Independent time markers validate 210Pb chronologies for two shallow Argentine lakes in Southern Pampas

FRANCISCO CÓRDOBA; EDUARDO PIOVANO; LUCÍA GUERRA; SANDOR MULSOW; FLORENCE SILVESTRE; MARCELO ZÁRATE

QUATERNARY INTERNATIONAL

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2016

1040-6182

We report here the results of detailed 210Pb analysis from two lake sediment cores collected from LagunasEncadenadas del Oeste (LEO), located in the southern Argentinean Pampas (37S, 62W). Non-exponentialand non-monotonic 210Pbuns depth-profiles in the sedimentary record of these shallow lacustrine systemsindicate the interaction of complex processes behind radionuclide fluxes and lake sedimentation. Thechronologies and sediment accumulation rates (SAR) for the lake sediment sequences were modeledusing different 210Pb-based mathematical models. Since modeled 210Pb ages must be validated againstindependent stratigraphic markers of known age, two chrono-stratigraphic markers were selected tocontrol the upper and lowermost parts of the 210Pb dated sediments. The younger stratigraphic marker ofAD 1980 ± 2 corresponds to an uppermost organic carbon-rich mud accumulated by 1977e78 matchingthe most noticeable lake highstand occurred during the 20th century, registered on instrumental andpaleolimnological records across the Pampean Plains. The oldest stratigraphic marker corresponds to AD1878 ± 10 matching with a high lake productivity and wet phase related to anomalously intense rainfalland flooding events in southeastern South America for AD 1877e1878. When comparing the resultingages to the stratigraphic markers, our results show that CRS-model (constant rate of supply) performsbetter than the other models. Thus, these independent chronostratigraphic markers used along thesedimentary records were critical to validate 210Pb-derived ages and therefore to select the mostappropriate model to establish the chronological framework of the recent sediments of the LEO system.The CRS-model appears to be an adequate technique for deriving ages and SAR in the LEO sedimentaryrecord and other Pampean lacustrine systems under strong hydrological variability.