Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If you need an accessible version of this item please contact JSTOR User Support

Origin of Enigmatic Structures: Field and Geochemical Investigation of Columnar Joints in Sandstones, Island of Bute, Scotland

Grant M. Young
The Journal of Geology
Vol. 116, No. 5 (September 2008), pp. 527-536
DOI: 10.1086/590137
Stable URL: http://www.jstor.org/stable/10.1086/590137
Page Count: 10
  • Read Online (Free)
  • Download ($19.00)
  • Cite this Item
If you need an accessible version of this item please contact JSTOR User Support
Origin of Enigmatic Structures: Field and Geochemical
Investigation of Columnar Joints in Sandstones, Island of Bute, Scotland
Preview not available

Abstract

Abstract Columnar joints, resembling those in igneous rocks, are present in Devonian and Early Carboniferous sandstones at two localities on the Island of Bute in southwestern Scotland. New data concerning field relations and geochemical changes constrain processes responsible for generation of columnar fracture patterns in sedimentary rocks. The columns are mostly normal to bedding and occur at several discrete stratigraphic levels. The host rocks are cut by Early Carboniferous volcanic necks or plugs, which acted as heat sources, but development of columnar jointing was strongly controlled by small sills and dikes of a recessive, purple, fine-grained rock. Geochemistry of these rocks points to an igneous origin. Where contacts are exposed, columnar joints appear above subconcordant intrusions and disappear upward. The lowest parts of the columnar-jointed sandstones are Si depleted and enriched in Ca, Mg, Fe, Al, rare earth elements (REEs), and some base metals. REE patterns from columnar-jointed sandstones near contacts with intrusions resemble those of the igneous rocks, probably as a result of hydrothermal activity. Because most of the columns are approximately normal to bedding, intrusion probably took place before folding of the host rocks and possibly before complete consolidation.

Page Thumbnails

  • Thumbnail: Page 
527
    527
  • Thumbnail: Page 
528
    528
  • Thumbnail: Page 
529
    529
  • Thumbnail: Page 
530
    530
  • Thumbnail: Page 
531
    531
  • Thumbnail: Page 
532
    532
  • Thumbnail: Page 
533
    533
  • Thumbnail: Page 
534
    534
  • Thumbnail: Page 
535
    535
  • Thumbnail: Page 
536
    536