Figure F33. SEM image of greigite cube (3 µm length), Hole U1501A. Material was magnetically separated with a rare earth magnet from a slurry prepared from core catcher sample.

<figure><img src="image_237.png" /></figure>

Many of the AF-demagnetized discrete samples reveal trends showing reversed or normal polarity in the last step of demagnetization (50 mT).

Thermal demagnetization shows removal of a steep low-temperature normal component which is carried up to 300°C.

## Magnetostratigraphy

Inclination, declination, and intensity for Holes U1501A–U1501D are reported in Figures F37, F38, and F39. We constructed the magnetostratigraphy of Site U1501 based on the polarity assigned to the archive-half cores and recognized polarity reversals in Hole U1501D (Figures F39, F40, F41; Tables T12, T13). We did not use data from Hole U1501C from ~240 m to the bottom of the hole (Cores 35F through 62X) because a decrease in NRM moment hampers the determination of magnetic polarity.

Declinations from Holes U1501A and U1501B and Cores 368-U1501C-1H through 17H were corrected using the Icefield MI-5 core orientation tool (see Paleomagnetism in the Expedition 367/368 methods chapter [Sun et al., 2018a]). In Holes U1501C and U1501D, the interpretation of polarity deeper than 156.8 m is based only on the inclination data because the XCB and RCB coring processes disturb the geographic core orientation. Our interpretations of inclination are based on directions derived from the raw moments measured by the SRM at 25 mT and from the corroborative evidence from AF demagnetization of discrete samples.

We then correlated the magnetostratigraphic data of Site U1501 to the standard timescale (Ogg et al., 2016) and plotted them along with the tie points from the microfossil ages from shipboard paleontologists (Figures F40, F41). The paleomagnetic and paleontological age constraints match well over most of the section. A succession of eight normal and five reversed intervals was recognized in Hole U1501D (Table T13; Figure F39). The lack of fossils in Unit III prevents correlation of magnetostratigraphic features (n1 to n8 in Figure F39) to the geologic timescale. The apparently long n8 interval (~37.45 m thick) may only represent a relatively short duration (0.37 My) if the sedimentation rate was high (~100 mm/ky) at that time.

Figure F34. Variation of percentage of NRM left above 575°C, upper part of Hole U1501C (1H through 9H). Note the significant increase in the percentage below 60 m, which suggests an increasing contribution of maghemite or hematite.

<figure><img src="image_238.png" /></figure>

Figure F35. Magnetization normalized to NRM as a function of AF demagnetization, Hole U1501C. This behavior shows initially low coercivity below 30 mT followed by coercivity inversion (or plateau), generally attributed to magnetic self-reversal of greigite (e.g., Krs et al., 1992; Horng et al., 1998). Complete demagnetization requires AF fields >100 mT.

<figure><img src="image_239.png" /></figure>
Figure F36. Demagnetization plots of (A, D, E, G, H) archive-half sections and (B, C, F, I) discrete samples, Holes U1501C and U1501D. A, B, D, E, F, G, H: AF demagnetized; C, I: thermally demagnetized. Zijderveld plots: solid squares = declination, open squares = inclination. Stereographic plots: solid squares = positive (down) inclination, open squares = negative (up) inclination. Calculated ChRM (blue line; red squares = measurements used in calculation) using PCA are in good agreement for samples coming from same section and subjected to different treatments. Unit I: (A) reversed polarity, (B) normal polarity but with last step indicating a tendency to reversal, (C) reversed polarity. Unit II: (D) normal polarity, (E) reversed polarity, (F) normal polarity. Unit III: (G) normal polarity, (H) reversed polarity, (I) normal polarity.

