Transition metal and rare earth element (REE) data are presented
for various sedimentary materials from two Manganese Nodule
Program (MANOP) sites in the eastern tropical Pacific. These data
constrain the sources of elemental supply to the seafloor and the
processes that control ferromanganese nodule genesis. Investigation
of elemental partitioning between suspended particles, sediments,
ferromanganese nodules, crusts, and micronodules indicates that
particle settling dominates REE supply to the seafloor at MANOP site
H. Partitioning of the particle flux reveals that although detrital
and labile particles both convey REE to H sediments and nodules,
labile biogenic debris is the primary source of REE accreted by site
H nodules.
Evidence from REE abundance patterns and correlations of REE
with other elements define three basic processes of nodule accretion:
(1) hydrogenous or direct seawater precipitation; (2) oxic
diagenesis, referring to a variety of ferromanganese accretion processes
which occur in oxic sediments; and (3) suboxic diagenesis, in
which Mn is mobilized by the oxidation of sedimentary organic matter.
The REE geochemistry of site H nodules suggests an additional
accretionary process, resulting from the degradation of labile
organic matter in an oxic environment.
Contrasts in REE patterns, major element compositions, and
fluxes of various elements in sedimentary samples from MANOP site H
(a nodule-bearing site) with site M (a nodule-free site) reveal
differences in the sources of material to the seafloor in the two
environments. Geochemical data imply a greater hydrothermal influence
and a greater accumulation of organic carbon in site M sediments
relative to those at site H. Comparisons of the REE and major
element geochemistry of H and M sediment traps, sediments, and
crusts, as well as nodules from site H, imply that the reductive
mobilization of Mn and geochemically similar elements is controlled
primarily by surface water biological productivity and the accumulation
of organic carbon in the sediments. The organic flux to the
sediments determines the degree of depletion of oxidants, which
governs the reduction, mobilization, and supply of metals to nodule
surfaces. It appears that the depth to the Mn redox boundary and
possibly seasonal variations in the flux of organic material to the
seafloor determine whether nodules grow or whether Mn is exported to
bottom waters. / Graduation date: 1985
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29593 |
| Date | 28 June 1984 |
| Creators | Murphy, Kim Marie |
| Contributors | Dymond, Jack |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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