Shell strength of Eucallista purpurata (Bivalvia) from life and death assemblages on sandy beaches of the Bonaerense coast, southwest Atlantic Argentina

Abstract

Mollusc shells are among the most abundant and well-preserved organisms in sediments worldwide, but their shells are usually subject to fragmentation due to exposure time in the TAZ, which compromises their preservation potential. The shell strength of valves from life and death assemblages from the sandy beaches of Santa Clara (37°50′49″S, 57°30′16″W) and Mar Chiquita (37°44′45″S, 57°25′1.5″W) on the Bonaerense coast, southwest Atlantic Argentina, was analysed to capture the effect of taphonomic processes over time and to determine how intrinsic properties and taphonomic variables influence their shell strength. To achieve this, the mechanical resistance profile of the bivalve Eucallista purpurata was assessed using point load and microindentation tests, and the mineralogical composition and organic matter content of the shell, as well as morphological variables, were measured. We concluded that, as expected, shells from life assemblages were more resistant to compression than those from death assemblages, but surprisingly, right valves were more resistant to compression than left valves in both Mar Chiquita and Santa Clara death assemblages. No differences were observed between broken and unbroken shells.