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doi:10.2204/iodp.proc.347.105.2015

Physical properties

This section summarizes the preliminary physical property results from Site M0061. Three holes were drilled at this site. Hole M0061A was drilled to 25.2 mbsf, Hole M0061B to 28.7 mbsf, and Hole M0061C to 23.1 mbsf. Additionally, three Rumohr cores (Holes M0061K, M0061L, and M0061M; <1 m in length) were collected at this site to attempt to capture the water/sediment interface and the uppermost surface sediments. Physical property measurements were not performed for these Rumohr cores. For Holes M0061A, M0061B, and M0061C, all physical property measurements described in “Physical properties” in the “Methods” chapter (Andrén et al., 2015a) were conducted. As the discrete moisture and density (MAD) and P-wave measurements are few in number, our interpretations are based primarily on the shipboard multisensor core logger (MSCL) data from Hole M0061B, which had the greatest penetration.

Magnetic susceptibility and color reflectance

Magnetic susceptibility generally increases downcore with distinct variations noted at lithostratigraphic unit boundaries (Fig. F15). Values are relatively constant through Unit I, with a low-amplitude excursion at the Unit I/Subunit IIa boundary followed by a gradual decrease in the upper interval of Subunit IIa. Magnetic susceptibility then increases downcore in Subunit IIa before dropping to low values in Subunit IIb and returning to high values in Subunit IIc. Lithology is similar throughout Unit II. Therefore, the change in magnetic susceptibility likely reflects changing organic content (see “Lithostratigraphy”). Unit III is characterized by increasing magnetic susceptibility to the Unit IV boundary. Unit IV exhibits relatively constant values with some large excursions around 22 and 26 mbsf.

Color reflectance, in particular b*, reflects downcore changes in lithology (Fig. F15). Unit I exhibits relatively low (more blue) values, whereas Subunit IIa exhibits higher (more yellow) values. Subunit IIb is distinguished by increased blue reflectance, whereas Subunit IIc is characterized by increased yellow reflectance. Units III and IV are generally yellowish in color.

Natural gamma ray, noncontact resistivity, and P-wave velocity

Both natural gamma ray (NGR) and noncontact resistivity (NCR) increase through Units I and II, reaching peak values in the upper interval of Unit III (Fig. F15). There is a sharp decrease in both physical properties at ~9 mbsf in Unit III. That change could be related to a suggested erosional horizon at around that level (see “Stratigraphic correlation”). Although NGR returns to high values in the middle portion of Unit III, NCR remains low to the bottom of the hole. A similar trend in NGR data is observed at nearby Site M0062, located in Ångermanälven River estuary (see “Physical properties” in the “Site M0062” chapter [Andrén et al., 2015b]). Low NCR may indicate high water content in the cores, which is consistent with P-wave velocities in Unit IV that vary around ~1500 m/s (speed in water). In the upper sections of Hole M0061B, low P-wave velocities in Subunit IIa are likely caused by pervasive cracks. Low P-wave velocity spikes in portions of Units III and IV appear to result from core liners that were not fully filled with sediment.

Density

Gamma density was measured at 1 cm intervals during the offshore phase of Expedition 347 (Fig. F16). Gamma density increases from the core top to the upper interval of Unit III then decreases abruptly at ~11 mbsf before increasing again and remaining relatively constant to the bottom of the hole. Discrete bulk density measurements conducted during the Onshore Science Party (OSP) correlate well with the shipboard measurements (r2 = 0.93; Fig. F17).