A 368-U1501C-4H-7A, 17.5 cm

Dec 99.34°/Inc -23.71°

<figure><img src="image_240.png" /></figure>

B 368-U1501C-4H-7W, 41 cm

Dec 116.14°/Inc 34.80°

<figure><img src="image_241.png" /></figure>

C 368-U1501C-4H-7W, 45 cm

Dec 148.58°/Inc -10.32°

<figure><img src="image_242.png" /></figure>

D 368-U1501D-17R-4A, 582.05 m

Dec 228.62°/Inc 61.24°

<figure><img src="image_243.png" /></figure>

E 368-U1501D-15R-3A, 561.175 m

Dec 106.08°/Inc -46.16°

<figure><img src="image_244.png" /></figure>

F 368-U1501D-17R-2W, 58 cm

Dec 147.35°/Inc 52.79°

<figure><img src="image_245.png" /></figure>

G 368-U1501D-21R-1A, 610.7 m

Dec 0.87°/Inc 53.34°

<figure><img src="image_246.png" /></figure>

H 368-U1501D-20R-3A, 610.045 m

Dec 355.54°/Inc -65.46°

<figure><img src="image_247.png" /></figure>

I 368-U1501D-22R-3W, 95 cm

Dec 176.16°/Inc 44.86°

<figure><img src="image_248.png" /></figure>

Based on both inclination and declination, we placed the boundary between the Brunhes and Matuyama Chrons at ~24 m in Hole U1501C. Based on our shipboard paleomagnetic age model, the

middle/early Pleistocene boundary (0.78 Ma) is at ~24 m, the Pleistocene/Pliocene (2.58 Ma) boundary is at ~62 m, and the Pliocene/Miocene boundary (5.33 Ma) is at ~90 m (Table T12).
<figure><img src="image_249.png" /><figcaption>Figure F37. Magnetic measurements, Holes (A) U1501A and (B) U1501B. Inclination was used to determine polarity. AFD = AF demagnetization, TD = thermal demagnetization. Discrete samples are yellow and green.</figcaption></figure>

<figure><img src="image_250.png" /></figure>
<figure><img src="image_251.png" /><figcaption>Figure F38. Magnetic measurements, Hole U1501C. Inclination was used to determine polarity. Discrete samples are yellow and green.</figcaption></figure>
Figure F39. Magnetic measurements, Hole U1501D. Inclination was used to determine polarity. Magnetostratigraphic features are referred to as n1, etc., in a sequential manner for convenience and have no bearing on chron. GTS2016 = geomagnetic polarity timescale of Ogg et al. (2016). Green circles = discrete samples.

<figure><img src="image_252.png" /></figure>
<figure><img src="image_253.png" /><figcaption>Figure F40. Magnetic measurements and correlation to magnetostratigraphy (368-U1501C-1H through 17H). Age-depth model constructed from shipboard paleomagnetic analysis. Magnetostratigraphy converted to time and plotted against standard geologic timescale (GPTS2016; Ogg et al., 2016). Magnetostratigraphic features are referred to as n1, etc., in a sequential manner for convenience and have no bearing on chrons. B/M = Brunhes/Matuyama Chron boundary, M/G = Matuyama/Gauss Chron boundary. Discrete samples are yellow and green.</figcaption></figure>
Figure F41. Magnetic measurements and correlation to magnetostratigraphy (U1501C-18F through 40X-2). Age-depth model constructed from shipboard paleomagnetic analysis. Magnetostratigraphy converted to time and plotted against standard geologic timescale (GPTS2016; Ogg et al., 2016). Magnetostratigraphic features are referred to as n1, etc., in a sequential manner for convenience and have no bearing on chron. Discrete samples are yellow and green.

<figure><img src="image_254.png" /><figcaption>Table T12. Paleomagnetic age datums, Hole U1501C. Download table in CSV format.</figcaption></figure>

