Paleoenvironments and taphonomy of a Triassic lacustrine system (Los Rastros Formation, central-western Argentina)

• Main Authors: Mancuso, Adriana Cecilia, Marsicano, Claudia Alicia
• Language: unknown
• Published: 2008
• Subjects: black shale; deltaic deposit; facies analysis; fossil assemblage; lacustrine environment; paleoenvironment; sandstone; siltstone; taphonomy; trackway; Triassic; Argentia; Canada; Newfoundland; Newfoundland and Labrador; North America; Amphibia; Blattaria; Coleoptera; Conchostraca; Coniferophyta; Cycadophyta; Dinosauria; Equisetophyta; Ginkgophyta; Hemiptera; Hexapoda; Invertebrata; Pteridophyta; Therapsida; Vertebrata; Argentina
• Online Access: https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_08831351_v23_n8_p535_Mancuso; https://hdl.handle.net/20.500.12110/paper_08831351_v23_n8_p535_Mancuso

The Triassic Ischigualasto-Villa Unión Basin is an extensional basin located in central-western Argentina. It includes the Los Rastros Formation, a lacustrine-deltaic sequence comprising several coarsening-upward cycles of black shale, siltstone, and sandstone. We performed a taphonomic analysis of the floral and faunal fossils of the Los Rastros succession and have defined five plant taphofacies, four invertebrate taphofacies, and four vertebrate taphofacies. Our taphonomic model characterizes four subenviroments within the lacustrine-deltaic environment of Los Rastros Formation. These include 1) offshore lacustrine, 2) prodelta, 3) deltaic mouth bar, and 4) deltaic plain subenvironment. Our analysis of fossil assemblages allows us to reconstruct the structure of the original ecosystem. The lake margins were vegetated with small ginkgophytes, corystosperms, and sphenophytes. River margins were characterized by riparian thickets of sphenophytes, while the proximal floodplains supported closed woodlands of corystosperms, cycadophytes, and pteridophytes. More distal floodplains were covered with open conifer forests. The invertebrate fauna included insects (Blattoptera, Hemiptera, Coleoptera) associated with lakeshore vegetation and conchostracans that inhabited both the lake shoreline and smaller ponds in the floodplains. Fish and temnospondyl amphibians probably inhabited the delta plain and incoming fluvial systems. The activity of nonmammalian therapsids, crurotarsal archosaurs, and putative dinosaurs is recorded by trackway surfaces in the lake shoreline subenvironment. Copyright © 2008, SEPM (Society for Sedimentary Geology). Fil:Mancuso, A.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Marsicano, C.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.