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Ferromanganese crusts as indicators for paleoceanographic events in the NE Atlantic

Geologische Rundschau

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Abstract

Hydrogenetic ferromanganese crusts reflect the chemical conditions of the seawater from which they formed. Fine-scale geochemical analysis of crust layers in combination with age determinations can therefore be used to investigate paleoceanographic changes which are recorded in geochemical gradients in the crusts. At Tropic seamount (off northwest Africa), uniform crust growth influenced by terrigenous input from the African continent occurred during approximately the past 12 Ma. Phosphatization of these crusts is minor. In contrast, crusts from Lion seamount, located between Madeira and the Portuguese coast, display a much more variable growth history. A pronounced increase in Ni, Cu, and Zn is observed in some intervals of the crusts, which probably reflects increased surface productivity. A thick older phosphatized generation occurs in many samples. Hydrographic profiles indicate that Mediterranean outflow water (MOW) may play an important role in the composition of these crusts. 10Be dating of one sample confirms that the interruption of the MOW during the Messinian salinity crisis (6.2-5 Ma ago) resulted in changes in element composition. Sr-isotope dating of the apatite phase of the old crust generation has been carried out to obtain a minimum age for the older generation of Atlantic crusts and to determine whether crust phosphatization in the Atlantic can be related to phosphatization episodes recorded in Pacific crusts. The preliminary data show that the old phosphatized crust generation might be as old as approximately 30-40 Ma.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Ferromanganese crusts as indicators for paleoceanographic events in the NE Atlantic
Series title:
Geologische Rundschau
Volume
85
Issue:
3
Year Published:
1996
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geologische Rundschau
First page:
567
Last page:
576
Number of Pages:
10