<table><caption>Table T11. Mean and standard deviation (SD) of the data sets of physical property measurements for sediment (0–1379.1 m) and underlying basalt, Site U1500. High SDs for magnetic MS and NGR in basalt reflect the presence of voids in the core liner between rock pieces. Download table in CSV format.</caption><thead><tr><th></th><th>NGR mean (cps)</th><th>NGR SD (cps)</th><th>Density mean (g/cm³)</th><th>Density SD (g/cm³)</th><th>MS mean (10⁻⁵ SI)</th><th>MS SD (10⁻⁵ SI)</th><th>P-wave velocity mean (m/s)</th><th>P-wave velocity SD (m/s)</th><th>Porosity mean (%)</th><th>Porosity SD (%)</th><th>Thermal conductivity mean (W/[m·K])</th><th>Thermal conductivity SD (W/[m·K])</th></tr></thead><tbody><tr><td>Sediment</td><td>54.67</td><td>20.69</td><td>1.88</td><td>0.33</td><td>40.64</td><td>23.68</td><td>2456</td><td>707</td><td>31.9</td><td>9.8</td><td>2.35</td><td>0.79</td></tr><tr><td>Basalt</td><td>3.45</td><td>1.84</td><td>1.74</td><td>1.07</td><td>992.8</td><td>695.6</td><td>5177</td><td>353.4</td><td>9.1</td><td>5.8</td><td>1.62</td><td>0.05</td></tr></tbody></table>

properties (wet bulk density, dry bulk density, sediment grain density, porosity, and void ratio).

For Cores 367-U1500B-57R through 82R, P-wave measurements were made with the caliper on individual basalt core pieces without the core liner. For Cores 57R through 60R within the basalt, discrete samples were shared between paleomagnetism and physical property analyses. First, samples were measured for paleomagnetism using AF demagnetization but no heating. Afterwards, we soaked the same samples in salt water for 24 h under a vacuum and then performed P-wave and MAD measurements (see Physical properties in the Expedition 367/368 methods chapter [Sun et al., 2018a]). The samples were then returned for further paleomagnetic measurements that included thermal demagnetization.

Throughout all cores, thermal conductivity was measured on section halves with a puck probe. For each core, three measurements were conducted on the same piece, usually in the middle section. The small puck probe measurements showed unstable results and notable differences between the three measurements on samples with high amounts of fractures. Therefore, no measurement was implemented on some of the cores (e.g., Cores 49R through 53R). Hard rock pieces from Cores 57R through 73R were placed in a seawater bath for 4 h before thermal conductivity was measured with a large puck in the bath.

In addition, wireline log data were acquired below the bottom of the casing (846 m) in Hole U1500B (see Downhole measurements).

## Data cleaning and depth correction

Data measured using automatic systems such as the WRSML, NGRL, and SHMSL (point magnetic susceptibility) can contain data outliers (e.g., data from voids in the core, unrealistic high values, etc.) that must be removed. This cleaning is required before the integration of these data into the models (e.g., synthetic seismograms).

We defined values exceeding $μ ± Nσ$ (with $N = 2$), where $μ$ is the mean and $σ$ is the standard deviation of the data set, as outliers and removed them from the data set. Because the values in the basalt layer are very different from those in the sediment, we estimated the mean and standard deviation for the two data sets separately and cleaned the data accordingly (Table T11). The WRMSL measurements on the basalt cores (from Core 367-U1500B-57R to the bottom of the hole) show very scattered values due to voids in the liner between rock pieces. The corresponding standard deviation is very high. We also smoothed the data when it was used for modeling computation by applying a moving-average filter. SHMG data were usually considered to be reliable because the operator checks the result as it is acquired. For the MAD data, we observed very few outliers with values exceeding $μ ± 2σ$.

To insure the homogeneity of the descriptions and the comparisons of our measurements to other core characteristics collected in other laboratories, we used sample depths below seafloor

calculated by core depth below seafloor, Method A (CSF-A; see http://www.iodp.org/top-resources/program-documents/policies-and-guidelines/142-iodp-depth-scales-terminology-april-2011/file). It is important to note that depths calculated this way do not account for core expansion, including cores that have >100% recovery.

## Density

GRA bulk density was measured automatically every 2 cm by the WRMSL. In addition, bulk density was measured on discrete core samples with the MAD system (~10 cm³ volume each, usually three samples per core according to recovery). Both types of density measurements show similar variations (Figure F45). It should be noted that the reduced diameter of the RCB cores does not completely fill the core liner and causes lower density values during WRMSL measurements. No data could be collected for intervals penetrated without coring (0–378 and 495–641 m) or for intervals of poor core recovery within lithostratigraphic Unit IV that are presumed to be sand/sandstone. A few MAD samples were collected in the basalt of Unit VIII. No MAD samples were collected from Core 367-U1500B-61R to the bottom of the hole because we did not expect much variability in the MAD values in the relatively uniform basalts recovered and because these cores should mostly be preserved for higher priority postcruise research.

In Unit I (378–410 m), GRA bulk density decreases slightly with depth, ranging between 2.1 and 1.4 g/cm³ (Figure F45). Unit II has such low recovery that no trend can be observed. However, the shallowest part (446–449 m) has slightly higher density values (up to 2.04 g/cm³) than the deeper part (485–487 m), which has values only up to ~1.96 g/cm³. MAD bulk density in Units I and II shows similar trends and generally increases from 1.86 to 1.99 g/cm³. Below the second interval penetrated without coring, GRA bulk density data are highly scattered because of the presence of cracks and gaps in the more lithified core pieces, with values ranging between 1.5 and 2.5 g/cm³. Within Unit III through Subunit VA (641–1272 m), MAD bulk density increases slightly with depth from ~2.0 to 2.3 g/cm³, with some measurements as high as 2.9 g/cm³. In Subunit VB (1272–1311 m), MAD bulk density significantly increases with depth from ~2.3 to 2.5 g/cm³, whereas in lithostratigraphic Units VI and VII (1311–1379 m), it decreases with depth from 2.3 to 2.0 g/cm³. Grain densities of discrete samples from Units I–VII (378–1370 m) stay relatively constant, ranging between 2.7 and 2.85 g/cm³. The basalts in Unit VIII (1370 m to the bottom of the hole) have much higher GRA bulk density values, ranging mainly between 2.3 and 2.6 g/cm³. Three discrete samples were taken in Unit VIII, yielding MAD bulk density values between 2.67 and 2.75 g/cm³. Grain densities of these samples range between 2.84 and 2.86 g/cm³.

Porosity decreases with depth within the upper two lithostratigraphic units (378–495 m), ranging between 45% and 52%. From 641 to 1370 m, porosity shows a less steep decrease with depth from
Figure F45. Physical property measurements, Holes U1500A and U1500B. Solid black line = boundary between sediment and basalt, dashed lines = lithostratigraphic unit boundaries (see Lithostratigraphy). Note that magnetic susceptibility (MS) plot has a log scale.

<figure><img src="image_190.png" /></figure>

42% to ~20%. In carbonate-rich Subunit VB (1272–1311 m), there is a significant drop in porosity data from 33% to 20%. Porosity data from the basalts show very low values between 2% and 9%.

## Magnetic susceptibility

Magnetic susceptibility was measured on the WRMSL and the SHMSL (point). Magnetic susceptibility is sensitive to magnetic mineral content and mineralogy of the formation (e.g., Clark and Emerson, 1991). Magnetic susceptibility data were collected every 2 cm, and point magnetic susceptibility data were collected every 1 cm. Magnetic susceptibility and point magnetic susceptibility values are in very good agreement throughout the entire cored section (Figure F45).

Magnetic susceptibility values show a strong decrease with depth within Unit I (378–410 m) from $95 \times 10^{-5}$ to $15 \times 10^{-5}$ SI (Figure F45). Deeper values show much smaller variability from ~410 to ~1233 m, around $30 \times 10^{-5}$ to $40 \times 10^{-5}$ SI on average. The lowermost part of lithostratigraphic Subunit VA (~1260–1272 m) has magnetic susceptibility values of ~60 $\times 10^{-5}$ SI that are higher than in the sediment above and include a local high of up to $150 \times 10^{-5}$ SI (Core 367-U1500B-45R; ~1270–1272 m). Within Subunit VB (1272–1311 m), magnetic susceptibility exhibits relatively lower values, ~20 $\times 10^{-5}$ SI on average. Still significantly lower magnetic susceptibility values were measured in Unit VI (1311–1370 m); they increased with depth between ~5 $\times 10^{-5}$ and $15 \times 10^{-5}$ SI. In the basalt of Unit VIII, magnetic susceptibility values are two orders of magnitude higher than in the sediment units and increase to about $2390 \times 10^{-5}$ to $2980 \times 10^{-5}$ SI. The data are very scattered but appear to correlate with alteration reactions in new fractures and veins (Figure F46; see Paleomagnetism).

## P-wave velocity

P-wave velocity was not measured with the WRMSL on Site U1500 cores due to the gap between liner and sample but was measured directly on the split cores with the X-caliper. The values show a gradual increase with depth from 1630 m/s near 360 m to 2570 m/s at 1270 m (Figure F45). Some isolated measurements in lithostratigraphic Units III and IV show significantly higher values ranging between ~3880–4720 m/s, corresponding either to sandstone layers interbedded with claystone in Unit III or to single pieces in the low-recovery cores of Unit IV. In carbonate-rich Subunit VB (1270–1310 m), P-wave velocity increases with depth from 2380 to 3400 m/s, which is higher than the over and underlying sediment units. There is a steep increase in P-wave velocity values (4430–5710 m/s) in the basalt of Unit VIII.

## Natural gamma radiation

In lithostratigraphic Unit I (378–410 m), NGR values decrease with depth from ~60 to ~40 counts/s, coinciding with a decrease in magnetic susceptibility within this unit (Figure F45). NGR values show very low variability, remaining around 60–70 counts/s between 410 and 1272 m. In Unit II, NGR values range between 45–60 counts/s with no clear trend due to the low recovery. NGR slightly increases with depth in Units III and IV (641–1233 m), ranging from ~20 to 80 counts/s. NGR significantly decreases from ~80 counts/s near 1270 m to 25 counts/s at 1310 m, coinciding with an increase in carbonate contents at the boundary between Subunits VA and VB. Basalts in Unit VIII have very low NGR values, almost entirely <10 counts/s, as expected for basalt.
<figure><img src="image_191.png" /><figcaption>Figure F46. Physical properties measurements of Unit VIII basalts, Hole U1500B. Alteration rank observed by petrologists. Note that MS plot has a log scale.</figcaption></figure>

We estimated concentrations of K, U, and Th using NGR and bulk density measurements (Figure F47), based on a study from De Vleeschouwer et al. (2017). The general trend of each element concentration is similar to the total NGR count values.

## Thermal conductivity

Thermal conductivity increases slightly with depth from 1.1 W/(m·K) at 381 m to 2.2 W/(m·K) at 1214 m (Figure F45). Some measurements in lithified pieces from lithostratigraphic Units III and IV have significantly higher values between ~2.8 and 3.8 W/(m·K). These very high values could be spurious and related to measurement problems with the contact probe. Thermal conductivity decreases significantly to 1.5 W/(m·K) in the chalks of Subunit VB. Values measured in the basalt of Unit VIII are relatively uniform around 1.6 W/(m·K) (Figure F46).

## Data interpretation and lithology correlation

### Correlation with lithology

The claystones, siltstones, and sandstones of lithostratigraphic Units II–IV (410–1233 m) do not display large contrasts (Figure F45). However, some deeper layers exhibit variations that can be correlated to the lithology. For example, clear changes in NGR (low), density (high), velocity (as high as 3400 m/s), porosity (low), and thermal conductivity (low) are associated with the high carbon-

ate contents (up to 40 wt%) in Subunit VB (1272–1311 m). However, no significant increase in magnetic susceptibility data could be observed, similar to the carbonate-rich layer at Site U1499 (Subunit VIIIB). The content in magnetic minerals and their mineralogy are reflected in magnetic susceptibility measurements in claystone, siltstone, or sandstone, which likely explains the variations in depth of magnetic susceptibility and NGR in Unit I and the relatively high magnetic susceptibility values in the lower part of the brownish claystone in Subunit VA. Meanwhile, NGR values vary not only with lithology but also within the same sediment type. Unit VIII, which consists mainly of basalt, causes a significant change in the physical property measurements.

### Unit VIII basalt

Cores 367-U1500B-57R through 73R recovered basalt. Magnetic susceptibility values are very high in Unit VIII but vary depending on the alteration grade within the basalt (Figure F46). Zones where alteration is significant generally have lower magnetic susceptibility. However, some variations do not appear to be directly related to alteration and might correspond to changes in the nature of the magnetized minerals or the grain size (see Paleomagnetism). Compared to the sedimentary rocks above, the P-wave velocities of the basalts are quite high (~4430–5710 m/s). NGR and porosity are quite low, whereas density is much higher.
<figure><img src="image_192.png" /><figcaption>Figure F47. Core NGR measurements, Holes U1500A and U1500B. Estimates of K, U, and Th concentrations are derived from NGR and GRA density measurements using the method of De Vleeschouwer et al. (2017).</figcaption></figure>

## Downhole measurements
### Wireline downhole logging

Downhole logging measurements at Site U1500 were performed as the last operations of Expedition 367 and ended just before the 1 day transit to Hong Kong. The collected raw data were sent to Lamont-Doherty Earth Observatory for postprocessing and were not available before the end of the expedition. Therefore, the following chapter focuses mainly on logging operations and tool setups, as well as preliminary results based on real-time observations (e.g., caliper measurements for description of borehole conditions) that were not depth corrected. The processed data were made available online to the Expedition 367 scientists immediately following the expedition and were also sent back to the ship during the port call for the Expedition 368 scientists to use.

## Logging operations and tools

Downhole logging operations started at 1400 h on 6 April 2017 after finishing RCB coring to 1529 m. Three logging string tools were run in Hole U1500B (Figure F48). The first tool string was a modified triple combo tool string that included the following tools:

* DSI for acoustic velocity,

* HRLA/DIT for electrical resistivity,

* HLDS for caliper data (no source was included to acquire density data due to unstable borehole conditions experienced when raising the drill string out of hole), and

* HNGS/EDTC-B for NGR.

At 1630 h, the modified triple combo tool string reached the end of casing at 4655 m WRF at a speed of ~600 m/h (Figure F49). The end of casing is easily detected by a substantial change in resistivity and sonic velocity. The tool string was lowered out of the end of the casing at 842 m drilling depth below seafloor (DSF) and into the open hole (previously RCB cored to a total depth of 1529 m DSF). The tool string encountered an obstruction at 4946 m WRF (~1133 m). We were unsuccessful in getting the tool string to pass below this depth. We opened the caliper and collected data from 4946 m WRF (~1133 m) up to 4800 m WRF (~987 m). We then closed the caliper arm and lowered it back down, but it could not get back to the previous depth and this time reached 4925 m WRF (~1112 m), ~21 m shallower than the first run. We then opened the caliper arm and collected log data at a speed of ~600 m/h over the entire open hole from 4925 m WRF (~1112 m) up to the base of the casing (4655 m WRF; 842 m).

The second tool string run started at ~0300 h 7 April. This tool string included the FMS to collect borehole resistivity images and the HNGS and EDTC-B for NGR and correlating with the previous logging runs.

HNGS data were collected while lowering the tools into the borehole (Figures F48, F49). The tool string could only reach a total depth of 4857 m WRF (~1044 m), and we opened the FMS arms and collected FMS and HNGS data from that depth up to the bottom of the casing at 4655 m WRF (842 m).

We started assembling our third logging string at 0700 on 7 April. The third tool string consisted of the EDTC-B and VSI. Routine IODP protected-species procedures were implemented leading
<figure><img src="image_193.png" /><figcaption>Figure F48. A–C. Downhole logging tool string configurations for logging Runs 1–3, Hole U1500B. LEH-MT = logging equipment head-mud temperature. HLDS is without nuclear source.</figcaption></figure>

up to and throughout use of the seismic source. The seismic source was deployed 38 m from the moon pool and 7 m below the sea surface using the aft port crane (Figure F50). No protected species were observed, and a soft ramp-up of the gun was performed to a maximum pressure of 2000 psi. The VSI tool string reached a total depth of 4843 m WRF (~1031 m). We set the VSI tool at that depth, activated the seismic source four times, and acquired two good data records for stacking. No other good location in the open hole was found in the restricted time left for the experiment. We set the VSI tool again at 4595 m WRF (~783 m; in the casing) and got two good data records. After the VSI station, the tool was brought back to the surface and rigged down. The rig floor was then cleared of logging

equipment at 1430 h on 7 April for a total of ~24 h for logging operations.

## Borehole conditions and expected data quality

Before starting the downhole measurements, conditions in the deeper part of the hole deteriorated significantly while pulling out of the hole to release the drill bit on the seafloor. For the details of hole preparation, see **Operations**. While pulling the bit out of the hole, the drill string became stuck at ~1240 m. Unfortunately, during these operations the weighted (11.0 lb/gal) mud that had been pumped into the hole to help stabilize it for downhole measurements was displaced out of the hole. There were no other problems.
<figure><img src="image_194.png" /><figcaption>Figure F50. Deployment scheme of seismic source used during VSI tool string logging run.</figcaption></figure>

<figure><img src="image_195.png" /></figure>

log pulling the bit out of the hole; however, we suspected that the borehole conditions were not ideal for logging. We released the bit on the seafloor, reentered Hole U1500B, set the end of the pipe at 30 m (inside the casing), and prepared the rig floor for logging.

During the first logging run, low tension was noticed at 4907 m WRF (1094 m), which most probably was caused by a ledge or bridge. Subsequently, caliper data in this region show that the hole is enlarged from 4892 to 4901 m WRF (1079–1088 m) and at 4902 m WRF (1089 m), the hole diameter narrows to ~6 inches, less than the bit size. We were able to get the tool string through this barrier after hitting it a second time. However, the tool string could not pass below 4946 m WRF (1133 m), and log data could only be col-

lected to that depth. It appears that this depth correlates to the top of a low-recovery zone that only returned sandstones with a high P-wave velocity (~4.5 km/s). The total depth of the hole kept decreasing for each subsequent logging run.

The quality of the collected FMS images could be estimated only on the screen during their acquisition. The images are of variable quality due to large variations in borehole diameter, but there are at least three intervals that are several tens of meters thick where the FMS pads had good contact with the borehole walls and we obtained good quality images. The collected log data are in DOWN-HOLE in **Supplementary material**.
# Correlation to seismic data

We used physical property measurements on cores and samples and other available data to correlate Site U1500 data with the available seismic reflection profiles. We also used the Site U1500 density and velocity data to create synthetic seismograms that provided additional constraints on the correlation. All correlations of the seismic reflection data with the Site U1500 core data, as well as the synthetic seismogram tests, were performed onboard using the Petrel software.

## Velocity and density data

Velocity data in Holes U1500A and U1500B were acquired in the laboratory from split-core sections (PWC), and density data were acquired both in whole-round core sections (GRA density) and split-core sections (MAD; see Physical properties). For seismic correlation, we used PWC velocity and MAD density values.

### Time-depth relations from the velocity data

TDRs are generally assumed to be quadratic polynomial functions from the interpolation of depth-velocity data. From the depth-velocity data, we computed the incremental TWT ($T_i$) as

$$T_i = [(d_n - d_{n-1})/V_n] \times 2 \times 1000,$$

where $d_n$ is the depth of the n-th layer and $V_n$ is the relative velocity. The incremental $T_i$ is multiplied by 2000 for conversion into TWT expressed in milliseconds.

From $T_i$ we derived the cumulative TWT ($T_c$) expressed as

$$T_c = T_{c-1} + T_i,$$

and finally, the TWT adjusted from the seafloor ($T_a$) was calculated as

$$T_a = T_c + T_a,$$

where $T_a$ is the TWT of the seafloor expressed in milliseconds.

If the TDR is referred to the seafloor, the intercept of the interpolated quadratic polynomial functions is set to 0.

Figure F51 shows the Site U1500 velocity and density values collected with the PWC and MAD measurements and the TDR computed relative to the seafloor.

The resulting quadratic polynomial function is

$$d = 0.0003t^2 + 0.6204t,$$

where $d$ is the depth in meters and $t$ is the TWT in milliseconds.

### Comparison of time-depth relations

We compared our Site U1500 TDR with the Site U1499 TDR and other relations collected in previous expeditions in the SCS (Shipboard Scientific Party, 2000; Li et al., 2008, 2015a). Figure F52 shows the comparison of Site U1500 TDR to those for IODP Sites U1499, U1431, and U1433 and Site 1148. Our Site U1500 and U1499 TDRs are in substantial agreement with each other. The analyzed TDRs collected during previous SCS expeditions are in general agreement for the upper sediments (0–400 m). However, the TDR from Site 1148 shows higher velocities in the deeper layers.

<figure><img src="image_196.png" /><figcaption>Figure F52. Site U1500 TDR compared to Sites U1499, U1431, U1433, and 1148 (Li et al., 2008).</figcaption></figure>

<figure><img src="image_197.png" /></figure>

## Data correlations with Petrel

Using the TDR based on Site U1500 data, we correlated the site survey seismic reflection data with the data collected from the whole-round cores (GRA density, magnetic susceptibility, and NGR) and split cores (MAD and PWC). We also plotted other data collected on board, such as core recovery, lithostratigraphic unit description, and carbonate contents. All of these properties were plotted over the seismic section with Petrel (Figure F53).

The following import flow process was used:

1. The coordinate system of the project was set (for Expedition 367: WGS1984_UTM50N),

2. A new seismic folder and a new survey were created,
Figure F53. Seismic section across Site U1500 (northwest-southeast). The site is located where the lithostratigraphic column is plotted (black = Unit I, yellow = Unit II, light blue = Unit III, blue = Unit IV, pink = Subunit VA, purple = Subunit VB, cyan = Unit VI, green = Unit VIII). Hole U1500A and U1500B core recovery is also shown (black = 100%, white = 0%). Other Site U1500 data are offset from site location. See CORRELATION in Supplementary material for original profile from Petrel software in the reversed direction.

<figure><img src="image_198.png" /></figure>

3. SEGY data were imported with presettings (after the check of the Trace Header Information with the SeisSee software),

4. The “Well” was created,

5. The TDR file was imported (the file must have the depth-TWT adjusted with respect to the seafloor), and

6. Well logs (ASCII files) for all the properties of interest were imported (the file must be tab delimited and can be directly imported from the Laboratory Information Management System database; we chose to import CSF-B depths and the values of interest).

We cleaned the data to remove the outliers before importing the values in Petrel (see **Physical properties**). An additional moving-average smoothing filter was also applied for GRA density. For the velocity data, more cleaning was applied. We manually checked the differences that might be created by manual or automatic picking of the first break for the caliper data and discarded the manually picked values that appeared doubtful because of a large difference from the surrounding values.

