Seasonal records of climatic change in annually laminated tufas: short review and future prospects

摘要: Many Recent and fossil freshwater tufa stromatolites contain millimetre-scale, alternating laminae of dense micrite more porous or sparry crystalline calcites. These have been interpreted to represent seasonally controlled differences in the biotic activity microbes, and/or changes rate calcification. Either way, couplets these microbially mediated calcified are generally agreed annual seasonality. Combined stable isotope (d18O d13C) trace element (Mg, Sr, Ba) geochemistry from show that seasonal climatic information is available Variability d18O (and one case Mg concentration) has shown be primarily by stream temperature change, usually driven solar insolation. In arid climates, evaporation can also cause enrichment at least 1‰. d13C results potentially from: (1) change plant uptake 12C-enriched CO2; (2) degassing CO2 aquifer system; (3) precipitation calcite along river flow path, a process increases dissolved inorganic carbon (DIC) remaining water. Mechanisms 2 3 linked because precipitates aquifers where occurs, e.g. air pockets. The latter mechanism for sympathetic variation between element/Ca ratios elements with partition coefficients much greater than 1 (e.g. remain preferentially solution. Since pockets will enhanced during decreased recharge when water saturation lowest, possible index therefore intensity. High-resolution geochemical data well-dated great potential Quaternary palaeoclimate reconstructions, possibly allowing recovery including rainfall However, careful consideration diagenetic effects, particularly aggrading neomorphism, needs next step.