Quartz osl dating
We interpret that carbonate recrystallization or uptake of organic matter after tufa formation are responsible for the younger radiocarbon ages compared to quartz OSL ages in the older tufa samples. Equivalent doses distributions have overdispersion between 19% and 81%, indicating that the studied samples comprise well bleached as well as poorly bleached sediments.
For these samples, age differences vary up to tens of thousands years between deposition of quartz grains and the last episode of carbonate recrystallization or organic matter uptake. The quartz grains extracted from the studied tufas show an OSL signal dominated by the fast component and reliable dose response curves, with saturation doses (2D0) ranging from 35 to 210Gy.
Most of the samples has low radiation dose rates (0.40±0.02 to 0.78±0.05Gy/ka), with variation in the water content due to compaction and matrix recrystallization, being the major factors that could induce dose rate changes through time.
Hard tufa samples with intense carbonate cementation show quartz OSL ages from 51.9±4.8 to 150.3±35.9 years.
The De is calculated by the intercept of the natural luminescence signal with the generated curve. G., 2000, Luminescence dating of quartz using an improved signle-aliquot regenerative-dose protocol: Radiation Measurements, v.
A curve is generated for each aliquot (subsample), multiple aliquots are needed to obtain an accurate De. J., 1998, An introduction to optical dating: The dating of Quaternary sediments by the use of photon-stimulated luminescence: Oxford, University Press, 267 p.
Consequently we believe that the obtained OSL ages are the best estimates for the starting deposition time of the studied tufa samples.
AB - Robust chronologies for Quaternary fluvial carbonate sediments (tufas) from Brazil are still challenging.
Optically stimulated luminescence is a method of determining the age of burial of quartz or feldspar bearing sediments based upon principles of radiation and excitation within crystal lattices, and stems from the fact that imperfections in a crystal lattice have the ability to store ionizing energy (Radiation is absorbed by the crystal lattice upon sediment burial, and over time, excites electrons causing them to migrate within the crystal and become stored in traps resulting from crystal lattice defects.Through geologic time, quartz minerals accumulate a luminescence signal as ionizing radiation excites electrons within parent nuclei in the crystal lattice.A certain percent of the freed electrons become trapped in defects or holes in the crystal lattice of the quartz sand grain (referred to as luminescent centers) and accumulate over time (Aitken, 1998).Robust chronologies for Quaternary fluvial carbonate sediments (tufas) from Brazil are still challenging.We obtain Optically Stimulated Luminescence (OSL) ages of Brazilian tufa deposits using the Single Aliquot Regeneration (SAR) dose protocol applied to single grains and multigrain aliquots of quartz extracted from tufa matrix.