Oxygen isotope analyses of fine silica grains using laser-extraction technique: Comparison with oxygen isotope data obtained from ion microprobe analyses and application to quartzite and silcrete cement investigation

Abstract

The laser fluorination technique reported here for analyzing the oxygen isotope composition (d 18 O) of fine quartz size fractions 50-20, 20-10, 10-5, 5-2, 2-1 and <1 lm has been validated by comparison with the ion microprobe technique. It yields accurate d 18 O data with an external precision better than 0.15&. This is a significant methodological improvement for isotopic studies dealing with materials such as soil or biogenic oxides and silicates: particles are often too small and recovered in insufficient amount to be easily handled for ion microprobe analysis. Both techniques were used to investigate d 18 O composition of a Cretaceous quartzite and silcrete sequence from the South-East of France. Quartzite cements average 31.04 ± 1.93&. They formed from Mid-Cretaceous seawater. Higher in the series, silcretes cements average 26.66 ± 1.36&. They formed from Upper-or post-Upper-Cretaceous soil water and groundwater. Oxygen isotope data show that the silicification steps from one mineralogical phase to another and from one layer to another (including from an upper pedogenic silcrete to a lower groundwater silcrete) occurred in a closed or weakly evaporating hydrological system.

A review of diatom δ18O in palaeoceanography

“…Odiatom can also be analysed using an ion microprobe, difficulties in obtaining the larger amounts of material required for this may limit the application of this technique (Alexandre et al, 2006). Regardless, though, of whether CIE, SWF or iHTR is used, it should be noted that the magnitude of analytical reproducibility for δ Odiatom records from Lake Baikal, Russia (Morley et al, 2005) and Lake Tilo, Eithiopia (Lamb et al, 2007).…”

Paleogene landscape evolution of the central North American Cordillera: Developing topography and hydrology in the Laramide foreland

“…A comparison of sample runs with replicate analyses of NBS-22 (oil), PEF-1 (polyethylene foil), NBS-30 (biotite), and laboratory standards yielded a relatively poor precision of ±6‰. Oxygen isotope analyses of prepared chert samples were made using infrared laser fl uorination (method modifi ed from Sharp, 1990;Alexandre et al, 2006): 700-900 μg of chert chips were reacted with BrF 5 , and liberated oxygen gas was introduced directly into the dual inlet system of a Finnigan MAT 252 mass spectrometer. Replicate analyses of laboratory standards Lausanne-1 (quartz) and UWG-2 (garnet) gave a precision of ±0.2‰.…”

The oxygen isotopic composition of phytolith assemblages from tropical rainforest soil tops (Queensland, Australia): validation of a new paleoenvironmental tool

“…A value of 8 ‰ was attributed to quartz particles as it is in the lower range of δ 18 O values measured worldwide for detrital quartz of metamorphic origin (e.g. Garlick and Epstein, 1967;Savin and Epstein, 1970;Clayton et al, 1972;Eslinger et al, 1973;Blatt, 1986;Graham et al, 1996;Alexandre et al, 2006). 18 O leaf silica-stem silica = 12.5/ h − 13.…”

“…Two aliquots of 1.6 mg of the same sample were exchanged with vapor from two waters of a known isotopic composition (Crespin et al, 2008). Oxygen extractions were then performed using the IR Laser-Heating Fluorination Technique as described in Alexandre et al (2006) and Crespin et al (2008). Oxygen gas samples were directly sent to and analyzed by a dual-inlet mass spectrometer (ThermoQuest Finnigan Delta Plus).…”