Figure F18. Magnetization intensity vs. inclination showing effect of steep drilling overprint and core disturbance in Cores 368-U1505C-48X through 64X. Red dashed line = mean inclination for Cores 48X through 64X, black dashed line = mean inclination for Cores 1H through 47F.

<figure><img src="image_465.png" /></figure>

Figure F19. Magnetic measurements, Hole U1505C. Inclination was used to determine polarity. AFD = AF demagnetization. Magnetostratigraphic features are referred to as n1, etc., in a sequential manner for convenience and have no bearing on chronS. Discrete samples are yellow and green. GPTS2016 = geomagnetic polarity timescale of Ogg et al. (2016).

<figure><img src="image_466.png" /></figure>
Figure F20. AMS data, Hole U1505C. A. Stereonet of AMS principal directions (lower hemisphere, equal-area projection). K₁ = maximum axis, K₂ = intermediate axis; K₃ = minimum axis. Confidence ellipses at 95% level (same color convention) show dominantly planar and subhorizontal fabric (oblate), consistent with sedimentary fabric acquired in a calm pelagic environment. Tensorial means are shown with larger symbols of same color. B. Degree of magnetic anisotropy (P') vs. magnetic susceptibility (Km). C. Shape parameter (T) vs. P' showing dominantly oblate symmetry of sedimentary fabric.

<figure><img src="image_467.png" /></figure>

<figure><img src="image_468.png" /></figure>

<figure><img src="image_469.png" /></figure>

## Geochemistry

Hydrocarbon gases were detected in deeper sediments only at Site U1505 and not at shallow depths. Thus, the base of the hole has methane distributions similar to those at Site U1499 (which has methane at depth), whereas the uppermost section is similar to Site U1501, which is barren of methane. Except for the shallowest 30 m of sediment, TOC, TN, and TS contents were mostly low in shallow lithostratigraphic Unit I, but TS and TOC were slightly higher in Unit II. Thus, in terms of solid organic geochemistry, Sites U1505 and U1501 are similar. Instances of high carbonate content are associated with bioclastic oozes. Interstitial water chemistry has two important features. The upper part exhibits patterns similar to those at Site U1501 in several respects (e.g., inhibited sulfate reduction), and there is evidence of freshwater input in deeper sediments (based on low chlorine, bromide, and salinity). Inductively coupled plasma-atomic emission spectroscopy analysis was not performed on samples collected at Site U1505.

## Headspace gas

Headspace gas samples were taken at a frequency of one sample per core or per 10 m of drilling advance for routine safety monitoring. As at Site U1501, methane was not abundant in shallow sediments at Site U1505 (uppermost 50 m), although it was detected deeper in the hole at ~150 and ~400 m. Concentrations range from 70 to 3899 ppmv from 380 to 438 m, with a single instance of ethane found at this depth. A small concentration of methane was also detected at 150 m.

## Bulk sediment geochemistry

Solid geochemistry parameters are listed in Table T10.

### Lithostratigraphic Unit I

As seen at Site U1501, the uppermost black mud (lithostratigraphic Subunit IA) has relatively high TOC and TN contents relative

<caption>Table T10. Carbon, nitrogen, and sulfur, Hole U1505C. **View table in PDF format. Download available in CSV format.**</caption>

to the units beneath. Sulfur content, although low in this unit, is higher than in the subunits immediately beneath it (Figure F21). Lithostratigraphic Subunits IB and IC have generally low TOC (<1 wt%) and low TS, which is also the case for Site U1501, where organic carbon is also least well preserved in these units.

### Lithostratigraphic Unit II

Lithostratigraphic Unit II has high sulfur and low carbonate content, and relative to Subunits IB and IC, it has significant organic carbon content (typically 0.5 wt%). The TOC/TN ratio for the interval is low, indicating high-nitrogen material, which would classically be interpreted as well-preserved organic matter of aquatic origin (Hedges et al., 1988).

High carbonate contents were found in bioclast-rich Subunits IB and IC. On a crossplot, Subunit IA and Unit II both have distinctively low carbonate contents and low TOC/TN ratios (Figure F22), indicating a high proportion of aquatic organic matter, and Subunits IB and IC appear to have organic matter that has been more heavily degraded or is terrestrial in origin (Hedges et al., 1988). On a carbon-sulfur crossplot, the distinctively high sulfur content in Unit II is a little unusual because it does not have much organic matter. The unit appears to have a high abundance of reduced sulfur, whereas Subunit IA has low sulfide content, given that it is relatively organic carbon-rich marine mud (Berner and Raiswell, 1984).