The physical properties are displayed over the seismic data to allow a direct comparison between the reflectors and the properties trends. Figure F53 shows the data using the computed Site U1500 TDR (Figure F51). The figure shows good correlation between the main reflectors and the measured physical properties. In particular,

there is an abrupt decrease in magnetic susceptibility and NGR values and a corresponding increase in carbonate contents, density, and P-wave velocity at ~1280 m, in agreement with the high-amplitude reflector at ~6.3 s TWT. This reflector seems to be related to the carbonate-rich interval within lithostratigraphic Unit V; a similar correlation was observed between the core and seismic data at Site U1499. At ~1380 m, abrupt changes can be observed in all the physical properties, especially the steep increase in magnetic susceptibility, density, and P-wave velocity values (the boundary between the sediments of Unit VII and the basalt of Unit VIII; see **Physical properties**). This depth is well correlated with the main seismic reflector at ~6.4 s TWT.

## Synthetic seismograms with Petrel

We used the seismic interpretation module in Petrel to compute synthetic seismograms to further constrain the TDR relation. The parameters that need to be defined to compute synthetic seismograms are the seismic source signature, density values, and velocity values. Petrel allows the choice of single frequency-centered sources. We chose Ricker wavelets centered at the mean values of the frequency content in our seismograms. For Site U1500, we used the density data derived from the MAD measurements and the PWC velocity. The resulting synthetic seismogram for the main deep reflectors (900–1400 m) is shown in Figure F54.
<figure><img src="image_199.png" /><figcaption>Figure F54. Synthetic seismogram computed for the deeper part (800–1400 m) of Site U1500 (southeast–northwest). Panels from left to right: density (blue) and velocity (black) values, reflection coefficient (RC), and real seismic traces with synthetic seismogram inserted in the center. TVD = true vertical depth computed by Petrel program based on TDR quadratic equation given in TDRs from the velocity data and plotted in Figure F51.</figcaption></figure>

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https://doi.org/10.14379/iodp.proc.367368.105.2018

## Site U1501¹

<figure><img src="image_200.png" /></figure>

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Hans Christian Larsen, Zhimin Jian, Carlos A. Alvarez Zarikian, Zhen Sun, Joann M. Stock, Adam Klaus, Jacopo Boaga, Stephen A. Bowden, Anne Briais, Yifeng Chen, Deniz Cukur, Kelsie A. Dadd, Weiwei Ding, Michael J. Dorais, Eric C. Ferré, Fabricio Ferreira, Akira Furusawa, Aaron J. Gewecke, Jessica L. Hinojosa, Tobias W. Höfig, Kan-Hsi Hsiung, Baoqi Huang, Enqing Huang, Xiao-Long Huang, Shijun Jiang, Haiyan Jin, Benjamin G. Johnson, Robert M. Kurzawski, Chao Lei, Baohua Li, Li Li, Yanping Li, Jian Lin, Chang Liu, Chuanlian Liu, Zhifei Liu, Antonio Luna, Claudia Lupi, Anders J. McCarthy, Geoffroy Mohn, Lachit Singh Ningthoujam, Michael Nirrengarten, Nobuaki Osono, David W. Peate, Patricia Persaud, Ning Qiu, Caroline M. Robinson, Sara Satolli, Isabel Sauermilch, Julie C. Schindlbeck, Steven M. Skinner, Susanne M. Straub, Xiang Su, Liyan Tian, Froukje M. van der Zwan, Shiming Wan, Huaichun Wu, Rong Xiang, Rajeev Yadav, Liang Yi, Cuimei Zhang, Jinchang Zhang, Yang Zhang, Ning Zhao, Guangfa Zhong, and Lifeng Zhong<fnref n="2" />

**Keywords:** International Ocean Discovery Program, IODP, JOIDES Resolution, Expedition 367, Expedition 368, Site U1501, northern South China Sea, continent-ocean transition zone, outer margin high, hyperextension, continental breakup, thinning, rifting, basement, Cenozoic, Mesozoic, prerift, land facies, Eocene marine deposition, subsidence

## Site summary

### Background and objectives

Site U1501 (proposed Site SCSIII-41A; 18°53.0923'N, 115°45.9455'E) (Sun et al., 2016) within the South China Sea (SCS) northern margin (Figure F1) is located on a broad regional base-ment high (outer margin high [OMH]). The OMH is the most land-ward of four distinct highs within the continent-ocean transition (COT) and is followed seaward by Ridges A, B, and C (Figures F2, F3, F4). Site U1501 is located at 2845.8 m below sea level (mbl). Small rift basins of presumed Paleogene age are located on top of the OMH (Figure F2). These basins can be traced landward into much deeper half-graben basins that formed during the main phase of crustal extension. The rift basins located on the OMH, therefore, offer options to recover the stratigraphy of these basins by drilling to moderate depths, testing existing stratigraphic interpretations, and extrapolating the findings margin wide. Recovering and charac-terizing these sequences were key objectives at Site U1501, and the

specific goal was to constrain the timing and duration of crustal ex-tension, the tectonic vertical movements during rifting, and the subsequent postrift thermal subsidence. The crystalline basement at Site U1501 is most likely located far below the acoustic basement at ≈600 m and was not an objective for this site.

At 2846 mbl, Site U1501 is one of the few Ocean Drilling Pro-gram (ODP) and Integrated Ocean Drilling Program sites in the SCS above the modern carbonate compensation depth (CCD) of the SCS. Sites U1504 and U1505, also at the OMH, are situated at <3000 mbl. The younger stratigraphy is therefore also the focus of some secondary scientific objectives related to Neogene environmental development of the SCS and adjacent landmasses of Southeast Asia. Among these secondary objectives are to (1) reconstruct the history of the east Asian monsoon evolution and of deepwater exchanges between the SCS and Pacific Ocean and (2) explore the sedimentary responses to the Cenozoic regional tectonic and environmental de-velopment of the Southeast Asia margin.

## Contents

1 Site summary

6 Background and objectives

7 Operations

11 Lithostratigraphy

24 Structural geology

26 Biostratigraphy

33 Paleomagnetism

41 Geochemistry

49 Physical properties

53 Downhole measurements

56 Correlation to seismic data

61 References

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<footnote n="1">¹ Larsen, H.C., Jian, Z., Alvarez Zarikian, C.A., Sun, Z., Stock, J.M., Klaus, A., Boaga, J., Bowden, S.A., Briais, A., Chen, Y., Cukur, D., Dadd, K.A., Ding, W., Dorais, M.J., Ferré, E.C., Ferreira, F., Furusawa, A., Gewecke, A.J., Hinojosa, J.L., Höfig, T.W., Hsiung, K.-H., Huang, B., Huang, E., Huang, X.-L., Jiang, S., Jin, H., Johnson, B.G., Kurzawski, R.M., Lei, C., Li, B., Li, L., Li, Y., Lin, J., Liu, C., Liu, C., Liu, Z., Luna, A., Lupi, C., McCarthy, A.J., Mohn, G., Ningthoujam, L.S., Nirrengarten, M., Osono, N., Peate, D.W., Persaud, P., Qui, N., Robinson, C.M., Satolli, S., Sauermilch, I., Schindlbeck, J.C., Skinner, S.M., Straub, S.M., Su, X., Tian, L., van der Zwan, F.M., Wan, S., Wu, H., Xiang, R., Yadav, R., Yi, L., Zhang, C., Zhang, J., Zhang, Y., Zhao, N., Zhong, G., and Zhong, L., 2018. Site U1501. *In Sun, Z., Jian, Z., Stock, J.M., Larsen, H.C., Klaus, A., Alvarez Zarikian, C.A., and the Expedition 367/368 Scientists, South China Sea Rifted Margin. Proceedings of the International Ocean Discovery Program, 367/368: College Station, TX (International Ocean Discovery Program). https://doi.org/10.14379/iodp.proc.367368.105.2018*</footnote>

<footnote n="2">² *Expedition 367/368 Scientists' addresses.*</footnote>

<footnote>MS 367368-105: Published 28 September 2018</footnote>

<footnote>This work is distributed under the **Creative Commons Attribution 4.0 International** (CC BY 4.0) license.</footnote>

<footnote>CC BY</footnote>
Figure F1. Bathymetric maps showing Expedition 367/368 sites (stars), and (A) regional and (B) local coverage of multichannel seismic reflection data and OBS data. Thick blue and red lines are key seismic lines used for planning of the drilling transect. A. Magnetic isochrons (orange lines) from Briais et al. (1993). B. Magnetic picks (orange squares) from the same reference, extracted from the Seton et al. (2014) compilation. Chron labels for the picks correspond to the old edge of the normal polarity intervals (see Ogg et al. [2016] timescale for ages). Orange square = Leg 184 Site 1148, yellow squares = Expedition 349 Sites U1432 and U1435.

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## Operations

We conducted operations in four holes at Site U1501. In Holes U1501A and U1501B, Core 1H missed the sediment-water interface and retrieved full core barrels, indicating that the core was shot from below the seafloor. Hole U1501C (18°53.0919′N, 115°45.9485′E; 2846 mbsl) was cored with the advanced piston corer (APC) system from the seafloor to 461.8 m and recovered 447.8 m (96.3%). Hole U1501D (18°53.0929′N, 115°45.9370′E; 2846 mbsl) was drilled without coring from the seafloor to 433.5 m and then cored with the rotary core barrel (RCB) system to 644.3 m. A

total of 78.8 m of core was recovered (37.4%). Hole U1501D was logged with the triple combo tool string from 113 to 299.3 m.

## Lithostratigraphy

The sedimentary succession recovered at Site U1501 is composed of clay-rich nannofossil ooze, silty clay, clayey silt, sand, siltstone, sandstone with minor conglomerate, and rare volcanic ash. The succession is divided into three major lithostratigraphic units (I, II, and III) distinguished on the basis of sediment composition, particularly the relative abundance of the calcareous and siliciclastic fractions (Figure F30).

Lithostratigraphic Unit I is a 303 m thick, Holocene–upper Oligocene succession dominated by clay-rich nannofossil ooze and nannofossil ooze with clay, with minor amounts of nannofossil-rich foraminifer sand or silty sand. A felsic volcanic ash layer occurs in Section 368-U1501A-1H-7, and an ash pod was observed in Section 368-U1501C-3H-1. Unit I is divided into the following subunits:

* Subunit IA (0–25.47 m),

* Subunit IB (25.47–66.17 m),

* Subunit IC (66.30–156.70 m),

* Subunit ID (156.80–191.99 m),

* Subunit IE (191.99–293.09 m), and

* Subunit IF (293.90–303.01 m).

These divisions are based on changes in lithology, particularly the clay to nannofossil ratio, the presence and abundance of foraminifers, and/or physical properties. The lower contact of Unit I is erosional and marked by the emplacement of a poorly sorted sandy layer. At the boundary, marked changes in P-wave velocity, natural gamma radiation (NGR), magnetic susceptibility, porosity, moisture and density (MAD), color, carbonate content, and biostratigraphy indicate a small hiatus (Figure F30). Unit I was deposited in a deep-marine environment, and lithologic changes between subunits likely reflect the amount of terrigenous input into a relatively open ocean setting. This input may be delivered as buoyant sediment plumes from shallower shelf environments and rarely by weak (distal) turbidity currents. Soft-sediment deformation in Subunit IB indicates slumping downslope of parts of the sequence.

Lithostratigraphic Unit II is 296 m thick and late Oligocene to late Eocene in age. The unit consists of variable amounts of clay, silt, and sand with minor nannofossil-rich clay, nannofossil ooze, and silt with organic matter. Gravel-sized grains occur, including shell fragments and glauconite, as well as carbonate and pyrite concretions. Unit II is divided into six subunits:

* Subunit IIA (303.01–385.26 m),

* Subunit IIB (388.80–452.69 m),

* Subunit IIC (452.60–482.33 m),

* Subunit IID (491.00–519.80 m),

* Subunit IIE (529.30–548.64 m), and

* Subunit IIF (548.64–598.91 m).

The uppermost two subunits define a fining-upward succession of glauconite-sand dominated to siltstone and clay overlain by clay with nannofossils. Subunits IIC and IE are dominated by sandstone with calcite; Subunit IID has more fine-grained, organic-rich lithologies; and Subunit IIF is similar to Subunit IIB but has more coarse-grained sediment and distinctive weak red and reddish gray intervals within the green glauconite-bearing sands. Coarse sand–to pebble-sized shell fragments are common in Unit II, and coral fragments were occasionally observed in the upper part of the unit.
Figure F2. Deep crustal time-migrated seismic reflection data without and with interpretation. Note the rather thin lower crust (two layers) above a strong Mohorovičić seismic discontinuity (Moho) reflector that can be followed oceanward. Moho reflection is weak to absent seaward from around the interpreted COT. Wide-angle seismic data (Yan et al., 2001) confirm ~6 km thick ocean crust (OC) seaward of COT. Large detachment fault ~150 km inland of COT separates more stable crust landward from that of highly extended crust seaward. OMH is a fairly consistent feature margin along this margin segment. Key seismic unconformities are shown in purple (T70; ~32 Ma breakup unconformity?) and blue (T60; ~23 Ma regional basin event). These ages are inferred from long distance (>100 km) correlation of seismic unconformities with industry holes and ODP Leg 184 Site 1148 (T60); ages need confirmation by coring and are only tentative. Tg reflector (green) is basement. Arrows = approximate positions of seafloor magnetic anomalies with chron numbers. Seismic data are from Line 04ec1555-08ec1555 (courtesy of Chinese National Offshore Oil Corporation [CNOOC]). Location of line is shown in Figure F1. C11n, C10n, and C9n = possible chrons. MSB = midslope basin.

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Glauconite and quartz minerals dominate the siliciclastic grain component. Diagenetic pyrite is common. Unit II most likely represents a gradual change upward from shallow-water (outer shelf or upper continental slope) to deepwater (lower slope) depositional environments. The Unit II/III boundary was not recovered but is marked by an abrupt change in magnetic susceptibility, NGR, and P-wave velocity. A change in the apparent dip of strata from near horizontal in Unit II to ~20° in Unit III suggests that the contact is unconformable.

Lithostratigraphic Unit III (598.91 m to the bottom of the hole) is well lithified and composed of poorly sorted, feldspar-rich sandstone interbedded with moderately to well-sorted, medium- to fine-grained sandstone and, rarely, siltstone and poorly sorted conglomerate. The age is unknown because no fossils were recognized. Unit III is divided into two subunits: IIIA (598.91–629.79 m) and IIIB (629.79–643.56 m). Subunit IIIA is composed of coarse-grained heterolithic sandstone, sandstone with calcite clasts, and minor conglomerate and siltstone. Pebble- to cobble-sized clasts include felsic intrusive and volcanic rocks, sedimentary rocks, metamorphic rocks, and rare gabbro. Subunit IIIB consists of sandstone and minor sandstone with organic matter. Subunit IIIB is finer grained than Subunit IIIA and has finely laminated intervals. We speculate that Unit III was formed in continental to littoral environments with a provenance not far from the site.

## Structural geology

Unit I shows predominantly horizontal to subhorizontal bedding with local soft-sediment deformation structures such as slump folds. Unit I is devoid of any structures related to tectonic deformation, apart from some rare normal faults with minor offsets.

Unit II is characterized by subhorizontal to gently dipping bedding. Steep dips up to 40° are locally observed in close relation to parallel lamination and are therefore interpreted as cross-laminae. In contrast to Unit I, deformation structures were observed within Unit II, although their occurrence is rather heterogeneously distributed. Planar to irregular millimeter-scale normal faults and joints were observed in Subunit IIA, typically with offsets ranging from 0.1 to 0.5 cm and apparent dips of 10°–40°. Striations and slickensides were documented locally where the surfaces of such structures are exposed. Deformation in the underlying Subunits IIC–IIF is essentially characterized by randomly distributed occurrence of single to branched uniform calcite and quartz veins. Recognition of deformational structures was difficult due to drilling disturbance throughout this unit.

The acoustic basement marks the top of Unit III. This unit shows a weak tilting of stratified beds expressed in apparent dips on split core surfaces up to ~20°. Again, deformation structures remain scarce and heterogeneously distributed in Unit III. The recognized
Figure F3. Two-way traveltime to (A) basement (Tg reflector) and (B) T60 unconformity. Proposed drilling transect (thick black line) is approximately at the center of a margin segment bounded to the southwest by a transform fault. Northeastern boundary of margin segment around Site U1435. At this location, OMH and Ridge A seem to coalesce, and Ridges B and C in COT become indistinct toward the northeast within the next margin segment. Note that OMH is slightly oblique to more parallel Ridges A, B, and C.

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structures consist of veins, fractures, and local microfaults associated with cataclastic fault gouge.

In conclusion, despite the various tilting of reflectors (~5°) and the proximity of extensional structures observed on seismic profiles, only weak evidence of bedding tilting and/or deformation

Figure F4. Bathymetry with seismic lines, Site U1501. Note that site is not at the exact crossing of seismic Lines 15ecLW8 and 15ecLW1.

<figure><img src="image_205.png" /></figure>

structures was observed at this site, possibly due to the nature of the sediments.

## Biostratigraphy

All core catcher samples at Site U1501 were analyzed for calcareous nannofossils, diatoms, and foraminifers, with select core catchers examined for ostracods. Additional samples were taken from the split working-half sections when necessary to refine the ages between core catcher samples. Preservation of calcareous microfossils varies from good in Unit I (Cores 368-U1501A-1H, 368-U1501B-1H, and 368-U1501C-1H through 44X) to poor in Units II and III (Cores 368-U1501C-45X through 62X and 368-U1501D-2R through 5R). Planktonic foraminifers and calcareous nannofossils are abundant in Unit I, common to rare in Unit II and upper Unit III, and barren in the rest of Unit III (Cores 368-U1501D-6R through 27R). Diatoms are few with moderate preservation in Samples 368-U1501A-1H-CC, 368-U1501B-1H-CC, and 368-U1501C-1H-CC and 2H-CC. The rest of the core catcher samples are barren of diatoms with the exception of Samples 368-U1501C-3H-CC, 4H-CC, 33F-CC through 35F-CC, and 46X-CC, in which diatoms are rare with poor preservation. Diatoms are common in burrows found in interval 368-U1501C-35F-1, 118–119 cm, with poor preservation.

Forty biostratigraphic datums were identified in a mostly continuous succession from the Eocene to Holocene, which indicates that Holes U1501C and U1501D penetrated late Eocene or older strata (Figure F30). The Pleistocene/Pliocene boundary (~2.6 Ma) was placed within Core 368-U1501C-7H, the Pliocene/Miocene boundary (~5.3 Ma) within Core 9H, the Miocene/Oligocene boundary (~23.0 Ma) between Cores 41X and 42X, and the Oligocene/Eocene boundary (~33.9 Ma) between Cores 53X and 54X. Sedimentation rates vary from ~13 mm/ky in the early Oligocene, ~11 mm/ky in the Miocene, and ~14 mm/ky in the Pliocene to 24 mm/ky in the Pleistocene. Low sediment accumulation rates (~3.6
mm/ky) during the late Eocene through the early Oligocene and in the late Miocene suggest the presence of hiatuses in the sedimentary record during these periods. In contrast, higher sediment accumulation rates (35 mm/ky) exist during the late Oligocene and the early Miocene.

Predominance of shallow-water benthic foraminifer and ostracod assemblages in Cores 368-U1501C-45X through 62X and 368-U1501D-2R through 6R indicate an upper bathyal to continental shelf paleoenvironment during the Eocene to the early Oligocene. Predominantly abyssal benthic foraminifers and ostracods above Core 368-U1501C-44X indicate that deepwater conditions existed in this part of the SCS since the early Oligocene.

## Paleomagnetism

Paleomagnetic investigations combined measurement and in-line alternating field (AF) demagnetization of archive-half sections on the 2G Enterprises superconducting rock magnetometer (SRM) with the measurement of discrete samples either AF or thermally demagnetized.

The rock magnetic experiments on six representative samples from Hole U1501C show saturation remanent magnetization (SIRM)/χ ratios between 12.8 and 14.6 kA/m, indicating the predominance of greigite in Unit I of Hole U1501C, also documented by scanning electron microscopy (SEM) in 2–10 µm grains. Thermal demagnetization behaviors show that greigite dominates the natural remanent magnetization (NRM), at least downhole to 83 m. However, the magnetic remanence left above 575°C suggests contributions from additional phases such as maghemite (Curie temperature [$T_C$] = ~590°–675°C) or hematite ($T_C$ = ~675°C).

Both AF and thermal treatments on discrete samples successfully removed the steep low-temperature/coercivity component that represents the drilling overprint. The mean inclination gathered from the high-temperature component is 37.3° ± 6.6°, corresponding to a paleolatitude of 20.8° ± 3.3° for Unit I (see Lithostratigraphy). Many of the AF-demagnetized discrete samples reveal trends of reversed or normal polarity in the last step of demagnetization (50 mT) and are more difficult to interpret.

The magnetostratigraphy in Holes U1501C and U1501D is based on directions derived from the raw moments measured by the SRM after 25 mT demagnetization step and from the corroborative evidence from discrete samples. Magnetostratigraphy was correlated to the standard timescale and plotted along with the tie points from the microfossil ages from shipboard paleontologists. The paleomagnetic and paleontological age constraints match well over most of the section (Figure F30). A succession of eight normal and five reversed events was recognized in Hole U1501D. However, the lack of biostratigraphic constraints throughout Hole U1501D prevented even a tentative correlation of these events with the standard timescale.

## Geochemistry

Interstitial water samples were obtained downcore to 450 m (Subunit IIB). Within Unit I, variations are mainly the result of diagenetic and microbial processes, and measurements of alkalinity, phosphate, ammonia, and sulfate are within the typical ranges for the region (3.5–5 mM alkalinity, 250–510 µM phosphate, <30 µM ammonia, and <26 µM sulfate). However, more atypically (particularly when compared to Expedition 367 Site U1499), the main changes associated with microbial processes are notable only within the uppermost 25 m in Subunit IA and are typical of organic matter degradation. Deeper than 25 m within Unit I, changes in interstitial

water chemistry appear inhibited until 300 m. These changes may be a consequence of the low organic carbon concentration and high carbonate content (~50 wt%) of Unit I. Decreases in sulfate concentrations with depth are more pronounced in Unit II (>300 m), and within this zone there is heavy pyritization and total sulfur (TS) contents are high, suggesting sulfate reduction has taken place. Within the uppermost part of Unit II (300–370 m), chloride, bromide, and sodium are notably lower (chloride = 500 mM, cf. 565 mM; bromide = 0.75 mM, cf. 0.9 mM; and sodium = 410 mM, cf. 480 mM). This difference in interstitial water chemical composition is sharp and could result from pressure-isolated units retaining a distinct formation water chemistry or from the migration of chloride-poor formation water.

