Oxygen isotope microanalyses of diagnetic quartz: Possible low temperature occlusion of pores
Geochemica et Cosmochimica Acta, Vol. 59, No. 12, pp. 2537-2543,
Copyright © 1995 Elsevier Science Ltd.
Richard L. Hervig1, Lynda B. Williams1, Ian K.
and Fred J. Longstaffe3
1Center for Solid State Science Arizona State University, Tempe,
AZ 85287, USA
2Department of Geology and Geophysics, University of Calgary, Calgary, Alberta T2N 1N4, Canada 3Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada
(Received October 3, 1994; accepted in revised form March 20, 1995)
Secondary ion mass spectrometry (SIMS) was used to obtain delta18O measurements on ~10 µm spots in authigenic and detrital quartz from Mississippian sandstones of the Western Canada sedimentary basin. Detrital quartz shows a large range in delta18O (from 5 to 25‰) which overlaps the analyses of authigenic cements (20-34‰). Combining these data with the burial history and precipitation sequence of minerals indicates that meteoric water may have precipitated quartz at temperatures between 15 and 35ºC over a period of 180 MA (300-120Ma). This nearly isothermal precipitation may have occluded pores in samples from the central portion of the basin, but quartz precipitation continued up ~75ºC at the basin margin. Conventional bulk analyses of these samples gave delta18O values of 13.4‰ for detrital quartz and 19.8‰ for authigenic quartz. Models based on bulk isotopic analyses can bias the interpretation of the timing of diagenetic quartz precipitation toward much higher temperatures. The SIMS measurements in diagenetic silicates can identify discrete episodes of precipitation allowing a more accurate interpretation for the timing of diagenetic events.