<table><thead><tr><th>Polarity chron</th><th>Age of chron base (Ma)</th><th>Depth CSF-A (m)</th></tr></thead><tbody><tr><td>C1n (Brunhes)</td><td>0.773</td><td>24.00</td></tr><tr><td>C1r.1r</td><td>1.008</td><td>28.40</td></tr><tr><td>C1r.1n (Jaramillo)</td><td>1.076</td><td>30.00</td></tr><tr><td>C1r.2r</td><td>1.189</td><td>32.10</td></tr><tr><td>C1r.2n (Cobb Mountain)</td><td>1.221</td><td>33.05</td></tr><tr><td>C1r.3r</td><td>1.775</td><td>38.50</td></tr><tr><td>C2r.1n (Feni)</td><td>2.155</td><td>47.00</td></tr><tr><td>C2r.2r</td><td>2.61</td><td>61.90</td></tr><tr><td>C2An.1n</td><td>3.032</td><td>68.05</td></tr><tr><td>C2An.1r (Keana)</td><td>3.116</td><td>70.10</td></tr><tr><td>C2An.3n</td><td>3.596</td><td>72.80</td></tr><tr><td>C2Ar</td><td>4.187</td><td>78.20</td></tr><tr><td>C3n.2n (Nunivak)</td><td>4.631</td><td>81.70</td></tr><tr><td>C3n.2r</td><td>4.799</td><td>84.20</td></tr><tr><td>C3An.1n</td><td>6.252</td><td>91.60</td></tr><tr><td>C3Br.2r</td><td>7.454</td><td>102.40</td></tr><tr><td>C4An</td><td>9.105</td><td>112.45</td></tr><tr><td>C5n.2n</td><td>11.056</td><td>122.35</td></tr></tbody></table>

<table><thead><tr><th>Polarity chron</th><th>Age of chron base (Ma)</th><th>Depth CSF-A (m)</th></tr></thead><tbody><tr><td>C5Bn.1r</td><td>15.032</td><td>161.40</td></tr><tr><td>C5Bn.2n</td><td>15.16</td><td>164.20</td></tr><tr><td>C5Br</td><td>15.974</td><td>173.14</td></tr><tr><td>C5Cn.1n</td><td>16.268</td><td>174.80</td></tr><tr><td>C5Cn.1r</td><td>16.303</td><td>176.12</td></tr><tr><td>C5Cn.3n</td><td>16.721</td><td>180.04</td></tr><tr><td>C5Cr</td><td>17.235</td><td>186.06</td></tr><tr><td>C5Dn</td><td>17.533</td><td>191.50</td></tr><tr><td>C5Er</td><td>18.748</td><td>204.25</td></tr><tr><td>C6n</td><td>19.722</td><td>211.50</td></tr><tr><td>C6r</td><td>20.04</td><td>213.50</td></tr><tr><td>C6An.1n</td><td>20.213</td><td>216.24</td></tr><tr><td>C6Ar</td><td>21.083</td><td>222.25</td></tr><tr><td>C6AAr.1n</td><td>21.483</td><td>225.52</td></tr><tr><td>C6Bn.2n</td><td>22.268</td><td>234.97</td></tr><tr><td>C6Br</td><td>22.564</td><td>237.08</td></tr></tbody></table>
<table><caption>Table T13. Interpreted possible magnetic polarity sequence, Hole U1501D.
Download table in CSV format.</caption><thead><tr><th rowspan="2">Possible magnetic<br>polarity</th><th colspan="2">Depth CSF-A (m)</th></tr><tr><th>Upper boundary</th><th>Lower boundary</th></tr></thead><tbody><tr><td>n1</td><td>491.000</td><td>492.285</td></tr><tr><td>n2</td><td>510.200</td><td>511.125</td></tr><tr><td>n3</td><td>539.000</td><td>539.925</td></tr><tr><td>r1</td><td>548.700</td><td>549.275</td></tr><tr><td>r2</td><td>558.275</td><td>562.575</td></tr><tr><td>r3</td><td>564.000</td><td>570.725</td></tr><tr><td>n4</td><td>570.725</td><td>573.805</td></tr><tr><td>n5</td><td>577.400</td><td>582.505</td></tr><tr><td>n6</td><td>586.900</td><td>589.590</td></tr><tr><td>r4</td><td>589.625</td><td>591.355</td></tr><tr><td>r5</td><td>596.500</td><td>597.860</td></tr><tr><td>n7</td><td>598.805</td><td>599.940</td></tr><tr><td>n8</td><td>606.100</td><td>643.550</td></tr></tbody></table>

