Mineralized microbialites as archives of environmental evolution, Laguna Negra, Catamarca Province, Argentina

Abstract

Environmental fluctuations are recorded in a variety of sedimentary archives of lacustrine depositional systems. Geochemical signals recovered from bottom sediments in closed‐basin lakes are among the most sensitive paleoenvironmental indicators and are commonly used in reconstructing lake evolution. Microbialites (i.e., organosedimentary deposits accreted through microbial trapping and binding of detrital sediment or in situ mineral precipitation on organics [Palaios, 2, 1987, 241]), however, have been largely overlooked as paleoenvironmental repositories. Here, we investigate concentrically laminated mineralized microbialites from Laguna Negra, a high‐altitude (4,100 m above sea level) hypersaline, closed‐basin lake in northwestern Argentina, and explore the potential for recovery of environmental signals from these unique sedimentary archives. Spatial heterogeneity in hydrological regime helps define zones inside Laguna Negra, each with their own morphologically distinct microbialite type. Most notably, platey microbialites (in Zone 3A) are precipitated by evaporative concentration processes, while discoidal oncolites (in Zone 3C) are interpreted result from fluid mixing and biologically mediated nucleation. This spatial heterogeneity is reflected in petrographically distinct carbonate fabrics: micritic, botryoidal, and isopachous. Fabric type is interpreted to reflect a combination of physical and biological influences during mineralization, and paired C‐isotope measurement of carbonate and organic matter supports ecological differences as a dominant control on C‐isotopic evolution between zones. Laminae of Laguna Negra microbialites preserve a range of δ13Ccarb from +5.75‰ to +18.25‰ and δ18Ocarb from −2.04‰ to +9.28‰. Temporal trends of lower carbon and oxygen isotopic compositions suggest that the influence of CO2 degassing associated with evaporation has decreased over time. Combined, these results indicate that microbialite archives can provide data that aid in interpretation of both lake paleohydrology and paleoenvironmental change.

Variability of Carbonate Isotope Signatures in a Hydrothermally Influenced System: Insights from the Pastos Grandes Caldera (Bolivia)

“…This dispersion is among the highest known in the Central Andes (Figure 9) and elsewhere (Figure S3). A greater dispersion of isotope values has only been observed at Laguna Negra in Argentina (17.3% in δ 13 C; 11.3% in δ 18 O) where the amplitude results not only from temporal variations in moisture, which are recorded in microbialites (temporal amplitude varying from 4% to 11% for δ 13 C, and 3% to 8% for δ 18 O) [9], but also from spatial controls driven by the diversity of depositional environments (inlet mixing with lake, or lake alone) [9,56]. Differences in depositional environments strongly affect the isotope record, even over short distances.…”

“…The strong enrichment in heavy carbon isotopes in carbonates may track the rise of CO 2 in systems influenced by volcanism, even in the quiescent stage. These abiotic processes are also enhanced by the long water residence time in perennial lakes that favors storage of heavy isotopes such as oxygen [9,43]. These values can be further amplified by photosynthesis and microbial methanogenesis activities [11].…”

“…Figure 9.  18 O-13 C cross-plot comparing carbonates from Laguna Pastos Grandes (dashed line, in blue) and recent to present-day carbonates from other Andean locations, influenced by the same arid, high-altitude climate, as follows: a-Laguna Negra, Argentina[9,11]; b-Laguna Seca, Chile[3]; c1,2-Las Coladas, Argentina[4]; d1,2-Las Peladas, Argentina[4]; e-Lake Chungará, Argentina[59]; f-Laguna del Negro Francisco, Chile[3]; g-Laguna Miscanti, Chile[3]; h-Tauca and Coipasa lake highstand, Bolivia[6]; i-San Francisco, Argentina[4]; j-El Peinado[4]. Recent to present-day locations with high 13 Ccarb values suggest volcanic influence (CO2 input).…”

Controls of extreme isotopic enrichment in modern microbialites and associated abiogenic carbonates

“…The evaporative lake Laguna Negra (Catamarca Province, Argentina) contains microbialites and abiogenic carbonate structures with carbonate that is highly enriched in 13 C and 18 O. These isotopic compositions have been hypothesized to arise from the interactions of microbial, geochemical, and hydrological processes, and variability in isotopic compositions across sequential laminae within individual carbonate structures have been interpreted to reflect changes in environmental conditions temporally at the lake (Buongiorno et al, 2019). However, isotopic trends are also present in the overall dataset complicating our ability to interpret the meaning of the temporal variability in the isotopic compositions preserved within individual carbonate structures.…”

Microbially influenced lacustrine carbonates: A comparison of Late Quaternary Lahontan tufa and modern thrombolite from Fayetteville Green Lake, NY

“…Lake sediments, and carbonates in particular, preserve a variety of geochemical proxies that may be used for reconstruction of lake paleoenvironments (e.g., Newell, Jensen, Frantz, & Vanden Berg, ; Yang et al, ). Modern microbialites have been demonstrated to capture geochemical signals related to water balance variability in Laguna Negra, Argentina (Buongiorno, Gomez, Fike, & Kah, ), and microbialites from the Great Salt Lake, Utah, have been used to interpret biogeochemical fluctuations during the Pleistocene (Newell et al, ).…”