Workshop on the Establishment of a Geological Model of ...

Applicability of the model of von Stackelberg & Beiersdorf (1991) in terms of local nodule facies
in the Clarion Clipperton Zone
The SO‐25 and VA‐18 areas are representative for the CCZ in terms of their basic geological properties: their
sub‐bottom consists of oceanic crust with a sediment cover. However, there are significant differences between
areas within this region. With the increasing age of the oceanic crust away from the active seafloor spreading
centre, the Pacific Rise, the relief of the crust and its topographic structure changes as a consequence of past
changes in spreading rates (see Beiersdorf, 1987. In: Von Stackelberg, U. & Beiersdorf, H., compilers, 1987),
subsequent crustal sagging, loading by sediments, erosion, and submarine weathering. The relief of the crust
becomes “veiled” or obliterated by the sediment cover resulting in the present abyssal hill topography. This cover
varies in thickness and lithologic composition. Both are related to changes of the depositional regimes and states
of diagenesis in space and time.
Since economically valuable nodule deposits (high‐grade, high abundance “Hamburger“‐type nodules) are
found throughout the “nodule belt”, which is associated with the northern part of the siliceous ooze zone, the
depositional regime favourable for their formation must have existed ubiquitously throughout the “nodule belt” as
explained in the previous chapter. Therefore, on a local scale, the model of von Stackelberg & Beiersdorf (1991)
also seems to be applicable.
What is needed to delineate the nodule belt more precisely and to estimate the total size and
value of economically interesting areas within “blocks”of the total claim area?
The formation and growth of manganese nodules in the CCZ is a function of availability of nuclei, particularly
during times of very low or zero sedimentation rates, as well as:
• Subsequent accumulation of sediments attractive to benthic life as well as at rates which are in balance
with benthic lifting
• Availability of metal and other ions in seawater and porewater needed in nodule formation
• Benthic lifting.
The ideal seabed‐mining area needs to be large and have large nodules that are rich in copper and high
abundance resting on a flat seafloor. Such areas are rare because of the geological complexity of nodule formation
and preservation. An ideal area would require a sediment layer immediately underlying the seafloor with the
following origin and history:
• Deposited on a flat “basement” of large areal extent
• Experienced at least one hiatus to have allowed nucleation and initiation of nodule growth
• Experienced a post‐hiatal sedimentation for a long period of time to allow growth of large nodules,
• Formed by particles which were able to supply “building” materials for nodule formation to bottom
water and during diagenesis to pore water
• Maintained, during the long time of nodule growth (several millions of years), the delicate balance
between sedimentation and burial‐preventing biogenic nodule‐lifting
• Has escaped significant erosion and re‐deposition.
The large size of the total claim area in the CCZ suggests that the ideal layer characteristics are met here
frequently. Prospecting and exploration results confirm the existence of ideal but patchy conditions. However,
patches of economically interesting nodule covers are difficult to predict. The prediction of patches ideal for
seabed mining is the objective of modelling. For such modelling, the rules of correspondence between sets of
variables involved in sediment‐layer and manganese‐nodule formation need to be known. Geological modelling
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