COMPARATIVE TAPHONOMY OF MOLLUSK ASSEMBLAGES IN QUATERNARY FRESHWATER SEQUENCES FROM THE SALADO RIVER BASIN, BUENOS AIRES --- Preprint doi: 10.5710/AMGH.28.11.2017.3139

María F. Pisano, Nicole M. Pommares, Mariel S. Luengo, Enrique E. Fucks

Abstract


From the analysis of taphonomic attributes of specimens of Heleobia parchappii found in fluvial and paleolacustrine sequences of the lower basin of the Salado River, the surface alteration of their shells was studied comparatively in order to assess differences between both environments. Main results obtained through NMDS and ANOSIM test (R=0.31, p<0.01), allowed recognition and statistical differentiation of both groups of samples. The taphonomic characteristics of those recovered from the paleolacustrine environment are more similar to each other while those from the fluvial environment showed greater dispersion. Through the SIMPER analysis we could determine that the discoloration and dissolution variables were the most important features to differentiate both groups, and the values of the indexes (Total Taphonomic Grades) were always higher in the paleolacustrine assemblages, showing greater decay. The differences of preservation could be explained by the residence time of the remains near the water-sediment interface, as well as by the differences in the sedimentation rate in both environments, which control the different exposure cycles of the shells.
These differences would be related to changes in the hydrological regime (fluctuations in surface and groundwater levels) that, although affecting the entire study area, are more intense and frequent in shallow lakes favoring decay of the shells accumulated in this environment.

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