EXPERIMENTAL TAPHONOMY OF FRESHWATER DIATOMS: DISCRIMINATING BETWEEN CHEMICAL AND PHYSICAL CAUSES OF FRUSTULE FRAGMENTATION

HASSAN, GABRIELA S.; DIAZ, MARISEL

PALAIOS

SEPM-SOC SEDIMENTARY GEOLOGY

Lugar: Lawrence; Año: 2023 vol. 38 p. 125 - 135

0883-1351

Frustule fragmentation is one of the major taphonomic factors affecting diatompreservation in Pampean shallow lakes. Although this has been demonstrated bytaphonomic studies conducted on extant and fossil material, little is known about thecauses of frustule breakage and its environmental significance. Field studies alongmodern environmental gradients showed a low but significant correlation betweendissolution and fragmentation. Reworking of sediments by wind action has also beensuggested as a plausible explanation for the fragmentation patterns observed in thefield. To evaluate the relative importance of chemical and physical causes of diatomfragmentation, three laboratory experiments were conducted to test for 1) the effect ofphysical agitation, 2) the effect of chemical dissolution, and 3) the joint effect of bothvariables on diatom fragmentation. Diatom samples were subjected to physicalagitation with a reciprocating shaker at 250 rpm for 20 days. Chemical dissolution wastested by mixing diatom assemblages with solutions of different concentrations of NaCland NaHCO 3 , and pH 10 for 20 days. The joint effect of both processes was testedby dissolving diatom assemblages in salt solutions and subjecting them simultaneouslyto agitation for 20 days at 250 rpm. In all cases, aliquots of each assemblage weresampled at initial and final experimental times and their preservation analyzed via theapplication of fragmentation and dissolution indices. Significant and similar differencesin fragmentation indices were observed in both dissolution alone and combinedexperiments, but no differences were found in samples subjected to agitation alone. Inall cases, dissolution and fragmentation indices were correlated, suggesting a causalrelationship between them. Overall, our results suggest that the debilitation of thediatom frustule by chemical dissolution may be the main cause of the fragmentationpatterns observed in surface sediments of Pampean shallow lakes.