Lyell Collection
Geological Society, London, Special Publications
Lyell Centre  |   Lyell Collection  |   Subscriptions   |   Geological Society  |   Email alerts  |   Online bookshop  |   Help

Keywords:
Author:
Advanced search>>
This Article
Right arrow Full Text (PDF)
Right arrow References
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Rhoads, D. C.
Right arrow Articles by Stolz, J. F.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation
Geological Society, London, Special Publications; 1991; v. 58; p. 187-199;
DOI: 10.1144/GSL.SP.1991.058.01.13
© 1991 Geological Society of London

Ancient Shelf Anoxia

The dysaerobic zone revisited: a magnetic facies?

Donald C. Rhoads1,2, Sandor G. Mulsow2, Raymond Gutschick3, Christopher T. Baldwin2 & John F. Stolz4

1 Science Applications International Corp., (SAIC) 89 Water Street, Woods Hole, Massachusetts, 02543, USA
2 Geology Department, Boston University, 675 Commonwealth Ave., Boston, Massachusetts, 02215, USA
3 Emeritus Professor of Geology, University of Notre Dame, 2901 Leonard Street, Medford, Oregon 97504, USA
4 Biochemistry Department, University of Massachusetts, Amherst, Massachusetts 01003, USA

The original dysaerobic zone concept defined a unique assemblage of benthic organisms and sedimentary fabrics associated with dissolved oxygen concentrations ranging between 0.3 and 1.0 ml/l. Subsequent studies of the Santa Barbara Basin and oxygen minimum zone (OMZ) off the California coast suggest that this facies is bounded by dissolved oxygen in the range 0.1 to 0.5 ml/l.

This range of dissolved oxygen is optimal for the growth of magnetotactic bacteria. We present a hypothesis predicting that the dysaerobic zone should be associated with a high inventory of biogenic magnetite and that this magnetite can be used as a palaeo-oxygen indicator.

We have tested this hypothesis with a magnetic analysis of samples from aerobic, anaerobic, and dysaerobic sediments taken off the Peruvian coast. The mean magnetic susceptibility of the dysaerobic zone is 3 to 5 times higher than the aerobic and anaerobic parts of the Peruvian oxygen minimum zone (OMZ). Micrographs (TEM) of these sediment samples indicate that only the dysaerobic zone contains appreciable amounts of fine-grained magnetite.