Taphonomic analysis of Spinicaudata from two Triassic lacustrine systems affected by different volcanic processes

Abstract

Spinicaudata are freshwater branchiopods. The growth and development of spinicaudata populations in freshwater environments depend on various physical, chemical, and biological factors. The action of volcanism modifies the limnological parameters in the process of fossilization of lacustrine deposits. This study identifies spinicaudatan assemblages in two Triassic lake systems in Argentina, and analyzes the dynamics of shell preservation according to the volcanic activity involved. Two taphonomic grades divided into three different second taphonomic grades were defined. The focus on taphonomic and chemistry studies addresses changes in spinicaudata abundance and richness through time, in different paleoenvironmental conditions, and shell preservation and chemical composition. The discussion highlights the importance of lava flow inflow and volcanic ash fall in the different lake systems. We emphasize the importance of taphonomic studies on the spinicaudata groups to understand their autochthonous and allochthonous populations in Triassic lake systems. In turn, we conclude that the post mortem processes experienced by the shells, the exposure time at the water-sediment interface, and the chemical alteration of the water into the paleolakes produced by the surrounding volcanic activity can explain the development and preservation of spinicaudata in these two Triassic lacustrine systems.