## Raman and surface-enhanced Raman spectroscopy

Surface-enhanced Raman measurements were performed on shallow core and mudline samples from Holes U1505A–U1505D. Concentrations are reported as nanograms asphaltene per gram of sediment in Figure F23.
<figure><img src="image_470.png" /><figcaption>Figure F22. Crossplot of organic geochemical parameters, Site U1505. Solid circles = lithostratigraphic Subunit IA, open squares = Subunit IB, crosses = Subunit IC, open circles = Unit II.</figcaption></figure>

<figure><img src="image_471.png" /></figure>

## Interstitial water chemistry

Shipboard analyses were performed on interstitial water squeezed from 5–20 cm long whole-round sediment samples from Hole U1505C. From Cores 1H through 46F, 5–15 cm long intervals were squeezed for interstitial water and yielded >30 mL per sample. From Cores 46F through 64X, 20 cm long whole-round sediment cores were squeezed and yielded 5–20 mL of interstitial water.

Interstitial water geochemical parameters are presented in Table T11 and Figure F24.

In general, the geochemical parameters of interstitial water at Site U1505 are similar to those at Site U1501. We also defined three geochemical interstitial water zones at Site U1505 based on the variations of geochemical parameters (listed in Table T11). Interstitial water Zone 1 (interval 368-U1505C-1H-2, 0–5 cm, to 3H-4, 0–
<figure><img src="image_472.png" /><figcaption>Table T11. Interstitial water analyses, Hole U1505C. View table in PDF format. Download available in CSV format.</figcaption></figure>

<figure><img src="image_473.png" /><figcaption>Figure F24. Interstitial water alkalinity, major cations, and anions, Site U1505.</figcaption></figure>

10 cm) comprises samples obtained close to the mudline (sediment/water interface). Within this interval, the maximum values of sulfate, alkalinity, and phosphate were observed and are likely related to degradation of organic matter. In interstitial water Zone 2 (interval 4H-4, 0–10 cm, to 56X-4, 0–20 cm), sulfate decreases and alkalinity is buffered by high carbonate concentrations within foraminifer-rich oozes. Atypically for this marine setting (Li et al.,

2015), in which sulfate reduction is prevalent in marine sediments, diffusion processes dominate the sulfate profile. Decreasing K and Mg and increasing Ca reflect the typical diffusion-formed profile of interstitial water. In interstitial water Zone 3 (interval 57X-4, 0–20 cm, to 64X-4, 0–20 cm), sodium, chloride, and bromide concentrations are anomalously low.
Alkalinity varies within Hole U1505C, ranging from 1.0 to 8.3 mM (Figure F24). In interstitial water Zone 1, alkalinity increases to a peak concentration of 7.9 mM at 15.65 m (Sample 2H-5, 0–5 cm). The change in alkalinity is most likely caused by degradation of organic matter. In interstitial water Zone 2, alkalinity decreases to <3 mM at 90 m and remains constant until 185 m. Alkalinity increases again to a peak concentration of 6.8 mM at 308 m and then decreases downhole to the base of interstitial water Zone 2. The pH value decreases slowly from the seafloor to the bottom of interstitial water Zone 2 and then increases to a maximum (pH = 7.82) at the bottom of interstitial water Zone 3 (Sample 63X-4, 0–20 cm).

Profiles of Cl, Br, and Na are similar (Figure F24). In interstitial water Zone 1, Cl, Br, and Na concentrations increase slightly with depth. In interstitial water Zone 2, Cl, Br, and Na remain constant to 322 m (Sample 48X-4, 0–20 cm) with concentrations similar to seawater, and then between 322 and 400 m, Cl and Na concentrations vary. Interstitial water Zone 3 has low Cl, Br, and Na concentrations that decrease to a minimum in interstitial water Zone 3. A similar phenomenon was also observed in Hole U1501C, although the depth at which it occurs is different. In both cases, this minimum corresponds to the stratigraphic level of the T60 seismic unconformity. This correlation is discussed in detail later.

