Paleogene Phytogeography and Climatology of South America

Abstract

Paleogene, Maastrichtian, and Miocene floras are reviewed. They are located on continental margins, where several sedimentary basins developed. The affinities of the fossil genera to living ones allow the recognition of three paleofloras: Neotropical, Mixed, and Antarctic. These could be the forerunners, respectively, of the presently more humid dominions in Neotropical Region (Caribbean, Amazonic, and Guayano), of the drier ones (Chaquefto and Andino-Patagonico), and ofthe Subantarctic Dominion of the Antarctic Region. The South American climate, as indicated by the fossil floras, showed a trend to higher temperatures during the Paleocene and Lower Eocene, and a deterioration through the Middle and Upper Eocene. The purpose of the present work is to review the Paleogene taphofloras of South America and to analyze their paleophytogeographical and paleoclimatical significance. This problem has interested botanists and paleontologistsin the past. Berry (1921,1938,1940) published several reviews as a direct result of his work in the continent. More recently, Menendez (1964, 1969, 1971) detailed the taphofloras and the areas occupied by the different types of vegetation, and Volkheimer (1971) gathered evidence about the paleoclimatology of Argentina. Later, Archangelsky and Romero (1974) analyzed the environmental conditions based on the pollen record of the southern South American Paleogene, and Aragon and Romero (1984), Romero (1978), Romero and Arguijo (198 1b, 1982), and Romero and Dibbern (1984) analyzed some taphofloras of the same region. Therefore, much new geological, botanical, and paleontological evidence has been gathered, warranting a new review. The present paper is arranged in two parts. The first one reviews every published outcrop with impressions known to the author from the Paleogene of South America, complemented with information about fruit casts, petrified wood, and palynology. Data about some Maastrichtian and Miocene floras have been added to show more general trends in the changes. The age of the deposits was updated according to recent publications. The second part discusses the phytogeographical areas that could have existed during that time, and the climate under which they have developed. There is not an agreement on the terminology to be used in biogeographical discussions, especially among paleobotanists. I shall use a few of them, in an attempt to reach more accuracy and clarity, but without discussing their antecedents or convenience, which surpasses the limits of the present paper. They are: Flora. The list of the plants living together in a given area at a given moment. They may be fossil or living. Vegetation. Plant cover in a given area at a given moment, fossil or living. Their association, ecology, and life forms, rather than their taxonomic identity, are considered. Taphoflora. The list of the fossil plants preserved in a given outcrop. They represent the original flora, as affected by dispersal, burial in that place, diagenesis, and differential alteration. They are the smallest real evidence to be used in paleophytogeography. Paleoflora. A fossil flora that may be characterized by its systematic list, and so differentiated from other fossil floras. Each paleoflora may comprise several taphofloras. From the characteristic systematic list a characteristic plant association may be hypothesized, and so vegetational features suggested. A REVIEW OF THE PALEOGENE TAPHOFLORAS