Fossil woods from the early Paleocene of the Cerro Bororó Formation (central Argentine Patagonia): systematics and palaeoenvironmental considerations

Abstract

The Cerro Bororó Formation (Danian) crops out in the Bororó Hill in the centre of the Chubut Province (central Argentine Patagonia). Palaeontological studies on this formation are scarce, among them is Petriella [Estudio de maderas petrificadas del Terciario Inferior del área central de Chubut (Cerro Bororó). Revista del Museo de La Plata (Nueva Serie). Sección Paleontología 1972;4:159–254] who made the first and only descriptions of fossil woods from the Cerro Bororó Formation. We re-examined the six angiosperm fossil woods previously described by Petriella in the 1970s and analysed 10 additional samples. We studied the specimens under light and scanning electron microscopy. In addition, the angiosperm diversity, the growth rings, the mesomorphy and vulnerability indices, and the wood anatomical characteristics influenced by the environment were used to get a general idea of the conditions in which these trees would have grown. Our analyses revealed that the fossil wood assemblage includes Podocarpoxylon mazzonii and Brachyoxylon raritanense in the conifer fossiliferous level and Elaeocarpoxylon sloaneoides, Euxylophoroxylon chiquichanense, Laurinoxylon americanum comb. nov., Weinmannioxylon multiperforatum, and cf. Chalkoxylon sp. in the angiosperm fossiliferous level. These findings suggest that the region experienced a warm-temperate, humid climate, which agrees with previous studies of the Cerro Bororó Formation.