Headspace gas concentrations are below background laboratory levels in all samples collected from Site U1501 (<1% ppmv). Total organic carbon (TOC) content is typically <0.5 wt% in Unit I, except from 0 to 50 m (Subunit IA). Within this interval, a typical black marine mud has a TOC of ~1 wt%. TOC was also typically <0.5 wt% in Units II and III, except for a few carbonaceous lithologies: sandstones with plant phytoclasts associated with an ash-rich boghead coal in Unit II (interval 368-U1501D-9R-1, 10–15 cm) and a bitumen-impregnated sandstone in Unit III (interval 27R-1, 12–16 cm). TS content is low in Unit I: ~1 wt% in Subunit IA and below effective shipboard detection limits of 0.01 wt% for the rest of Unit I. TS content is higher in Unit II; >1 wt% in the muddier uppermost part of Unit II and an average of 0.5 wt% in the sandier, deeper part.

Elemental compositions primarily reflect geological units and changes in lithology. Within Unit I, carbonate contents are high and exceed 50 wt% within foraminifer-rich intervals (compositionally a limestone). Within Units II and III, carbonate is less common, and the units are predominantly siliciclastic with a distinction between units that are mud rich and feldspathic and sandier units toward the base of the hole. Calcium and strontium are associated with biogenic sediments in Unit I, but in deeper units they covary with aluminum. Within the base of Units II and III, sodium and potassium are both high, which is consistent with the dominant presence of feldspathic sediments. The higher aluminum proportion within the uppermost part of Unit II is consistent with the muddier, clay-rich lithologies present here.

## Physical properties

Hole U150A is divided into four units based on the sediment and rock physical properties. Physical properties (PP) Unit 1 (0–300 m) experienced the most evident changes in sediment compaction, which is expressed by increasing bulk density (from 1.4 to 2.0 g/cm³) and P-wave velocities (from 1450 to 1930 m/s) and decreasing porosity (from 85% to 45%) with depth. Because PP Unit 1 consists mostly of calcareous ooze, it has relatively low NGR (between 20 and 40 counts/s) and magnetic susceptibility (between $10^{-6}$ and $10^{-5}$ SI). The onset of PP Unit 2 (300–450 m) is marked by a rapid increase in NGR and porosity values and a rapid decrease in bulk densities and P-wave velocities, corresponding to a shift to a different lithologic unit with sand, silt, and clay-enriched sediments. Within the entire unit, NGR is persistently high (60–80 counts/s), whereas magnetic susceptibility remains as low as $10 \times 10^{-5}$ SI. P-wave velocities and bulk densities continue to increase with core depth. Most physical properties of PP Unit 3 (450–600 m) have similar values to those of Unit 2, except that P-wave velocities are extremely high, up to 4000–6000 m/s at some interbeds, and bulk densities and porosities increase and decrease to 2.6 g/cm³ and 2%–3%, respectively, at parallel depths. PP Unit 4 (600–657 m) is dis-
tinct from other units due to higher mean values of NGR (80 counts/s), bulk density (2.6 g/cm³), magnetic susceptibility (500 x 10⁻⁵ SI), and P-wave velocity (4500 m/s). Throughout the hole (0–657 m), thermal conductivities increase from 0.7 to 3.4 W/(m·K), most likely as a result of increasing sediment compaction and changes in sediment compositions. L* reflectance values are highly relevant to weight percent carbonate in sediments, which exhibit relatively high L* values between 100 and 160 in the upper 300 m and thereafter remain as low as 90.

## Downhole measurements

Wireline logging was conducted in Hole U1501D using a modified triple combo tool string that included the Hostile Environment Natural Gamma Ray Sonde (HNGS), Hostile Environment Litho-Density Sonde (HLDS), High-Resolution Laterolog Array (HRLA), and magnetic susceptibility sonde (MSS). The triple combo run collected good data between 115.1 m (base of the drill pipe) and 300 m, where it encountered an impenetrable obstruction. Four logging units are defined:

* Logging Unit 1 (base of the drill pipe to 190 m wireline depth below seafloor [WSF]) is characterized by intervals of large hole diameter and relatively high variability in NGR and magnetic susceptibility.

* Logging Unit 2 (190–260 m WSF) is characterized by a relatively constant hole diameter, relatively homogeneous logs, and sub-meter-scale layering.

* Logging Unit 3 (260–275 m WSF) again shows a relatively large hole diameter, as well high variability in NGR, density, and resistivity logs.

* Logging Unit 4 (275–300 m WSF) exhibits relatively large values of resistivity and magnetic susceptibility.

The upward log pass indicated a collapsed hole at ~156.3 m drilling depth below seafloor (DSF) on the caliper curve, and for safety reasons no further attempts to descend deeper than that undergauge spot were made. Because the interval of the collapsed hole was located only ~40 m below the base of the pipe, the originally planned Formation MicroScanner (FMS)-sonic tool string was not run. Four in situ formation temperature measurements were made in Hole U1501C, yielding a geothermal gradient of 81.4°C/km and a calculated heat flow of 100.1 mW/m². These values are comparable to the relatively high values observed at some ODP and Integrated Ocean Drilling Program sites in this part of the SCS.

## Background and objectives

Site U1501 is located at 2845.8 mbsl on a broad, regional basement high (OMH) within the SCS northern margin (Figures F2, F4). The OMH features prominently in the two-way traveltime (TWT) depth to basement map and is one of four distinct basement highs found across the COT. The OMH is the most landward of these highs within the COT and is followed seaward by Ridges A, B, and C (Figure F3). The crustal thickness below the OMH is significantly greater than that of the ridges located more seaward within the COT. Site U1501 is located near the crossing of seismic Lines 15ecLW8 and 15ecLW1 (Figures F5, F6).

Small rift basins are located on top of the OMH (Figure F3). An important feature of these OMH basins is that they can be traced landward on seismic data into much deeper half-graben basins that formed during the main phase of crustal extension. The sediment fill of these basins shows development from initial rifting and half-

Figure F5. Original and predrilling interpretation of seismic dip Line 15ecLW1 crossing with seismic Line 15ecLW8 (red tick mark) and CDPs (CDP distance = 6.25 m). Seismic stratigraphic Unconformities T20 (2.6 Ma), T30 (5.3 Ma), T32 (10.0 Ma), T40 (16 Ma), T50 (19.1 Ma), T60 (23.0), T80 (38.0 Ma), and T83 (unknown age) and acoustic basement Reflector Tg are shown. The clear but not extensively coherent seismic reflectors below Tg to ~4.7 s TWT are semiconcordant to highly discordant to Tg and interpreted as pre-Cenozoic sediments. Origin of deep, quite strong reflectors (~5 s TWT) is not interpreted.

<figure><img src="image_206.png" /></figure>

graben fill to subsequent postrift subsidence (Figure F2). The seismic stratigraphy established on industry seismic data (with well control) from the inner margin is extrapolated into these deep fault basins, including those located on the OMH (Figure F5). Therefore, the latter offers options to recover the stratigraphy of these basins by moderately deep drilling, testing existing stratigraphic interpretations, and extrapolating the findings margin wide. The key objective of Site U1501 is to sample the stratigraphic record from one of the small rift basins on top of the OMH. Ideally, the sequence targeted by Site U1501 would represent all stages from prerift sediments through synrift to postrift fill. To recover and characterize these sequences are key objectives of Site U1501, with the specific goal of constraining the timing and duration of crustal extension, the tectonic vertical movements during rifting, and the subsequent postrift thermal subsidence. Unlike the basement at Ridges A, B, and C, the nature of the crystalline basement below the OMH is not an objective at Site U1501 and is most likely located far below the Tg horizon planned as the deepest target at the site.

The predrilling interpretation of the seismic unconformities (T30 to T83 and Tg; see Correlation to seismic data in the Expedition 367/368 methods chapter [Sun et al., 2018a]) around Site U1501 is shown in Figure F5. There are clear indications of seismic reflectors below the Tg reflector in this location, so it is not interpreted as crystalline basement. Poorly constrained seismic velocities of these strata (stacking velocities; CNOOC, unpubl. data)
Figure F6. Original and predrilling interpretation of seismic strike Line 15ecLW8 crossing with seismic Line 15ecLW1 (red tick mark) and CDPs (CDP distance = 6.25 m). See Figure F5 for description of seismic interpretations. Dashed lines = unconformities, red solid lines = faults.

<figure><img src="image_207.png" /></figure>

suggest that older sediments could be present. The sub-Tg reflec-
tors seem to be approximately conformal with the overlying pack-
age of sediments just around Site U1501. However, further to the
southwest of the site around common depth point (CDP) 2800, the
seismic data suggest that sub-Tg strata form a tight, synclinal struc-
ture truncated by the Tg reflector (Figure F5). The nature and age of
the strata represented by these deeper sub-Tg reflectors are com-
pletely unknown but are generally considered to be of pre-Cenozoic
age in this location.

Site U1501 is located on seismic Line 15ecLW1 at CDP 3421 (Figure F5). This seismic line is interpreted to be close to a true dip line with regard to the tilted faults blocks (tilted northeast) because crossing seismic Line 15ecLW8 (Figure F6) generally shows more horizontal orientation of the strata (i.e., strike line) within the fault blocks. Note, however, that the position of Site U1501 is projected ~1700 m from the northeast into Line 15ecLW8. This projection in a structurally complex area like the OMH must therefore be accounted for in any interpretation. Nevertheless, using the velocity structure obtained from drilling for depth conversion, the dip of the post-Tg strata within the fault block drilled at Site U1501 is estimated to be ~5° toward the northeast and likely to be close to the actual dip. Using the same velocity model (see Physical properties and Correlation to seismic data), the normal faults associated with the block rotation are estimated to dip 55°-65° southwest.

The faults offset the Tg reflector as much as 75 ms TWT (90-
120 m pending seismic velocities). The faults also affect the inter-
preted T60 unconformity, but in most places these offsets are inter-
preted to be more like drape structures over a tectonically generated
relief with only minor fault offsets, possibly generated by differential
compaction. In some places, however, the T60 unconformity can be
interpreted as having been significantly faulted (e.g., around CDP
2600 at Line 15ecLW1). Nevertheless, the main faulting is inter-

preted to be between the age of the lowermost post-Tg strata and
the age of the T60 unconformity. This entire interval is therefore an
important objective with regard to the timing and environment of
rifting, including vertical crustal movements.

The predrilling interpretation of the seismic stratigraphy of this
critical interval shows the T83 (unknown age) and T80 (38.0 Ma)
unconformities to be present above the Tg reflector and below the
T60 unconformity (23.0 Ma). Sampling this interval will help us de-
termine the environment before the SCS ocean basin formed, possi-
bly including its earliest transgression history. However, the T70
unconformity (33.9 Ma), interpreted to represent final breakup and
the approximate start of seafloor spreading, is interpreted (predrilling
to have been eroded away at the OMH by the younger T60 un-
conformity (Figure F5). However, enough of the rift-to-drift
sequence would likely be in place at Site U1501 to meet our objec-
tives, and despite several alternate drill sites that were identified,
none held better prospects to recover the T70 unconformity than
Site U1501. The basin-wide T60 unconformity is prominently pres-
ent at Site U1501. The nature of this profound unconformity is an
objective together with the post-T60 unconformity stratigraphic in-
terval. This upper interval is expected to provide information on
paleowater depth changes within the lower to middle Miocene de-
posits and thereby constrain the rate of thermal subsidence follow-
ing initial tectonic subsidence.

The younger stratigraphy is the focus of some secondary scien-
tific objectives related to Neogene environmental development of
the SCS and adjacent landmasses of Southeast Asia. Among these
objectives are (1) to reconstruct the history of the East Asian mon-
soon evolution and of deepwater exchanges between the SCS and
Pacific Ocean and (2) to explore the sedimentary responses to the
Cenozoic regional tectonic and environmental development of the
Southeast Asia margin.

The water depth (2850 m) at Site U1501 makes it one of the few
ODP and Integrated Ocean Drilling Program sites within the SCS
above the modern CCD. Its hemipelagic deposits, rich in calcareous
microfossils, enable the application of stable isotopes and faunal
analyses. Key objectives were reconstructions of the monsoonal cli-
mate changes of the SCS and surrounding land and upper and deep
water variations in the western Pacific Ocean. Particularly, through
a comparative study with ODP Leg 184 and IODP Expedition 349
sites, Site U1501, with its sequence of prerift, synrift, and postrift
sediments, will greatly help us to understand the sedimentary and
paleoenvironmental responses to the tectonic events and the basin
evolution experienced by the SCS.

Operations

We conducted operations in four holes at Site U1501. The origi-
nal plan included two holes. The first hole was to be cored to ~650
m with the APC/extended core barrel (XCB) system, followed by
downhole measurements with the triple combo and FMS-sonic tool
strings. The second hole was to have a reentry system to ~640 m
followed by coring to ~1063 m and logging with the triple combo,
FMS-sonic, and Versatile Seismic Imager (VSI) tool strings. Actual
operations differed significantly from the original plan. Mudlines
were missed in Holes U1501A and U1501B, with Core 1H for each
hole retrieving a full core barrel. Hole U1501C (18°53.0919′N,
115°45.9485′E; 2845.8 m water depth) was cored from the seafloor
to 461.8 m and recovered 447.8 m (96%). Hole U1501D
(18°53.0929′N, 115°45.9370′E; 2845.8 m water depth) was drilled
without coring from the seafloor to 433.5 m and cored to 644.3 m,
recovering 78.8 m of core (37%). Coring summaries for Holes U1501A–U1501D are presented in Table T1. We also document our port call activities at the start of the expedition in this section.

## Hong Kong port call

Expedition 368 South China Sea Rifted Margin started at 0754 h (all times presented are UTC + 8 h) on 9 April 2017 with the first line ashore at the China Merchants Wharf in Hong Kong. After the ship cleared immigration and customs, the Expedition 368 Co-

Chief Scientists, IODP staff, and a group of 11 scientists representing each ship laboratory moved onto the ship and started crossover with their Expedition 367 counterparts. Loading and offloading operations began after clearance was issued. Sixty tons of barite were loaded. The rig crew began breaking down 68 stands of 5½ inch drill pipe and laying them out on the riser hold hatch. All life rafts were offloaded for inspection and returned prior to sailing.

The rest of the Expedition 368 scientists boarded the ship on the morning of 10 April and settled into their rooms. Later that morn-

<table><caption>Table T1. Site U1501 core summary. DRF = drilling depth below rig floor, DSF = drilling depth below seafloor. NA = not applicable. Core type: H = advanced piston corer, F = half-length advanced piston corer, X = extended core barrel, R = rotary core barrel, numeric core type = drilled interval. APCT-3 = advanced piston corer temperature tool. (Continued on next two pages.) Download table in CSV format.</caption><thead><tr><th colspan="3">Hole U1501A</th><th colspan="3">Hole U1501B</th></tr></thead><tbody><tr><td>Latitude:</td><td colspan="2">18°53.0922'N</td><td>Latitude:</td><td colspan="2">18°53.0922'N</td></tr><tr><td>Longitude:</td><td colspan="2">115°45.9483'E</td><td>Longitude:</td><td colspan="2">115°45.9483'E</td></tr><tr><td>Seafloor (drill pipe measurement below rig floor, m DRF):</td><td colspan="2">2857.11</td><td>Seafloor (drill pipe measurement below rig floor, m DRF):</td><td colspan="2">2852.11</td></tr><tr><td>Time on hole (days):</td><td colspan="2">0.66</td><td>Time on hole (days):</td><td colspan="2">0.05</td></tr><tr><td>Total depth (drill pipe measurement from rig floor, m DRF):</td><td colspan="2">2868</td><td>Total depth (drill pipe measurement from rig floor, m DRF):</td><td colspan="2">2863</td></tr><tr><td>Distance between rig floor and sea level (m):</td><td colspan="2">10.89</td><td>Distance between rig floor and sea level (m):</td><td colspan="2">10.89</td></tr><tr><td>Total penetration (drilling depth below seafloor, m DSF):</td><td colspan="2">9.5</td><td>Total penetration (drilling depth below seafloor, m DSF):</td><td colspan="2">9.5</td></tr><tr><td>Total length of cored section (m):</td><td colspan="2">9.5</td><td>Total length of cored section (m):</td><td colspan="2">9.5</td></tr><tr><td>Total core recovered (m):</td><td colspan="2">9.73</td><td>Total core recovered (m):</td><td colspan="2">9.83</td></tr><tr><td>Core recovery (%):</td><td colspan="2">102.42</td><td>Core recovery (%):</td><td colspan="2">103.47</td></tr><tr><td>Drilled interval (m):</td><td colspan="2">NA</td><td>Drilled interval (m):</td><td colspan="2">NA</td></tr><tr><td>Total cores (no.):</td><td colspan="2">1</td><td>Total cores (no.):</td><td colspan="2">1</td></tr><tr><th colspan="3">Hole U1501C</th><th colspan="3">Hole U1501D</th></tr><tr><td>Latitude:</td><td colspan="2">18°53.0919'N</td><td>Latitude:</td><td colspan="2">18°53.0929'N</td></tr><tr><td>Longitude:</td><td colspan="2">115°45.9485'E</td><td>Longitude:</td><td colspan="2">115°45.9370'E</td></tr><tr><td>Seafloor (drill pipe measurement below rig floor, m DRF):</td><td colspan="2">2845.81</td><td>Seafloor (drill pipe measurement below rig floor, m DRF):</td><td colspan="2">2845.82</td></tr><tr><td>Time on hole (days):</td><td colspan="2">3.53</td><td>Time on hole (days):</td><td colspan="2">5.15</td></tr><tr><td>Total depth (drill pipe measurement from rig floor, m DRF):</td><td colspan="2">2856.7</td><td>Total depth (drill pipe measurement from rig floor, m DRF):</td><td colspan="2">2856.7</td></tr><tr><td>Distance between rig floor and sea level (m):</td><td colspan="2">10.89</td><td>Distance between rig floor and sea level (m):</td><td colspan="2">10.88</td></tr><tr><td>Total penetration (drilling depth below seafloor, m DSF):</td><td colspan="2">461.9</td><td>Total penetration (drilling depth below seafloor, m DSF):</td><td colspan="2">644.3</td></tr><tr><td>Total length of cored section (m):</td><td colspan="2">461.9</td><td>Total length of cored section (m):</td><td colspan="2">210.8</td></tr><tr><td>Total core recovered (m):</td><td colspan="2">444.77</td><td>Total core recovered (m):</td><td colspan="2">78.77</td></tr><tr><td>Core recovery (%):</td><td colspan="2">96.29</td><td>Core recovery (%):</td><td colspan="2">37.37</td></tr><tr><td>Drilled interval (m):</td><td colspan="2">NA</td><td>Drilled interval (m):</td><td colspan="2">433.5</td></tr><tr><td>Total cores (no.):</td><td colspan="2">62</td><td>Total cores (no.):</td><td colspan="2">26</td></tr></tbody></table>