The dissolved sulfate profile decreases from 27.1 mM at the seafloor to <2 mM at the bottom of Hole U1505C (Figure F24). In interstitial water Zone 1, sulfate concentrations decrease sharply, most likely caused by bacterially mediated organic matter diagenesis in upper sediments. In interstitial water Zone 2, this decline is gradual until near-minimum concentrations are observed. In interstitial water Zone 3, sulfate concentrations are low.

Dissolved $NH_4^+$ concentrations increase from 143.6 µM at 2.96 m to a maximum of 1874 µM at the bottom of Hole U1505C. In interstitial water Zone 1, a sharp increase in $NH_4^+$ was observed that would typically be explained by degradation of organic matter releasing reduced nitrogen. In interstitial water Zones 2 to 3, continuous increases in $NH_4^+$ concentration suggest the existence of a source of $NH_4^+$ that diffuses upward from the bottom. A maximum dissolved phosphate concentration was observed in interstitial water Zone 1 (54.85 µM at 15.65 m). In interstitial water Zones 2–3, phosphate concentrations are generally low (several micromolar concentration).

The $K^+$ and $Mg^{2+}$ profiles decrease in a similar way to each other from the surface to the bottom of the hole. The decreases of K and Mg are possibly due to diagenetic reactions occurring in sediment, such as clay ion exchange. Contrary to the K and Mg pore water profiles, the $Ca^{2+}$ profile increases from the surface to a maximum concentration (33.5 mM) at the bottom of Hole U1505C. Changes in calcium concentration are mostly caused by carbonate diagenesis (i.e., dissolution of biogenic carbonate and recrystallization of authigenic carbonates).

# Discussion

## Sulfate-methane transition zones

Figure F25 illustrates geochemical parameters that help explain the shallow biogeochemical processes occurring in SCS sediments. The sulfate-methane transition zone (SMTZ) occurs where organic matter degradation consumes dissolved substrates (foremost oxygen and then others such as phosphate, ammonium, etc.) and anaerobic conditions develop (Barnes and Goldberg, 1976). The SMTZ can be defined by the depletion of sulfate within pore water and the beginning of methanogenesis (elevated methane concentrations

within sediments). Site U1499 has an SMTZ at ~70 m that likely reflects present-day processes. Site U1505 has a possible SMTZ at ~400 m, but it is not sharply defined (e.g., sulfate does not sharply inflect at this depth).

Both sedimentation rate and the presence of organic matter are important for the development of an SMTZ. TOC contents are essentially comparable between the three sites, with Site U1499 perhaps having a lower TOC because of a high input of sediment (sediment dilutes the organic carbon content). Despite the low absolute TOC, the net accumulation rate per unit time may still be comparable for all three sites. Thus, differing supply of organic carbon is not likely to be a key factor, with differences in sedimentation rate being the more likely differentiator between sites. High sedimentation rates promote anaerobic conditions by more rapidly burying organic matter to depths below which oxygen can diffuse (Demaison and Moore, 1980).

Evidence of past SMTZs can be preserved in a number of ways: high methane concentrations may remain in hydrostatic waters and reduced sulfur (sulfide) may mineralize in the form of sulfide minerals such as pyrite or greigite. Thus, a past SMTZ may be preserved beneath the T60 unconformity at Site U1505 where low pore water sulfate, high methane, and high TS are observed. Seepage from this zone at 400 m may also thus explain the methane present at shallower depths. The three sites together form an interesting study potentially demonstrating that the T60 unconformity surface is an important boundary affecting biogeochemical processes by controlling the flux of deeper fluids to shallower sediments.

## Sub-T60 unconformity halide formation water anomaly

Important anions for understanding the formation water anomaly in chloride and bromide beneath the T60 unconformity are shown in Figure F26. Any such explanation must take account of the conservative nature of the halide ions—they are not generated from diagenetic reactions typical of marine sediments. Any explanation must also allow for the linear changes in depth (reflecting temperature) observed in the major cations such as magnesium, calcium, and potassium.

