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 HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Föllmi, K. B.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation
Geological Society, London, Special Publications; 1990; v. 52; p. 237-252;
DOI: 10.1144/GSL.SP.1990.052.01.17
© 1990 Geological Society of London

Condensation and phosphogenesis: example of the Helvetic mid-Cretaceous (northern Tethyan margin)

Karl B. Föllmi

Earth Sciences Board, University of California, Santa Cruz, CA 95064, USA
Geological Institute, ETH-Zentrum, CH 8092 Zürich, Switzerland

The Aptian to Lower Cenomanian condensed phosphatic beds, deposited in the Helvetic Shelf along the northern Tethyan margin, consist of thin strata (generally <50 cm) of densely packed phosphatized particles and crudely laminated crusts embedded in glauconitic sands, marls, and pelagic micrites. The beds record very low net sediment-accumulation rates (typically 2–20 cm Ma–1). The presences of complex internal and laterally rapidly changing microstratigraphies, multiple phosphate generations, intimate mixtures of fossils from different biostratigraphical zones and ecological habitats, a proximal transition into bioturbated glauconitic sands, and a distal transition into allochthonous sediments deposited in channel and fan systems, indicate that the condensed phosphatic beds formed along the axis of a stable westward-flowing current system contouring the northern Tethyan margin. Repetitive cycles of deposition, phosphogenesis, re-exposure and reworking, and deposition (Baturin Cycles), caused by current-induced lateral migration of sand bodies, shaped the internal stratification and composition of the condensed phosphatic beds. Catastrophic burial of entire benthic communities was crucial to phosphogenesis. The sudden presence of large amounts of organic matter buried in siliciclasts created a reactive environment favourable for the concentration and precipitation of phosphates, probably with the help of physicochemical cycles of the Fe3+-Fe2+ and Mn4+-Mn2+ redox pairs.





This article has been cited by other articles:


Home page
 Geological Society, London, Special PublicationsHome page
H. Huneke
Pelagic carbonate ooze reworked by bottom currents during Devonian approach of the continents Gondwana and Laurussia
Geological Society, London, Special Publications, 2007; 276: 299 - 328.
[Abstract] [PDF]