Geology of parts of the central and eastern Clarion Clipperton Zone

Figures & data

Figure 1. Survey areas, sub-areas and 1:250 K map sheets. NORI stands for Nauru Ocean Resources Incorporated; TOML for Tonga Offshore Mining Limited; Marawa for Marawa Research and Exploration Limited.

An illustrative map of the central-eastern Clarion Clipperton Zone showing the extents of exploration contract areas, priority sub-areas and areas surveyed by multibeam echosounder.

Figure 2. Deposit scale survey areas (a) basement ages and (b) extrapolated stratigraphy. Green isochrons at left are from Barckhausen et al. (2013), while the brown isochrons are from Müller et al. (2016) DSDP site 159 information is from van Andel et al. (1973a), site 160 from van Andel et al. (1973b) and migration estimates based on the work of van Andel et al. (1975).

An illustrative map and comparative section of the age of seabed and the types and ages of sediment in each area as deduced from nearby drill-holes.

Figure 3. Example potholes. (a) Circular and ‘trough’ shaped features in Sheet 1, (b) potholes grading to escarpments in western Sheet 2, (c) line of potholes associated with a dyke off the volcanic edifice to the NW in eastern Sheet 2, (d) association of potholes only with a wider hill in Sheet 3, (e) smaller potholes in Sheet 4D, (f) potholes amongst artefacts in the bathymetry in western Sheet 7.

Example images of multibeam bathymetry with pot-hole formations circled.

Figure 4. Example Carbonate Strata Breccia in sub-bottom profile (SBP) data. (a) Breakthrough type carbonate strata breccia (CSB) bounded by a large dyke in map sheet 2; (b) breakthrough CSB transitioning to a stratabound CSB in map sheet 3; (c) stratabound CSB in centre and breakthrough CSB’s nearer to the valley margin in map sheet 2; (d) small stratabound CSB in map sheet 4.

Sub-bottom sonar profiles from different parts of the mapped areas showing calcic-sedimentary and volcanic features of interest.

Figure 5. Example variable clay-ooze map in SBP data. SBP line is CCZ15-M08, in sheet 4. Clay-ooze of the Clipperton formation is above the pink dashed line.

Sub-bottom sonar profile from one part of the mapped areas showing siliceous-sedimentary features of interest.

Figure 6. Example knolls and seamount on MBES. (a) Carbonate capped ‘pancake’ mound, sheet 1; (b) low backscatter reflectance knolls, sheet 2; (c) composite knolls, sheet 2; (d) coherent-lava seamount, sheet 4; (e) knolls aligned along a depression, sheet 3; (f) knoll split across an abyssal ‘valley’.

Example images of multibeam bathymetry and backscatter responses for a variety of different volcanic units.

Figure 7. Example intrusions in SBP data. (a) Dyke swarm (with hornfels); (b) and sill with feeders.

Sub-bottom sonar profiles from different parts of the mapped areas showing volcanic-intrusion features of interest.

Table 1. MBES 1:250,000 interpretation – detailed legend.