Two possible explanations for the sub-T60 unconformity halide anomaly are postdepositional recharge under a hydrodynamic regime or trapping of an original fresher water body depleted in these ions. The salinities and halide concentrations observed are low for marine water but toward the high end of brackish water. Such a water body might have been deposited with the sediment or potentially moved into the sediment very early in its history through subtidal pumping (Shum and Sundby, 1996), albeit only during storm events for deeper water sediments. The origin of the bromide, chloride, and sodium anomaly can best be explained by a trapped water body depleted in these anions and subsequent alteration of calcium, magnesium, and potassium in pore waters during diagenesis. Were the current water hydrodynamically emplaced after deposition, it would have to contain exactly the correct proportions of calcium, magnesium, and potassium to not disturb the depth-dependent trend.

Instead, it is more feasible that subsequent diagenetic processes such as smectite-illite transformation (Boles and Franks, 1979) or cation exchange involving carbonate minerals, which are temperature dependent (depth dependent), has released or taken up calcium, magnesium, and potassium from pore waters and thereby altered a trapped water body. A trapped water body would not be
<figure><img src="image_474.png" /><figcaption>Figure F25. Comparison of SMTZs and key biogeochemical elements at Sites U1499, U1501, and U1505. T60 unconformity is a basin-wide regional marker.</figcaption></figure>

able to acquire a new halide-anion composition but would be able to equilibrate during diagenesis and produce the linear increase with depth seen here in calcium, magnesium, and potassium. Such a trapped water body might also cause a formation to be lithostatically

pressured and hence undercompacted, leading to the higher porosities observed in the sub-T60 unconformity lithologies (Bethke, 1986).
<figure><img src="image_475.png" /><figcaption>Figure F26. Data illustrating sub-T60 unconformity halide interstitial water anomaly at Site U1505 and comparators at Sites U1499 and U1501.</figcaption></figure>

## Physical properties

Whole-round measurements of magnetic susceptibility, gamma ray attenuation (GRA) bulk density, P-wave velocity (P-wave logger [PWL]), and NGR were made on each core recovered from Holes U1505C (0–480.2 m) and U1505D (0–184 m). Only nondestructive

measurements were performed on the cores from Hole U1505D, which is a duplicate of Hole U1505C downcore to 184 m. P-wave velocity was also measured on working-half sections using the P-wave caliper (PWC) system. Thermal conductivity was measured on one section, typically Section 3, for each core. Additionally, discrete samples from Hole U1505C were analyzed for bulk density,
<figure><img src="image_476.png" /><figcaption>Figure F27. Physical properties, Hole U1505C. cps = counts per second.</figcaption></figure>

porosity, and dry and grain density. Color reflectance, RGB color spectra, and point magnetic susceptibility were measured on all ar-chive-half sections from Holes U1505C and U1505D.

Because the cores recovered from Hole U1505D sampled the same lithologic section as in the uppermost ~180 m in Hole U1505C, the discussion here will focus on Hole U1505C. Based on the physical property characteristics, the lithologic sequence recov-ered from Hole U1505C was divided into two petrophysical (PP) units, PP Units 1 and 2, with a boundary at 403 m (Figure F27). This boundary corresponds to the boundary between lithostratigraphic Units I and II. The interface between these two units is marked by an abrupt shift in physical property measurements. The entire se-quence recovered from Hole U1505D was assigned to PP Unit 1 (Figure F28). Hole U150C cores show some drilling disturbance deeper than ~250 m (see Lithostratigraphy).

## Natural gamma radiation

NGR values in PP Unit 1 are represented by three major inter-vals (Figure F27). The upper interval from the seafloor to ~65 m ranges from ~20 to ~45 counts/s, and NGR values peak around the middle of this depth range. The second interval (~65–~335 m) is also marked by initially increasing NGR between ~20 and ~55 counts/s. NGR values then gradually decrease at the bottom of this interval to 35 counts/s at ~335 m. The lowermost interval of PP Unit 1 displays a general increase in NGR. This interval ends with an abrupt decrease in NGR to 35 counts/s close to 403 m, followed

by a sharp increase to ~75 counts/s at ~403 m associated with the top of PP Unit 2. In PP Unit 2, NGR decreases to ~45 counts/s at 440 m and then increases.

## P-wave velocity

In PP Unit 1, P-wave velocity values gradually increase with depth from ~1470 m/s at the seafloor to ~1765 m/s at ~335 m, fol-lowed by an increase that reaches ~2166 m/s at ~403 m (Figure F27). P-wave velocity values decrease sharply at the PP Unit 1/2 boundary to 1725 m/s and then remain relatively constant at ~2000 m/s from this point downhole to ~480 m.