<table><thead><tr><th>Core</th><th>Type</th><th>Top of interval DSF (m)</th><th>Bottom of interval DSF (m)</th><th>Interval advanced (m)</th><th>Core recovered length (m)</th><th>Curated length (m)</th><th>Recovery (%)</th><th>Time on deck UTC (h)</th><th>Time to cut core (min)</th><th>Core barrel</th><th>Mud pumped (bbl)</th><th>Driller's notes</th></tr></thead><tbody><tr><td>368-U1501A-1</td><td>H</td><td>0.00</td><td>9.5</td><td>9.5</td><td>9.73</td><td>9.73</td><td>102</td><td>4/15/2017 16:10</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td></td><td></td><td colspan="5">Hole U1501A totals:</td><td>102</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>368-U1501B-1</td><td>H</td><td>0.00</td><td>9.5</td><td>9.5</td><td>9.83</td><td>9.83</td><td>103</td><td>4/15/2017 17:25</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td></td><td></td><td colspan="5">Hole U1501B totals:</td><td>103</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>368-U1501C-1</td><td>H</td><td>0.0</td><td>9.3</td><td>9.3</td><td>9.24</td><td>9.24</td><td>99</td><td>4/15/2017 21:30</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>2</td><td>H</td><td>9.3</td><td>18.8</td><td>9.5</td><td>8.68</td><td>8.68</td><td>91</td><td>4/15/2017 22:35</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>3</td><td>H</td><td>18.8</td><td>28.3</td><td>9.5</td><td>9.76</td><td>9.76</td><td>103</td><td>4/15/2017 23:35</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>4</td><td>H</td><td>28.3</td><td>37.8</td><td>9.5</td><td>9.78</td><td>9.78</td><td>103</td><td>4/16/2017 00:20</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>5</td><td>H</td><td>37.8</td><td>47.3</td><td>9.5</td><td>9.15</td><td>9.15</td><td>96</td><td>4/16/2017 01:30</td><td>5</td><td>Nonmagnetic</td><td>APCT-3</td><td></td></tr><tr><td>6</td><td>H</td><td>47.3</td><td>56.8</td><td>9.5</td><td>9.77</td><td>9.77</td><td>103</td><td>4/16/2017 02:25</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>7</td><td>H</td><td>56.8</td><td>66.3</td><td>9.5</td><td>9.42</td><td>9.42</td><td>99</td><td>4/16/2017 03:30</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>8</td><td>H</td><td>66.3</td><td>75.8</td><td>9.5</td><td>9.51</td><td>9.51</td><td>100</td><td>4/16/2017 04:45</td><td>5</td><td>Nonmagnetic</td><td>APCT-3</td><td></td></tr><tr><td>9</td><td>H</td><td>75.8</td><td>85.3</td><td>9.5</td><td>9.70</td><td>9.70</td><td>102</td><td>4/16/2017 05:40</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>10</td><td>H</td><td>85.3</td><td>94.8</td><td>9.5</td><td>9.61</td><td>9.61</td><td>101</td><td>4/16/2017 06:25</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>11</td><td>H</td><td>94.8</td><td>104.3</td><td>9.5</td><td>10.11</td><td>10.11</td><td>106</td><td>4/16/2017 07:50</td><td>5</td><td>Nonmagnetic</td><td>APCT-3</td><td></td></tr><tr><td>12</td><td>H</td><td>104.3</td><td>113.8</td><td>9.5</td><td>9.67</td><td>9.67</td><td>102</td><td>4/16/2017 09:00</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>13</td><td>H</td><td>113.8</td><td>123.3</td><td>9.5</td><td>10.03</td><td>10.03</td><td>106</td><td>4/16/2017 09:50</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>14</td><td>H</td><td>123.3</td><td>132.8</td><td>9.5</td><td>8.23</td><td>8.23</td><td>87</td><td>4/16/2017 11:05</td><td>10</td><td>Nonmagnetic</td><td>APCT-3</td><td></td></tr><tr><td>15</td><td>H</td><td>132.8</td><td>142.3</td><td>9.5</td><td>9.39</td><td>9.39</td><td>99</td><td>4/16/2017 12:10</td><td>10</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>16</td><td>H</td><td>142.3</td><td>151.8</td><td>9.5</td><td>9.50</td><td>9.50</td><td>100</td><td>4/16/2017 14:15</td><td>10</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>17</td><td>H</td><td>151.8</td><td>156.8</td><td>5.0</td><td>4.95</td><td>4.95</td><td>99</td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>
<table><caption>Table T1 (continued). (Continued on next page.)</caption><thead><tr><th>Core</th><th>Type</th><th>Top of interval DSF (m)</th><th>Bottom of interval DSF (m)</th><th>Interval advanced (m)</th><th>Core recovered length (m)</th><th>Curated length (m)</th><th>Recovery (%)</th><th>Time on deck UTC (h)</th><th>Time to cut core (min)</th><th>Core barrel</th><th>Mud pumped (bbl)</th><th>Driller's notes</th></tr></thead><tbody><tr><td>18</td><td>F</td><td>156.8</td><td>161.5</td><td>4.7</td><td>4.92</td><td>4.92</td><td>105</td><td>4/16/2017 15:40</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>19</td><td>F</td><td>161.5</td><td>166.2</td><td>4.7</td><td>4.80</td><td>4.80</td><td>102</td><td>4/16/2017 16:30</td><td>10</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>20</td><td>F</td><td>166.2</td><td>170.9</td><td>4.7</td><td>3.77</td><td>3.77</td><td>80</td><td>4/16/2017 17:20</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>21</td><td>F</td><td>170.9</td><td>175.6</td><td>4.7</td><td>5.07</td><td>5.07</td><td>108</td><td>4/16/2017 18:10</td><td>10</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>22</td><td>F</td><td>175.6</td><td>180.3</td><td>4.7</td><td>5.00</td><td>5.00</td><td>106</td><td>4/16/2017 19:00</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>23</td><td>F</td><td>180.3</td><td>185.0</td><td>4.7</td><td>4.15</td><td>4.15</td><td>88</td><td>4/16/2017 19:50</td><td>10</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>24</td><td>F</td><td>185.0</td><td>189.7</td><td>4.7</td><td>4.47</td><td>4.47</td><td>95</td><td>4/16/2017 20:45</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>25</td><td>F</td><td>189.7</td><td>194.4</td><td>4.7</td><td>3.65</td><td>3.65</td><td>78</td><td>4/16/2017 21:35</td><td>10</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>26</td><td>F</td><td>194.4</td><td>199.1</td><td>4.7</td><td>3.98</td><td>3.98</td><td>85</td><td>4/16/2017 22:20</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>27</td><td>F</td><td>199.1</td><td>203.8</td><td>4.7</td><td>4.98</td><td>4.98</td><td>106</td><td>4/16/2017 23:20</td><td>10</td><td>Nonmagnetic</td><td>15</td><td></td></tr><tr><td>28</td><td>F</td><td>203.8</td><td>208.5</td><td>4.7</td><td>4.90</td><td>4.90</td><td>104</td><td>4/17/2017 00:10</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>29</td><td>F</td><td>208.5</td><td>213.2</td><td>4.7</td><td>4.22</td><td>4.22</td><td>90</td><td>4/17/2017 01:05</td><td>10</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>30</td><td>F</td><td>213.2</td><td>217.9</td><td>4.7</td><td>4.39</td><td>4.39</td><td>93</td><td>4/17/2017 01:50</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>31</td><td>F</td><td>217.9</td><td>222.6</td><td>4.7</td><td>3.68</td><td>3.68</td><td>78</td><td>4/17/2017 02:40</td><td>10</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>32</td><td>F</td><td>222.6</td><td>227.3</td><td>4.7</td><td>3.87</td><td>3.87</td><td>82</td><td>4/17/2017 03:30</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>33</td><td>F</td><td>227.3</td><td>232.0</td><td>4.7</td><td>4.53</td><td>4.53</td><td>96</td><td>4/17/2017 04:20</td><td>10</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>34</td><td>F</td><td>232.0</td><td>236.7</td><td>4.7</td><td>3.72</td><td>3.72</td><td>79</td><td>4/17/2017 05:15</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>35</td><td>F</td><td>236.7</td><td>241.4</td><td>4.7</td><td>3.43</td><td>3.43</td><td>73</td><td>4/17/2017 06:05</td><td>10</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>36</td><td>F</td><td>241.4</td><td>246.1</td><td>4.7</td><td>3.88</td><td>3.88</td><td>83</td><td>4/17/2017 06:55</td><td>10</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>37</td><td>F</td><td>246.1</td><td>250.8</td><td>4.7</td><td>3.25</td><td>3.25</td><td>69</td><td>4/17/2017 07:45</td><td>10</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>38</td><td>F</td><td>250.8</td><td>255.5</td><td>4.7</td><td>2.72</td><td>2.72</td><td>58</td><td>4/17/2017 08:45</td><td>10</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>39</td><td>F</td><td>255.5</td><td>257.0</td><td>1.5</td><td>1.36</td><td>1.36</td><td>91</td><td>4/17/2017 09:30</td><td>10</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>40</td><td>X</td><td>257.0</td><td>264.0</td><td>7.0</td><td>8.35</td><td>8.35</td><td>119</td><td>4/17/2017 11:20</td><td>35</td><td></td><td></td><td></td></tr><tr><td>41</td><td>X</td><td>264.0</td><td>273.7</td><td>9.7</td><td>9.91</td><td>9.91</td><td>102</td><td>4/17/2017 12:45</td><td>40</td><td></td><td></td><td></td></tr><tr><td>42</td><td>X</td><td>273.7</td><td>283.3</td><td>9.6</td><td>9.76</td><td>9.76</td><td>102</td><td>4/17/2017 14:05</td><td>30</td><td></td><td></td><td></td></tr><tr><td>43</td><td>X</td><td>283.3</td><td>292.9</td><td>9.6</td><td>9.85</td><td>9.85</td><td>103</td><td>4/17/2017 15:30</td><td>35</td><td></td><td></td><td></td></tr><tr><td>44</td><td>X</td><td>292.9</td><td>302.5</td><td>9.6</td><td>9.66</td><td>9.66</td><td>101</td><td>4/17/2017 16:50</td><td>30</td><td></td><td></td><td></td></tr><tr><td>45</td><td>X</td><td>302.5</td><td>312.1</td><td>9.6</td><td>9.70</td><td>9.70</td><td>101</td><td>4/17/2017 18:15</td><td>40</td><td></td><td></td><td></td></tr><tr><td>46</td><td>X</td><td>312.1</td><td>321.7</td><td>9.6</td><td>9.71</td><td>9.71</td><td>101</td><td>4/17/2017 19:40</td><td>30</td><td></td><td></td><td></td></tr><tr><td>47</td><td>X</td><td>321.7</td><td>331.3</td><td>9.6</td><td>9.48</td><td>9.48</td><td>99</td><td>4/17/2017 21:15</td><td>45</td><td></td><td></td><td></td></tr><tr><td>48</td><td>X</td><td>331.3</td><td>340.8</td><td>9.5</td><td>9.13</td><td>9.16</td><td>96</td><td>4/17/2017 23:10</td><td>40</td><td></td><td>15</td><td></td></tr><tr><td>49</td><td>X</td><td>340.8</td><td>350.4</td><td>9.6</td><td>9.65</td><td>9.69</td><td>101</td><td>4/18/2017 00:50</td><td>40</td><td></td><td></td><td></td></tr><tr><td>50</td><td>X</td><td>350.4</td><td>360.0</td><td>9.6</td><td>9.21</td><td>9.28</td><td>96</td><td>4/18/2017 02:20</td><td>40</td><td></td><td></td><td></td></tr><tr><td>51</td><td>X</td><td>360.0</td><td>369.6</td><td>9.6</td><td>9.88</td><td>9.98</td><td>103</td><td>4/18/2017 03:40</td><td>35</td><td></td><td></td><td></td></tr><tr><td>52</td><td>X</td><td>369.6</td><td>379.2</td><td>9.6</td><td>9.97</td><td>10.04</td><td>104</td><td>4/18/2017 05:10</td><td>45</td><td></td><td></td><td></td></tr><tr><td>53</td><td>X</td><td>379.2</td><td>388.8</td><td>9.6</td><td>6.13</td><td>6.13</td><td>64</td><td>4/18/2017 06:50</td><td>50</td><td></td><td></td><td></td></tr><tr><td>54</td><td>X</td><td>388.8</td><td>398.4</td><td>9.6</td><td>9.99</td><td>9.99</td><td>104</td><td>4/18/2017 08:40</td><td>50</td><td></td><td>20</td><td></td></tr><tr><td>55</td><td>X</td><td>398.4</td><td>408.0</td><td>9.6</td><td>9.90</td><td>9.90</td><td>103</td><td>4/18/2017 10:25</td><td>45</td><td></td><td></td><td></td></tr><tr><td>56</td><td>X</td><td>408.0</td><td>417.6</td><td>9.6</td><td>9.85</td><td>9.85</td><td>103</td><td>4/18/2017 12:45</td><td>55</td><td></td><td></td><td></td></tr><tr><td>57</td><td>X</td><td>417.6</td><td>427.2</td><td>9.6</td><td>9.99</td><td>10.02</td><td>104</td><td>4/18/2017 14:35</td><td>50</td><td></td><td>20</td><td></td></tr><tr><td>58</td><td>X</td><td>427.2</td><td>436.8</td><td>9.6</td><td>9.92</td><td>9.92</td><td>103</td><td>4/18/2017 16:10</td><td>45</td><td></td><td></td><td></td></tr><tr><td>59</td><td>X</td><td>436.8</td><td>446.3</td><td>9.5</td><td>9.90</td><td>9.90</td><td>104</td><td>4/18/2017 17:35</td><td>35</td><td></td><td></td><td></td></tr><tr><td>60</td><td>X</td><td>446.3</td><td>448.3</td><td>2.0</td><td>1.67</td><td>1.67</td><td>84</td><td>4/18/2017 18:50</td><td>15</td><td></td><td></td><td></td></tr><tr><td>61</td><td>X</td><td>448.3</td><td>454.9</td><td>6.6</td><td>4.72</td><td>4.72</td><td>72</td><td>4/18/2017 20:50</td><td>60</td><td></td><td></td><td></td></tr><tr><td>62</td><td>X</td><td>454.9</td><td>461.9</td><td>7.0</td><td>3.20</td><td>3.20</td><td>46</td><td>4/18/2017 22:50</td><td>60</td><td></td><td></td><td></td></tr><tr><td colspan="12">Hole U1501C totals: 461.9 444.77 445.11 96.37</td></tr><tr><td colspan="12">368-U1501D-</td></tr><tr><td>1</td><td>1</td><td>0.0</td><td>433.5</td><td>433.5</td><td colspan="2">*****Drilled interval*****</td><td colspan="2">4/20/2017 22:45</td><td>540</td><td>Nonmagnetic</td><td>150</td><td></td></tr><tr><td>2</td><td>R</td><td>433.5</td><td>443.1</td><td>9.6</td><td>7.62</td><td>7.62</td><td>79</td><td>4/21/2017 00:35</td><td>30</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>3</td><td>R</td><td>443.1</td><td>452.6</td><td>9.5</td><td>5.19</td><td>5.19</td><td>55</td><td>4/21/2017 02:10</td><td>50</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>4</td><td>R</td><td>452.6</td><td>462.2</td><td>9.6</td><td>1.84</td><td>1.84</td><td>19</td><td>4/21/2017 03:45</td><td>50</td><td>Nonmagnetic</td><td>15</td><td></td></tr><tr><td>5</td><td>R</td><td>462.2</td><td>471.8</td><td>9.6</td><td>0.48</td><td>0.48</td><td>5</td><td>4/21/2017 04:55</td><td>25</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>6</td><td>R</td><td>471.8</td><td>481.4</td><td>9.6</td><td>0.15</td><td>0.15</td><td>2</td><td>4/21/2017 06:00</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>7</td><td>R</td><td>481.4</td><td>491.0</td><td>9.6</td><td>0.95</td><td>0.95</td><td>10</td><td>4/21/2017 07:40</td><td>45</td><td>Nonmagnetic</td><td>15</td><td></td></tr><tr><td>8</td><td>R</td><td>491.0</td><td>500.6</td><td>9.6</td><td>1.64</td><td>1.64</td><td>17</td><td>4/21/2017 08:35</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>9</td><td>R</td><td>500.6</td><td>510.2</td><td>9.6</td><td>1.22</td><td>1.22</td><td>13</td><td>4/21/2017 09:25</td><td>5</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>10</td><td>R</td><td>510.2</td><td>519.7</td><td>9.5</td><td>0.94</td><td>0.94</td><td>10</td><td>4/21/2017 11:25</td><td>75</td><td>Nonmagnetic</td><td>15</td><td></td></tr><tr><td>11</td><td>R</td><td>519.7</td><td>529.3</td><td>9.6</td><td>0.12</td><td>0.12</td><td>1</td><td>4/21/2017 12:35</td><td>10</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>12</td><td>R</td><td>529.3</td><td>539.0</td><td>9.7</td><td>0.13</td><td>0.13</td><td>1</td><td>4/21/2017 14:10</td><td>20</td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>13</td><td>R</td><td>539.0</td><td>548.6</td><td>9.6</td><td>1.05</td><td>1.05</td><td>11</td><td>4/21/2017 15:50</td><td>45</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>14</td><td>R</td><td>548.6</td><td>558.2</td><td>9.6</td><td>0.74</td><td>0.74</td><td>8</td><td>4/21/2017 18:30</td><td>20</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>15</td><td>R</td><td>558.2</td><td>567.8</td><td>9.6</td><td>4.44</td><td>4.44</td><td>46</td><td>4/21/2017 19:35</td><td>15</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>16</td><td>R</td><td>567.8</td><td>577.4</td><td>9.6</td><td>6.08</td><td>6.08</td><td>63</td><td>4/21/2017 20:50</td><td>25</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>17</td><td>R</td><td>577.4</td><td>586.9</td><td>9.5</td><td>5.39</td><td>5.39</td><td>57</td><td>4/21/2017 22:20</td><td>40</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>18</td><td>R</td><td>586.9</td><td>596.5</td><td>9.6</td><td>4.51</td><td>4.51</td><td>47</td><td>4/21/2017 23:25</td><td>20</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>19</td><td>R</td><td>596.5</td><td>606.1</td><td>9.6</td><td>3.45</td><td>3.45</td><td>36</td><td>4/22/2017 01:15</td><td>75</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>20</td><td>R</td><td>606.1</td><td>609.6</td><td>3.5</td><td>4.11</td><td>4.11</td><td>117</td><td>4/22/2017 04:20</td><td>100</td><td>Nonmagnetic</td><td></td><td></td></tr></tbody></table>
<table><caption>Table T1 (continued).</caption><thead><tr><th>Core</th><th>Type</th><th>Top of interval DSF (m)</th><th>Bottom of interval DSF (m)</th><th>Interval advanced (m)</th><th>Core recovered length (m)</th><th>Curated length (m)</th><th>Recovery (%)</th><th>Time on deck UTC (h)</th><th>Time to cut core (min)</th><th>Core barrel</th><th>Mud pumped (bbl)</th><th>Driller's notes</th></tr></thead><tbody><tr><td>21</td><td>R</td><td>609.6</td><td>615.7</td><td>6.1</td><td>5.07</td><td>5.07</td><td>83</td><td>4/22/2017 07:15</td><td>140</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>22</td><td>R</td><td>615.7</td><td>620.2</td><td>4.5</td><td>3.98</td><td>3.98</td><td>88</td><td>4/22/2017 11:15</td><td>150</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>23</td><td>R</td><td>620.2</td><td>625.2</td><td>5.0</td><td>4.94</td><td>4.94</td><td>99</td><td>4/22/2017 17:05</td><td>255</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>24</td><td>R</td><td>625.2</td><td>629.7</td><td>4.5</td><td>4.23</td><td>4.23</td><td>94</td><td>4/22/2017 21:30</td><td>180</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>25</td><td>R</td><td>629.7</td><td>634.7</td><td>5.0</td><td>2.68</td><td>2.68</td><td>54</td><td>4/23/2017 01:15</td><td>140</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>26</td><td>R</td><td>634.7</td><td>639.2</td><td>4.5</td><td>3.46</td><td>3.46</td><td>77</td><td>4/23/2017 05:50</td><td>190</td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>27</td><td>R</td><td>639.2</td><td>644.3</td><td>5.1</td><td>4.36</td><td>4.36</td><td>85</td><td>4/23/2017 09:50</td><td>110</td><td>Nonmagnetic</td><td>40</td><td></td></tr><tr><td colspan="12">Hole U1501D totals including drilled interval: 644.3</td></tr><tr><td colspan="12">Hole U1501D totals excluding drilled interval: 210.8</td></tr><tr><td colspan="12">Hole U1501D totals excluding drilled interval: 78.77</td></tr><tr><td colspan="12">Hole U1501D totals excluding drilled interval: 78.77</td></tr><tr><td colspan="12">Hole U1501D totals excluding drilled interval: 12.23</td></tr><tr><td colspan="12">Hole U1501D totals excluding drilled interval: 37.37</td></tr></tbody></table>

ing, they were introduced to life on board the R/V JOIDES Resolution and participated in the laboratory and ship safety tours. Loading and offloading operations continued with the loading of 40 short tons of sepiolite and the containerized science ocean freight, along with fresh and refrigerated food products and 300 metric tons of potable water. Cores from the two previous expeditions (366 and 367) were offloaded from the vessel and loaded into refrigerated containers for shipment to the Kochi Core Center (Japan) and Gulf Coast Repository (US), respectively. Ninety joints of 5½ inch drill pipe were offloaded to the pier, and another 72 were broken down and stowed on the riser hold hatch.

On 11 April, major port call activities included loading of 1212 metric tons of marine gas oil and 40 short tons of sepiolite mud (total = ~80 short tons). All dry food for Expedition 368 was loaded. The rest of the 204 joints of 5½ inch drill pipe were broken down and offloaded to the pier to be returned for inspection and refurbishment. The vessel continued conducting annual class, radio, and lifeboat surveys. Tours were conducted for members of the Hong Kong Sea Cadet Corps and Hong Kong Baptist University.

On 12 April, casing-loading operations were initiated and tours were conducted for students and faculty from the Southern University of Science and Technology. On 13 April, casing-loading operations were completed. Mud motors, underreamers, and reentry equipment were all loaded and stowed for transit. Annual lifeboat inspections and all other certifications were completed. All equipment was secured for sailing.

At 0600 h on 14 April, Hong Kong immigration authorities boarded the ship and cleared the personnel and vessel for departure. The harbor pilot arrived on board shortly after 0900 h, and with assistance from two harbor tugs, the JOIDES Resolution was underway, with the last line released at 0912 h. We proceeded to the pilot station, and after a 6 nmi transit, the pilot disembarked the ship at 0954 h. The sea voyage continued for the next 24 h. During the transit, the Co-Chief Scientists presented the scientific objectives for Site U1501 and the Captain held the first fire and boat safety drill. Later that day, the Co-Chief Scientists, key JOIDES Resolution Science Operator staff, and ship's crew met to review the coring and logging plan for Site U1501. The scientists moved into their working shifts, and the noon-to-midnight shift resumed laboratory activities. The 255 nmi transit from Hong Kong to Site U1501 was completed at 0837 h on 15 April at an average speed of 10.6 kt.

## Holes U1501A–U1501C

After arriving at Site U1501, we lowered the thrusters, deployed a seafloor beacon, and put together the APC/XCB bottom-hole assembly (BHA) and started lowering it to the seafloor (2857 mblsl) in

preparation for coring. The calculated precision depth recorder (PDR) depth for the seafloor at Site U1501 was 2873.4 meters below rig floor (mbrf), and we chose to place the bit at 2868 mbrf to take the first core. An APC core barrel was lowered to the bit, and coring in Hole U1501A started at 2345 h on 15 April 2017. The mudline core recovered 9.5 m of sediment, and the seafloor depth was calculated to be 2868 mbrf (2857.1 mblsl). Hole U1501A was terminated at 0025 h on 16 April, and the drill string was repositioned to attempt to core a better mudline at the site. With the bit at 2863 mbrf, we started Hole U1501B at 0100 h and again recovered a full core barrel, indicating once again that the APC was fired at or below the seafloor, and Hole U1501B was terminated. The vessel was offset 10 m east. The bit was raised to 2843 mbrf in an attempt to start Hole U1501C, but the core barrel was retrieved empty. We then lowered the bit to 2848 mbrf for a second spud attempt at 0300 h and retrieved another empty core barrel. We then lowered the bit to 2856.4 mbrf and successfully spudded Hole U1501C at 0510 h, recovering 9.3 m of core and establishing a seafloor depth at 2856.7 mbrf (2845.8 mblsl).

Hole U1501C was cored to 156.8 m using the full-length APC coring system. The half-length APC (HLAPC) was deployed to deepen the hole to HLAPC refusal at 257 m. We changed to the XCB system and deepened the hole to a final depth of 469.1 m. Nonmagnetic core barrels were used on all cores. All full-length APC cores were oriented using the Icefield MI-5 core orientation tool. The APC system recovered 156.5 m of core (100%). Temperature measurements were taken on Cores 5H (47.3 m), 8H (75.8 m), 11H (104.3 m), and 14H (132.8 m). Partial strokes were recorded on Cores 16H and 17H (151.8 and 156.8 m, respectively). The HLAPC system penetrated 100.2 m and recovered 88.54 m (88%). Partial strokes were recorded on Cores 22F (180.3 m) and 25F through 39F (189.7–257.0 m). The bit was advanced 4.7 m after each core despite the partial strokes and 1.5 m after Core 39F.

The XCB system was deployed to core to refusal, recovering 199.5 m (97%). A hard layer was met at 383.5 m (Core 53X), and a small piece of sandstone was recovered in the cutting shoe after retrieving the core barrel. Core recovery after that consisted of mudstone. Three more hard layers were found at 447.1, 454, and 460 m. Refusal was reached after no advancement was accomplished for ~10 min at 469.1 m. There were no indications that casing would be needed to core deeper using the RCB system at this site. The bit was then retrieved to the rig floor, clearing the seafloor at 0935 h and clearing the rotary table at 1420 h on 19 April. Overall, 62 cores were taken over a 461.9 m interval with 444.8 m of recovery (96%). Time spent in Hole U1501C was 84.75 h (3.5 days).
## Hole U1501D

The vessel was offset 20 m west for Hole U1501D. The RCB outer core barrel was set up in the rotary table, and the core barrels were spaced out. While making up the BHA, at 1600 h on 19 April 2017 a leak was detected in the low clutch diaphragm. The diaphragm was replaced and back on line by 0500 h on 20 April. The core barrels were prepared and spaced out, the remainder of the RCB BHA was made up, and the drill string was run in the hole to 2816 mbrf. The top drive was picked up, and the bit was spaced out to start Hole U1501D.

