Geochemical constraints on the formation of Late Cenozoic ferromanganese micronodules from the central Arctic Ocean

• Main Authors: Bryce L. Winter, Clark M. Johnson, David L. Clark
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1997
• Subjects: Arctic; Arctic Ocean; Foraminifera*
• 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

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