EVIDENCES OF AN EARLY CRETACEOUS FLORISTIC CHANGE IN PATAGONIA, ARGENTINA

Abstract

A new lithostratigraphic scheme has been proposed for the previous Baqueró Formation (Santa Cruz Province, Argentina), which is now considered to be a Group including three formations: Anfiteatro de Ticó the oldest, Bajo Tigre the middle and Punta del Barco the youngest. The distribution of plant fossils at several localities where these formations occur has shown that there are two different plant assemblages that are consistently present over a wide area. A detailed study of the distribution of all plant species known to be present in the Baqueró Group led to define two biozones, viz. Ptilophyllum (lower) and Gleichenites (upper). The main differences concern the disappearance of all Bennettites and most Cycads and Ginkgoales in the upper biozone, which in turn is clearly dominated by a gleicheniaceous fern assemblage. The latest Barremian to early Aptian age that has so far been accepted for this fossil flora, and the change of components in both biozones, suggests that this time interval may well correspond to the late Barremian to Early Aptian extinction event that has been proposed in other regions. This event was closely related to a strong volcanic activity that has also been recorded in the Baqueró Group. It is suggested that the vegetation during the time span represented by the Baqueró Group developed under stressful conditions that caused extinctions and a consequent change of the environmental scenario.

KEY WORDS. Argentina. Patagonia. Early Cretaceous. Paleobotany. Biostratigraphy.