## Geochemistry

Headspace gas concentrations were below detection due to low TOC contents <0.25 wt% and low levels of thermal alteration within underlying units. The bulk sediment geochemistry was controlled by lithology. High calcium carbonate content in lithostratigraphic Unit I reflects its high biogenic carbonate content. TOC and sulfur are mostly low in Unit I, with higher sulfur concentrations observed in lithostratigraphic Unit II. The low TOC concentrations in much of Unit I likely reflect poor preservation under aerobic conditions. The interstitial water concentration depth profiles show atypical redox zones for marine sediments with rates of sulfate reduction appearing to be inhibited, much as methanogenesis has likely been inhibited at this site. Sulfate reduction is more pronounced in Unit II (>300 m), and within this interval there is also heavy pyritization. Raman spectroscopy was applied shipboard to organic materials and indicates a mild thermal history for Units I and II. Surface-enhanced Raman spectroscopy yielded Raman bands diagnostic of asphaltene within the sediments of Unit I.

## Headspace gas

Headspace gas samples were taken at a frequency of one sample per core or per 10 m of drilling advance for routine safety monitoring. Where possible, samples were collected from sections adjacent to interstitial water samples. At no point did hydrocarbon gas levels exceed a 12 ppmv detection limit—a limit corresponding to background values in air. Methane was detected in standard reference materials and within a paleomagnetism sample obtained from the core catcher of Core 368-U1501C-62X that evidenced drilling disturbance (frictional heating induced by rotation). A typical safety gas chromatogram is shown in Figure F42, in which hydrocarbons up to propane ($C_4H_{10}$) can be seen in the drilling-disturbed sample (propane is the highest carbon number that is quantified by the method used). Also shown are data for the analysis of a paleomagnetism sample obtained from the core catcher that was altered by drilling disturbance and contains light hydrocarbon gases. Analytical methods were capable of detecting light hydrocarbon gases, but none were present at significantly high concentrations within safety gas samples. Traces of propene were also detected, particularly from headspace samples collected close to the core liner and from RCB cores.

Figure F42. Gas chromatograms showing low levels of methane present in headspace samples, Hole U1501C. Detection of hydrocarbon gases in a drilling-disturbed sample obtained from a core catcher is shown for comparison. Relatively high proportions of ethene are consistent with generation of hydrocarbons by frictionally induced flash pyrolysis.

<figure><img src="image_255.png" /></figure>

## Bulk sediment organic geochemistry

Bulk sediment organic geochemical parameters are presented by depth in Figure F43 and Table T14 and cross-plotted by unit in Figure F44.

### Lithostratigraphic Unit I

Sediments from the uppermost 30 m of lithostratigraphic Unit I (seafloor to Core 368-U1501C-5H) generally have high TOC and low carbonate contents. The top of the section to ~25 m has low but measurable sulfur contents. Otherwise, lithostratigraphic Subunits IB-IF have very low sulfur values. This is distinct from the underlying members of Unit I that have an average carbonate content of ~40 wt% and low TOC, typically <0.25 wt%. Given the fossiliferous nature of the lithologies (nannofossil ooze with foraminifers), it is unlikely that these carbon results represent low levels of biological productivity. More likely, they represent poor preservation of organic matter, which is typical of accumulation under aerobic rather than anaerobic conditions (Demaison and Moore, 1980). The preservation of sulfur in sediments is biologically mediated by sulfate reduction to form sulfide, which in turn forms pyrite (Berner and Raiswell, 1984). Under aerobic conditions, this process is inhibited and would not occur as readily, although organic matter starvation also inhibits sulfate reduction because organic matter forms part of the vital redox couple for sulfate reduction. Whatever the cause, dissolved sulfate concentrations within interstitial water, as described later, did not decline markedly within Subunits IB-IF, supporting the notion that TS levels are low because sulfur has not been reduced during early diagenesis and fixed as pyrite. The instances of very high TOC/total nitrogen (TN) ratios (>10) may reflect an autochthonous input of terrestrial-derived organic matter to the sediments but may also be produced by a lower detection limit for organic carbon than for nitrogen (Hedges et al. 1988).

