Skip to main content


hardground A term first introduced into geologic literature in 1897, drawn from an oceanographic source but used in a narrower sense to describe a specific horizon that had initially been lithified a short distance beneath the sea floor. Lithification resulted from calcite precipitation around local foci, giving rise to concretions. The sediment above and surrounding the concretions remained soft and was consequently bioturbated (see BIOTURBATION). The initial cementation of the hardground may have been triggered by the chemical influence of organisms that dwelt within the sediment. Progressive encroachment of the cemented areas on to the soft sediment gradually resulted in total lithification. ‘Incipient’ hardgrounds represent periods of arrestation in the cementation process, with the result that nodular and softsediment units alternate one with the other. The cemented hardground may itself support a fauna of fixed or cemented organisms and may be bored extensively by bivalves (Bivalvia). Pyrite films may line burrows, which may also be filled by silica.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"hardground." A Dictionary of Earth Sciences. . 18 Sep. 2019 <>.

"hardground." A Dictionary of Earth Sciences. . (September 18, 2019).

"hardground." A Dictionary of Earth Sciences. . Retrieved September 18, 2019 from

Learn more about citation styles

Citation styles gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, cannot guarantee each citation it generates. Therefore, it’s best to use citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

The Chicago Manual of Style

American Psychological Association

  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.