## Thermal conductivity

Thermal conductivity values show a well-defined trend in the designated petrophysical units. PP Unit 1 has a gradual increasing trend with depth. In this unit, thermal conductivity ranges from 0.906 to 1.684 W/(m·K) (Figure F27). The trend is interrupted with scattered values at ~250–270 m. This scatter could be due to drilling disturbance. PP Unit 2 shows a sudden drop in thermal conductivity with values ranging from 1.248 to 1.314 W/(m·K). In PP Unit 2, more measurements could not be done due to the high drilling dis-turbance in the cores.

## Density and porosity

In PP Unit 1 (0–403 m), bulk density increases with depth from 1.4 g/cm³ at the seafloor to ~2.1 g/cm³ at the base of the unit (Fig-
<figure><img src="image_477.png" /><figcaption>Figure F28. Physical properties, Hole U1505D.</figcaption></figure>

Porosity shows an inverse trend to density and decreases from ~80% to ~35%. Grain density varies between 2.7 and 2.8 g/cm³ with no visible downcore trend (Figure F29). The interface between PP Units 1 and 2 (~403 m) is marked by an abrupt decrease in bulk density from 2.1 to 1.9 g/cm³ and dry density from 1.8 to 1.3 g/cm³. In contrast, porosity increases dramatically across this depth interval from ~34% to ~52%. This boundary coincides with the T60 seismic unconformity (see Correlation to seismic data) and can also be clearly recognized in other physical property data, including NGR, P-wave velocity, and color data (Figures F27, F29, F30, F31). In PP Unit 2 (403–480.2 m), bulk density increases slightly with depth from 1.86 to >1.96 g/cm³ and dry density increases from ~1.3 to ~1.5 g/cm³. Porosity decreases with depth from 51% to 35%.

## Color reflectance spectrophotometry

Sediment color reflectance values are in very good agreement between Holes U1505C and U1505D, as expected (Figure F30). L* represents luminosity, or total reflected light, and is well correlated to CaCO₃ content in sediments (see Geochemistry). In PP Unit 1, L* overall increases with depth from the seafloor to ~75 m; thereafter, downhole L* values fluctuate between 50 and 60 but overall remain relatively constant to ~400 m, where they drop to <40 in PP Unit 2.

Reflectance a* and b* values indicate redness and yellowness of sediments, respectively, and show consistent variations with core

depth (Figure F30). In PP Unit 1, both a* and b* gently increase in the upper portion (0 to ~180 m), followed by a section with high-amplitude variability between ~200 and 260 m, before they drop to minimum and relatively constant values to the base of the record. No significant shift in a* and b* was observed at the unit boundary.

## Magnetic susceptibility

Whole-round magnetic susceptibility and point magnetic susceptibility values show a good, consistent trend throughout all core sections from Holes U1505C and U1505D (Figures F27, F28). In PP Unit 1, the magnetic susceptibility profile can be viewed as three windows of different trends: (1) low and constant magnetic susceptibility from 0 to 30 m with a mean value of ~20 × 10⁻⁵ SI, (2) high and constant magnetic susceptibility from 30 to 80 m with a mean value of ~45 × 10⁻⁵ SI, and (3) gradually decreasing magnetic susceptibility from 80 to 403 m. In PP Unit 1, the trend is frequently interrupted by spikes downcore. Finally, PP Unit 2 is associated with a persistently low and constant magnetic susceptibility of ~5.

## RGB

RGB in PP Unit 1 steadily increases with depth from the seafloor to 70 m, reaching a maximum of 130 followed by constant values until the bottom of PP Unit 1 (Figure F31). At 403 m, corresponding to the boundary between PP Units 1 and 2, RGB values show a marked decrease (from 110 to 75). Below this depth, RGB remains relatively constant to the bottom of PP Unit 2.
<figure><img src="image_478.png" /><figcaption>Figure F30. Sediment color reflectance parameters L\*, a\*, and b\* for Holes U1505C and U1505D and CaCO₃ content for Hole U1505C (see Geochemistry).</figcaption></figure>

<figure><img src="image_479.png" /></figure>

Discussion and summary

The observed physical properties allow us to characterize two major petrophysical units at Site U1505. The sediments recovered display a distinct color change from greenish and brownish light gray to greenish dark gray at 403 m (see Lithostratigraphy). This boundary, which represents the seismic stratigraphic T60 unconformity, is associated with a sharp change in physical properties.

