SERIAL PLANKTONIC FORAMINIFERA FROM THE PALEOGENE OF THE TIERRA DEL FUEGO ISLAND, SOUTH AMERICA

摘要

In the lower Paleogene of the Austral (Magallanes) basin, planktonic foraminifera are small and very scarce. Those in the Fuegian Andes, the orogenic margin of the basin, are serial forms that are also relatively minute and generally scarce. These include species of Chiloguembelina coeval with chiloguembelinid abundance peaks in the Atlantic that have been associated with nutrient-enriched waters. The Punta Noguera Formation, which is rich in radiolarians and phosphatic nodules, yielded only two planktonic foraminiferal species, both of Chiloguembelina. One is C. wilcoxensis (Cushman and Ponton), a well-known index species that constrains the minimum age of the unit to the early Eocene. The other, C. noguerensis n. sp., is geographically restricted, and it is distinguished by its test surface that is covered with a conspicuous, irregular reticulation formed of coalescing pustules. In the Fuegian Andes, the triserial planktonic foraminifera Jenkinsina triseriata (Terquem) occurs in the upper lower Eocene section, but there is no record of serial planktonic foraminifera in the middle Eocene, partially due to an unconformity. Higher in the section, upper Eocene strata yield abundant C. ototara in association with Praetenuitella insolita (Jenkins), and Oligocene strata have scarce C. cubensis (Palmer).