congresos y reuniones científicas
LATE-HOLOCENE PALEOENVIRONMENTAL CHANGES OF LAGUNA BLANCA GRANDE (BUENOS AIRES, ARGENTINA) INFERRED FROM MULTI-PROXY LACUSTRINE RECORDS
RODRIGUEZ ABAUNZA G. ALEJANDRA; LOPEZ-BLANCO CHARO; PEREZ LAURA; SEITZ CARINA; CUÑA RODRIGUEZ CAROLINA; OXMAN BRENDA; BENNET KEITH; FONTANA SONIA
Congreso; REUNIÃO REGIONAL PALEO RS 2017; 2017
SOCIEDADE BRASILEIRA DE PALEONTOLOGIA
The Pampean plain, located in Central-East of Argentina, is a strategic area for paleo-climatic studies, given the large number of lakes that provide continuous records of local environmental changes. Two consecutive sediment cores were recovered from the deepest part of the Laguna Blanca Grande and were sub-sampled every 5 cm for diatoms, cladocerans and ostracods. The sediment chronology is based on three 14C dates from bulk sediment, which dated the sediment record back to 800 years BP. Regarding the diatom record it was registered a total of 55 taxa (30 were identified to species level), representing 34 genera. The dominant taxa were planktonic, i.e., Aulacoseira and Cyclotella genera, but it was also registered with lower abundance some benthic diatom taxa, e.g., Fragilaria construens and Staurosira longirostris. Most of the diatom species are related to freshwater, alkaline, and eutrophic inland water systems. Cladoceran assemblages are characterized by the dominance of the planktonic Bosmina and by other littoral-benthic cladocerans, whose relative abundance are lower throughout the whole sediment record (Chydorus cf. sphaericus, Leydigia cf. leydigii, Coronatella sp., Alona affinis, Pleuroxus sp.). Changes in relative abundance of the planktonic Bosmina at expenses of the benthic Leydigia suggest minor water level changes during the last millennium. About ostracods, four species of ostracods were recorded: Limnocythere cusminskyae, Heterocypris incongruens, Cyprideis salebrosa and Ilyocypris ramirezi. Limnocythere cusminskyae was the dominant species, suggesting strong alkalinization processes in the lake. The population structure suggests that the ostracod assemblages deposited in situ, representing an autochthonous thanatocoenosis characteristic of depositional environments with moderate to -high energy levels. As preliminary results, all three biological proxies are indicating that Laguna Blanca Grande prevailed with eutrophic and alkaline conditions, with relatively high energy levels, and with minor water level changes during the last millennium. Furthermore, since 300 years BP an increase in the benthic diatoms and presence of high trophic indicator species would suggest more marked changes with the decrease in the water level and nutrient enrichment of the lake.