Hole U1501D was drilled without coring to 433.5 m, and then RCB coring penetrated from that depth to 644.3 m. The hole was conditioned for logging, the rotary shifting tool was run to release the bit, heavy mud was spotted at the bottom of the hole, the top drive was set back, and the bit was raised to 113 m for logging.

With an average heave of <1 m, the rig floor was set up for logging, and a modified triple combo tool string was made up and run into the open hole. During its descent, the tool string hung up at ~3030 mbrf (173.3 m). After six attempts, the tool string finally passed through the obstruction with significant drag and then continued downhole smoothly until it reached 3156 mbrf (299.3 m). At that depth, the full weight of the tool hung up, and it would no longer advance. The consensus between the wireline engineer and the drilling and operations personnel was that the hole was collapsed and logging would have to be conducted from that depth upward.

During the logging run, there was significant overpull at ~173.3 m. The caliper log indicated that the hole was collapsed to approximately the same diameter as the tool itself. It was deemed unsafe to go below that depth with any subsequent passes; therefore, the rest of the logging program was terminated. The drill pipe was recovered to the rig floor, clearing the seafloor at 1225 h on 24 April and the rotary table at 1715 h.

A total of 90 cores were recorded for the site. The full-length APC system was deployed 19 times. The HLAPC system was deployed 22 times, the XCB coring system was deployed 23 times, and the RCB coring system was deployed 26 times. The total drilled interval was 433.5 m without recovery. The interval cored with the APC system was 175.8 m with a recovery of 176.6 m (100%). The interval cored with the HLAPC system was 100.2 m with a recovery of 88.54 m (88%). The interval cored with the XCB system was 204.9 m with a recovery of 199.53 m (97%). The RCB system cored 210.8 m and recovered 78.77 m (37%). Total core recovered at Site U1501 was 543.10 m, and the overall recovery was 79%. Total time spent at Site U1501 was 224.75 h (9.4 days).

## Lithostratigraphy

We constructed a composite lithostratigraphy by combining Holes U1501A–U1501D (Figure F7). We defined three lithostratigraphic units at Site U1501 based on visual core description, smear slide and thin section inspection, and X-ray diffraction (XRD) analysis (see Lithostratigraphy in the Expedition 367/368 methods chapter [Sun et al., 2018a]). The lithostratigraphic units and subunits are primarily defined by principal lithology. Several of the subunits exhibit gradual changes, complicating a sharp definition of their boundaries. The precise depth of boundaries between certain lithostratigraphic subunits in intervals of poor core recovery was difficult to determine; therefore, the boundaries were refined using physical property measurements (e.g., magnetic susceptibility, color reflectance spectroscopy, and seismic velocity) (see Physical properties; also see Physical properties in the Expedition 367/368 methods chapter [Sun et al., 2018a]) and CaCO₃ measurements in Figure F8.

The sedimentary succession recovered at Site U1501 extends from the pre-Cenozoic(?) to the Holocene and is dominated by clay-rich nannofossil ooze, silty clay, clayey silt, sand, and sandstone. The succession is divided into three major lithostratigraphic units (I, II, and III) that are distinguished on the basis of sediment composition, particularly the relative abundance of calcareous and siliciclastic fractions. Unit I is dominated by clay-rich nannofossil ooze and nannofossil ooze with clay. The transition from Unit I to Unit II is abrupt and erosive and marked by a change from nannofossil-rich sediment in Unit I to siliciclastic-dominated clay, silt, and sand in Unit II.

The Unit II/III boundary was not recovered, but it is marked by an abrupt change in magnetic susceptibility, NGR, and P-wave velocity. Unit III is well lithified and comprises sandstone, sandstone with gravel, and minor conglomerate and laminated siltstone. Units I–III are further divided into several subunits.

## Unit descriptions

### Unit I

Intervals: 368-U1501A-1H-1, 0 cm, to 1H-CC, 14 cm;

368-U1501B-1H-1, 0 cm, to 1H-7, 14 cm;

368-U1501C-1H-1, 0 cm, to 45X-1, 51 cm

Depths: Hole U1501A = 0–9.73 m; Hole U1501B = 0–9.77 m;

Hole U1501C = 0–303.01 m

Age: Holocene to Oligocene

### Lithology and sedimentary structures

Lithostratigraphic Unit I, in the upper part of the stratigraphy, was fully recovered in Hole U1501C. The top of Unit I was also recovered in Holes U1501A and U1501B. The dominant lithologies are clay-rich nannofossil ooze and nannofossil ooze with clay. Both lithologies can additionally have foraminifers, silt, or ash (e.g., “with foraminifers” as suffix) and minor amounts of nannofossil-rich foraminifer sand or silty sand. One discrete volcanic ash layer was found in Section 368-U1501A-1H-7, and an ash pod was found in Section 368-U1501C-3H-1. Ash is present in small amounts in some smear slides taken from other cores (e.g., Samples 368-U1501C-6H-5, 88 cm, and 6H-6, 78 cm). Unit I is divided into six subunits (IA–IF) based on minor changes in lithology and/or physical properties (Figure F9).

### Bulk mineralogy and chemistry

The bulk mineralogy results of XRD analyses are listed in Table T2. Unit I sediments are composed mainly of calcite; halite; quartz; plagioclase; K-feldspar; clay minerals including smectite, illite, kaolinite, and/or chlorite; and minor amounts of pyrite. Calcite is present throughout Unit I (mostly in the form of nannofossils and foraminifers). Other minor minerals were observed in smear slides, but it was not possible to detect them through XRD analysis of bulk samples.

Figure F8 shows the downcore variations in the relative abundance of minerals identified by XRD in bulk sediments at Site U1501. The percentages of most terrigenous minerals in Unit I (quartz, plagioclase, authigenic halite, and clay minerals such as ilite, kaolinite, and/or chlorite) decrease downcore, whereas calcite and pyrite increase. In contrast, K-feldspar decreases downcore for the upper 60 m, increases between 60 and 140 m, and then decreases.
<figure><img src="image_208.png" /><figcaption>Figure F7. Lithostratigraphic summary of Site U1501 with simplified lithology and unit description of combined Holes U1501A–U1501C and U1501D. Upper cores are from Hole U1501C (1H through 61X); lower cores are from Hole U1501D (4R through 27R).</figcaption></figure>

creases again from 140 to 280 m. These general characteristics are consistent with the observed lithologic change from clay-rich nannofossil ooze to nannofossil ooze with clay.

Compositional analyses of the nannofossil ooze in Sections 368-U1501C-44X-7, 44X-CC, and 45X-1 (Subunit IF) were made directly on the archive half of the core using the handheld portable X-

ray fluorescence spectrometer (pXRF) (see Igneous and metamorphic petrology in the Expedition 367/368 methods chapter [Sun et al., 2018a]). The pXRF data are shown in Table T3. Eleven intervals of the nannofossil ooze show no variation in composition (CaO = 25–28 wt%, SiO₂ = ~20 wt% and lower, Al₂O₃ = 4–5 wt%, Fe₂O₃ < 2 wt%, and MgO < 2 wt%). The lowermost few centimeters of Subunit
<figure><img src="image_209.png" /><figcaption>Figure F8. (A) Bulk mineralogy (XRD) and (B) carbonate content, Holes U1501C and U1501D.</figcaption></figure>

IF close to the contact with Unit II contain black sand and have lower CaO (~18 wt%) and higher SiO₂, Al₂O₃, and Fe₂O₃ (~25 wt%, ~5 wt%, and ~3 wt%, respectively). The dark nodules at the base of Subunit IF are iron and silica rich (Fe₂O₃ = ~10 wt% and SiO₂ = 26 wt%). The Zr content of Subunit IF varies between 50 and 75 ppm. The ooze has high Sr (>750 ppm) and low Ni (<20 ppm) contents, whereas the nodules have low Sr (<100 ppm) and higher Ni (100 ppm) contents.

## Subunit IA

Intervals: 368-U1501A-1H-1, 0 cm, to 1H-CC, 14 cm;
368-U1501B-1H-1, 0 cm, to 1H-7, 14 cm;
368-U1501C-1H-1, 0 cm, to 3H-5, 84 cm

Depths: Hole U1501A = 0–9.73 m; Hole U1501B = 0–9.77 m;
Hole U1501C = 0–25.47 m

Age: Holocene to late Pleistocene

Subunit IA spans the uppermost 25.47 m of Unit I and is domi-
nated by clay-rich calcareous ooze and clay-rich nannofossil ooze.
The color of the ooze gradually changes from dark greenish gray to
greenish gray. A distinct light-brown oxidized layer occurs at the
top of this unit. The ooze comprises calcareous nannofossils and
foraminifers, siliceous diatoms, sponge spicules, radiolarians, rare
silicoflagellates, and terrigenous grains, including quartz, feldspar,
clay minerals, and rare ferromagnesian minerals.

Bioturbation is moderate to heavy (apart from the slightly bio-
turbated top layer) with no clear layering visible. Individual burrows
are difficult to distinguish but are mostly horizontal to inclined with
recognizable *Planolites*, *Thalassinoides*, and *Ophiomorpha* (Figure
F10). Distinct intervals (368-U1501C-1H-5, 6.0–6.5 cm, and 1H-5,
7.5–8.5 cm) contain more silt, and thin silt laminations are often
disrupted by bioturbation (interval 3H-3, 89–133 cm).

Subunit IA has a discrete light gray silt-sized volcanic ash layer in interval 368-U1501A-1H-7A, 45–51 cm, and a centimeter-sized pod of volcanic ash in interval 368-U1501C-3H-1A, 29 cm. The ash is composed of silicic, platy, bubble wall, and lesser pumiceous glass shards and rare (1%–5%) plagioclase crystals (Figure F11). Although the mudline was not recovered in Hole U1501A, the drilling log indicates that the drill string was raised by 10 m before drilling

of Hole U1501C commenced. The ash layer is found at 9.05 m in Hole U1501A, which is consistent with the depth of the ash patch in Hole U1501C (19.08 m). Furthermore, because the ash texture and composition is similar in the two holes, we assume that both intervals are the deposit of the same eruption. No other discrete ash intervals were observed at Site U1501.

Subunit IA shows a gradual lithologic transition into Subunit IB but with a clear change in magnetic susceptibility, porosity, density, and seismic velocity. From this boundary, there is an upward increase in biogenic silica, including diatoms, sponge spicules, and radiolarians.

## Subunit IB

Interval: 368-U1501C-3H-5, 84 cm, to 7H-CC, 11 cm
Depth: 25.47–66.17 m

Age: late Pleistocene to Pliocene

Subunit IB comprises a monotonous sequence of greenish gray and minor gray and dark greenish gray clay-rich nannofossil ooze. Minor dark greenish gray clay-rich nannofossil ooze with ash was found in Sections 6H-5 and 6H-6. The ooze comprises mainly calcareous nannofossils and foraminifers with minor quartz and clay minerals. Single foraminifer tests are visible on the core surface and become more abundant below Section 7H-3. Diagenetic pyrite grains are common.

The upper part of the subunit (Sections 3H-5 through 3H-7) is marked by slumping with inclined and convolute lamination and patchy color changes. Below these sections, bedding is difficult to determine due to lack of grain size or color variation and moderate bioturbation. Individual burrows are difficult to distinguish but are mostly horizontal to inclined with recognizable *Planolites* and *Thalassinoides* (Figure F10).

The base of Subunit IB is marked by both a color change to
brown and light brownish sediment in Subunit IC and a lithologic
change that reflects an increase in the percentage of foraminifers.
This unit change is also seen in the progressive increase in mea-
sured carbonate content from ~20 wt% at the top of Subunit IB to
~40 wt% at the base (Figure F8).
<figure><img src="image_210.png" /><figcaption>Table T2. Mineral percentages, Site U1501. **View table in PDF format. Download table in CSV format.**</figcaption></figure>

<caption>Table T3. Major element oxides and minor elements in sediments, Site U1501. **View table in PDF format. Download table in CSV format.**</caption>

## Subunit IC

Interval: 368-U1501C-8H-1, 0 cm, to 17H-4, 60 cm

Depth: 66.30–156.70 m

Age: Pliocene to middle Miocene

Subunit IC comprises an alternating sequence of gray, light gray, light brownish gray, greenish gray, and light greenish gray clay-rich nannofossil ooze with foraminifers; brown clay-rich nannofossil ooze with calcite; light brownish gray clay-rich nannofossil ooze and nannofossil ooze; light brownish gray silty sand; and greenish gray foraminifer-rich silty sand. The proportion of foraminifer-rich silty sand intervals increases from Core 16H to the base of the subunit.

Vague layering in the core is defined by color change. Boundaries between brownish and grayish intervals are mostly gradational, such as the color changes in Core 16H (Figure F12A), but sharp boundaries also occur, such as the one at Section 11H-6, 135 cm. Variation in color may indicate grading with fining-upward intervals recognized in Cores 11H, 14H, 16H, and 17H (Figure F12).

Boundaries are usually horizontal but are inclined in Sections 10H-3 and 10H-4, possibly indicating intraformational slumping. The number of sand-sized fining-upward laminations increases from Core 15H to Core 17H.

Bioturbation varies from slight to heavy, but more intense bioturbation may be masked by the homogeneous sediment composition. Some burrows are filled with silty sand that consists mainly of foraminifers (Figure F10). Burrows are mostly horizontal to inclined, but some are vertical with recognizable *Planolites*.

The boundary between Subunits IC and ID is defined by a change in lithology from foraminifer-rich silty sand and nannofossil ooze with foraminifers (Subunit IC) to nannofossil ooze with clay (Subunit ID).

## Subunit ID

Interval: 368-U1501C-18F-1A, 0 cm, to 25F-2, 78 cm

Depth: 156.80–191.99 m

Age: middle to early Miocene

Subunit ID is dominated by nannofossil ooze with clay. The color changes gradually from the top of the subunit to the bottom from gray to light greenish gray to greenish gray to light brownish gray and gray. The sediment is well sorted and well consolidated.
<figure><img src="image_211.png" /><figcaption>Figure F11. A. Pale brownish ash layer (368-U1501A-1H-7, 45–51 cm), Subunit IA. B. Magnetic susceptibility of core interval with ash layer, Hole U1501A. The ash layer has a significantly higher magnetic susceptibility than the nannofossil ooze. C. Smear slide image of ash layer. The ash is compositionally dominated by transparent glass shards and rare colored minerals (feldspar and ferromagnesian minerals). D. Pale brownish ash patch (368-U1501C-3H-1, 29 cm), Subunit IA.</figcaption></figure>

<figure><img src="image_212.png" /></figure>

The average grain size is clay, and fine sand is the maximum grain size.

Contacts between layers are planar or irregular inclined and gradational horizontal. Some contacts between layers are also bioturbated. Bioturbation in Subunit ID is moderate to heavy.

The sediment is dominated by clay minerals and calcareous nannofossils, but quartz crystals are common and rare foraminifers are present, as well as traces of organic matter and pyrite. Measured carbonate content ranges from 18 to 48 wt% (Figure F8).

The lower boundary between Subunits ID and IE is characterized by a change in color and lithology, with more clay minerals in Subunit IE. A distinct increase in magnetic susceptibility and a slight decrease in NGR were observed at the transition.

## Subunit IE

Interval: 368-U1501C-25F-2, 78 cm, to 43X-CC, 38 cm

Depth: 191.99–293.09 m

Age: early Miocene to Oligocene

Subunit IE is composed of monotonous greenish gray clay-rich nannofossil ooze (Figure F13) that is well consolidated and well sorted with either silt or very fine sand as the maximum grain size. There is little perceptible variation in grain size, with only minor thin silt laminations. Contacts are horizontal and gradational. One thick (~1 cm) lamination with upward fining was observed. Light-colored foraminifer grains and pyrite were observed on the core surface. Pyrite also forms rare laminae. Another diagenetic feature
Figure F12. Subunit IC. A. Core composite image. Red stars = thin fining-upward intervals. These intervals are interpreted as distal turbidites. B. Fining-upward interval with sharp bottom contact and diffuse top.

<figure><img src="image_213.png" /></figure>

is a 1 cm wide patch of calcite or dolomite (interval 27F-1, 29–30 cm). Bioturbation is moderate to high throughout the sequence, causing lens- and podlike textures.

The nannofossil ooze of Subunit IE exhibits consistently low magnetic susceptibility (less than $-20 \times 10^{-5}$ SI), low NGR (<50 counts/s), high bulk reflectance, and low red color (reflectance a*), which is consistent with dilution by high carbonate content (31–46 wt%; Figure F8). Accordingly, nannofossils and foraminifers are common to abundant (50%–75%), whereas the amounts of quartz (<5%) and feldspar (<5%) are low.

The lower contact to Subunit IF is marked by the occurrence of nannofossil ooze with clay and a color change to gray and light greenish gray. Drilling disturbance varies from slight to high, and “biscuits” are the most common disturbance type.

## Subunit IF

Interval: 368-U1501C-44X-1, 0 cm, to 45X-1, 51 cm

Depth: 293.90–303.01 m

Age: Oligocene

Subunit IF is a short interval (~11 m) of mainly gray to light greenish gray and greenish gray, well-sorted, well-consolidated nannofossil ooze with clay. The lowermost ~51 cm (interval 45X-CC, 0–51 cm) of this subunit is poorly sorted, matrix-supported

Figure F13. A. Clay-rich nannofossil ooze, Subunit IE. Monotonous sedimentation with pyrite patches. B. Close-up image (red square in A) of pyrite patches. C. Smear slide image of clay-rich nannofossil ooze with pyrite grains.

<figure><img src="image_214.png" /></figure>

sand with gravel. The lithologic components are heterogeneous and include cobble-sized rip-up clasts of nannofossil ooze with clay, pebble-sized botryoidal concretions (Figure F14), and sand-sized grains of glauconite and quartz embedded in a matrix of biogenic silt and clay (measured carbonate content = ~60 wt%; Figure F8). Subunit IF sediment fines upward in grain size and is heavily bioturbated. The cores are slightly to moderately biscuited or fractured due to drilling disturbances.

The lower contact of Subunit IF, which is also the base of litho-stratigraphic Unit I, is erosional and marked by the emplacement of a poorly sorted sandy layer (Figure F14). The lower Subunit IF boundary is also marked by distinct discontinuities in P-wave velocity, NGR, magnetic susceptibility, porosity, MAD, red-green-blue color space (RGB) colors, and blue color (reflectance b*; see *Igneous and metamorphic petrology* in the Expedition 367/368 methods chapter [Sun et al., 2018a]) but does not represent a major gap in sediment age (all Oligocene; see *Biostratigraphy*). Measured carbonate contents markedly decrease from 56–66 wt% in Subunit IF to 2–10 wt% in Subunit IIA.

## Unit II

Intervals: 368-U1501C-45X-1, 51 cm, to 62X, 39 cm; 368-U1501D-2R-1, 0 cm, to 19R-2, 135 cm

Depths: Hole U1501C = 303.01–458.09 m (base of Unit II not recovered); Hole U1501D = 433.5–598.91 m (top of Unit II not recovered)

Age: Oligocene to Eocene
Figure F14. Contact between Units I and II (368-U1501C-45X-1, 50 cm). Nannofossil ooze with clay dominates Subunit IF with centimeter-sized concretions at the lower boundary and rip-up clasts. Subunit IIA is dominated by nannofossil-rich clay. Photomicrographs show (top) nannofossil ooze with clay, (middle) concretions, and (bottom) nannofossil-rich clay.

<figure><img src="image_215.png" /></figure>

## Lithology and sedimentary structures

Lithostratigraphic Unit II was recovered in Holes U1501C and U1501D. It consists of variable amounts of clay, silt, and sand (clay, silty clay, clayey silt, sandy silt, silty sand, and sand, which may be clay rich, with sand or with clay) with some nannofossil-rich clay (Figure F14), clay with nannofossils and minor nannofossil ooze, and clayey silt and silt with organic matter. In addition, gravel-sized grains include shell fragments and glauconite, as well as carbonate and pyrite concretions. The overall carbonate contents of Unit II is significantly lower (2–10 wt%) than that of Unit I (12–66 wt%) (Figure F8). Unit II is divided into six subunits (Figure F15) based on minor changes in lithology and grain size.

## Bulk mineralogy and chemistry

The bulk mineralogy results of XRD analyses are listed in Table T2. Unit II sediments are composed mainly of glauconite, quartz,

plagioclase, K-feldspar, clay minerals (including smectite, illite, and kaolinite), and minor amounts of pyrite and halite.

Figure F8 shows the downcore variations in the relative contents of minerals identified by XRD in bulk sediments at Site U1501. Compared to Unit I, Unit II has distinct higher percentages of authigenic glauconite and terrigenous minerals, including quartz, plagioclase, K-feldspar, and clay minerals (illite and kaolinite). Unit II sediments have lower contents of calcite, pyrite, chlorite, and smectite. Most of the terrigenous minerals (illite, kaolinite, K-feldspar, and plagioclase) increase downcore in Unit II. We can only trace the downcore trend of glauconite content, rather than its precise abundance, because of its very poor crystallinity (wide peak around 7–8.9°Δ2θ) at the study site and the lack of a shipboard standard for calibration.

Compositional analyses of the clay in Sections 368-U1501C-45X-1 and 45X-2 were made directly on the archive half of the core using the handheld pXRF instrument (see Igneous and metamorphic petrology in the Expedition 367/368 methods chapter [Sun et al., 2018a]). The pXRF data are shown in Table T3. The nine analyzed intervals show no significant trends downhole. The clay has SiO₂ contents between 30 and 38 wt%, Al₂O₃ contents between 8 and 11 wt%, and low CaO contents (<5 wt%). The intervals in Section 45X-2 have sulfur contents between 690 and 4600 ppm. Zr contents are constant at ~70 ppm.

The uppermost two subunits of Unit II define a fining-upward succession from glauconite sand dominated in Sections 61X-CC through 59X-5 to siltstone and clay in Sections 59X-5 through 53X-1 (Subunit IIB) and clay with nannofossils in Core 53X through Section 45X-1 (Subunit IIA). Subunit IIC is dominated by sandstone with calcite but shows poor recovery. Subunit IID is distinctive with more fine grained, organic-rich lithologies. Subunit IIE is similar to Subunit IIC, whereas Subunit IIF repeats Subunit IIB but has more coarse-grained sediment and distinctive weak red and reddish gray intervals between the green glauconite-bearing sands.

The sediment in Unit II is matrix supported and moderately to poorly sorted. Coarse sand- to pebble-sized shell fragments are common. Coral fragments occur occasionally in the upper part of the unit. Glauconite and quartz minerals dominate the siliciclastic grain component. Diagenetic pyrite concretions, patches, or laminae are common throughout Unit II (Figure F16). Locally, carbonate and clay concretions are found. The measured carbonate content of Subunits IIA and IIB ranges from 2 to 10 wt% (Figure F8).

