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Is the Chalk a Chemical Deposit?

Published online by Cambridge University Press:  01 May 2009

W. A. Tarr
W. A. Tarr
Affiliation:
University of Missouri.
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Extract

The composition of chalk has been shown to consist dominantly of three types of material, in the order of their importance, (1) amorphous, or extremely fine-grained material, (2) spheres, and (3) organic remains.

The first, the writer believes, represents chemically precipitated calcite and aragonite, the second a chemically formed oolite, and the last the normal organic constituents.

Recent studies have shown that the surface waters of the ocean in favourable localities are saturated with CaCO3 and that variations in amount of CO2 mean either solution or precipitation. It is believed that the physical conditions of the Cretaceous sea favoured precipitation. Bacteria may have been a contributing factor.

It is hoped that the above suggestion of the possible chemical origin of a part of the chalk (the larger part) will cause those who have the opportunity of study to apply it further, for until the great amount of extremely fine material is accounted for the origin of chalk is not settled. The writer regards the chemical origin with favour because it seeks to explain the origin of chalk in the light of present knowledge of the precipitation of calcium carbonate from sea water.

Type
Original Articles
Information
Geological Magazine , Volume 62 , Issue 6 , June 1925 , pp. 252 - 264
Copyright
Copyright © Cambridge University Press 1925

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References

page 254 note 1 Jukes-Browne, , and Hill, , The Cretaceous of Britain, vol. ii, 1903, p. 540.Google Scholar

page 255 note 1 Italics by W. A. T.Google Scholar

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page 260 note 1 Vaughan, T. W.Google Scholar, ibid.

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page 261 note 1 Ibid., pp. 741–2.

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page 262 note 3 Drew, G. H., ‘On the Precipitation of CaCO3 in the Sea by Marine Bacteria and on the Action of Denitrifying Bacteria in Tropical and Temperate Seas’: Carnegie Inst. of Washington, Pub. 182, vol. v, 1914, 7–15.Google Scholar

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page 263 note 2 Vaughan, T. W.Google Scholar, ibid., p. 307.

page 263 note 3 Ibid., p. 729.