Albian and Cenomanian angiosperm dominated floras from the Austral Basin, Argentina

Abstract

We described compression floras dominated by angiosperm in two Cretaceous formations in the area of the Tres Lagos town, Santa Cruz Province, Southern Patagonia. Four localities comprise a new flora at the highest levels of Piedra Clavada Formation (middle to upper Albian), which exhibit thirteen different leaf angiosperm forms of which only two are known in the overlying floras (middle Cenomanian) from Mata Amarilla Formation. Most leaf forms (MPM-PB) correspond to simple leaves of entire margin and pinnate venation with intramarginal veins and well developed drip-tips, follow in abundance by acrodromous and semicraspedodromous veined leaves, and palmatilobed forms. Associated to leaves there were found seeds, fruits, and flowers. The review of these floras and their recent certification of ages, state down that diversification and dominance of angiosperms occur very early in time at the Austral Basin. These data strengthen previous hypothesis based on palynofloras, establishing a floristic change characterized by a rapid diversification of angiosperms in the Albian. The new data suggest the need of a review of angiosperm evolutionary patterns in Patagonia with more precise geochronologic dates. During the Cenomanian, several floras of the world show the beginning and dominance of angiosperms in certain paleo-environments. But, it is evident that the flora of Piedra Clavada Formation is preserving a significant radiation of flowering plants that partly continue into the middle Cenomanian. The clues of this early radiation are unknown, but probably could be correlated with paleogeographic and paleoclimatic events at the middle Cretaceous and the angiosperm leaf photosynthetic capability.