Compositional fidelity and taphonomy of freshwater mollusks in three pampean shallow lakes of Argentina

TIETZE, ELEONOR; DE FRANCESCO, CLAUDIO GERMÁN

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2017 vol. 54 p. 208 - 223

0002-7014

Three shallow lakes from the southeastern pampas, which exhibit differences in their physic-chemical characteristics of water and substrate, were studied with the aim of comparing live/dead fidelity and preservation of mollusk shells. The studied lakes were Las Mostazas (LM; 37°9´57″S; 57°14´50″W), Los Carpinchos (LC; 37°3´34″S; 57°19´56″W) and Nahuel Rucá (NR; 37°37´21″S; 57°25´42″W). The three lakes exhibited differences in specific richness, abundance, compositional fidelity, and taphonomic alteration. The lake that presented the higher values of conductivity (3.34±0.72), hardness (286±83 mgl-1) and carbonates saturation index (SIcalcite= 1.95±0.21) was the one that recorded lower specific richness in living assemblages, differences in richness and diversity between living and death, and was the only lake where the number of species was higher in dead assemblages (R=5) than in living communities (R=2), suggesting a higher residence time in the taphonomically active zone. On the other hand, the lakes with lower values of the same characteristics (conductivity= 2.2±1.2; 0.8±0.5; hardness= 157±55; 250±127 mgl-1; SIcalcite= 0.35±0.15; 0.43±0.36, for LC and NR respectively) showed a higher species richness, lower number of species in dead assemblages (8 species) than in living communities (10 species) and taphonomic attributes that suggested recently dead and deposited individuals. All these results suggest that water conditions in these lakes decreases the preservation of carbonate remains in comparison with the previously mentioned lake. Even though the lakes are located close from each other and have similar shape and depth, the differences in water characteristics may be affecting shell preservation giving rise to different fossil assemblages.