Horizontal lamination and ripple lamination can be recognized even though the entire interval is variably affected by drilling disturbance. Cross-bedding is present, as well as occasional fining-upward lamination, mostly in Subunit IIB. Bioturbation in Unit II is moderate. Burrows are horizontal to gently dipping and belong to the Zoophycos ichnofacies in Subunit IIA.

Drilling disturbance within Unit II varies from slight to high. Cores are slightly to heavily biscuited and partly fractured. Core 368-U1501C-62X has basal flow-in, and Cores 368-U1501D-2R, 8R, and 15R have soupy intervals.

## Subunit IIA

Interval: 368-U1501C-45X-1, 51 cm, to 53X-CC, 26 cm

Depth: 303.01–385.26 m

Age: Oligocene to late Eocene

Subunit IIA is characterized by an overall fining-upward sequence from sand with clay to nannofossil-rich clay and clay-rich
<figure><img src="image_216.png" /><figcaption>Figure F15. Simplified lithology and unit description overview, Unit II.</figcaption></figure>

nannofossil ooze. The sediments are well consolidated and well sorted. Sections 45X-1, 51 cm, to 49X-CC, 39 cm, are composed of greenish gray to very dark greenish gray nannofossil clay and clay-rich nannofossil ooze with a maximum grain size of silt to fine sand. Several intervals fine upward from coarse sand to clay (e.g., intervals 48X-2, 103–151 cm, and 48X-3, 136–151 cm). Boundaries between sediment layers are horizontal and gradational. Very dark greenish gray silty clay with nannofossils was recovered from Section 50X-1, 0 cm, to 51X-CC, 34 cm. This interval shows cross-bedding, lamination, and a maximum grain size of fine sand. Grain size changes to silty clay with sand in Sections 52X-1, 0 cm, to 52X-CC, 45 cm. From Section 53X-1, 0 cm, to 53X-CC, 26 cm, the grain size increases from clayey silt with sand to silty sand and sand with clay (Figure F17). Boundaries between layers are gradational and horizontal, and lenticular bedding was observed in interval 53X-3A, 124–134 cm. The sediment is greenish gray and rich in sand-sized glauconite and quartz crystals. Shell fragments as large as 1 cm and foraminifers are common. Pyrite patches a few centimeters in size (Figure F16) occur throughout Subunit IIA. Bioturbation is moderate in the lower part of Subunit IIA (Sections 53X-1, 0 cm, to 53X-CC, 26 cm) and heavy in the upper part. The Subunit IIA/IIB boundary is characterized by a change in grain size. The recovered sediments are slightly to moderately disturbed with biscuits and fractures.

## Subunit IIB

Intervals: 368-U1501C-54X-1, 0 cm, to 61X-CC, 7 cm; 368-U1501D-2R-1, 0 cm, to 3R-CC, 40 cm

Depths: Hole U1501C = 388.80–452.69 m; U1501D = 433.5–448.24 m (top of Subunit IIB not recovered)

Age: Eocene

Subunit IIB has well-consolidated sediment with fining-upward intervals that vary in grain size from clayey silt with sand to silty sand with clay to sand. The color changes from greenish gray (Core 368-U1501C-54X) to dark greenish gray (Sections 55X-1 through 57X-5) to very dark greenish gray (Sections 57X-6 through 58X-CC). The average grain size is silt to coarse sand, with a maximum grain size of granule and pebble. The sorting of the intervals in this subunit is moderate to poor.

Boundaries between sediment layers are gradational and horizontal, and layers fine upward (e.g., Section 59X-3). The sediment is rich in sand-sized glauconite and quartz crystals (Figure F17). There are pyrite patches throughout the subunit, especially in Sections 55X-1, 55X-2, 55X-5, 59X-3, 59X-5, 59X-6, and 60X-1 and in all sections of Core 61X. Shell fragments are common and horizontally oriented within the sediment (Figure F16). Calcite concretions occur in Section 58X-1, 42 cm, and interval 58X-CC, 16–18 cm. Bioturbation in Subunit IIB is moderate.

The Subunit IIB/IIC boundary is characterized by a change from glauconite-rich sand/sandstone to sandstone with calcite.
<figure><img src="image_217.png" /><figcaption>Figure F16. Special features, Subunits IIA and IIB. A. Thin parallel laminations. B. Gastropod shell filled with pyrite. C. Calcite concretion. D. Pyrite nodule. E. Coral fragment.</figcaption></figure>

NGR values decrease at the transition from Subunit IIB to IIC (see **Physical properties**). The sediment in Subunit IIB is biscuited due to drilling, with disturbance intensities from moderate to high.

<caption>Figure F17. Glauconite sand, Unit II. A. Glauconite-rich sand, Subunit IIA. Rounded green glauconite grains in smear slide image. B. Glauconite-rich sand, Subunit IIB. Thin section is dominated by quartz and glauconite grains.</caption>

## Subunit IIC

Intervals: 368-U1501C-61X-CC, 7 cm, to 62X-CC, 39 cm; 368-U1501D-4R-1, 0 cm, to 7R-1, 93 cm

Depths: Hole U1501C = 452.69–458.09 m (base of subunit IIC not recovered); Hole U1501D = 452.60–482.33 m

Age: Eocene

Subunit IIC is composed of gray sandstone with calcite, silty sandstone with calcite, and minor gray clayey silt with organic matter (Figure F18). The average grain size is coarse sand with a maximum of granule and pebble sizes, and the sediment is well to moderately sorted. Boundaries between sediment layers are planar and horizontal or erosive and curved. Recovery was very low (<10%) in this subunit (Figure F7). Shell fragments are abundant, and pyrite patches and calcite veins occur. The lithified sandstone is slightly bioturbated.

Drilling disturbance is moderate to high throughout Cores 368-U1501C-61X through 62X. The sediment is biscuited, fractured, and brecciated. Soft sediment recovered in Core 62X is interpreted as fall-in and basal flow-in and is therefore not described in any detail.

The boundary between Subunits IIC and IID is marked by a distinctive change from calcite-rich sandstone to more fine grained clay and organic-rich lithologies in Subunit IID.

## Subunit IID

Interval: 368-U1501D-8R-1, 0 cm, to 11R-CC, 10 cm

Depth: 491.00–519.80 m

Age: Eocene

Subunit IID is composed of alternating laminae of dark gray to very dark gray clayey silt with organic matter or lignite (Figure F19).

<figure><img src="image_218.png" /></figure>

The sediment is slightly consolidated with an average grain size of silt and a maximum grain size of medium sand. The sediment is well to moderately sorted and characterized by very fine laminations and minor pebble-sized wood fragments. The organic matter occurs in clasts, lenses, or laminae. There is no bioturbation. The sediment is slightly soupy. Sandstone layers, similar to those described in Subunit IIC, are intercalated with the clayey silt.

Similar to Subunit IIC, recovery in this unit is also very low (<10%). The boundary between Subunits IID and IIE is characterized by a lack of organic-rich layers and a change to calcite-rich sandstone in Subunit IIE.
Figure F18. A. Calcite-rich sandstone with calcite-filled veins, Subunits IIC and IIE. B. Close-up image (red square in A) of calcite veins. C. Smear slide image of sandstone that is dominated by quartz crystals and calcite matrix.

<figure><img src="image_219.png" /></figure>

## Subunit IIE

Interval: 368-U1501D-12R-CC, 0 cm, to 14R-1, 4 cm
Depth: 529.30–548.64 m
Age: Eocene

Subunit IIE is composed of gray silty sand with calcite, silty sandstone with calcite, and sandstone with calcite. The sediment is well consolidated to lithified, and the average grain size is fine to medium sand. The sediment is well sorted. Bioturbation is slight to moderate. The sediment is slightly fragmented due to drilling. This subunit appears similar to Subunit IIC (Figure F18).

Recovery in this subunit is extremely low (<6%). Subunit IIE is similar to Subunit IIC, whereas Subunit IIF repeats Subunit IIB. The boundary between Subunits IIE and IIF is marked by a change from sandstone with calcite to gray and dark greenish gray glauconite-bearing silty sand and silty sandstone.

## Subunit IIF

Interval: 368-U1501D-14R-1, 4 cm, to 19R-2, 135 cm
Depth: 548.64–598.91 m
Age: Eocene

Subunit IIF is composed of gray, dark greenish gray, greenish gray silty sand, sandy silt and sand, and silty sandstone, as well as weak red silty sand and silty sandstone. A color change to weak red is observed in Sections 17R-1, 101 cm, to 17R-2, 47 cm. The consolidation

Figure F19. A. Subunit IID is characterized by the presence of thin layers of organic matter within a clayey silt. Red square = location of B, B, C. Close-up images of organic-rich layers and bedding structures. Layers of organic-rich material are intercalated with clayey silt layers. D. 5 cm of lignite-rich silt.

<figure><img src="image_220.png" /></figure>

varies from well consolidated to lithified. The average grain size is from fine to coarse sand to a maximum of granule, and the sediment is well to moderately sorted. The bedding thickness is medium to thick (see Lithostratigraphy in the Expedition 367/368 methods chapter [Sun et al., 2018a]), and contacts between the beds are planar to gradational and horizontal to curved. The majority of the beds fine upward or are massive (Figure F20). The sands are rich in glauconite and quartz minerals. Pyrite is common, and patches are as large as centimeter sized (e.g., interval 16R-2, 77–129 cm). The sediment and lithified sandstone are slightly to moderately bioturbated. The sandstone is slightly fractured due to drilling disturbance. The contact with Unit III was not recovered, but Subunit IIF has marked brown- to ochre-colored alteration patches at the base (Figure F21).

## Unit III

Interval: 368-U1501D-19R-3, 0 cm, to 27R-4, 71 cm
Depth: 598.91–643.56 m
Age: pre-Eocene

## Lithology and sedimentary structures

Unit III was only recovered in Hole U1501D and consists of lithified sandstone, sandstone with gravel, and minor conglomerate and laminated siltstone. Unit III is divided into two subunits (Figure F22). Pebble- to cobble-sized clasts include felsic volcanic and plutonic rocks, sedimentary rocks, metamorphic rocks, and rare gabro (Figure F23).
Figure F20. A. Glauconite-rich coarse sandstone, Subunit IIF. The interval fines upward from very coarse sand to medium sand. B. Thin section image of glauconite sandstone dominated by quartz and glauconite. C. Glauconite-rich sandstone with burrows and blotches.

<figure><img src="image_221.png" /></figure>

The contact between Units II and III was not recovered. The base of Section 19R-2 represents Unit II, and the top of Section 19R-3 is in Unit III (Figure F21). However, the low recovery (26%) indicates that intervals are missing. The boundary is marked by an abrupt downhole increase in magnetic susceptibility, NGR, and P-wave velocity, so it is assumed that this boundary is sharp. A change in the apparent dip of strata from approximately horizontal (seismics show ~5°) in Unit II to ~20° in Unit III (see Structural geology) suggests that the contact is unconformable.

## Bulk mineralogy

The bulk mineralogy results of XRD analyses are given in Table T2 and Figure F8. Unit III sediments are composed mainly of quartz, plagioclase, and K-feldspar, as well as minor amounts of kaolinite and mica. Compared to Units I and II, Unit III sediments have much higher K-feldspar and plagioclase abundances but almost no calcite, glauconite, or pyrite.

## Subunit IIIA

Interval: 368-U1501D-19R-3, 0 cm, to 25R-1, 9 cm

Depth: 598.91–629.79 m

Age: pre-Eocene

Figure F21. Composite of core section images showing the lithologic change from greenish gray medium coarse sand with glauconite in Subunit IIF to gray lithified coarse sandstone in Subunit IIIA, Hole U1501D. Lower part of Subunit IIF (19R-2) shows irregular brown to ochre and purple patches inferred to be related to diagenetic alteration.

<figure><img src="image_222.png" /></figure>

Subunit IIIA is composed of light gray to gray lithified sandstone, sandstone with gravel, and sandstone with calcite clasts (Figure F24), along with minor conglomerate and siltstone. The average grain size is medium to very coarse sand, and the maximum grain size is as large as cobble sized. The sorting is well to moderate, but some intervals are poorly sorted because of large pebbles or cobbles. The pebble- to cobble-sized clasts consist of felsic volcanic and plutonic rocks (granite), sedimentary rocks, and rare gabbro. The bottom contacts of beds are planar, erosional, gradational, and horizontal. The sandstone layers are massive or fine upward. Interval 22R-3, 80–102 cm, contains an ~22 cm thick interval of dark gray siltstone. The contact with the overlying sandstone was not recovered, but the bottom contact with the underlying conglomerate is erosive and inclined. Intervals 22R-3, 102–105 cm, and 22R-CC, 0–19 cm, are composed of poorly sorted conglomerate.
This subunit consists of heterolithic, densely packed, moderately sorted siltstone to coarse-grained heterolithic sandstone rich in quartz, feldspar, and sedimentary lithoclasts (mudstone) (Figure F24). The grains are cemented with a mixture of clay and calcite. There are minor amounts of mica, amphibole, and opaque minerals, as well as traces of glauconite pellets. Igneous (volcanic and plutonic) and metamorphic lithoclasts (quartzite) are rare. Alteration is pervasive, and most feldspar grains have been pseudomorphed by clay minerals. A cobble of slightly recrystallized granite was recovered in interval 19R-3, 13–28 cm, and is composed of quartz, feldspar, mica, and amphibole with traces of apatite and zircon.

A distinctive thick bed of dark brown clay-rich silty sandstone and clay-rich silty sandstone with gravel occurs in Sections 23R-2 (Figure F24) and 23R-3. This bed has a massive base and grades into gray silty sandstone with gravel in Section 23R-4. The fine-grained upper interval of the bed is poorly sorted with millimeter-sized feldspar grains in a fine-grained red clayey matrix.

The transition to Subunit IIIB is sharp and marked by a change from sandstone and sandstone with gravel to sandstone and sandstone with silt. Magnetic susceptibility decreases toward the base of Subunit IIIA.

<figure><img src="image_223.png" /><figcaption>Figure F23. A–D. Diverse lithologies of pebble- to cobble-sized clasts in Unit III sandstone.</figcaption></figure>

<figure><img src="image_224.png" /></figure>

## Subunit IIIB

Interval: 368-U1501D-25R-1, 9 cm, to 27R-4, 71 cm

Depth: 629.79–643.56 m

Age: pre-Eocene

Subunit IIIB consists of light gray, gray, and minor dark gray sandstone, sandstone with silt, and minor sandstone with organic matter (Figure F24). This subunit is different from Subunit IIIA in that it is finer grained overall and has finely laminated intervals. The average grain size is fine to very coarse sand, and the maximum grain size is as large as pebble sized. The sediment is very well to moderately sorted, but some intervals are poorly sorted because of pebbles. The pebble-sized clasts consist of felsic volcanic rocks and fine-grained quartzite. The bottom contacts of the beds are planar to erosional to gradational and subhorizontal to horizontal. The sandstone layers are massive or fine upward.

Interval 26R-3, 7–54 cm, has convolute lamination intercalated between planar laminated intervals that is interpreted as soft-sediment deformation. Some intervals of fine sandstone and siltstone have plane and ripple cross-lamination. However, most beds are fairly massive or show weak grading. A bituminous clast was recovered in Section 27R-1 (Figure F24).

# Discussion

## Depositional environment of Unit III

Unit III consists of poorly sorted, feldspar-rich, coarse-grained sandstone with pebbles or cobbles that is interbedded with light gray and gray to dark gray moderately to well-sorted medium- to fine-grained sandstone and rarely siltstone and poorly sorted conglomerate. Both massive bedding and fining-upward grading is common in the coarse-grained sandstone and conglomerate, whereas the relatively well sorted medium- to fine-grained sandstone intervals have thin parallel bedding. Finely rippled cross-lamination, convolute bedding, pyrite patches, and organic-rich laminae and lenses were found in the fine-grained interbeds. In addition, glauconite particles occur in some thin sections. No fossils were found. In general, we speculate that Unit III was formed in a terrestrial to littoral environment with a provenance not far from the site (Figure F25). The well-sorted sandstone with parallel to low-angle cross-lamination could have been formed by wave re-
Figure F24. Sandstone, Unit III. A. Subunit IIIA is dominated by gray coarse-grained sandstone rich in feldspar. B. Thin section image of heterolithic feldspar-rich sandstone showing rounded sedimentary, volcanic, and metamorphic (mica-bearing quartzite) lithic grains. Subunit IIIB is dominated by gray sandstone with (C) very thin laminae, (D) calcite clasts, and (E) bituminous clasts.

<figure><img src="image_225.png" /></figure>

working in a littoral environment. Overall, the downhole color change from more or less brownish to grayish rock and the decrease in average grain size may indicate a change to a deeper water environment.

## Transition between Units II and III

The boundary between Units II and III is in Core 368-U1501D-19R at around 598.91 m. The boundary separates the overlying greenish to dark greenish and less consolidated glauconite-bearing silty sand/sandstone of Unit II from the underlying dark brownish to gray and well-lithified sandstone with minor conglomerate and siltstone interbeds. The Unit II/III boundary is marked by an abrupt change in magnetic susceptibility, NGR, and P-wave velocity. In the seismic data, the boundary is tied to the acoustic basement (Tg), a high-amplitude reflector separating the overlying high-amplitude reflections in Unit II from the underlying low-amplitude reflections in Unit III (see Background and objectives).

We speculate if the Tg reflector between Units II and III might represent a boundary between possible early synrift (Paleocene?) deposits and the Eocene synrift sediments of Unit II or simply a hiatus between the Eocene synrift deposits of Unit II and a pre-Cenozoic basement (Unit III) (Shi et al., 2014; Dai et al., 2015). In the first case, Unit III could be similar to the Paleocene nonmarine sandstone and conglomerate successions common in the petroleum-bearing basins of eastern China. However, we found glauconite particles in the Unit III sandstone, which is commonly an indicator of marine environments (McRae, 1972; Wigley and Compton, 2007; Harris and Whiting, 2000). Most importantly, the sandstone in Unit

Figure F25. Preliminary model for deposition and sedimentary environments at Site U1501 showing deposition of prerift sediment and formation of the different units during and after rifting of the SCS.

<figure><img src="image_226.png" /></figure>

III is quite different from the overlying sand/sandstone in Unit II in terms of color, composition of clastic components, degree of lithification, and physical properties, including seismic velocity (see Physical properties). Therefore, we suggest the transition from Unit II to III represents a significant hiatus that formed in late Mesozoic to perhaps early Cenozoic time and that the sand-dominated terrigenous clastic rocks of Unit III represent a pre-Cenozoic basement succession. Regional geologic research (e.g., Yao et al., 1994; Zhou et al., 1995, 2006) indicates that in the late Mesozoic there was an active continental margin in eastern Asia, including the northern SCS margin, where the paleo-Pacific Ocean plate was subducted under the Eurasia plate. Therefore, the Unit II/III boundary could represent the transition from an active margin to a passive margin setting. Obviously, postexpedition research is needed to further constrain the age and nature of the boundary between Units II and III.

## Depositional environment of Unit II

Unit II most likely represents a gradual change from shallow-water (outer shelf or upper continental slope) to deepwater (lower slope) depositional environments (Figure F25). In general, the sediments of the lower part, including Subunits IIB–IIF, are dominated by terrigenous materials (quartz and clay minerals) and/or authigenic minerals (glauconite and calcite), with very rare calcareous nannofossils or foraminifer tests. Moreover, the glauconite (Figure F17) and large shell fragments become more common downhole and are even abundant in these subunits.

Glauconite is a clay- or mica-like mineral that usually forms from the absorption of potassium and iron by a degraded-layer sili-
cate lattice. Glauconite formation appears related to organic activity because grains are often found with decaying organic matter or the tests of marine organisms (McRae, 1972). Glauconite grains may form as clasts or fecal pellets or by accretionary growth, leading to a wide range of external morphologies (McRae, 1972). Glauconite clasts in Unit II have a range of morphologies from angular to well rounded and equant to more elongate. Some well-rounded glauconite grains occur mixed with subangular terrigenous quartz grains (Figure F17), suggesting that the rounded morphology is not a result of reworking but due to their formation as fecal pellets.

Modern deposits typically occur at low latitudes (temperatures ranging from 7° to 15°C) (Margielewski et al., 2017) and where there are low oxygen contents, mostly in the shelf to lower-slope environments from 20 to 700 mbsl (e.g., Drzewiecki and Simó, 2002; Margielewski et al., 2017) but also (less common) in anoxic and salty lake or marginal sea environments such as the Black Sea (Suttill, 2009). Glauconite forms where sedimentation rates are low and the formation can be stopped by rapid sedimentation. Glauconite grains are often associated with marine transgressions, unconformities, condensed sections, or transgressive systems tracts (McRae, 1972; Wigley and Compton, 2007; Harris and Whiting, 2000). However, because glauconite can form in a wide range of environments, it may not be a good tool for use in paleoenvironmental studies (McRae, 1972). Margielewski et al. (2017) found that glauconite grains are not destroyed when transported for short distances but break down to become part of the finer sediment fraction in high-energy environments. Glauconite grains could therefore be found in redeposited sediment sequences but only if mechanical abrasion and chemical destruction is limited.

A remarkably similar Tertiary sequence was described by Exon et al. (2002) for sites drilled during ODP Leg 189 offshore Tasmania. The glauconite-bearing silty claystone and clayey siltstone was deposited very slowly, representing a condensed sequence with sedimentation rates of <1 cm/ky. The comparable sediment at Site U1501 was deposited at an approximate rate of 2.5–3 cm/ky based on a preliminary shipboard age/depth curve. This rate is much greater than expected for a sediment-starved glauconite sand shelf and supports redeposition of the glauconite-bearing silts and sands in Subunits IIA, IIB, and IIF.

Subunit IID, between the calcite-rich sandstones of Subunits IIC and IIE, is different than other parts of Unit II and is characterized by alternating laminae of dark gray clayey silt with organic matter or lignite. The lack of marine fossils and authigenic glauconite and the frequent thin organic-rich laminae with pyrite and very fine grained clayey silt sediment likely indicate a very low sedimentation rate and a reducing, coastal brackish environment. A similar depositional environment was observed in a petroleum well of the eastern Pearl River Mouth Basin (Shao et al., 2016). Therefore, this unit may represent a temporary switch from shallow-marine environment to brackish facies.

The upper section of Unit II fines upward from sandy, silty, and clayey sediment in Subunit IIB to clayey sediment in Subunit IIA. This trend is accompanied by an upward increase in bioturbation intensity. The occurrence of a *Zoophycos* trace fossil assemblage in Subunit IIA indicates a moderate- to deepwater environment. We propose that this gradual transition is the result of a deepening of the basin. Benthic foraminifers from Subunit IIA suggest water depths of 300–800 m.

