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doi:10.2204/iodp.proc.347.104.2015

Stratigraphic correlation

At Site M0060, two holes were drilled, Holes M0060A (232.5 mbsf) and M0060B (85.7 mbsf). Hole M0060B was heavily subsampled offshore for microbiological studies, and the remaining core material after whole-round subsampling (see “Microbiology”) was limited. Thus, it was not possible to produce a continuous splice record for this site. However, sediment cores from Hole M0060B were logged before subsampling using the Fast-track multisensor core logger (MSCL) (see “Physical properties”). Magnetic susceptibility data (4 cm resolution) from the Fast-track MSCL together with standard MSCL magnetic susceptibility measurements from Hole M0060A (2 cm resolution) enable correlation between holes and construction of a composite section for Site M0060 (Fig. F21).

The meters composite depth scale for Site M0060 is based primarily on correlation of magnetic susceptibility between holes (Fig. F21). Before analysis/correlation, all magnetic susceptibility data were cleaned for the top (0–5/20 cm) of each section, removing any outliers from the measurements. The depth offsets that define the composite section for Site M0060 are given in Table T13. Correlation between the susceptibility anomalies/data in Holes M0060A and M0060B is mainly good downhole to the end of Hole M0060B. Because of limited core material from Hole M0060B and the single hole recovery below 85.7 mbsf, there are several gaps in the composite record, and it was not possible to make a single spliced record for this site.

Similar to Site M0059, a compression or expansion correction was not applied to the data, so the offset within each core was equal for all points. Therefore, it might be that some features are not similarly aligned between holes. Thus, the meters composite depth values will approximately, but not precisely, correspond to the same stratigraphic horizons in adjacent holes.

Seismic units

Seismic sequence boundary-sediment core-MSCL log (magnetic susceptibility) correlations are shown in Figure F22. Correlation is based on the integration of seismic data and lithostratigraphy (see “Lithostratigraphy”). Two-way traveltime (time elapsed between when the acoustic pulses are sent to seabed and when they are received back at the surface) values were calculated for each lithostratigraphic unit boundary using sound velocity values measured during the OSP and offshore (see “Physical properties”; Table T14). Lithostratigraphic units and unit boundaries were examined at these calculated two-way traveltime values to define the extent of agreement between seismic boundaries and actual lithologic transitions and/or where the physical properties data indicate disconformable surfaces. Uncertainties in the time-depth function could have resulted in minor inconsistencies between seismic features, sedimentological observations from cores, and MSCL logs.

Seismic Unit I

• Two-way traveltime: 0.0541 ms
• Lithology: fine to medium thickly bedded sand (lithostratigraphic Unit I)
• Depth: 0–6.0 mbsf

This unit is characterized by strong reflectors in the seismic profile, as well as in physical properties like high magnetic susceptibility values measured in sediment cores.

Seismic Unit II

• Two-way traveltime: 0.0768 ms
• Lithology: interlaminated sandy clayey silt and fine–medium sand with dispersed clasts (lithostratigraphic Unit II)
• Depth: 6.0–23.84 mbsf

Unit II shows increasing magnetic susceptibility values downcore. In the seismic profile, the lower limit of Unit II is visible, but it is not very clear at Site M0060 because of a strong seabed multiple in the seismic profile. At the lower limit of this unit, magnetic susceptibility values decrease rapidly.

Seismic Unit III

• Two-way traveltime: 0.1495 ms
• Lithology: laminated clay and silt with dispersed clasts (lithostratigraphic Unit III)
• Depth: 23.84–79.52 mbsf

This seismic unit shows faint parallel layering in the seismic profile. Magnetic susceptibility values of this unit show high variability. The lower boundary of this unit corresponds relatively well to a change into a more seismically chaotic unit.

Seismic Unit IV

• Two-way traveltime: 0.1683 ms
• Lithology: interbedded sand, silt, and clay with dispersed clasts and clast-poor diamicton (lithostratigraphic Unit IV)
• Depth: 79.52–95.04 mbsf

At this unit boundary, magnetic susceptibility values increase rapidly downcore.

Seismic Unit V

• Two-way traveltime: 0.1947 ms
• Lithology: sandy silty clay with dispersed clasts (lithostratigraphic Unit V)
• Depth: 95.04–116.7 mbsf

Unit V coincides with a locally (partly) stratified seismic unit.

Seismic Unit VI

• Two-way traveltime: 0.2282 ms
• Lithology: fine to medium massive well-sorted sand (lithostratigraphic Unit VI)
• Depth: 116.7–146.1 mbsf

Unit VI is characterized by a more chaotic seismic structure and relatively high magnetic susceptibility values. At the lower boundary of Unit VI, magnetic susceptibility values decrease rapidly downcore.

Seismic Unit VII

• Two-way traveltime: 0.3215 ms
• Lithology: sandy diamicton (lithostratigraphic Unit VII)
• Depth: 146.1–229.6 mbsf

This unit shows some inclining seismic structures/reflectors. Some strong seismic reflectors occur in the lowermost part of this unit, but they are not seen in the lithology. However, some high magnetic susceptibility values might correspond to these seismic reflectors.

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