Computer Science
Scientific paper
Dec 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987gecoa..51.3113b&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 51, Issue 12, pp.3113-3118
Computer Science
2
Scientific paper
The stable oxygen and hydrogen isotopic composition of crystallization water in gypsum has been measured in the Zechstein Billingham Main Anhydrite in north-east England. The samples represent a vertical drillcore section through the formation at about 40 metres depth, and have suffered alteration by groundwater from above and below. This has resulted in a central zone of relict anhydrite surrounded by hydrated zones, in which alteration developed symmetrically. The object of the study was to obtain evidence about the nature of the gypsification process--the groundwater flux involved, the geochemistry, and the possible timing. Minor element contents (Na, K, Mg, Sr, Cl) of both anhydrite and bulk gypsum were similar. Anomalously high concentrations of Cl, Mg, Na and K in the hydration transition zone correlate with the presence of trace halide and sulphate minerals, and suggest localised leaching of these elements during the hydration process. However, Sr is markedly uniform, indicating immediate reprecipitation as SrSO 4 during the hydration process. The 18 O/ 16 O and 2 H/ 1 H data for crystallization water form a very marked trend with depth, with a characteristic slope for 2 H versus 18 O of about --5 ( , 1978) which corresponds to the calculated Rayleigh-type isotopic fractionation experienced by water when reacting with anhydrite to form gypsum in a closed system. Taken together, the stable isotopic, geochemical and petrographie data indicate that the hydration reaction involved a very restricted flux of water, just sufficient for the hydration. The penetration of water probably occurred through micro-fractures accompanying late Tertiary to Quarternary uplift and denudation. The process of gypsification self-seals the micro-fracture network and thereby controls influx in an environment of limited groundwater circulation.
Bath A. H.
Darling Gerry W.
George I. A.
Milodowski A. E.
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