Ar-40/Ar-39 age determination of 67.31 +/- 0.55 Ma from a basalt flow 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 resolution-multi 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 Penas Coloradas Formation (Rio Chico Group), and (4) paleomagnetic results indicating that the Salamanca Formation in this area is entirely of normal polarity, with reversals occurring in the Rio 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 paleobotanical assemblages from this area are here assigned to C28n (64.67-63.49 Ma), similar to 2-3 million years older than previously thought, adding to growing evidence for rapid Southern Hemisphere floral recovery after the Cretaceous-Paleogene extinction. Important Peligran and %26quot;Carodnia%26quot; zone vertebrate fossil assemblages from coastal BNI and Penas Coloradas exposures are likely older than previously thought and correlate to the early Torrejonian and early Tiffanian North American Land Mammal Ages, respectively.

• 出版日期2014-4