### Lithostratigraphic Unit II

Lithologies within lithostratigraphic Unit II include both high and low TOC members that likely reflect sandy and mud-rich litho-
<figure><img src="image_256.png" /><figcaption>Table T14. Carbon, nitrogen, and sulfur, Holes U1501C and U1501D. View table in PDF format. Download table in CSV format.</figcaption></figure>

<figure><img src="image_257.png" /><figcaption>Figure F44. Crossplot of organic geochemical parameters: carbonate vs. carbon/nitrogen ratio and TS vs. TOC. Black circles = lithostratigraphic Subunit IA, open triangles = Subunits IB-IF, crosses = Unit II, green circles = Unit III.</figcaption></figure>

logies. The highest TOC values have the highest TOC/TN ratio, consistent with organic carbon being derived from terrestrial organic matter (Hedges et al., 1988). This unit also has high sulfur content, likely reflecting the fixation of interstitial water sulfate as sulfide that becomes incorporated within sulfide minerals during diagenesis (Raiswell and Berner, 1984). The unit has low carbonate contents relative to Unit I, but overall an 8–10 wt% carbonate con-

tent is still significant and must represent either a bioclastic or authigenic component.

## Lithostratigraphic Unit III

Only a few lithologies within lithostratigraphic Unit III were analyzed (three samples in all). A TOC content of 0.5 wt% was obtained for gray mudstone, but otherwise Unit III sediments have
very low TOC and carbonate contents. The sulfur content of <0.5 wt% is low but higher than might be expected given the unit's lithologic associations (gravel) and when compared to Unit I (see Lithostratigraphy).

## Raman and surface-enhanced Raman spectroscopy

Conventional Raman spectroscopy was applied to organic materials, including samples of amber, ash-rich lignite, and bitumen. For reference purposes, they are compared to a sample of Midlothian bituminous coal from the Midlothian coalfields (Scotland) and a sample of pre-oil-window oil-shale from the Brora Coal Member (Caithness, Scotland). Raman spectra are shown in Figure F45. Raman spectra obtained from solid carbon-rich fossil organic matter typically have two broad composite bands (or peaks). The first is centered at 1460 cm⁻¹, is relatively broad and wide, and is termed the disordered band (D-peak). Another band at 1600 cm⁻¹ is produced by vibrational modes generated by aromatic sheets with a graphite-like structural ordering (Pasteris and Wopenka, 2003) and is termed the graphite (G) or ordered (O) peak.

Fluorescence dominates the spectra obtained for the amber sample (368-U1501C-61X-1, 70 cm), with no clear band distinguished at 1460 or 1600 cm⁻¹, although the broad band observed around 1550 cm⁻¹ likely derives from the ordering of π-bonded aromatic sheets with graphite-like structures. A D-peak is also present, but is so broad it cannot be reasonably interpreted. Thus, the sample can be shown to contain organic carbon, but beyond this no other information can be obtained. Relative to the high molecular weight aromatic compounds within humic organic macerals or kerogen, amber comprises plant resins that are highly aliphatic, lack strong aromatic cores, and fluoresce strongly. These qualities make these materials poorly suited for analysis by Raman spectroscopy using a 532 nm light source.

The sample of lignite (light brown streak, no cleats, and partial humification; Sample 368-U1501D-9R-1, 78 cm) yielded broad D and G bands characteristic of levels of thermal maturation typical of brown coal (preoil and gas generation) and levels of thermal alteration that indicate heating at temperatures <40°C.

In most cases, the bitumen impregnating a sandstone clast from Section 368-U1501D-27R-1, 10–15 cm, yielded fluorescence only, but Raman spectra were obtained from a solvent-insoluble component present on the clast's exterior and within a fracture. The D band for these spectra was shrouded by fluorescence, but a G peak could be observed, and the Raman shift was notably high (equal to or greater than that of the coal, ~1600 cm⁻¹), possibly indicating a higher level of thermal maturity than observed for the lignite. This higher level would be consistent with the insolubility of the bitumen in solvent.

