Acta Palaeobotanica 41(2): 115–122, 2001

The Ticó Flora (Patagonia) and the Aptian Extinction Event

Summary: The Aptian Ticó Flora from southern Patagonia has been studied with detail for over 30 years. Fossils are found in the three formations that constitute the Baqueró Group: Punta del Barco the upper, Bajo Tigre the middle and Anfiteatro de Ticó de lower. Two biozones are recognized, viz. the lower Ptilophyllum and the upper Gleichenites Zone. The Ptilophyllum Zone is characterized by the dominance of bennettites conifers and presence of cycads, ginkgophytes, pteridosperms and pteridophytes. Angiosperms although present in this zone are scarce, represented by both macroscopic remains and palynomorphs. A unfossiliferous stratigraphic interval separates the lower zone from the upper Gleichenites Zone. Here ferns are dominant; conifers and cycads are present while bennettites and ginkgophytes are absent. The strong volcanic activity that occurred during the deposition of the Baqueró Group is a probable cause for the drastic floristic change. A brief analysis of the vegetation known in most palaeofloristic regions during the mid Cretaceous confirms that similar variations occurred at different latitudes and continents. During the Aptian, global vegetational changes, including extinctions at an order level, were initiated and later followed by gradual angiosperm radiation. From a palaeobotanical perspective, the Aptian Extinction Event is an episode of importance, deserving a higher status among other minor events. It may have a similar level that is adscribed to changes at the K T boundary.

Keywords: Ticó flora, Aptian, Cretaceous, Patagonia, Argentina