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Upright crinoids of the Thornton Reef, Wenlock (Silurian) of Illinois, USA

Geological Journal

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Abstract

The rare preservation of columns perpendicular to bedding may provide convincing evidence that ancient crinoids adopted an upright attitude during life. However, taphonomic and sedimentological analyses are important in determining whether such occurrences are truly in situ or represent unusual allochthonous accumulations. The Crinoid Biosome of the Thornton Reef Complex, Silurian of Illinois, USA, includes pluricolumnals preserved perpendicular to bedding, in association with more common specimens parallel or angled to bedding. Upright pluricolumnals are relatively shorter (<150 mm) than the longest non-upright specimens; they sometimes occur as imbricate accumulations and lack attachment structures (although these are preserved separately). Brachiopod valves and colonial corals may also be preserved perpendicular to bedding. These features suggest that the Thornton beds were formed as viscous mass flow deposits and that the upright crinoid columns are allochthonous or, at best, parautochthonous. ?? 1996 by John Wiley & Sons, Ltd.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Upright crinoids of the Thornton Reef, Wenlock (Silurian) of Illinois, USA
Series title:
Geological Journal
Volume
31
Issue:
4
Year Published:
1996
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geological Journal
First page:
369
Last page:
378