TAPHONOMIC ANALYSIS OF MOLLUSKS BELOW THE SEDIMENT-WATER INTERFACE IN NAHUEL RUCÁ LAKE (BUENOS AIRES PROVINCE, ARGENTINA). The preservation of mollusk remains below the sediment-water interface in Nahuel Rucá lake (37°37′S–57°25′W) was analyzed in order to determine the degree of taphonomic alteration and to estimate the vertical extension of the taphonomically active zone (TAZ). To achieve that, the preservation patterns observed in five cores sampled from the littoral zone were described, and the effect of depth and presence of periostracum on shell dissolution was assessed by means of a field experiment. In all cores the recovered remains were dominated by fragments. Seven species were found: Biomphalaria peregrina (d'orbigny, 1835), Drepanotrema kermatoides (d'Orbigny, 1835), Heleobia australis (d'Orbigny, 1835), H. parchappii (d'Orbigny, 1835), Pomacea canaliculata (Lamarck, 1801), Uncancylus concentricus (d'Orbigny, 1835) and Musculium argentinum (d'Orbigny, 1835). We concluded that the TAZ extends from the surface to a depth of approximately 25 cm. The highest destruction takes place in the first 10 cm and decreases gradually with depth. In a similar way, specific richness and abundance decrease downward through the TAZ, and only H. parchappii and unidentified fragments are found near the bottom. Dissolution was higher in shells without periostracum. No differences in dissolution were observed with depth.
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Vol. 49 • No. 4