Triassic charophytes (Porocharoideae and Stellatocharoidae) from Argentina (Cerro Puntudo Formation)

BENAVENTE, CECILIA ANDREA

Mendoza

Simposio; 6th International Symposium on Extant and Fossil Charophytes; 2012

University of Wollongong

Charophyte remains have been found in the Cerro Puntudo Formation (Anissian) constituting the first record of the group for Gondwana in the Triassic. The Cerro Puntudo Formation is part of the Cuyana Rift Basin continental infilling. The unit is mainly microbialitic carbonate and represents sedimentation in alluvial-fluvial and lacustrine settings. The limestones represent three main facies: Lmd (micritic disrupted limestone), Ls (stromatolitic limestone), and Lo (oncolitic limestone). Charophyte remains are gyrogonites and associated thalli. They are found in the Lo facies along with filamentous algae, sponges and ostracodes, constituting in cases, part of the oncolites nuclei. The gyrogonites were extracted from the rocks matrix with the copper sulfate method and needles. Their diagnostic features allowed the identification of two subfamilies Porocharoideae with subprolate, ellipsoidal to subobovoidal gyrogonites; and Stellatocharoideae, characterized by gyrogonites with an apical projection (neck-like). Unfortunately, due to preservation issues no generic status could be reached. Sedimentology and paleontology indicate deposition in a restricted Ca-rich pond setting that was probably sourced by springs in the rift context. So far, all registers of charophytes for the Triassic correspond to the northern hemisphere. The present finding constitutes the first record for the Triassic of Gondwana and allows expanding the distribution of the group up to approximately 40ºS into the southern hemisphere.