Rev. bras. paleontol. 16(1):39-46, Janeiro/Abril 2013 © 2013 by the Sociedade Brasileira de Paleontologia doi:10.4072/rbp.2013.1.03 39 LATE PLEISTOCENE AND HOLOCENE PALEOENVIRONMENTS IN PONDS AND ALLUVIAL SEDIMENTS OF UPPER PARANÁ RIVER, BRAZIL RENATO LADA GUERREIRO Instituto Federal de Educação, Ciência e Tecnologia do Paraná, Av. Cívica, 475, 85935-000, Assis Chateaubriand, PR, Brasil. renato.guerreiro@ifpr.edu.br JOSÉ CÂNDIDO STEVAUX Grupo de Estudos Multidisciplinares do Ambiente, UEM, Av. Colombo, 5790, 87020-900, Maringá, PR, Brasil. jcstevaux@uem.br MAURO PAROLIN Laboratório de Estudo Paleoambientais da FECILCAM, Rua Chafic Bader Maluf, 21, 87300-170, Campo Mourão, PR, Brasil. mauroparolin@gmail.com MARIO LUIS ASSINE Departamento de Geologia Aplicada, UNESP, Av. 24 A,1515, 13506-900, Rio Claro, SP, Brasil. assine@rc.unesp.br INTRODUCTION The Paraná River is South America’s second largest river and it forms the main trunk river of the La Plata Basin. The upper course of the Paraná River is located between the headwaters and the beginning of the reservoir of Itaipú Dam (formerly Sete Quedas Falls), near to the Piquiri River mouth on the border of Brazil and Paraguay. Stevaux (1993) recognized four geomorphologic units along the alluvial valley in the Taquarussu area. Most of those units are on the Paraná River’s right bank: (i) Porto Rico Unit, with colluvial deposits and/or pedogenesis of Caiuá Formation sandstones; (ii) Taquaruçu Unit, with alluvial-colluvial deposits and numerous ponds of varying formats similar to those of in the study area; (iii) Fazenda Boa Vista Unit, with depositional geoforms characteristics of braided river system that are partly covered by alluvial fans; and (iv) Paraná River Unit, which forms the modern fluvial plain. The presence of ponds, some of them interconnected with each other, is a defining geomorphological feature of Taquaruçu unit, particularly well developed on the right bank ABSTRACT – Freshwater sponge spicules were analyzed as a paleoenvironmental proxy indicator in five cores of ponds and alluvial fan sediments in the Upper Paraná River’s left bank, near Querência do Norte town, northwestern of State of Paraná, southern Brazil. Two optically stimulated luminescence (OSL) dates were obtained from sediments of ponds and one radiocarbon ( 14 C) date was obtained from the alluvial fan. Microscopic analysis of spicules preserved in the sediments allowed a determination of freshwater sponge species. The species assemblage provides evidence for dominantly dry conditions in the Upper Paraná River during the Late Pleistocene. A wetter climate phase was recognized at 14 C 7,540 yrs BP, with alluvial fan formation commencing at the transition of the dry Pleistocene climate to the Early Holocene wet climate. This wet interval was characterized by a sponge assemblage marked by the presence of the Neotropical families and typically associated with lotic environments. Sponge spicules analysis from pond sediments reject the possibility that lotic environments contributed to pond genesis and evolution. Key words: freshwater sponge spicules, Quaternary, paleoclimate, ponds, alluvial fan, Paraná River. RESUMO – Foram analisados espículas de esponjas de água doce como indicadores proxy de condições paleoambientais em cinco testemunhos recuperados em lagoas e leque aluvial da margem esquerda do alto rio Paraná, próximo à cidade de Querência do Norte, noroeste do Estado do Paraná, sul do Brasil. Duas datações por luminescência opticamente estimulada (LOE) foram obtidas nos sedimentos lacustres e uma datação 14 C em sedimentos do leque aluvial. Com base na determinação específica de esponjas de água doce foi possível evidenciar condições ambientais mais secas que as atuais no alto rio Paraná do Pleistoceno tardio até o inicio do Holoceno. Registra-se a transição de climas secos pleistocênicos para climas úmidos no Holoceno, com a formação de leque aluvial, cujos sedimentos foram datados em 14 C 7.540 anos AP. Dados de espículas de esponjas nos sedimentos lacustres permitiram descartar a contribuição de ambientes lóticos da gênese e evolução das lagoas. Palavras-chave: espículas de esponjas de água doce, Quaternário, paleoclima, lagoas, leque aluvial, rio Paraná.