Surface-enhanced Raman spectroscopy detected 0.2–2 ng asphaltene/g sediment in lithostratigraphic Units I and II. Detection required deconvolution of surface-enhanced Raman spectra (Figure F46). Primarily, two components were considered: solvent extracts of sedimentary organic matter (SOM) that exhibited relatively narrow Raman bands at shifts of 1310, 1448, and 1650 cm⁻¹ and asphaltene that exhibited broad Raman bands at 1380 and 1575–1585 cm⁻¹ (Alabi et al., 2015). A small Raman band at ~1522 cm⁻¹ was often left as a residual. The two broad Raman bands are at positions consistent with previous studies of asphaltene and are similar to the D and G bands of solid carbonaceous materials, whereas the band at ~1522 cm⁻¹ is a position, based on previous surface-enhanced Raman scattering studies, that likely corresponds to carotenoids (Wil-

<figure><img src="image_258.png" /><figcaption>Figure F45. Raman spectra of carbonaceous materials collected from reference materials and Holes U1501C and U1501D. AU = arbitrary units.</figcaption></figure>

son et al., 2007), which are also a likely component of marine SOM. The detection of surface-enhanced Raman scattering bands diagnostic for asphaltene and thereby residual petroleum (asphaltene is the most resistant component of petroleum and bitumen and accumulates as residues) is important given the context of the SOM. There is no evidence of recent petroleum migration at Site U1501, and indeed headspace hydrocarbon gases remained below detection. The single instance of bitumen was a highly thermally matured solid component, unlikely to have migrated in recent geological history.

## Interstitial water chemistry

Shipboard analyses were performed on interstitial water squeezed from 5–15 cm long whole-round sediment samples from Hole U1501C. For Cores 1H through 10H, 5 cm long interstitial water samples were squeezed and yielded >40 mL of interstitial water per sample. For Cores 11H through 37F, 10 cm long whole-round sediment cores were squeezed and yielded ~30 mL of interstitial water. For Cores 39F through 61X, 15 cm long whole-round interstitial water samples yielded <15 mL of interstitial water per sample. In Hole U1501D, only one sample from Core 2R yielded water on squeezing and then only at a maximum pressure of 30,000 lb for 6 h.

Interstitial water geochemical parameters are listed in Table T15 and presented by depth in Figures F47 and F48.

We defined four geochemical interstitial water zones at Site U1501 based on the variation of geochemical parameters (listed in Table T15). Interstitial water Zone 1 (interval 368-U1501C-1H-2, 0–5 cm, through 2H-5, 0–5 cm) comprises samples obtained close to the mudline (sediment/water interface). Within this interval, maximum sulfate, alkalinity, phosphate, ammonium, boron, silica, lithium, and manganese concentrations are likely related to degradation of organic matter. In interstitial water Zone 2 (interval 3H-2, 0–5 cm, through 43X-4, 0–15 cm), sulfate slightly decreases and alkalinity is buffered by high carbonate concentrations within foraminifer-rich oozes. Atypically for this marine setting (Li et al., 2015a), in which sulfate reduction is prevalent in marine sediments, diffusion processes dominate the sulfate profile. Decreasing K and Mg and increasing Ca and Li reflect the typical diffusion-formed profile of interstitial water, but in interval 19F-3, 0–15 cm, and Section 27F-2, there is an obvious increase in Fe, Si, and Mn and a slight
<figure><img src="image_259.png" /><figcaption>Table T15. Interstitial water analyses, Hole U1501C and U1501D. **View table in PDF format. Download table in CSV format.**</figcaption></figure>

decrease in Na, Cl, and Br. This atypical profile is similar to that of the deep fluids in Hole U1502A, which are suggested to derive from basalt. In interstitial water Zone 3 (interval 44X-4, 0–15 cm, through 50X-4, 0–15 cm) sulfate, chloride, and bromide concentrations are anomalously low. One possible origin for this fluid migration is along sand and silt layers in which a fluid depleted in Cl, Br, and Na migrates. Alternatively, the chemical composition may be explained by a sand body or sand-rich unit being isolated by differential compaction within a hydraulically sealed mudstone; in such a case, the water would represent relict formation water. In interstitial water Zone 4 (interval 53X-4, 0–15 cm, through 61X-2, 0–15 cm), all major anion and cation concentrations are normal for that depth and the region (Li et al., 2015a).

