Composição cianobacteriana e química dos estromatólitos da lagoa Salgada, Neógeno do estado do Rio de Janeiro, Brasil

Abstract

Disponível on-line no endereço www.igc.usp.br/geologiausp -95 -Resumo A lagoa Salgada é um corpo aquático costeiro, situada no norte do estado do Rio de Janeiro. A evolução geológica da lagoa está associada às oscilações do nível do mar durante o Neógeno e apresenta esteiras microbianas, estromatólitos estratiformes e estromatólitos individuais e contínuos. Estromatólitos são estruturas carbonáticas laminadas formadas pela atividade metabólica de esteiras microbianas. O estudo permitiu a identificação de 31 espécies de cianobactérias nos estromatólitos e nas esteiras microbianas. A família de maior frequência é a Synechococcaceae. Nove espécies ocorrem nos estágios de desenvolvimento dos estromatólitos. Os tipos de esteiras são lisa, tufada, poligonal e em bolha, tendo como seus principais agentes produtores as cianobactérias filamentosas. Os restos esqueletais incluem bivalves, gastrópodes, ostracódios, foraminíferos e outros táxons. A alta frequência de cianobactérias ocorre pela adaptação à salinidade aliada à baixa competição na área. Os resultados possibilitam inferir os paleoambientes e eventos de sedimentação ocorridos na lagoa e podem ser aplicados na interpretação dos estromatólitos pretéritos.Palavras-chave: Cianobactérias; Esteiras microbianas; Estromatólitos recentes; Lagoa Salgada; Brasil. AbstractSalgada lagoon is a coastal aquatic body in northern Rio de Janeiro state. The geological evolution of the lagoon is associated with the oscillation of sea level during the Late Neogene. The lagoon presents microbial mats, stratiform stromatolites, individual and continuous stromatolites. Stromatolites are laminated carbonate build-ups formed by the metabolic activity of microbial mats. This study identified 31 species of cyanobacteria in stromatolites and microbial mats. The Family Synechococcaceae is the most frequent. Nine species are usual throughout the evolution of the calcareous stromatolites. Microbial mat types include flat, tufted, polygonal and blister forms, all produced mainly by filamentous cyanobacteria. Skeletal remains include bivalves, gastropods, ostracods, foraminifers and other taxons. The high frequency of cyanobacteria in the area occurs because of their adaptation to hypersalinity allied to low competition. The results indicate that a variety of paleoenvironmental and sedimentary events occurred in the lagoon and may be applied to the interpretation of ancient stromatolites.

Mid–late Holocene event registered in organo-siliciclastic sediments of Lagoa Salgada carbonate system, southeast Brazil

“…Geomorphological characteristics and seasonal variability modified the geochemistry of the lake, influencing the sedimentation and precipitation of salts and carbonates that formed biosedimentary structures of stromatolites, thrombolites, and oncoids (Silva e Silva et al, 2005, 2008.…”

Lagoa Salgada: An Overview of a Brazilian Hypersaline Lagoon Environmental Studies Over the Last 5000 Years Using Radiocarbon Date Corrections

“…Then, Iespa et al (2012) demonstrated that it is possible to carry out a paleoenvironmental analysis on stromatolite using the petrographic technique, showing that the bioerosion and dissolution varied along the stromatolite, thus indicating changes in the lagoon, such as increased pH, reduced turbulence and water circulation and reduced biological activity, with filamentous cyanobacteria settling on the upper layer of the stromatolites. Silva et al (2013) identified 21 species of cyanobacteria in stromatolites from Lagoa Salgada, the most representative of which are Microcoleus chthonoplastes and Lyngbya aestuarii. Callefo (2014) studied biominerals as a way of understanding microbial biosignatures and Silva et al (2018) mapped microbialites types, identifying damage and threats and providing suggestions for local geoconservation.…”

Mid-Late Holocene event registered in organo-siliciclastic-sediments of Lagoa Salgada carbonate system, Southeast Brazil

“…alkaline (Dupraz et al, 2009) and precipitate carbonates (Xu et al, 2006). Silva et al (2013) identified twenty-one species of cyanobacteria in stromatolites of the Lagoa Salgada, with the most representative being Microcoleus chthonoplastes and Lyngbya aestuarii, which are diazotrophic cyanobacteria present in coastal microbial mats. In hypersaline lakes, such as Salgada, microbial mats precipitate CaCO 3 as a by-product of CO 2 capture through photosynthesis by cyanobacteria (Jonkers et al, 2003;Ludwig et al, 2005).…”