A new protocol for oxygen isotope analysis of authigenic and biogenic fine silica grains using laser-extraction technique

We report here a 30 W CO₂ laser heating protocol for analyzing oxygen isotope composition (δ¹⁸O in ‰ vs. V-SMOW) of quartz and amorphous silica grains lower than 50 and 2 μm with a good external precision (1σ < 0.15‰). This technique is used to investigate δ¹⁸O composition of macro-, micro- and crypto-crystalline quartz cements of quartzite levels occurring in a sand sequence from the South of France (Apt Series), after a physical separation of the quartz cements. δ¹⁸O data obtained from this technique are compared with δ¹⁸O data obtained from in situ ion microprobe analyses. This study also presents promising results on δ¹⁸O analysis of phytoliths obtained with the laser heating protocol (1σ < 0.1‰).