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Stratigraphic correlation

Two holes were drilled at Site M0066: Holes M0066A (28 mbsf) and M0066B (27.25 mbsf). The meters composite depth (mcd) scale for Site M0066 was based on correlation of magnetic susceptibility between holes (Fig. F13). Sediment cores were logged with the standard MSCL to enable precise hole-to-hole correlation and to construct a composite section for Site M0066 (Fig. F13). Before analysis, all magnetic susceptibility data were cleaned from the top of each section, removing any outliers from the measurements. The depth offsets that define the composite section for Site M0066 are given in Table T5 (affine table).

Correlation between the susceptibility data in Holes M0066A and M0066B is relatively good between 2 and 15 mbsf, enabling the production of a continuous splice record for this site (Table T6). However, there are some gaps in the splice record, as Section 347-M0066B-2H-3 was appended to Section 347-M0066B-3H-1 and Section 347-M0066A-3H-2 was appended to Section 347-M0066A-4H-1. Correlation and therefore splicing was not possible deeper than Cores 347-M0066A-6H and 347-M0066B-7H. The lowermost part of Hole M0066A was therefore appended in the splice record. The accuracy of the correlation was visually checked from scanned core slab images using Corelyzer software. No expansion or compression corrections were applied to the data, so the offset within each core was equal for all points. Therefore, it is possible that some features are not similarly aligned between holes.

Seismic units

Seismic sequence boundary-sediment core-MSCL log (magnetic susceptibility) correlations are shown in Figure F14. The correlation is based on the integration of seismic data and lithostratigraphy. Two-way traveltime values were calculated for each lithostratigraphic unit boundary using sound velocity values measured during the OSP (see “Physical properties”; Table T7). Lithostratigraphic units/unit boundaries (see “Lithostratigraphy”) were examined at these calculated two-way traveltime values to define the extent of agreements between seismic boundaries and actual lithologic and/or physical properties disconformable surfaces. Uncertainties in the time-depth function and effects from gas-saturated sediments could have resulted in moderate inconsistencies between seismic features and sedimentological observations from cores and MSCL logs.

Seismic Unit I

Seismic Subunit Ia
  • Two-way traveltime: 0.118 ms
  • Lithology: laminated silty clay and silty fine sand (lithostratigraphic Subunit Ia)
  • Depths: 2.0–4.92 mbsf (M0066A); 2.0–5.56 mbsf (M0066B)

Subunit Ia corresponds to a relatively strong reflector in the upper part of the seismic profile. Magnetic susceptibility values are low in this unit, but they increase downcore at the Subunit Ia/Ib boundary (see “Physical properties”).

Seismic Subunit Ib
  • Two-way traveltime: 0.122 ms
  • Lithology: laminated silty clay and silty fine sand with dispersed clasts (lithostratigraphic Subunit Ib)
  • Depths: 4.92–8.60 mbsf (M0066A); 5.56–9.60 mbsf (M0066B)

Subunit Ib is characterized by relatively high magnetic susceptibility values and parallel reflectors in the seismic profile.

Seismic Unit II

  • Two-way traveltime: 0.130 ms
  • Lithology: parallel bedded massive medium sand with centimeter- to decimeter-scale laminated silt and clay interbeds (lithostratigraphic Unit II)
  • Depths: 8.6–15.2 mbsf (M0066A); 9.6–15.4 mbsf (M0066B)

The boundary between Subunit Ib and Unit II coincides with a strong reflector in the seismic profile. Magnetic susceptibility values are low at the top of Unit II but increase downcore and are highest in the lowermost part of the unit.

Seismic Unit III

  • Two-way traveltime: 0.135 ms
  • Lithology: clast-rich muddy diamicton and clayey silt with dispersed clasts (lithostratigraphic Unit III)
  • Depths: 15.2–19.51 mbsf (M0066A); 15.4–19.4 mbsf (M0066B)

Unit III is characterized by high magnetic susceptibility values that decrease downcore. Parallel reflectors are visible in the seismic profile.

Seismic Unit IV

  • Two-way traveltime: 0.147 ms
  • Lithology: parallel-bedded dark greenish gray massive medium sand (lithostratigraphic Unit IV).
  • Depths: 19.51–28.00 mbsf (M0066A); 19.4–27.25 mbsf (M0066B)

Unit IV possibly corresponds to strong parallel reflectors visible in the seismic profile. The boundary between Unit III and Unit IV coincides with a strong reflector, indicating a probable unconformity/erosion. Magnetic susceptibility values of this unit are again relatively low.