PP Unit 1 shows overall gradually increasing NGR, bulk density, P-wave velocity, and thermal conductivity and decreasing magnetic

susceptibility and porosity (Figures F27, F28). In contrast, PP Unit 2 (403–480 m) is characterized by a sharp change in physical properties at its upper boundary (403 m) but a relatively constant trend downhole within the unit.

In PP Unit 1 (0–403 m), sediments are composed of foraminifer-rich nannofossil ooze with clay in the upper part, which gradually changes to clay-rich nannofossil ooze in the lower portion of the unit. This transition is well reflected in NGR, which increases with depth. The higher NGR in PP Unit 2 is related to sediment that pri-
<figure><img src="image_480.png" /><figcaption>Figure F31. RGB values, Holes U1505C and U1505D.</figcaption></figure>

marily consists of silty clay (Figures F27, F28). The NGR and magnetic susceptibility trends have frequent spikes.

Density, porosity, and P-wave velocity suggest compaction is a major factor responsible for the observed downhole trend in PP Unit 1. Sediments in PP Unit 1 show porosity values similar to those recorded at nearby Site U1501 at a similar depth interval, suggesting the same compaction history. In PP Unit 2, density and P-wave velocity decrease abruptly at the boundary and then increase relatively constantly downhole, whereas porosity shows the opposite trend (Figures F27, F29). Thermal conductivity overall increases with depth. The higher magnetic susceptibility values in the upper portion of PP Unit 1 could be due to higher concentrations of magnetic materials like magnetite.

In the PP units, reflectance L* and RGB channels show similar trends that are well correlated with the percent carbonate trend. The higher L* and RGB values reflect higher carbonate contents. Lower values in L* and RGB correspond to the dark gray sediments in PP Unit 2 (Figures F30, F31).

## Downhole measurements
### Logging operations

After coring to 480.3 m in Hole U1505C, a wiper trip was made to verify hole conditions and allow debris collected around the drill collars to fall into the bottom of the hole. After the last core, the rotary core barrel (RCB) drill bit was released at the bottom of the hole. The drill pipe was raised to 78 m prior to logging (Figure F32). Rig-up for downhole logging started at 0930 h (local time; UTC + 8 h) on 2 June 2017. The modified triple combo tool string started downhole at 1130 h on 2 June. The uphole pass of the triple combo run began at 1350 h. After completing two down- and uphole passes, the tool string reached the seafloor at 1550 h, and the logging tools were rigged down at 1910 h. The wireline active heave compensator (AHC) was used throughout the logging operations.

<figure><img src="image_481.png" /><figcaption>Figure F32. Logging operations summary, Hole U1505C.</figcaption></figure>

Because the drill hole diameter for most of the logging depth was greater than 14–16 inches, it was decided not to run a second logging run with the FMS tool string.

The modified triple combo tool string included the HNGS, HLDS, HRLA, MSS, and DSI (Figure F33). The tool string encountered difficulty going down at approximately 341.2 m, where several attempts to pass that depth failed; thus, the logging depth was 341.2 m.

## Logging units

The triple combo run in Hole U1505C allowed us to define six logging units that are correlated with hole conditions, lithostratigraphic units, lithology, and physical properties (Figure F34).

### Logging Unit 1: seafloor to base of drill pipe

Logging Unit 1 extends from the seafloor to the base of the drill pipe at 78 m. The natural gamma ray (total spectral gamma ray [HSGR] and computed gamma ray [HCGR]) is highly attenuated inside the drill pipe. The potassium, thorium, and radium components of the natural gamma ray are also attenuated.

### Logging Units 2 and 3: base of drill pipe to 136 m

Logging Unit 2 is from the base of the drill pipe to 96 m. The drill hole diameter is unknown for this unit. The natural gamma ray (HSGR and HCGR) of this unit is about 50% of the values of the formation below. The logging density (high-resolution corrected bulk density) is low at 90–96 m, which might reflect a relatively large hole diameter.

