ASSESSING THE INFLUENCE OF SALINE AND ALKALINE ENVIRONMENTS IN THE PRESERVATION OF PAMPEAN DIATOMS: AN EXPERIMENTAL APPROACH

DIAZ, MARISEL; HASSAN, GABRIELA

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Año: 2019 vol. 56 p. 471 - 492

0002-7014

Diatom dissolution is controlled by environmental conditions prevailing during fossilization. In Pampean shallow lakes, diatomdissolution showed important correlations with gradients of salinity, pH, carbonate, and bicarbonate, being these the most probable causes ofthe observed shifts in Holocene assemblages preservation. In the present contribution, a series of experiments were conducted in order todemonstrate the effect that physical-chemical lake characteristics exert on Pampean diatom assemblages preservation. three experimentalassemblages were subjected to the effect of three concentrations of two salts, NaCl (0.6, 1.2 and 3M) and NaHCo3 (0.6, 0.9, and 1.2M), and twopH values (7 and 10). Aliquots of the experimental solutions were removed once each five days for 20 days, and analyzed for changes in dissolvedsilica concentration (SiDi), relative and absolute abundances of diatoms, and dissolution indices (DDI) based on the target taxon Cyclotellameneghiniana. All the experimental solutions increased the SiDi significantly, particularly since day 10. these increased SiDi values wereaccompanied by significant changes in the DDI, which reached maximum values at pH 10, and by evidence of dissolution observed in SEM images,whereas no significant changes in relative or absolute abundances of diatoms were registered. these experimental results demonstratedthe impact that water chemistry can exert on diatom dissolution in Pampean shallow lakes, even during short-term exposures. Given thenaturally high pH, NaCl and NaHCo3 concentrations characteristic of many of these lakes, these experimental findings can be confidently extrapolatedto the interpretation of the dissolution trends found in modern and fossil sedimentary assemblages.