Unit/Code	Example	Description
Abyssal hills likely nodule bearing Ab_s		Abyssal hills with moderate backscatter (−27 to −36 dB). 6° taken as the slope margin for the hills. Effectively the default unit within the CCZ, seen to make way for Ab_c in SE Sheet 7 and Ab_d in southern Sheet 5 survey areas. Nodule abundance can be very high in this unit especially if the nodules are of smaller diameter Terrain ruggedness index generally > 2.3
Abyssal hills likely nodule bearing – soft Ab_c		Extensive areas of abyssal hills with more moderate-low backscatter than Ab_s (∼ −5 dB). This might relate to a slightly higher carbonate content in the clay-ooze although samples show siliceous sediment within the surficial decimetres. Nodule abundance seems to be slightly lower on this unit relative to nearby Ab_s. Terrain ruggedness index generally > 2.3 but includes common areas <2.3 indicating a correlation with frequently fewer abyssal hills
Flatter area of abyssal hills likely nodule bearing Abl_s		Subdued to absent abyssal hills with moderate backscatter and usually frequent volcanic knolls and mounds. Nodule abundance can be very high in this unit especially if the nodules are of smaller diameter. Terrain ruggedness index generally < 2.3
Flatter area of abyssal hills likely nodule bearing – soft Abl_c		As per Ab_c but with subdued to absent abyssal hills and usually frequent volcanic knolls and mounds. Nodule abundance varies but seems to be often slightly lower on this unit relative to nearby Abl_s. Terrain ruggedness index generally well < 2.3
high volume nodule bearing sediment hN		Discrete zones of frequently higher backscatter response (−20 to −30 dB) within Ab_s or Abl_s and rarely within Ab_c and Abl_c. In the northern part of the NORI A area this unit has distinctly very high reflectance and a dredged sample returned nodules up to 15 cm across. In Sheet 3 this unit has abundant medium sized nodules ∼ 5 cm across. Thought to correlate with abundant and/or larger nodules.
Abyssal hills likely nodule poor or free Ab_d		Areas of very low acoustic return tend often form drift-like bodies in valleys and slopes to one side or around the base of seamounts. Nodule abundance thought to be very low to absent.
Chalk outcrop Ab_k		Areas with similar low acoustic return to Ab_d thus often impossible to discriminate. Mapped where hill-top morphology is more supportive. Nodule abundance can be high in parts of this unit in areas where thin siliceous clay-ooze cover is present.
Abyssal hill slopes S1_NE_h S1_NE_s S1_SW_h S1_SW_s S2_NE_h S2_NE_s S2_SW_h S2_SW_s		Generated at > =  6° then selected to more likely be associated with the graben and horst related normal faults associated with abyssal hills. Circular features are not included (volcanic units or potholes). S1 orientation is the most common regionally including irregular slopes often associated with offset faults and valley terminations. NE facing is net aspect between 315 and 135° SW facing is net aspect between 135 and 315° _s has less backscatter reflectance −30.5 dB or less – interpreted to be predominantly carbonate outcrop ± sedimentary cover _h has more backscatter reflectance −30.5 or more – interpreted to include common volcanic outcrop. Nodule abundance is generally very low to absent unless there is siliceous clay-ooze cover in flatter parts of the slope. Preservation of the semi-liquid layer is unlikely to be widespread at slopes >6°
Seamount – coherent facies V1_m		Bathymetry illustrates composite dome and mound formation; very high backscatter reflectance is interpreted as all being lava. Slopes are around 20° but locally up to 30°. No significant nodules known.
Seamount – talus V2_t		Only one example; slopes are around 10° but locally as high as 20°. Nodule abundance potential likely to depend on cover, e.g. per V1_k (three historical samples from near the base of the slope returned 10–13 kg/m^2 but 1–1.3% Ni and 24–31% Mn).
Sheet flows V1_s		High reflectance suggests lava but very low aspect unit over long distances is problematic (slopes are often less than 2°). May be breaching sill? Else some type of high reflectance gravity density flow.
		Nodule abundance unknown (one historical sample on the edge of a unit returned low abundance and grade).
Knoll/mound – hard V1_k Composite knolls – hard V1_c		Irregular of the ocean crust basalts that constitute the Abyssal Hills/Valleys. Characterised by standing proud in the bathymetry and having very high backscatter (0 to −20 dB). Variety of landforms not discriminated (e.g. pancakes, cones ridge complexes). Often associated with basins. Distal flows not seen larger edifices formed from compound short range flows (likely pillows). Origin is either off-axis during spreading or later (decompression or hot-spot related). Nodule abundance likely to be highly variable. In exposed volcanic areas will likely be patchy with some occurrences in areas where thin siliceous clay-ooze cover is present. In covered shallow mounds will likely be the same as Ab_s.
Knoll/mound – soft V2_k Composite knolls – soft V2_c		Characterised by lower ‘moderate’ backscatter than the volcanic unit (similar to that of high nodule abundance areas) despite often steep landforms. Seen only in TOML Area B and NORI Area A. These may represent more fragmental volcanic products (scoria or even covered by density current flows). Nodule abundance potential expected to be the same as for V1_k/c.
Fissure lavas/dyke V1_f		Relatively uncommon linear high reflectance bodies and mounds. Nodule abundance potential expected to be the same as for V1_k/c.
Pothole/trough zone PH		Groups of these indicated with a general outline on these preliminary maps as they are too small at this scale of interpretation. These small depressions commonly form in lines along ridge tops. They can grade into scarps. In NORI A they also grade into long trough structures parallel to the abyssal hills. Rare in the east (Sheet 7).
Tb		Major topographic break-line separating distinct domains based on relative water depth.

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Data availability statement

GIS data can be provided on written request to the authors.