A Paleocene lowland macroflora from Patagonia reveals significantly greater richness than North American analogs

IGLESIAS, A.; WILF, P.; JHONSON, K.; ZAMUNER, A.; CUNEO, R.; MATHEOS S. D.; SINGER, B.

GEOLOGY

GSA

Lugar: Tulsa (USA); Año: 2007 vol. 35 p. 947 - 950

0091-7613

Few South American macrofloras of Paleocene age are known, limiting knowledge of diversity and composition between the end-Cretaceous event and the Eocene appearance of high floral diversity. We report new, unbiased collections of 2516 compression specimens from the Paleocene Salamanca formation (~61.7 Ma), from two localities in the Palacio de los Loros (PL) exposures in southern Chubut, Patagonia, Argentina. Our samples reveal considerably greater richness than was previously known from Paleocene Patagonia, including 36 species of angiosperm leaves as well as angiosperm fruits, flowers, and seeds; ferns; and conifer leaves, cones, and seeds. The floras, from siltstones and sandstones deposited on low-relief floodplain landscapes in a humid, warm temperate climate, are climatically and paleoenvironmentally comparable to many quantitatively collected Paleocene floras from the Western Interior USA. Adjusted for sample size, there are more than 50% more species at each PL quarry than in any comparable U.S. Paleocene sample. These results indicate more vibrant terrestrial ecosystems in Patagonian than in North American floodplain environments ~4 m.y. after the end-Cretaceous extinction, and they push back the timeline 10 m.y. for the evolution of high floral diversity in South America. The cause of the disparity is unknown but could involve reduced impact effects because of greater distance from the Chicxulub site, higher latest Cretaceous diversity, or faster recovery or immigration rates.