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Table T4. Intervals with evidence for mass transport deposits (MTDs) identified by visual core description (VCD) and X-ray computed tomography (CT), Hole C0018A.

Interval Core, section, interval (cm) Depth (mbsf) Thickness (m) Internal structures and observation from X-ray CT Thickness (m) Description notes
Core, section, interval (cm) Depth (mbsf)
Top Bottom Top Bottom Top Bottom Top Bottom
  333-C0018A- 333-C0018A-       333-C0018A- 333-C0018A-        
1 1H-3, 45 1H-5, 56.4 1.425 4.277 2.852 1H-3, 45 1H-3, 135 1.425 2.3 0.875 Coherent interval with relatively higher CT number, consistent tilt of strata (as evidenced by high-CT number lines).*
1H-3, 135 1H-5, 56.4 2.3 4.277 1.977 Mud clasts “flowing” in matrix, which shows some sort of lamination in the lower part of this interval.
Subvertical high-CT number lines extend for several tens of centimeters and crosscut layers and clast.
Base is defined by a sharp change in CT number from lower (above) to higher (below); there potentially could be a thin layer but CT image is not conclusive.
The strata immediately above the base is faintly horizontally “laminated,” which may indicate shear. The reasoning behind this interpretation is that primary lamination in bioturbated strata is not expected.
It cannot completely excluded from CT scan that below, there is some more tilted and deformed strata. Therefore the base of this interval is not clearly defined.
2 5H-5, 35.3 6H-2, 90.5 39.451 46.727 7.276 5H-5, 24 5H-5, 35.3 39.346 39.451 0.105 Succession of thin, few millimeter thick volcaniclastic sand laminae, overlying a thin 1 cm thick layer with mud clasts. This layer immediately overlies the “debrite” defined as top of MTD Interval 2 and is interpreted as the turbidite deposit associated to this “mass-movement event.”
5H-5, 35.3 5H-8, 44 39.451 43.579 4.128 Chaotic mixed sediment, convolute bedding with folded and disturbed ash layers (debrite).
5H-8, 44 6H-2, 90.5 43.579 46.727 3.148 Tilted strata as evidenced both from inclined layers and tilted orientation of high-CT number lines.
Boundary between upper mixed sediment and lower tilted strata is a thin millimeter thick inclined higher CT number laminae that truncates high-CT number lines.
High-CT number lines immediately below this thin layer are all oriented parallel to this inclined layer, possibly indicating shear.
Interval 6H-2, 90 cm, prominent, slightly inclined contact between high CT number (above) and low CT number (below). High-CT number lines are well pronounced and parallel to inclined contact and may indicate shear. Below in low-CT number strata, no occurrence of high-CT number lines, but homogeneous bioturbated mud. Ash layer below at interval 6H-3, 10–20 cm, is horizontally stratified and looks undisturbed.
3   7H-05, 24   8H-3, 59.5   58.013   65.745   7.732   7H-5, 24 7H-5, 60.3 58.013 58.342 0.329 This interval has been described as mixed sediment on VCD. In CT images no associated features can be identified.
7H-5, 60.3   8H-3, 59.5   58.342   65.745   7.403   Below interval 7H-5, 61 cm, high-CT number lines are chaotically oriented in the uppermost part but develop clear tilted orientation further downsection.
Dipping layers occur at intervals 7H-7, 38 cm; 7H-10, 29 cm; 7H-11, 28 cm; and 7H-11, 63 cm.
Persistent orientation of tilted high-CT number lines occasionally abruptly change orientation along inclined millimeter thick layers with higher CT numbers (interval 7H-10, 29–31 cm, and 7H-11, 81–91 cm). These layers possibly indicate internal shear zones.
A structure indicating folding of a diffuse, slightly higher CT number layer is observed in interval 7H-8, 18–22 cm.
The base of interval 8H-3, 60 cm, is a thin, high CT number, 2 mm thick layer, mapped as clay in VCD. Above, high-CT number lines are scattered but show a clear tendency to orient parallel to the clay layer immediately above it, possibly indicating enhanced shear above this clay layer, which may potentially represent the base of MTD within this interval. Below, high-CT number lines are rare, and normal faults are present.
4 8H-4, 20.6 8H-4, 75.5 66.437 66.934 0.497 8H-4, 20.6 8H-4, 75.5 66.437 66.934 0.497 Folded volcaniclastic sand or ash layer (smear slide description shows texture = 60% sand, and composition = dominant volcanic glass) identified in VCD. X-ray CT is inconclusive because of heavy gas expansion at the top of this layer; however, fold axis appears to be perpendicular to coring axis.
