Actualistic Taphonomy of freshwater mollusks from the Argentine pampas: an overview of recent research progress

DE FRANCESCO, CLAUDIO G.; HASSAN, GABRIELA S.; CRISTINI, PAULA A.; TIETZE, ELEONOR

Montevideo

Workshop; First Workshop Actualistic Taphonomy in South America; 2017

Universidad de la República, Facultad de Ciencias

Historically, the development of taphonomic studies in freshwater environments hasbeen scarce and mainly restricted to the Northern Hemisphere, with almost noinformation on how taphonomic processes work (and eventually differ) in theSouthern Hemisphere. We present here an overview of the main results obtained inactualistic taphonomic studies on freshwater mollusks conducted in the Pampa Plainof Argentina, since 2008. Research included patterns of distribution of live and deadmollusks, live/dead fidelity at local and regional scales and dead and fossil shellpreservation. Studies were conducted above and below the sediment-water interface(SWI), including both descriptive and experimental approaches. Live/dead fidelityand taphonomic studies were compared between streams and lakes (the two mostconspicuous aquatic environments in the area) and among shallow lakes exhibitingdifferences in water quality and substrate. Additionally, a field experiment of two anda half years of duration was placed in one of these lakes to evaluate shell dissolutionbelow the SWI. Overall, results indicated that DAs reflected the richness andevenness of modern communities as well as shell size, and exhibited variations due tolocal environmental conditions (salinity, hardness, productivity). Fidelity inabundance of single species was poor, with dead shells being more abundant inhigher saline lakes. The taphonomically active zone occupies the first 10 cm belowthe SWI. Below that depth no significant differences in preservation are observed.The main process affecting shell surface was dissolution probably due to changesproduced by microbial maceration of organic matrix. Preservation was better insaline lakes, which may allow to explain the high concentration of well-preservedshells usually found in Holocene sedimentary successions.