Antiphase hydrogen and oxygen isotope periodicity in chert nodules

Details Antiphase hydrogen and oxygen isotope periodicity in chert nodules Antiphase hydrogen and oxygen isotope periodicity in chert nodules

Sep 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002gecoa..66.2865s&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 66, Issue 16, pp.2865-2873

Computer Science

8

Scientific paper

Oxygen and hydrogen isotope analyses were made of Jurassic-age chert nodules from the Holy Cross Mountains, SE Poland, along radial transects at high spatial resolution. There is a radial "sigmoidal" periodicity for both isotope ratios, but the two are out of phase, with high D values corresponding to low 18 O values. Periodicity for a 100- to 120-mm diameter nodule is approximately 16 mm, increasing slightly toward the rim, with amplitudes approaching 20 and 3.0 for hydrogen and oxygen, respectively. The combined hydrogen-oxygen isotope data for one nodule fall on a published curve for chert forming in equilibrium with seawater (Knauth and Epstein, 1976 ); the range of delta values corresponds to temperature variations of ~10°C. Data for a second chert fall on a subparallel D- 18 O line with D values that are almost 50 lower. The D- 18 O patterns for the nodules cannot be explained by periodic mixing of meteoric and ocean water because the hydrogen and oxygen isotope data are out of phase. Two possible explanations for the antiphase periodicity are (a) cyclical temperature variations, perhaps related to an unstable convection system (e.g., Bolton et al., 1999) , and (b) self-organizing catalytic precipitation (e.g., Wang and Merino, 1990) . The systematic isotopic variations are difficult to explain by diagenesis and strongly suggest that primary isotopic compositions are preserved. The isotopic data provide important information on the thermal history of the sedimentary basin, if temperature variations are the cause of the isotopic periodicity.

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