The coexistence of deepwater nannofossils and shallow-water shell and coral clasts suggests that the sediment was deposited by resedimentation processes. This idea is supported by the matrix-

supported texture of the sediment and structures such as fining-upward strata and cross-bedding. These features indicate that the sediment may have been deposited by turbidity currents (Figure F20). We interpret the sediment intervals with horizontal and ripple laminations in Unit II as representing the Tc and Td divisions of a Bouma sequence.

## Transition between Units I and II

The boundary between Units I and II is located at Section 368-U1501C-45X-1, 51 cm, and corresponds to a high-amplitude seismic unconformity. The boundary is dated at 24–27 Ma by the shipboard paleontologists based on foraminifer and nannofossil assemblages. We suggest this boundary can be correlated with the T60 unconformity at ODP Site 1148 (Li et al., 2005) (Figure F5). Above the boundary, Unit I is dominated by carbonate sediment, whereas Unit II is dominated by terrigenous material. The color of the sediment also varies abruptly from light brown in Unit I to dark and very dark greenish gray in Unit II.

## Depositional environment of Unit I

Unit I was deposited in a deep-marine environment (Figure F25). The dominant lithologies are clay-rich nannofossil ooze and nannofossil ooze with clay. There are variable amounts of foraminifers. Lithologic changes between subunits likely reflect the amount of terrigenous input into a relatively open ocean setting. This input may be delivered as buoyant plumes from shallower shelf environments and rarely by weak (distal) turbidity currents. There is little change in the composition of the terrigenous grains, so we envisage a similar source for these grains throughout Unit I. Thin laminae of silt are found rarely but throughout Unit I. Some are graded, and all have sharp bases; however, many are disrupted by bioturbation and are interpreted as distal turbidites.

Soft-sediment deformation in Subunit IB, including inclined and convolute bedding, indicates slumping downslope of parts of the sequence. Bedding above and below this interval is consistently horizontal, indicating the deformation was synsedimentary.

## Structural geology

Site U1501 is located on the OMH in a water depth of 2846 m. The southwest-northeast-oriented seismic profile (Figure F5) across the OMH reveals the occurrence of extensional structures controlled by steeply dipping southwest-normal faults with obvious offset and tilting of seismic reflectors (~5°). The T60 seismic unconformity is supposed to represent the Oligocene/Miocene boundary. Downsection, the Tg reflector may mark the base of the Cenozoic sediments (Pang et al., 2007). This site was considered a high-priority target to recover pre- (below Tg), syn-, and postrift sediments (see also **Background and objectives**).

### Lithostratigraphic Unit I structures

Lithostratigraphic Unit I, which essentially consists of nannofossil oozes, has predominantly horizontal to subhorizontal bedding that in most cases is erased due to moderate to strong bioturbation. This unit is devoid of any structures related to tectonic deformation, apart from some rare normal faults, such as the one observed in interval 368-U1501C-19F-1, 109–127 cm (Figure F26), which preserves a high-angle planar normal fault with an apparent dip of 65° and an offset of 6 cm. In addition, local soft-sediment deformation structures such as slump folds were observed in Subunits IB and IC.
## Lithostratigraphic Unit II structures

Lithostratigraphic Unit II is characterized by subhorizontal to gently dipping bedding. Dips as steep as 40° were locally observed in close relation to parallel lamination and therefore interpreted as cross-laminae (see Lithostratigraphy). In contrast to Unit I, deformation structures were observed within Unit II, although their occurrence is rather heterogeneously distributed. Subunit IIA is affected by millimeter-scale normal faults and joints, especially across Cores 368-U1501C-47X and 48X (Figure F27). In these cores, normal faults are typically planar to irregular with small apparent offsets as large as 0.5 cm and apparent dips of 10°–40°. They form semiregular arrays with millimeter- to centimeter-scale spacing, often arranged in an “en echelon” geometry (e.g., interval 47X-6, 126–129 cm). Striations and slickensides were observed locally where the surfaces of such structures are exposed. The occurrence of slickensides and the overall polished appearance of such planes are clear evidence for a natural deformation process. However, the recognition of these original deformation structures remains locally difficult due to drilling disturbances caused by the XCB and RCB coring systems. Deformation in the underlying Subunits IIC–IIF is essentially characterized by the variably distributed occurrence of single to branched uniform calcite and quartz veins (Figure F28).

## Lithostratigraphic Unit III structures

The prominent Tg reflector marks the top of lithostratigraphic Unit III, which is composed of lithified sandstone, sandstone with gravel, and minor conglomerate and laminated siltstone. This unit shows weak tilting of stratified beds expressed in apparent dips on split core surfaces as shallow as approximately 20°, which are best observed in the two last cores (368-U1501D-26R and 27R). Again, deformation structures remain scarce and heterogeneously distributed in Unit III. The recognized structures consist of veins, fractures, and local microfaults associated with cataclastic fault gouge. Locally structures associated with soft-sediment deformation are preserved. Single, branched, and en echelon uniform veins are filled by calcite or quartz (e.g., Cores 25R and 27R) (Figure F29). Planar and straight fractures were also observed with various dips from 40° to 55° showing locally striations and slickensides. In the sandstones, these fractures are often associated with alteration zones and filled by green fine-grained minerals likely resulting from diffusion-controlled chemical reactions between the matrix and a migrating reducing fluid (Figure F29A, F29D). Finally, slump folds were recovered in Core 26R (Figure F29F), providing evidence for soft-sediment deformation during mass movements.

## Interpretation

Despite the various tilting of seismic reflectors in the proximity of extensional structures, especially between the T60 seismic unconformity and the Tg reflector observed on the seismic profile (Figure F5), no evidence of significant bedding tilting and/or deformation structures was observed at this site. However, the observed millimeter-scale normal faults in Unit II may be related to an extensional event during or soon after its deposition. In seismic data, the top of Unit II describes a wedge geometry controlled by southwestern-dipping normal faults (Figure F5). The end of this extensional event may correspond to the marked decrease of terrigenous input and the transition from clays, silts, and sands in Unit II to clearly pelagic nannofossil oozes in Unit I. In line with lithostratigraphic observations and physical properties, the boundary between Units I and II is extremely sharp, reflecting a switch from bathyal marine depo-

<figure><img src="image_227.png" /><figcaption>Figure F27. Deformation structures, Subunits IIA and IIB. A. Millimeter-scale normal faults and fractures. B. En echelon millimeter-scale normal faults and fractures. C. Millimeter-scale normal fault offsetting black layers from about 5 mm within the nannofossil-rich clay. D. Slickenslide on an exposed polished fault surface.</figcaption></figure>

<figure><img src="image_228.png" /></figure>

sitional conditions in Subunit IIA to deep-sea depositional conditions in Unit I.

Unit III records a slight tilting compared to Units I and II, suggesting an unconformable relationship between them. This unit was likely deposited before the main Cenozoic rifting of the SCS continental margin. Despite relatively minor evidence for internal deformation, the tilting of beds, the soft-sediment deformations, and the nature of the lithostratigraphic succession may suggest that this unit was deposited during active tectonic processes. Mesozoic basins documented onshore (e.g., Nanni et al., 2017) may represent a possible analog for the tectonic setting during Unit III deposition.
<figure><img src="image_229.png" /><figcaption>Figure F29. Deformation structures, Unit III. A. Straight fracture associated with a green alteration pattern. B. Fine-grained cataclastic fault gouge developing along a straight fracture. C. Single uniform quartz vein. D. Straight fracture associated with an alteration zone. E. En echelon uniform calcite vein. F. Convolute bedding associated with centimeter-scale slump fold.</figcaption></figure>

<figure><img src="image_230.png" /></figure>

## Biostratigraphy

All core catcher samples at Site U1501 were analyzed for calcareous nannofossils, planktonic and benthic foraminifers, diatoms, and ostracods. Additional samples were taken from intervals in the working-half cores when necessary to refine the ages. Preservation of calcareous microfossils is good to very good in samples from Cores 368-U1501A-1H, 368-U1501B-1H, and 368-U1501C-1H through 44X and moderate to poor in Cores 368-U1501C-45X through 62X and 368-U1501D-2R through 5R. Samples 368-U1501A-1H-CC, 368-U1501B-1H-CC, and 368-U1501C-1H-CC and 2H-CC are composed of as much as 10% diatoms with moderate preservation, whereas other core catcher samples are rare or barren of diatoms (Table T4). Planktonic foraminifers and calcareous nannofossils are abundant in Cores 368-U1501A-1H, 368-U1501B-1H, and 368-U1501C-1H through 44X; rare to common in Cores 368-U1501C-45X through 62X and 368-U1501D-2R through 5R; and barren in Cores 368-U1501D-6R through 27R.

Forty biostratigraphic datums were identified in a generally continuous succession from the Holocene to the late Eocene (Tables T5, T6; Figure F30).

The Pleistocene/Pliocene boundary is placed within Core 368-U1501C-7H, the Pliocene/Miocene boundary is placed within Core 9H, the Miocene/Oligocene boundary is placed between Cores 41X and 42X, and the Oligocene/Eocene boundary is placed between Cores 53X and 54X. Sedimentation rates varied from ~13 mm/ky in the early Oligocene to ~11 mm/ky in the early-middle Miocene, ~14 mm/ky in the Pliocene, and 24 mm/ky in the Pleistocene. Sedimentation rates during the late Oligocene and late Miocene were much lower (~36 mm/ky), suggesting hiatuses may be present during these periods, whereas a relatively higher sedimentation rate (35 mm/ky) existed during the upper late Oligocene to the lower early Miocene.

Relatively higher abundances of benthic foraminifers with dominant shallow-water marker species in Cores 368-U1501C-45X through 62X and 368-U1501D-2R through 5R indicate an upper slope environment during the Eocene to early Oligocene, whereas there is a higher abundance of planktonic foraminifers above Core 368-U1501C-44X, suggesting a deep ocean environment since the late Oligocene.

## Calcareous nannofossils

Core catchers from Holes U1501A-U1501D were examined (Table T7). Calcareous nannofossil biostratigraphy for Site U1501 was based mainly on the analysis of all core catcher samples from Hole U1501C. To better constrain biostratigraphic events, a number of samples from intervals within cores were analyzed.

Calcareous nannofossils are very abundant and well preserved in the upper part of the succession (Cores 368-U1501C-1H through 45X). Nannofossils in samples below Section 46X-CC (321.81 m) generally degrade to low abundance and moderate preservation with intermittent abundance increases down to the bottom of Hole U1501C. In Cores 368-U1501D-2R through 5R, nannofossils are rare to common with moderate preservation. Nannofossils are barren below Section 6R-CC (471.99 m) to the bottom of Hole U1501D. Some of the samples from Hole U1501C exhibit signs of slight reworking, overgrowth, and fragmentation.

Twenty-four nannofossil biostratigraphic datums were recognized in the Oligocene through Pleistocene sediment sequence at Site U1501 (Table T5). The oldest nannofossil event identified at Site U1501 is the last appearance datum (LAD) of *Coccolithus for-
mosus at 379.64 m (Sample 368-U1501C-52X-CC), which indicates an age older than 32.92 Ma.

## Pleistocene

The top of Hole U1501C (Samples 1H-CC to 2H-CC; 0–17.98 m) is dated as late Pleistocene based on the presence of *Emiliania huxleyi* (marker species for Zone NN21). The LAD of *Pseudoemiliania lacunosa* in Sample 3H-CC (28.56 m) defines the top of

<table><caption>Table T4. Distribution of diatom species, Site U1501. **View table in PDF format. Download table in CSV format.**</caption><thead><tr><th rowspan="2">Epoch</th><th rowspan="2"></th><th rowspan="2">Biozone (Martini, 1971)</th><th rowspan="2">Calcareous nannofossil event</th><th colspan="2">Top</th><th colspan="2">Bottom</th><th colspan="2">Age model</th></tr><tr><th>Core, section</th><th>Depth CSF-A (m)</th><th>Core, section</th><th>Depth CSF-A (m)</th><th>Depth (m)</th><th>Age (Ma)</th></tr></thead><tbody><tr><td rowspan="4">Pleistocene</td><td rowspan="4"></td><td>NN21</td><td>B Emiliania huxleyi</td><td>368-U1501C-2H-CC</td><td>17.98</td><td>368-U1501C-3H-CC</td><td>28.56</td><td>23.27</td><td>0.29</td></tr><tr><td rowspan="3">NN19</td><td>T Pseudoemiliania lacunosa</td><td>2H-CC</td><td>17.98</td><td>3H-CC</td><td>28.56</td><td>23.27</td><td>0.44</td></tr><tr><td>T Gephyrocapsa spp. &gt;5.5 µm</td><td>3H-CC</td><td>28.56</td><td>4H-CC</td><td>38.08</td><td>33.32</td><td>1.24</td></tr><tr><td>T Calcidiscus macintyrei</td><td>4H-CC</td><td>38.08</td><td>5H-CC</td><td>46.95</td><td>42.52</td><td>1.60</td></tr><tr><td rowspan="2">NN18</td><td rowspan="2"></td><td>T Discoaster brouweri</td><td>5H-CC</td><td>46.95</td><td>6H-CC</td><td>57.07</td><td>52.01</td><td>1.93</td></tr><tr><td>T Discoaster tamalis</td><td>6H-CC</td><td>57.07</td><td>7H-CC</td><td>66.22</td><td>61.65</td><td>2.80</td></tr><tr><td rowspan="2">NN16</td><td rowspan="2"></td><td>T Sphenolithus spp.</td><td>7H-CC</td><td>66.22</td><td>8H-CC</td><td>75.81</td><td>71.02</td><td>3.54</td></tr><tr><td>T Discoaster quinqueramus</td><td>8H-CC</td><td>75.81</td><td>9H-CC</td><td>85.50</td><td>80.66</td><td>5.59</td></tr><tr><td rowspan="10">Miocene</td><td rowspan="3">late</td><td>NN11</td><td>B Discoaster berggrenii</td><td>10H-CC</td><td>94.91</td><td>11H-CC</td><td>104.91</td><td>99.91</td><td>8.29</td></tr><tr><td>NN11</td><td>B Catinaster coalitus</td><td>11H-CC</td><td>104.91</td><td>12H-CC</td><td>113.97</td><td>109.44</td><td>10.89</td></tr><tr><td>NN8</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td rowspan="4">middle</td><td>NN7</td><td>T Discoaster kugleri</td><td>13H-CC</td><td>123.83</td><td>14H-CC</td><td>131.53</td><td>127.68</td><td>11.58</td></tr><tr><td>NN6</td><td>T Cyclicargolithus floridanus</td><td>14H-CC</td><td>131.53</td><td>15H-CC</td><td>142.19</td><td>136.86</td><td>11.85</td></tr><tr><td>NN5</td><td>T Sphenolithus heteromorphus</td><td>15H-CC</td><td>142.19</td><td>16H-CC</td><td>151.80</td><td>147.00</td><td>13.53</td></tr><tr><td>NN4</td><td>T Helicosphaera ampliaperta</td><td>21F-CC</td><td>175.97</td><td>22F-CC</td><td>180.60</td><td>178.29</td><td>14.91</td></tr><tr><td rowspan="4">early</td><td rowspan="4"></td><td>NN2</td><td>T Triquetrorhabdulus carinatus</td><td>23F-CC</td><td>184.45</td><td>24F-CC</td><td>189.47</td><td>186.96</td><td>18.28</td></tr><tr><td></td><td>B Sphenolithus belemnos</td><td>26F-CC</td><td>198.38</td><td>27F-CC</td><td>204.08</td><td>201.23</td><td>19.03</td></tr><tr><td></td><td>B Helicosphaera ampliaperta</td><td>27F-CC</td><td>204.08</td><td>28F-CC</td><td>208.70</td><td>206.39</td><td>20.43</td></tr><tr><td></td><td>B Sphenolithus disbelemnos</td><td>40X-CC</td><td>265.35</td><td>41X-CC</td><td>273.91</td><td>269.63</td><td>22.76</td></tr><tr><td rowspan="6">Oligocene</td><td rowspan="6"></td><td>NN1</td><td>T Sphenolithus delphix</td><td>41X-CC</td><td>273.91</td><td>42X-CC</td><td>283.46</td><td>278.69</td><td>23.11</td></tr><tr><td>NP25</td><td>T Sphenolithus ciperoensis</td><td>43X-CC</td><td>293.15</td><td>44X-CC</td><td>302.56</td><td>297.86</td><td>24.43</td></tr><tr><td>NP24</td><td>T Sphenolithus predistentus</td><td>44X-CC</td><td>302.56</td><td>45X-CC</td><td>312.20</td><td>307.38</td><td>26.93</td></tr><tr><td>NP24</td><td>B Sphenolithus ciperoensis</td><td>45X-CC</td><td>312.20</td><td>46X-CC</td><td>321.81</td><td>317.01</td><td>29.62</td></tr><tr><td>NP22</td><td>T Reticulofenestra umbilicus</td><td>48X-CC</td><td>340.46</td><td>49X-CC</td><td>350.49</td><td>345.48</td><td>32.02</td></tr><tr><td>NP21</td><td>T Coccolithus formosus</td><td>51X-CC</td><td>369.98</td><td>52X-CC</td><td>379.64</td><td>374.81</td><td>32.92</td></tr></tbody></table>

<caption>Table T5. Calcareous nannofossil biostratigraphic events, Site U1501. T = top/last appearance datum, B = bottom/first appearance datum. **Download table in CSV format.**</caption>

<table><caption>Table T6. Planktonic foraminifer events, Site U1501. T = top/last appearance datum, B = bottom/first appearance datum, Bc = bottom/first common appearance datum (acme). **Download table in CSV format.**</caption><thead><tr><th rowspan="2">Epoch</th><th rowspan="2">Biozone (Blow, 1969)</th><th rowspan="2">Events</th><th colspan="2">Top</th><th colspan="2">Bottom</th><th colspan="2">Age model</th></tr><tr><th>Core, section</th><th>Depth CSF-A (m)</th><th>Core, section</th><th>Depth CSF-A (m)</th><th>Depth (m)</th><th>Age (Ma)</th></tr></thead><tbody><tr><td rowspan="4">Pleistocene</td><td>N22</td><td>T Globigerinoides ruber (pink)</td><td>368-U1501C-1H-CC</td><td>9.24</td><td>368-U1501C-2H-CC</td><td>17.98</td><td>13.61</td><td>0.12</td></tr><tr><td>N22</td><td>Bc Globigerinoides ruber (pink)</td><td>2H-CC</td><td>17.98</td><td>3H-CC</td><td>28.56</td><td>23.27</td><td>0.40</td></tr><tr><td>N22</td><td>T Globigerinoides fistulosus</td><td>4H-CC</td><td>38.08</td><td>5H-CC</td><td>46.95</td><td>42.52</td><td>1.88</td></tr><tr><td>N20-N21</td><td>T Globorotalia multicamerata</td><td>5H-CC</td><td>46.95</td><td>6H-CC</td><td>57.07</td><td>52.01</td><td>2.18</td></tr><tr><td rowspan="2">Pliocene</td><td>N20-N21</td><td>T Dentoglobrina altispira</td><td>7H-CC</td><td>66.22</td><td>8H-CC</td><td>75.81</td><td>71.02</td><td>3.47</td></tr><tr><td>N19</td><td>T Globoturborotalita nepenthes</td><td>8H-CC</td><td>75.81</td><td>9H-CC</td><td>85.05</td><td>80.66</td><td>4.37</td></tr><tr><td rowspan="6">Miocene</td><td>N17</td><td>T Globoquadrina dehiscens</td><td>10H-CC</td><td>94.91</td><td>11H-CC</td><td>104.91</td><td>99.91</td><td>5.92</td></tr><tr><td>N12</td><td>T Fohsella fohsi</td><td>12H-CC</td><td>113.48</td><td>13H-CC</td><td>123.83</td><td>118.66</td><td>11.79</td></tr><tr><td>N8</td><td>B Praeorbulina sicana</td><td>22F-CC</td><td>180.60</td><td>23F-CC</td><td>184.45</td><td>182.53</td><td>16.38</td></tr><tr><td>N6</td><td>T Catapsydrax dissimilis</td><td>24F-CC</td><td>189.47</td><td>25F-CC</td><td>193.35</td><td>191.41</td><td>17.54</td></tr><tr><td>N5</td><td>T Globoquadrina binaiensis</td><td>27F-CC</td><td>204.08</td><td>28F-CC</td><td>208.70</td><td>206.39</td><td>19.09</td></tr><tr><td>N4</td><td>T Paragloborotalia kugleri</td><td>32F-CC</td><td>226.47</td><td>33F-CC</td><td>231.83</td><td>229.15</td><td>21.12</td></tr><tr><td rowspan="3">Oligocene</td><td>N4</td><td>T Globigerina ciperoensis</td><td>40X-CC</td><td>265.35</td><td>41X-CC</td><td>273.91</td><td>269.63</td><td>22.90</td></tr><tr><td>P21</td><td>T Paragloborotalia opima</td><td>43X-CC</td><td>293.15</td><td>44X-CC</td><td>302.56</td><td>297.86</td><td>26.93</td></tr><tr><td>P19</td><td>T Turborotalia ampliapertura</td><td>46X-CC</td><td>321.81</td><td>47X-CC</td><td>331.18</td><td>326.50</td><td>30.28</td></tr><tr><td>Eocene</td><td>P18</td><td>T Globigerinatheka subconglobata</td><td>53X-CC</td><td>385.33</td><td>54X-CC</td><td>398.79</td><td>392.06</td><td>33.89</td></tr></tbody></table>
<figure><img src="image_231.png" /><figcaption>Figure F30. Age-depth model, Site U1501. Plotted event data are in Tables T6, T7, and T13 (see Paleomagnetism; Figure F40).</figcaption></figure>

m). The Miocene/Pliocene boundary in Hole U1501C is placed between Samples 8H-CC (75.81 m) and 9H-CC (85.5 m) based on the LADs of *Sphenolithus* spp. (3.54 Ma) and *Discoaster quinqueramus* (5.59 Ma), respectively.

