Aportes de la palinología al conocimiento de los embalsados holocenos de Corrientes, Argentina

Contribution of the palynology to the knowledge of embalsados in the Holocene of Corrientes, Argentina. Floating or embalsados islands in warm water bodies have few studies and share some structural properties with temperate-cold weather peat bogs for which there is more information. In Argentina, the references are reduced to the middle and lower courses of the Parana River, where the embalsados have a low frequency. The palynological analyzes carried out in the San Cristobal, Cue and Miranda lakes aim to increase knowledge about the development of this biome in the Holocene of northeastern Ibera, central region of Corrientes Province. Three cores of the bottom of the lakes were obtained and the ages were estimated by applying the age-depth model calibrated with radiocarbon dates. The qualitative-quantitative analysis of 38 palynological associations allowed the distinction of two intervals. Between 4300 and 3600 years cal BP, the vegetation was dominated by herbaceous species of angiosperms and chlorophycean algae representatives of aquatic environments, marshes and reed beds and to a lesser extent by dammed-forming species. From 3500 years cal BP onwards, the frequency and variety of aquatic species of angiosperms and chlorophycean algae decreases and the predominance of grassland species and colonizers of water mirrors increases. This change suggests the development of embalsados with the formation of organic soils in the Late Holocene, probably as a result of a greater clogging of lakes and reduction of water mirror with oxygen deficit and water acidity. Keywords: embalsados, Holocene, Corrientes, palynology, reconstruction. As ilhas flutuantes ou “balsas” em corpos de agua quentes tem poucos estudos e compartilham algumas propriedades estruturais com turfeiras de clima temperado frio, para as quais ha mais informacoes. Na Argentina, as referencias sao reduzidas as regioes media e baixa do Rio Parana, onde os embalsados tem baixa frequencia. As analises palinologicas realizadas nos lagos San Cristobal, Cue e Miranda tem por objetivo aumentar o conhecimento sobre o desenvolvimento desse bioma no Holoceno do nordeste de Ibera, regiao central da Provincia de Corrientes. Foram obtidas 38 amostras de tres testemunhos no fundo dos lagos e as idades estimadas pela aplicacao do modelode profundidade-idade, calibradas com as datacoes radiocarbonicas. A analise qualitativa-quantitativa das associacoes palinologicas permitiu a distincao de dois intervalos. Entre 4300 e 3600 anos cal AP, a vegetacao estava dominada por especies herbaceas de angiospermas e algas cloroficeas, representantes de ambientes aquaticos, palustres, juncais e, em menor grau, por especies formadoras de embalsados. A partir de 3.500 anos cal AP, a frequencia e a variedade de especies aquaticas de angiospermas e algas cloroficeas diminui, e a predominância de especies de pastagens e colonizadoras de corpos d’agua aumenta. Essa mudanca sugere o desenvolvimento de embalsados com a formacao de solos orgânicos no Neo-holoceno, provavelmente como consequencia de maior colmatacao das lagoas, reducao do espelho d’agua, deficit de oxigenio e acidez da agua. Palavras-chave: embalsados, Holoceno, Corrientes, palinologia, reconstrucao.