Logging Unit 3 is at 96–136 m. The drill hole diameter reached the maximum caliper width of 18 inches for most of this unit. The natural gamma ray increases with depth. The logging compressional
<figure><img src="image_482.png" /><figcaption>Figure F33. Tools used in triple combo tool string, Site U1505.</figcaption></figure>

wave velocity ($V_p$) exhibits large fluctuations that could be due to the enlarged hole dimensions. The shear wave velocity ($V_s$) shows an anomalous value at 104–110 m for an unknown reason. Logging Units 2 and 3 both correspond to a section of lithostratigraphic Sub-unit IB (Figure F34; see Lithostratigraphy).

### Logging Units 4–6: 136–341.2 m

Logging Unit 4 is at 136–220 m. The upper portion of this unit has a relatively large hole diameter. Both $V_p$ and $V_s$ are relatively constant. This logging unit corresponds to a section of lithostratigraphic Subunit IB (Figure F34; see Lithostratigraphy).

Logging Unit 5 is at 200–296 m. The drill hole diameter is close to 14–16 inches for this logging unit. Resistivity increases with depth, whereas most of the other physical properties remain relatively constant. This logging unit corresponds to the bottom of lithostratigraphic Subunit IB and the top of Subunit IC (Figure F34; see Lithostratigraphy).

Logging Unit 6 is at 296–341.2 m. The drill hole diameter is relatively smaller for this unit. Magnetic susceptibility for this unit is greater than that of logging Unit 5. Logging Unit 6 corresponds to the lower part of lithostratigraphic Subunit IC (Figure F34; see Lithostratigraphy). Where the logging velocity has relatively good quality (~141.5–333.0 m), the logging $V_p$ is systematically greater than the P-wave velocity measured by caliper (PWC) on the working halves of the core sections.

### Downhole temperature and heat flow

Four downhole temperature measurements were conducted at Hole U1505C using the APCT-3. The temperature values range from 4.7°C at 36.7 m to 11.7°C at 122.8 m, giving a geothermal gradient of 84.6°C/km (Figure F35A). These values, together with the seafloor temperature of 1.4°C, indicate that the temperature increases linearly with depth.

Thermal conductivity under in situ conditions was estimated from laboratory-determined thermal conductivity from Hole U1505C using the method of Hyndman et al. (1974) (see Physical properties in the Expedition 367/368 methods chapter [Sun et al., 2018]). Thermal resistance (Figure F35C) was then calculated by integrating the inverse of the in situ thermal conductivity over depth (Figure F35B). A heat flow of 94.0 mW/m² was obtained from the linear fit between temperature and thermal resistance (Figure F35D) (Pribnow et al., 2000). The geothermal gradient and heat flow at Site U1505 are comparable to the relatively high values observed at a number of ODP, Integrated Ocean Drilling Program, and IODP sites in this part of the SCS, including Sites U1432 (100.1 mW/m²), U1499 (114 mW/m², this volume), and U1501 (100.2 mW/m², this volume).
<figure><img src="image_483.png" /><figcaption>Figure F34. Downhole logs, Hole U1505C. HSGR = total spectral gamma ray, HCGR = computed (U-free) gamma ray, HROM = high-resolution corrected bulk density, RT = "true" resistivity, MS = magnetic susceptibility, HTHO = HNGS thorium, HURA = HNGS uranium.</figcaption></figure>
Figure F35. Heat flow calculations, Site U1505. A. Sediment temperatures. B. Thermal conductivity data, Hole U1505C. C. Calculated thermal resistance. D. Bullard plot of heat flow calculated from a linear fit of temperature data.

<figure><img src="image_484.png" /></figure>

## Correlation to seismic data

We conducted two sets of analyses to correlate the core measurements (in meters below seafloor) to the time-based seismic data at Site U1505. First, we analyzed core data and investigated correlation to the seismic reflection profile. Second, we constructed synthetic seismograms using Site U1505 core data and compared the results with the traces in the seismic profile. Preliminary calculations were done during the expedition using a combination of Matlab scripts and Petrel software.

