Actualistic taphonomy of freshwater diatoms: Implications for the interpretation of the Holocene record in Pampean shallow lakes

Abstract

Recent findings of noticeable changes in diatom preservation in the Holocene record of Pampean shallow lakes evidenced the need for carrying out actualistic studies to decipher the environmental significance of taphonomic signatures. In this chapter, we review a series of field and experimental studies recently conducted, focusing on the effect of contemporary environmental gradients on the dissolution and fragmentation of diatomvalves. Field studies signaled salinity, carbonates, and bicarbonates as the main drivers of dissolution of the target taxon Cyclotella meneghiniana in shallow lakes covering wide environmental gradients. Laboratory controlled experiments demonstrated a negative effect of NaCl and HCO3Na on valve preservation, evidenced by an increase in dissolved silica and by the occurrence of valves showing advanced stages of dissolution. Detailed analysis of taphonomic attributes and their relationship with live/dead agreement at a freshwater lake showed that within-lake taphofacies are useful to discriminate between diatom subenvironments. The joint analysis of compositional and taphonomic variations in the recent sedimentary record of the lake demonstrated the usefulness of taphonomic analyses to uncover subtle paleoenvironmental variations,which could be overlooked if only traditional compositional analyses were performed. The strong link between compositional and taphonomic patterns at different working scales highlighted the usefulness of including taphonomic analyses when conducting diatom-based paleoenvironmental studies in environmentally heterogeneous shallow lakes.