Geochemical constraints on the formation of Late Cenozoic ferromanganese micronodules from the central Arctic Ocean
In order to determine geochemical compositions of Late Cenozoic Arctic seawater, oxide fractions were chemically separated from 15 samples of hand-picked ferromanganese micronodules (50-300 pm). The success of the chemical separation is indicated by the fact that ~97 % of the Sr in the oxide fractio...
| Main Authors: | , , |
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| Other Authors: | |
| Format: | Text |
| Language: | English |
| Published: |
1997
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| Subjects: | |
| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.490.6808 http://www.geology.wisc.edu/~unstable/PDF/Winter_et_al_1997_Marine_Geol.pdf |
| Summary: | In order to determine geochemical compositions of Late Cenozoic Arctic seawater, oxide fractions were chemically separated from 15 samples of hand-picked ferromanganese micronodules (50-300 pm). The success of the chemical separation is indicated by the fact that ~97 % of the Sr in the oxide fraction is seawater-derived. Rare-earth element (REE) abundances of the Arctic micronodule oxide fractions are much lower than those of bulk Fe-Mn nodules from other ocean basins of the world (e.g., 33 vs. 145 ppm Nd), but the Arctic oxides are enriched in Ce relative to Nd (Ce,/Nd, = 2.2 f 0.5) and have convex-upward, shale-normalized REE patterns ( NdN/GdN =0.61 f 0.06, GdN/YbN = 1.5 + 0.2, NdN/Yb, = 0.9 f 0.2), typical of other hydrogenous and diagenetic marine Fe-Mn-oxides. Bulk sediment samples from the central Arctic Ocean have REE abundances and patterns that are characteristic of those of post-Archean shale. Non-detrital fractions (calcite +oxide coatings) of Recent Arctic foraminifera have REE abundances and patterns similar to those of Recent foraminifera from the Atlantic Ocean. Electron microprobe analyses (n = 178) of transition elements in 29 Arctic Fe-Mn micronodules from five different stratigraphic intervals of Late Cenozoic sediment indicate that oxide accretion occurred as a result of hydrogenetic and diagenetic processes close to the sediment-seawater interface. Transition element ratios suggest hat no oxide accretion occurred during transitions from oxic to suboxic diagenetic onditions. Only K is correlated with Si and Al |
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