Above and below this layer the strata look undisturbed, however, affected by steeply dipping normal faults.
5 9H-3, 39.5 11H-6, 103.5 75.914 94.37 18.456 9H-3, 39.5 9H-4, 141 75.914 78.203 2.289 Because of heavy coring disturbance (likely due to gas expansion and the fact that this core got jammed in the core barrel) the top of this interval is not well defined. Top 39.5 cm of Section 9H-3 shows flow structures that may be related to coring disturbances.
Below Section 9H-3, 39.5 cm, clear evidence for mixed sediment including mud clasts and chaotically-to-partly consistent inclined orientation of high-CT number lines.
In the lowermost part of this interval identified as mixed sediment in VCD, is a subhorizontally stratified volcanic fine ash layer that is affected by normal faulting.
9H-4, 141 10H-8, 130 78.203 88.229 10.026 Below Section 9H-4, 141 cm, CT shows persistent orientation of tilted high-CT number lines that occasionally abruptly change orientation along inclined millimeter-thick layers (Section 10H-6, 38 cm). These layers possibly indicate internal shear zones.
Dipping beds occur at intervals 10H-8, 74 cm, and 10H-8, 130 cm. However, this interval also contains a subhorizontal ash layer at interval 10H-7, 141 cm.
Some flow structures occur in Section 10H-3 but may be due to coring disturbance/degassing.
10H-8, 130 10H-9, 10 88.229 88.422 0.193 Thin interval associated with disrupted ash layer showing mixed sediment with mud clasts.
10H-9, 10 11H-6, 27 88.422 93.712 5.29 This interval shows persistent orientation of tilted high-CT number lines that occasionally change orientation (interval 10H-6, 38 cm).
Dipping discrete (often ash) layers occur at intervals 10H-9, 93 cm; 11H-2, 10 cm; 11H-3, 15 cm; 11H-3, 60 cm; and 11H-1, 7–20 cm. The latter interval shows two subhorizontal ash layers, which are slightly dipping in two different directions, possibly indicating folding.
The character of persistent tilted high-CT number lines stops at interval 11H-6, 26 cm, immediately above a tilted ash layer.
11H-6, 27   11H-6, 103.5   93.712   94.37   0.658   Below this tilted ash layer, high-CT number lines are somewhat chaotically oriented in the upper part and become successively strongly aligned, forming subhorizontal lineaments. If high-CT number lines can be assumed to represent stretch lineations, this strongly indicates increased shear toward the bottom of this interval with evidence for MTD.
At interval 11H-6, 52 cm, a flat-lying fold with subhorizontal fold axis parallel to lineations indicates soft-sediment deformation in a ductile mode.
Below interval 11H-6, 103.5 cm, there is no evidence for deformed sediment in CT, even for the horizontally layered ash layer that appears as broken layer in the split image core photo.
6   15H-2, 91.5 23H-01, 68.7 127.545 188.573 61.028 15H-2, 83 15H-2, 91.5 127.474 127.545 0.071 Turbidite overlying MTD.
15H-2, 91.5 15H-3, 71 127.545 128.406 0.861 Mixed sediment, debrite.
15H-3, 71 15H-8, 60 128.406 133.345 4.939 Coherent intervals showing persistent orientation of inclined high-CT number lines perpendicular to tilted strata. Orientation of both high-CT number lines and tilted bed changes approximately between interval 15H-6, 135 cm, and 15H-7, 56 cm; in Section 15H-7, between 60 and 103 cm (this change is associated to a steeply dipping, almost vertical zone).
The whole interval occasionally shows internal contacts characterized by irregular transition “dissolving” into debrite. This is particularly evident for discrete beds in intervals 15H-4, 104 cm, and 15H-8, 60 cm.
Occasional occurrence of steeply dipping normal faults truncating high-CT number lines.
15H-8, 60 16H-10, 16.5 133.345 141.844 8.499 Mixed sediment, debrite.
CT scans show partly chaotic orientations of high-CT number lines and partly strongly elongated subhorizontal orientation.
Original flow structures and convolute structures can be clearly distinguished from drilling-induced flow-in structures to Section 15H-9, 120 cm.
Core 15H has coring-induced flow-in below interval 15H-9, 100 cm.
