Syn-Eruptive Taphoflora From The Agua De La Zorra Formation (Upper Triassic) Cuyana Basin, Mendoza, Argentina

Abstract

In the North of Mendoza Province, at Paramillos de Uspallata locality, Triassic sedimentary rocks outcrop. These Triassic beds are grouped in four formations: Paramillos, Agua de la Zorra, Portezuelo Bayo and Los Colorados. The Agua de la Zorra Formation is characterized by deposition in a deltaic and lacustrine system. The aims of this contribution are: (1) to realize a systematic study of new plant remains found in the Agua de la Zorra Formation and (2) to analize the influence of the potential of preservation and the volcanism in the Agua de la Zorra taphoflora in contrast with other Triassic units. Plant remains were systematically collected and compared with taphofloras from other Triassic formations of the Cuyana Basin. The systematic study from the Agua de la Zorra Formation allowed the determination of 21 taxa, nine of which have been cited in a previous contribution and 12 were described for the first time for the Agua de la Zorra Formation. There are differences in the taxonomic diversity between the taphofloras recovered from Potrerillos and Paramillos formations and these differences are linking with differences in biostratinomic process in each fluvial system and linked with the evidence of volcanic processes in these areas. The differences in diversity in the taphofloras of the Cacheuta and Agua de la Zorra formations can be more associated to ecological differences than variations in the taphonomic processes in each of the lake systems.

The influence of volcanic activity and trophic state on plant taphonomic processes in Triassic lacustrine-deltaic systems of western Gondwana

“…The palaeofloras diversity from the Potrerillos–Cacheuta sequence and the Agua de la Zorra Formation was discussed in a previus contribution (Pedernera et al . 2019) and the differences observed in the palaeoflora recorded in these units have been attributed to ecological differences than variations in the taphonomic processes in each of the lake systems (Pedernera et al . 2019).…”

“…2019) and the differences observed in the palaeoflora recorded in these units have been attributed to ecological differences than variations in the taphonomic processes in each of the lake systems (Pedernera et al . 2019). The underlying unit to the Agua de la Zorra Formation is the Paramillos Formation, which presents a high degree of volcanic influence, characterized as a pyroclastic flow that would have buried the forest floors that developed there (Brea et al .…”

Plant Taphonomy in a Lake Affected by Volcanism (Agua De La Zorra Formation, Upper Triassic) Mendoza, Argentina

“…The Agua de la Zorra Formation is interpreted as a deltaic-lacustrine system with episodic incursions of lava flows into an aquatic environment (Cortés et al 1997;Ottone et al 2011). It includes two facies association AZ-A and AZ-B (Table 1) (Pedernera et al 2019). The AZ-A facies association presents dark greenish-gray, fine-grained, well-sorted massive sandstone (Sm), with the sandstones in contact with basalts showing various types of alteration, as 5 mm diameter vesicles and carbonate cemented nodules; light brownish-gray massive muddy siltstone (Fm); moderate-light-gray coarse-grained, well-sorted ripple cross-stratified sandstone (Sr), and pebbly trough cross-stratified sandstone (St), interpreted as representing a delta associated with mouth bars at the delta front (Pedernera et al 2019).…”

“…It includes two facies association AZ-A and AZ-B (Table 1) (Pedernera et al 2019). The AZ-A facies association presents dark greenish-gray, fine-grained, well-sorted massive sandstone (Sm), with the sandstones in contact with basalts showing various types of alteration, as 5 mm diameter vesicles and carbonate cemented nodules; light brownish-gray massive muddy siltstone (Fm); moderate-light-gray coarse-grained, well-sorted ripple cross-stratified sandstone (Sr), and pebbly trough cross-stratified sandstone (St), interpreted as representing a delta associated with mouth bars at the delta front (Pedernera et al 2019). Facies association AZ-B is dominated by black, olive black, greenish-red, and greenish-black finely laminated mudstone (Fl); light brownish-gray massive muddy siltstone (Fm), horizontally laminated fine to coarse-grained well-sorted sandstone (Sh), and massive white tuff (Tf) interpreted as prodelta to offshore lacustrine deposits (Pedernera et al 2019).…”

“…The Agua de la Zorra paleoflora is diverse and includes vegetative parts (fronds and simple leaves) of Equisetales (Neocalamites), ferns (Cladophlebis), Umkomasiales (Dicroidium, Jhonstonia, Xylopteris, and Zuberia), Ginkgoales (Sphenobaiera), Voltziales (Heidiphyllum), Coniferales (Rissikia) and Gymnosperms of uncertain affinity (Linguifolium), including reproductive structures (strobili, ovules/seeds) (e.g., Cordaicarpus) (Ottone et al 2011;Pedernera et al 2019). Freshwater invertebrates, including conchostracans, have been described in the same lacustrine facies (Bustos Escalona et al 2019).…”