Sr-isotope chronostratigraphy of Paleogene-Neogene marine deposits: Austral Basin, southern Patagonia (Argentina)

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• 作者：Ana Parras^a ; ^{aparras@exactas.unlpam.edu.ar} ; George R. Dix^b ; ^{gdix@connect.carleton.ca} ; Miguel Griffin^c ; ^{miguelgriffin@aol.com}
• 关键词：Sr-isotope analysis ; San Juliá ; n Formation ; Monte Leó ; n Formation ; Paleogene&ndash ; Neogene boundary ; Austral Basin ; Patagonia
• 刊名：Journal of South American Earth Sciences
• 出版年：2012
• 期刊代码：50_08959811
• 类别：ear
• 出版时间：August, 2012
• 卷：37
• 期：Complete
• 页码：122-135
• 文件大小：2196 K

摘要

The Paleogene to Neogene San Juli谩n and Monte Le贸n formations underlie the central and eastern parts of the Austral Basin (Patagonia, Argentina), and represent coastal plain to shallow shelf systems within a retroarc foreland basin east of the Andes. The formations are characterized by prominent occurrences of thin (<1聽m) densely compacted fossil concentrations, including the large oyster Crassostrea? hatcheri. Formation ages have been problematic given macrofaunal provincialism effectively precluding precise extrabasinal correlations. A Sr-isotope chronostratigraphy based on fossil shell calcite from oysters, pectinids and brachiopods is presented for a regional NE-SW-oriented transect extending 鈭?00聽km along strike of the Austral Basin. The Paleogene-Neogene boundary (鈭?3聽Ma) may occur within the uppermost San Juli谩n Formation (22.68聽Ma, with a range between 22.22 and 23.22聽Ma), coincident with a prominent glauconitic interval, or in a meteorically altered erosional paleosurface that caps this formation and may correlate with an eustatic sea level fall coincident with the global boundary. The younger Monte Le贸n Formation is entirely of early Neogene (Aquitanian to early Burdigalian) age, with ages of 22.12聽Ma (21.68-22.58) at the base to 17.91聽Ma (17.51-18.29) at the top. The proposed new chronostratigraphic framework forms a foundation for future differentiation of local, regional, and global sedimentary patterns in the Austral Basin during the Paleogene/Neogene transition; in particular, with contemporaneous basins and tectonic blocks across the southern polar region, such as in Australia, New Zealand, and Antarctica.