## Velocity and density data and comparison with seismic reflectors

Whole-round core measurements were conducted from the seafloor to 480.3 m in Hole U1505C (Figure F36) and from the seafloor to 185 m in Hole U1505D. P-wave velocity was also measured along the x-axis with the PWC system on working-half sections. MAD measurements were performed on discrete samples, one every other section. In addition, HLDS density, $V_p$, and $V_s$ measurements were obtained from downhole logging in Hole U1505C at 78–341.2 m (see Physical properties and Downhole measurements). With the outliers filtered out, the whole-round PWL velocity and GRA density data show a good match with the PWC velocity and MAD density of core samples, respectively (Figure F36). However, the logging $V_p$ is systematically greater than PWC for depth intervals of good logging velocity data quality (Figure F37; see Downhole measurements).

A major change in $V_p$ and density was identified at ~403 m, coinciding with the lithologic change from nannofossil ooze–domi-

nated sediments to silt and clay–dominated sediments (Figure F36; see Lithostratigraphy). We hypothesized that the strong negative reflection (4374 ms two-way traveltime [TWT]) at Site U1505 corresponds to the basin-wide T60 seismic unconformity (reference Point 1; Figures F36, F38).

## Time-depth relationship

A time-depth relationship (TDR) model for Site U1505 was calculated using a polynomial function (Figure F38A):

$$d = 0.000285t^2 + 0.745t,$$

where d is depth in meters below seafloor and t is TWT in milliseconds.

We correlated a strong reflector (reference Point RP1; 4374 ms TWT) to a major change in $V_p$ and density at ~403 m (Figure F36). This calculated TDR function yields an interval velocity that increases with depth (red line in Figure F38B). Where the logging velocity values (blue dots in figure) are relatively good quality (~141.5–333.0 m), they are systematically greater than the PWC core values (green dots) by as much as ~200 m/s. The calculated interval velocity from the TDR model (red line in figure) is much closer to the observed logging $V_p$ than the PWC values.

Using the best-fitting TDR model for Site U1505 (red line in Figure F38A), we were able to convert “depth scale” to “timescale” for all core measurements. This conversion enabled us to display the core measurements directly on top of the time-based seismic sections, facilitating identification of correlated features, as illustrated in Figure F39.
<figure><img src="image_485.png" /><figcaption>Figure F36. Comparison of a subset of physical properties (MS, velocity, density, resistivity, and NGR) with seismic waveform (converted to depth scale using best-fitting TDR model) and seismic image (in timescale). Red circle = reference point (discussed in text).</figcaption></figure>

## Synthetic seismograms

To further illustrate the relationship between the core measure-
ments at Site U1505 and the seismic reflection profile, the “Seismic
interpretation” module in Petrel was used to compute synthetic
seismograms based on the relevant core measurements (Figure
F37). Synthetic traces were generated by convolving the reflectivity
from the density of core samples, an interval velocity model, and
with the source wavelet that best fits the seismic data (“Ricker 2”;
Figure F37).

Seismic impedance (SI) of a rock layer is the product of its aver-
age seismic velocity (Vp) and density (ρ) (i.e., SI = Vp × ρ). The seis-
mic reflection coefficient, in turn, equals the change in seismic
impedance between two adjacent rock layers. Thus, we can expect
greater amplitudes in the modeled seismogram for rock interfaces
with larger values of reflection coefficient. The resulting synthetic
seismogram shows a strong “negative” phase reflector at ~400–405
m, consistent with the observed depth of a strong seismic reflector
(Figure F37).
<figure><img src="image_486.png" /><figcaption>Figure F37. Synthetic seismogram, Site U1505. Panels from left to right: PWC seismic velocity used in the calculation, resultant reflection coefficient (RC), real seismic traces with synthetic seismogram inserted in the center, and seismic source function "Ricker 2_25 Hz" used in modeling. TVD = true vertical depth.</figcaption></figure>
Figure F38. A. Site U1505 TDR curve compared to Site U1501 TDR curve. Red circle = reference Point RP1 at 403 m, which coincides with noticeable changes in density and velocity. B. Hole U1505C PWC, logging $V_p$, and calculated interval velocity model from TDR model.

<figure><img src="image_487.png" /></figure>

Figure F39. Seismic section (seismic Line 04ec1555) at Site U1505 with lithostratigraphic units overlain at drill hole location. Also shown are selected core measurements converted to depth scale using best-fitting TDR model.

<figure><img src="image_488.png" /></figure>
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