Core 16H is heavily disturbed due to core liner splitting and working out from the core barrel, however, shows clear indication for mixed sediment (debrite). There are thin intervals (e.g., 16H-2, 4–97 cm; 16H-2, 105–115 cm; and 16H-4, 125 cm, to 16H-10, 10 cm) that show more coherent tilted strata and inclined high-CT number lines. These intervals can be possibly interpreted as clasts (bigger than core scale) within the debrite.
16H-10, 16.5 18H-2, 30 141.844 155.136 13.292 More coherent strata, showing subvertical orientation of high-CT number lines and subhorizontal sand layers (e.g., at interval 17H-1, 70 cm) in the upper part, and more steeply dipping beds (e.g., in Section 18H-2) and inclined high-CT number lines in the lower part. Internal, steeply dipping zones at intervals 17H-2, 110 cm; 17H-3, 50–60 cm; and 17H-6, 53–74 cm, separate individual coherent intervals showing persistent orientation of tilted high-CT number lines.
Steeply dipping normal faults and web structures (e.g., at interval 17H-7, 20 cm) are occasionally present.
18H-2, 30 18H-3, 90 155.136 157.092 1.956 Interval showing flow structures, mud clasts, near-vertical slightly folded contacts between two disintegrated sediment masses between intervals 18H-2, 120 cm, and 18H-3, 20 cm, and a slump fold at interval 18H-3, 90 cm.
19H-top 19H-5, 20 159.65 162.756 3.106 Coherent intervals showing persistent orientation of tilted high-CT number lines. Orientation of high-CT number lines changes along dipping and occasionally folded contacts (e.g., in Section 19H-3).
19H-5, 20 19H-5, 80 162.924 163.429 0.505 Interval with inclined thin (5 m scale) sand layers.
20H-2, 88 21H-2, 40 165.782 175.845 10.063 Core 20H top (above interval 20H-2, 80 cm) is fluidized and fully coring disturbed.
Coherent interval with interbedded thin subcentimeter to centimeter sand layers that are partly disrupted and partly show subhorizontal layering (e.g., in Section 20H-3) and coherent mud intervals showing subvertical orientation of high-CT number lines. Partial occurrence of thin intervals, where strata are more deformed (deintegrated: e.g., interval 20H-5, 0–40 cm) and slightly inclined 3 cm thick sand layer at interval 21H-1, 80 cm.
The lower parts of Core 20H-6, 1–6 cm, to 20H-CC: flow-in.
21H-2, 40 21H-4, 10 175.845 176.892 1.047 Interval with folded and distorted thin sand layers.
Upper boundary of this interval is a complex fault/shear zone structure.
Lower boundary is a ~45° dipping surface truncating inclined sand laminae. High-CT number lines above this contact are aligned, indicating shearing along this contact.
21H-4, 10 21H-5, 100 176.892 177.963 1.071 Dipping thin 0.5 cm sand laminae in cross-section view. Bedding change in dip at about interval 21H-5, 20 cm, where a fold can be observed in CT.
The lower part of Core 21H shows coring-induced flow structures at the bottom.
22H-1, 20 22H-4, 14 178.65 180.865 2.215 Top of interval 22H-1, 0–20 cm, is likely drilling disturbed with “flow-out” at the top.
Coherent-looking homogeneous interval with subvertical orientation of high-CT number lines, with occasional indication for folding (e.g., interval 22H-2, 86–120 cm) and higher CT number deeply inclined to subvertical layers, along which high-CT number lines are preferentially aligned, possibly indicating shear (e.g., in Section 22H-4).
22H-4, 14 22H-7, 10 180.865 181.94 1.075 Interval showing folds in CT, along which high-CT number lines are preferentially oriented.
22H-7, 10 22H-8, 56 181.94 183.8 1.86 First appearance on VCD is rather homogeneous with subhorizontal sand layer at interval 22H-7, 116 cm. In CT scan, high-CT number lines show clear preferred orientation (e.g., interval 22H-8, 13–40 cm, with a possible localized shear zone at ~28 cm) and occasional change in orientation along possible fold structures (e.g., interval 22H-7, 115 cm).
Section 22H-9 to base of core is coring-induced flow-in.
23H-1, 0 23H-1, 68.7 187.95 188.573 0.623 Interval heavily coring disturbed because of gas expansion in the underlying sand during core recovery.

* = the term “lines” is being used as a descriptive word here, describing the sublinear features showing high CT number indicative for FeS mineralization (pyrite); this may be either mineralized bioturbation burrows, stretched and/or aligned pyrite minerals occurring as patches in “background” sediment, or may also be related to so-far unknown mineralized dewatering/degassing structures.

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