Oxygen Isotope Analysis of Authigenic Quartz in Sandstones: A Comparison of Ion Microprobe and Conventional Analytical Techniques
- Richard H. Worden7,
- Sadoon Morad8
Published Online: 17 MAR 2009
Copyright © 2000 The International Association of Sedimentologists
Quartz Cementation in Sandstones
How to Cite
Lyon, I. C., Burley, S. D., McKeever, P. J., Saxton, J. M. and Macaulay, C. (2009) Oxygen Isotope Analysis of Authigenic Quartz in Sandstones: A Comparison of Ion Microprobe and Conventional Analytical Techniques, in Quartz Cementation in Sandstones (eds R. H. Worden and S. Morad), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304237.ch20
School of Geosciences, The Queen's University, Belfast, BT7 1NN, UK
Sedimentary Geology Research Group, Institute of Earth Sciences, Uppsala University, Norbyvägen 18 B, S–75236, Uppsala, Sweden
- Published Online: 17 MAR 2009
- Published Print: 3 MAR 2000
Print ISBN: 9780632054824
Online ISBN: 9781444304237
- oxygen isotope analysis of authigenic quartz in sandstones;
- cathodoluminescence (CL) or scanning electron microscopy;
- oxygen isotopes - constraining temperature of authigenic mineral precipitation;
- oxygen isotope analysis of quartz overgrowths in sandstones;
- high resolution oxygen isotope analysis;
- ion probe instrumentation;
- ion probe oxygen isotope measurements
This paper describes a methodological approach using an Isolab®54 ion microprobe to obtain accurate oxygen isotope ratio measurements at precise locations in authigenic quartz overgrowths. The analytical spot size may be as small as 10 µm or less and the position of analyses can be defined by previous examination of the sample using cathodoluminescence (CL) or scanning electron microscopy. The total volume analysed involves only picomoles of material, representing 10−7 of the sample size required by conventional fluorination oxygen isotope measurement. The data are compared with the methodology and results obtained by conventional fluorination techniques.
18O/16O ratio measurements were obtained of quartz overgrowths from a sample of the Penrith Sandstone (Permian) from northern England and a Piper Formation sandstone (Jurassic) from the UK North Sea. Analyses yielded an average δ18O value of +28.8‰SMOW ± 0.9‰ (1 SD) from nine analyses in one profile across an overgrowth in the Penrith Sandstone and +27.3‰SMOW ± 1.0‰ (1 SD) from a second profile of five spots. An average δ18O value of +22.7‰SMOW ± 1.8‰ was obtained from six profiles across an overgrowth in the Piper Formation sandstone compared with an average value of 10.6‰SMOW ± 1.3‰ (1 SD) from 17 spots on the detrital grain. These data are compared with δ18OSMOW measurements for overgrowths from the same sandstones using a technique involving point counting to determine the detrital quartz/overgrowth content of the sandstones followed by conventional fluorination analysis of sandstones without overgrowths and sandstones with abundant overgrowths. Agreement between δ18O values obtained by both methods is high for the Piper Formation sandstone but more divergent for the Penrith Sandstone.
Although the analytical precision obtained using the ion microprobe is not as high as that obtained using conventional bulk fluorination methods, this is offset by the ability to measure isotopic ratios in situ and with high spatial resolution. Moreover, the inherent shortcomings of mineral separation necessary with conventional methods mean that the ion microprobe represents a major advance in the determination of the oxygen isotope composition of diagenetic silicate minerals.