FLORA OF THE LA COLONIA FORMATION (MAASTRICHTIAN, LATE CRETACEOUS), CHUBUT, PATAGONIA, ARGENTINA

What little is known on Maastrichtian floras of Southern South America is based primarily on five floras, four from Chile (Río de las Chinas, Quiriquina, Pichasca, and Cerro Guido) and one from Argentina (Estancia La Sara), which have been characterized mostly by palynological data. In this contribution, we describe a new Maastrichtian flora, the La Colonia flora from Chubut, Patagonia, Argentina. The La Colonia Formation outcrops in an area known as the Somuncurá Massif, exposed between Telsen and Sierra Rosada in Chubut province. The formation is a homogeneous series of fining sediments divided into three portions: lower, middle, and upper. Argillaceous sediments characterize the lower and middle portions of the sequence, which is considered to be continental and probably represents lacustrine deposits. The upper portion of the sequence is a marginal to shallow marine environment. A diverse vertebrate fauna, including fishes, turtles, snakes, plesiosaurs, birds, mammals, and dinosaurs are known from the continental facies of the sequence. The fossils we report here were collected at the Cañadón del Irupé locality, from clay deposited in a littoral lagoon environment.

Previously, the paleoflora was known from its aquatic fern components (Paleoazolla, and Regnellidium). However, recent paleobotanical collections have revealed the presence of a more diverse plant assemblage associated with these aquatic ferns, including pteridophytes, gymnosperms, and several angiosperms. Angiosperms are represented by the aquatic Nymphaeaceae (seeds) and Nelumbonaceae (leaves and fruits), and at least five additional leaf morphotypes.