## Miocene

Three events occur in the upper Miocene strata of Hole U1501C. The top of Zone NN11 is defined by the LAD of *D. quin-

*queramus* (5.59 Ma) in Sample 9H-CC (85.5 m). The first appearance datum (FAD) of *Discoaster berggrenii* (8.29 Ma) was found in Sample 10H-CC (94.91 m). The FAD of *Catinaster coalitus* was used to mark the base of Zone NN8 (10.89 Ma) in Sample 11H-CC (104.91 m). The late/middle Miocene boundary in Hole U1501C was assigned between Samples 11H-CC (104.91 m) and 14H-CC (131.53 m) based on the FAD of *C. coalitus* (10.89 Ma) and the LAD of *Discoaster kugleri* (11.58 Ma), respectively.
Table T7. Nannofossil abundance, Site U1501. **View table in PDF format. Download table in CSV format.**

Four events occur in the middle Miocene strata of Hole U1501C. The LAD of *D. kugleri* (11.58 Ma) within Zone NN7 occurs in Sample 14H-CC (131.53 m). The top of Zone NN6 is marked by the LAD of *Cyclicargolithus floridanus* (11.85 Ma) in Sample 15H-CC (142.19 m). The top of Zone NN5 is marked by the LAD of *Sphenolithus heteromorphus* (13.53 Ma) in Sample 16H-CC (151.8 m). The top of Zone NN4 is defined by the LAD of *Helicosphaera ampliaperta* (14.91 Ma) in Sample 22F-CC (180.6 m). The middle/early Miocene boundary was assigned between Samples 22F-CC (180.6 m) and 24F-CC (189.47 m).

Four events occur in the lower Miocene strata of Hole U1501C. The top of Zone NN2 is marked by the LAD of *Triquetrorhabdulus carinatus* (18.28 Ma) in Sample 24F-CC (189.47 m). The bottom of Zone NN2 is approximated by the FAD of *Sphenolithus disbelemnos* (22.76 Ma) in Sample 40X-CC (265.35 m). Two additional events were found in Zone NN2: the FAD of *Sphenolithus belemnos* (19.03 Ma) in Sample 26F-CC (198.38 m) and the FAD of *H. ampliaperta* (20.43 Ma) in Sample 27F-CC (204.08 m). The Miocene/Oligocene boundary was assigned between Samples 40X-CC (265.35 m) and 42X-CC (283.46 m) based on the FAD of *S. disbelemnos* (22.76 Ma) and the LAD of *Sphenolithus delphix* (23.11 Ma), respectively.

## Oligocene

Six events were identified in the Oligocene strata of Hole U1501C. The LAD of *S. delphix* (23.11 Ma) within Zone NN1 occurs in Sample 42X-CC (283.46 m), the LAD of *Sphenolithus ciperoensis* (24.43 Ma) within Zone NP25 occurs in Sample 44X-CC (302.56 m), and the LAD of *Sphenolithus predistentus* (26.93 Ma) and FAD of *S. ciperoensis* (29.62 Ma) within Zone NP24 occur in Sample 45X-CC (312.2 m). The top of Zone NP22 is marked by the LAD of *Reticulofenestra umbilicus* (32.02 Ma) in Sample 49X-CC (350.49 m). The top of Zone NP21 is marked by the LAD of *C. formosus* (32.92 Ma) in Sample 52X-CC (379.64 m).

From Sample 52X-CC (379.64 m) to the bottom of Hole U1501C (Sample 62X-CC, 457.83 m), the nannofossil assemblage includes *Chiasmolithus altus*, *C. formosus*, *Discoaster nodifer*, *Discoaster tani*, *Discoaster williamsii*, *Helicosphaera bramlettei*, *Helicosphaera recta*, *Helicosphaera compacta*, *Lanternithus minutus*, *Pontosphaera exilis*, *Pontosphaera punctosa*, *Reticulofenestra circus*, *Reticulofenestra*, *R. umbilicus*, *Reticulofenestra erbae*, and *Reticulofenestra lockeri*. Such a nannofossil assemblage indicates a late Eocene age for the base of Hole U1501C.

The nannofossil assemblages in Cores 368-U1501D-2R through 5R are similar to those in samples from the bottom part of Hole U1501C, so they were also assigned to the late Eocene. Nannofossils are barren from Sample 6R-CC (471.99 m) to the bottom of Hole U1501D, so we cannot determine the age of these samples.

## Planktonic foraminifers

All core catcher samples and several additional samples from the split cores in Holes U1501A–U1501D were processed for planktonic foraminiferal analyses (Table T8). Planktonic foraminifers are well preserved and abundant for samples from Cores 368-U1501A-1H, 368-U1501B-1H, and 368-U1501C-1H through 44X and moderate to poorly preserved or even recrystallized and less abundant in Cores 368-U1501C-45X through 62X.

Table T8. Distribution of planktonic foraminifers, Site U1501. **View table in PDF format. Download table in CSV format.**

Only one core was drilled in Holes U1501A and U1501B. Abundant pink *Globigerinoides ruber* specimens were observed in the core catcher samples, indicating an age between 0.12 and 0.4 Ma for the bottom of these two holes. No planktonic foraminifer was observed in Hole U1501D.

Sixteen planktonic foraminiferal datums were recognized in Hole U1501C, spanning the late Eocene (<37.75 Ma) to the late Pleistocene (Plate P1; Table T6). The planktonic foraminiferal biostratigraphy for Hole U1501C was established by these events and the planktonic foraminiferal assemblages at successive depth intervals.

The Pleistocene planktonic foraminifers are composed of *G. ruber*, *Globigerinoides sacculifer*, *Globorotalia menardii*, *Pulleniatina obliquiloculata*, and *Neogloboquadrina dutertrei*. The LAD of pink *G. ruber* (0.12 Ma) and FAD of pink *G. ruber* acme (0.40 Ma) are placed between Samples 1H-CC and 2H-CC and Samples 2H-CC and 3H-CC, respectively. The LAD of *Globigerinoides fistulosus* (1.88 Ma) is located between Samples 4H-CC and 5H-CC and marks the Zone N22/N21 boundary. The LAD of *Globorotalia multicamerata* (2.18 Ma) is located between Samples 5H-CC and 6H-CC.

The Pliocene planktonic foraminiferal assemblage is characterized by the higher content of *Dentoglobigerina altspira* and *Sphaeroidinellopsis seminulina*. The LAD of *D. altspira* (3.47 Ma) is located between Samples 7H-CC and 8H-CC. The LAD of *Globoburotalita nepenthes* (4.37 Ma) is located between Samples 8H-CC and 9H-CC and defines the Zone N20/N19 boundary.

The middle-late Miocene foraminiferal assemblage is dominated by *D. altspira*, *Globoquadrina dehiscens*, and *Praeorbulina circularis/glomerosa*. The LAD of *G. dehiscens* (5.92 Ma) is located between Samples 10H-CC and 11H-CC and defines the boundary of Zones N18/N17. The LAD of *Fohsella fohsi* (11.79 Ma) is located between Samples 12H-CC and 13H-CC and defines the boundary of Zones N13/N12. The FAD of *Praeorbulina sicana* (16.38 Ma) is located between Samples 22F-CC and 23F-CC and marks the boundary of Zones N8/N7.

The late Oligocene-early Miocene planktonic foraminifers are characterized by *G. dehiscens*, *Globoquadrina venezuelana*, and *Paragloborotalia mayeri*. The LAD of *Catapsydrax dissimilis* (17.54 Ma) is located between Samples 24F-CC and 25F-CC and defines the boundary of Zones N7/N6. The LAD of *Globoquadrina binaiensis* (19.09 Ma) is located between Samples 27F-CC and 28F-CC. The LAD of *Paragloborotalia kugleri* (21.12 Ma) is located between Samples 32F-CC and 33F-CC as the boundary of Zones N5/N4. The LAD of *Globigerina ciperoensis* (22.90 Ma) is located between Samples 40X-CC and 41X-CC and represents the Miocene/Oligocene boundary.

Compared to the large planktonic foraminiferal components during the late Oligocene-early Miocene, the early Oligocene planktonic foraminifers are characterized by small *Paragloborotalia nana* and *Paragloborotalia opima*. The LAD of *P. opima* (26.93 Ma) is located between Samples 43X-CC and 44X-CC as the boundary of Zones P22/P21. The LAD of *Turborotalia ampliapertura* (30.28 Ma) is located between Samples 46X-CC and 47X-CC as the boundary of Zones P20/P19.
<figure><img src="image_232.png" /><figcaption>Plate P1. Principal planktonic foraminifers from Hole U1501C used in biostratigraphy analyses for Site U1501. 1: optical; 2–14: SEM. Scale bar = 100 µm. 1. *Globigerinoides ruber* pink (1H-CC). 2. *Globigerinoides fistulosus* (5H-CC). 3. *Globorotalia multicamerata* (7H-CC). 4. *Dentoglobigerina altispira* (9H-CC). 5. *Globroturborotalita nepenthes* (8H-CC). 6. *Globoquadrina dehiscens* (11H-CC). 7. *Fohsella fohsi* (15H-CC). 8. *Praeorbulina sicana* (23F-CC). 9. *Catapsydrax dissimilis* (26F-CC). 10. *Globoquadrina binaiensis* (28H-CC). 11. *Paragloborotalia kugleri* (32F-CC). 12. *Globigerina ciperoensis* (51X-CC). 13. *Paragloborotalia opima* (44X-CC). 14. *Globigerinatheka subconglobata* (54X-CC).</figcaption></figure>

In Sample 54X-CC, late Eocene planktonic foraminiferal com-
ponents such as *Globigerinatheka subconglobata* and *Globigeri-
natheka index rubriformis* were observed, suggesting a late Eocene
age. Because of the low abundance and poor preservation of the
planktonic foraminifers in Samples 368-U1501C-55X-CC to 62X-
CC and their absence from Samples 368-U1501D-2R-CC to 27R-
CC, a definite age for the lowest part of Holes U1501C and U1501D
could not be determined.

Benthic foraminifers

Benthic foraminifers in Samples 368-U1501C-41X-CC to 62X-
CC and 368-U1501D-2R-CC to 4R-CC were counted (~300 random
specimens) from the >150 µm size fraction (Figure F31). Benthic
foraminifers are abundant in Samples 368-U1501C-46X-CC and
368-U1501D-4R-CC and are more abundant than planktonic fora-
minifers in samples deeper than Sample 368-U1501C-54X-CC. Bu-
limina spp., Melonis spp., Cibicidoides spp., Lenticulina spp., and
some agglutinated benthic foraminifers were observed in these
samples. From the planktonic foraminifer/total foraminifer ratios, it

is inferred that the paleoenvironment at this site changed from shelf
(Samples 368-U1501C-54X-CC and 368-U1501D-4R-CC) to upper
slope (Samples U1501C-46X-CC to 53X-CC) and then to deep sea
(Samples 41X-CC to 45X-CC), clearly indicating an increasing wa-
ter depth.

Diatoms

Core catcher samples from Holes U1501A–U1501D were pro-
cessed into smear and strewn slides for diatom analysis. An addi-
tional 21 toothpick samples were taken from selected intervals of
the working-half cores for better resolution. Samples 368-U1501A-
1H-CC, 368-U1501B-1H-CC, and 368-U1501C-1H-CC and 2H-CC
are composed of as much as 10% diatoms with moderate preserva-
tion. Smear slides from Samples 368-U1501C-3H-CC, 4H-CC, 35F-
CC, 45X-CC, and 46X-CC contain <1% diatoms with poor preser-
vation. The rest of the core catcher samples from Cores 368-
U1501C-5H through 62X and 368-U1501D-2R through 27R are
barren of diatoms (Table T4).
<figure><img src="image_233.png" /><figcaption>Figure F31. Statistics of benthic foraminifers (368-U1501C-41X-CC to 62X-CC and 368-U1501D-2R-CC to 4R-CC). B = barren, P = present, R = rare, F = few, A = abundant, D = dominant.</figcaption></figure>

Toothpick samples of burrows in the working-half sections of Holes U1501C and U1501D were found to contain between 0% and 60% diatoms with poor to moderate preservations. Samples 368-U1501A-1H-CC, 368-U1501B-1H-CC, and 368-U1501C-1H-CC and 2H-CC contain a few specimens of *Fragilariopsis doliolus*, indicating an age of 2.0–0.6 Ma. A smear slide of a partially pyritized burrow in Sample 368-U1501C-35F-1, 118 cm, contains a few specimens of *Azpetia bukryi* with *Cestodiscus trochus* commonly observed, indicating an age range between 20.8 and 30.8 Ma (Table T9).

## Ostracods

A preliminary examination of ostracods was conducted in core catcher samples from Holes U1501C and U1501D (Table T10) to characterize the assemblage variability through time and to reconstruct paleoenvironmental changes throughout the Cenozoic. Ostracod abundance ranges from absent to >60 valves per sample, and preservation varies from good (mostly in the Pleistocene section) to poor, although most specimens are moderately preserved. The highest incidences of ostracods were observed in Samples 368-U1501C-10H-CC to 16H-CC (94–151 m), 27F-CC to 31F-CC (204–221 m), 40X-CC to 43X-CC (265–293 m), and in particular Samples

49X-CC to 51X-CC (350.44–369.9 m) and 60X-CC (447.92 m). In Hole U1501D, ostracods are only present in Samples 2R-CC to 6R-CC.

In Hole U1501C, lower bathyal to abyssal genera (*Krithe*, *Legitimocythere*, *Henryhowella*, *Bradleya*, *Abyssocythereis*, *Argilloecia*, *Pennyella*, *Poseidonamicus*, *Pelecocythere*, *Arcacythere*, *Cytheropteron*, *Eucythere*, *Abyssocythere*, and *Parakrithe*) dominate the Oligocene through Pleistocene assemblage, indicating that deepwater conditions have existed in the SCS since the early Oligocene. Below 349 m (Sample 50X-CC, 40–45 cm, estimated to be of late Eocene age), the assemblage is characterized by upper bathyal and continental shelf taxa (e.g., *Heinia*, *Cytheropteron*, *Xestoleberis*, *Abrocythereis*, *Neomonoceratina*, *Trachyleberis*, *Cytherelloidea*, and *Cytherella*), although deep-sea genus *Krithe* remains present. In Hole U1501D, Samples 2R-2, 111–114 cm, and 4R-CC to 6R-CC (estimated to be middle to late Eocene in age) are composed of *Paranesidea* sp., *Cytherelloidea* cf. *Cytherelloidea asatoensis* Nohara, *Coquimba* sp., *Schizocythere?* sp., and *Paijenborchella sinensis*, among others. Paleocologically, the absence of abyssal to upper bathyal or brackish water taxa in the assemblage indicates a shallow-marine environment (Plates P2, P3).
<table><caption>Table T9. Diatom biostratigraphic events, Site U1501. T = top/last appearance datum, B = bottom/first appearance datum. Download table in CSV format.</caption><thead><tr><th rowspan="2">Epoch</th><th rowspan="2">Biozone<br>(Scherer et al., 2007)</th><th rowspan="2">Diatom event</th><th colspan="2">Top</th><th colspan="2">Bottom</th><th rowspan="2">Age model range<br>(Ma)</th></tr><tr><th>Core, section</th><th>Depth CSF-A<br>(m)</th><th>Core, section,<br>interval (cm)</th><th>Depth CSF-A<br>(m)</th></tr></thead><tbody><tr><td>Pleistocene</td><td>Fragilariopsis<br>reinholdii</td><td>T Fragilariopsis reinholdii and<br>B Fragilariopsis doliolus</td><td>1H-CC</td><td>9.05</td><td>3H-CC</td><td>28.56</td><td>2.01-0.61</td></tr><tr><td>Pliocene</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>late Miocene</td><td></td><td></td><td colspan="4" style="text-align: center;">Barren</td><td></td></tr><tr><td>middle Miocene</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>early Miocene</td><td>Rossiella paleacea-<br>Rocella vigilans</td><td>T Cestodiscus trochus<br>B Azpetia bukryi</td><td>34F-CC</td><td>234.45</td><td>35F-1, 118</td><td>237.88</td><td>20.8-30.8</td></tr><tr><td>Oligocene</td><td></td><td></td><td colspan="4" style="text-align: center;">Barren</td><td></td></tr><tr><td>Eocene</td><td></td><td></td><td colspan="4"></td><td></td></tr></tbody></table>

<caption>Table T10. Distribution of ostracods, Holes U1501C and U1501D. View table in PDF format. Download table in CSV format.</caption>

Plate P2. Representative Miocene to Pleistocene abyssal ostracods, Hole U1501C. 1. *Henryhowella* sp. (1H-CC). 2. *Legitimocythere* sp. (1H-CC). 3. *Krithe* sp. (3H-CC). 4. *Poseidonamicus* cf. *Poseidonamicus* pintoi Benson, 1972 (6H-CC). 5. *Pennyella* sp. (12H-CC). 6. *Cytheropteron* cf. *Cytheropteron* uchioi Hanai, 1957 (13H-CC). 7. *Bradleya* cf. *Bradleya* metamorphica Whatley et al. (14H-CC). 8. *Arcacythere* sp. (43X-CC).

<figure><img src="image_234.png" /></figure>

Plate P3. Representative late Eocene shallow-water marine ostracods, Hole U1501D. 1. *Cytherelloidea* sp. C (4R-CC). 2. *Cytherelloidea* cf. *Cytherelloidea* asatoensis Nohara (4R-CC). 3. *Schizocythere?* sp. (4R-CC). 4. *Paijenborchella sinensis* (Liu, 1989) (4R-CC). 5. *Paranesidea* sp. (4R-CC). 6. *Coquimba* sp. (4R-CC).

<figure><img src="image_235.png" /></figure>
# Paleomagnetism
## Shipboard measurements

Shipboard paleomagnetic investigations combined three complementary approaches (see **Paleomagnetism** in the Expedition 367/368 methods chapter [Sun et al., 2018a]): (1) measurement and in-line AF demagnetization of archive-half sections on the pass-through 2G Enterprises SRM, (2) measurement and thermal demagnetization of oriented discrete samples on the SRM, and (3) measurement and AF demagnetization of oriented discrete samples on the spinner magnetometer (Agico JR-6A). Representative discrete samples were collected from every two sections (3 m), except where drilling disturbance was high or where core recovery was low.

First, we used scalar data from AF demagnetization up to 50 mT and thermal demagnetization on discrete samples to constrain the nature of the magnetic assemblage. Second, we used the directional and intensity data of archive-half sections, measured after the highest in-line AF demagnetization step (25 mT), to determine magnetic polarity along the core. Third, we used the directional and intensity data from discrete samples to validate the polarities inferred from section measurements. Directional data were analyzed using Zijderveld diagrams (Zijderveld, 1967), and the characteristic remanent magnetization (ChRM) direction(s) were calculated by principal component analysis (PCA) (Kirschvink, 1980) using the software PuffinPlot (version 1.03, 23 April, 2015) (Lurcock and Wilson, 2012).

## Demagnetization behavior and implications for magnetic assemblages

Stepwise demagnetization of the NRM shows that 91% of analyzed samples lost the bulk of their magnetic remanence between 200° and 300°C. For all steps of thermal demagnetization, the cumulative behavior of all samples was analyzed (each sample having the same statistical weight). The loss of remanent magnetization was normalized to NRM and expressed as a percentage (Figure F32). This behavior shows that one or several phases with low $T_C$, such as pyrrhotite ($T_C$ ≈ 325°C; Tauxe, 2010) or greigite ($T_C$ ≈ 330°C; Tauxe, 2010), dominate the NRM. High SIRM/χ ratios are widely considered characteristic of greigite in sediments (e.g., Snowball, 1991; Roberts, 1995; Roberts et al., 2011). The rock magnetic experiments on six representative samples from Hole U1501C (Table T11), after magnetic saturation at 2.3 T, show SIRM/χ between 12.8 and 14.6 kA/m. These values rule out pyrrhotite and confirm the predominance of greigite in lithostratigraphic Unit I of Hole U1501C. Using a rare-earth magnet on a slurry from Section 368-U1501A-1H-CC (PAL), greigite was separated and concentrated. The grains observed with an optical binocular microscope are subhedral, pale yellow, partially corroded metallic cubes (≤10 µm in length). These grains, documented with SEM (Figure F33), have physical sizes in the 2–10 µm range, which corresponds to pseudosingle to multidomain magnetic grain sizes (Roberts et al., 2011). Overall, thermal demagnetization behaviors suggest that greigite dominates the NRM, at least to 83 m. However, the magnetic remanence remaining above 575°C (Figure F34) strongly suggests contributions from additional phases such as maghemite ($T_C$ ≈ 590°–675°C; Tauxe, 2010) or hematite ($T_C$ ≈ 675°C; Tauxe, 2010). The NRM remaining above 575°C increases notably in the 50–85 m interval in Hole U1501C. The maximum field strength of in-line AF demagnetization used on the archive-half sections is limited because of the destructive

Figure F32. Percentage of NRM loss between stepwise thermal demagnetization of NRM as a function of demagnetization temperature. Magnetization normalized to NRM (78 samples from Hole U1501C) carry the same statistical weight. Samples from Holes U1501A and U1501B were excluded to avoid statistically over representing the upper part of Unit I. Most magnetization is lost between 200° and 300°C, which shows that either greigite or pyrrhotite carry the NRM.

<figure><img src="image_236.png" /><figcaption>Table T11. Rock magnetic properties of representative samples, Hole U1501C. Download table in CSV format.</figcaption></figure>

<table><thead><tr><th>Core, section, interval (cm)</th><th>SIRM<sub>2.3T</sub> (A/m)</th><th>χ (10<sup>-6</sup>), at 300 A/m</th><th>SIRM/χ (kA/m)</th></tr></thead><tbody><tr><td>368-U1501C-3H-7, 30-32</td><td>4.91</td><td>338</td><td>14.6</td></tr><tr><td>4H-1, 36-38</td><td>6.53</td><td>462</td><td>14.1</td></tr><tr><td>4H-5, 27-29</td><td>4.87</td><td>345</td><td>14.1</td></tr><tr><td>6H-3, 26-28</td><td>5.03</td><td>362</td><td>13.9</td></tr><tr><td>7H-3, 30-32</td><td>5.32</td><td>416</td><td>12.8</td></tr><tr><td>8H-2, 90-92</td><td>4.33</td><td>313</td><td>13.8</td></tr></tbody></table>

nature of the treatments and our limited ability to measure weak magnetizations in the magnetically noisy shipboard environment. To evaluate the effectiveness of AF demagnetization of the NRM, experiments were performed on six discrete samples from Hole U1501C (Table T11). These experiments reveal the existence of a high-coercivity phase characterized by self-reversal behavior (Figure F35). This self-reversal behavior is typical of greigite (Krs et al., 1992; Horng et al., 1998) and has recently been reported in Pleistocene sediments of the South Yellow Sea (Liu et al., 2014).

Typical behaviors of demagnetization from the three complementary approaches are shown in Figure F36. AF demagnetization of these samples with in-line AF produces demagnetization paths that are easier to interpret than the results of discrete samples subjected to AF demagnetization. Both AF and thermal treatments on discrete samples effectively remove a steep low-temperature/low-coercivity component, which represents the drilling overprint. However, thermal demagnetization is more effective at isolating ChRM, as evident by comparing results from twin samples collected from the same core and section (e.g., Figure F36C). The mean inclination gathered from the high-temperature component is 37.3° ± 6.6°, corresponding to a paleolatitude of 20.85° ± 3.3° for Unit I (see Lithostratigraphy).