Alkalinity varies within Hole U1501C, ranging from 1.5 to 8.8 mM (shown in Figure F47). In interstitial water Zone 1, alkalinity increases to a peak concentration of 7.1 mM at 16.72 m (Sample 2H-5, 0–5 cm). This change in alkalinity is most likely caused by degradation of organic matter. In interstitial water Zone 2, alkalinity decreases to ~3.5 mM at 59 m and remains constant at ~3.5 mM to 100 m. Alkalinity increases again to a peak concentration of 8.8 mM at 230 m and then decreases downhole to the base of interstitial water Zone 2. The changes of alkalinity in interstitial water Zone 2 are similar to those of carbonate, suggesting that alkalinity might be influenced by the dissolution of carbonate. The pH value decreases slowly from the seafloor to the bottom of interstitial water Zone 2 and then increases to a maximum (pH = 7.94) at the bottom of interstitial water Zone 4 (Sample 61X-2, 0–15 cm).

In interstitial water Zones 1 and 2, interstitial water chlorinity values are mostly ~560 mM, similar to the standard seawater value (559 mM; Figure F47). In interstitial water Zone 3, chlorinity values decrease to the minimum (498 mM) at 356 m. About 10% decreased

chlorinity implies that a “freshwater” component might be present. The bromide depth profile is similar to the variation observed for chlorinity but with a maximum that occurs at a different depth. Bromide concentration also decreases to a minimum in interstitial water Zone 3. It is worth noting that slightly decreased chlorinity and bromide concentrations were observed in Cores 19X-3 and 21X-3.

The dissolved sulfate profile decreases from 27.2 mM at the seafloor to 3.7 mM at the bottom of Hole U1501C (Figure F47). In interstitial water Zone 1, sulfate concentrations decrease sharply, most likely caused by bacterially mediated organic matter diagenesis in upper sediments. Downhole, this decline is more gradual and can best be explained by diffusion processes. The interstitial water contains significant amounts of sulfate (3.7 mM) to the bottom of the hole, indicating that sulfate is not completely consumed in Hole U1501C. A similar case was observed at IODP Site U1431 (Li et al., 2015b), but otherwise this lack of sulfate reduction is unusual. Dissolved $NH_4^+$ concentrations increase from 336 µM at 7.5 m to a maximum of 492 µM at 16 m in interstitial water Zone 1. Interstitial water Zones 2–4 have slight variations in $NH_4^+$ concentrations. A maximum in dissolved phosphate concentrations is 30.6 µM at 3 m in interstitial water Zone 1. In interstitial water Zones 2–4, phosphate concentrations are generally low, just about several micromolars.

The $Na^+$ profile is similar to $Cl^-$ and $Br^-$ (Figure F47). Sodium concentrations are mostly constant (~480 mM) in interstitial water Zones 1 and 4, decrease to a minimum (399 mM) in interstitial water Zone 3, and increase to standard seawater value (~480 mM) in interstitial water Zone 4 (likely representing contamination). Sodium concentrations in interstitial water Zone 3 are about 20% of that in other units. The $K^+$ and $Mg^{2+}$ profiles decrease in a similar way to each other from the surface to the bottom of the hole. Decreases in potassium and magnesium are possibly due to diagenetic reactions occurring in sediment, such as clay ion exchange. Contrary to the potassium and magnesium pore water profiles, the $Ca^{2+}$
<figure><img src="image_260.png" /><figcaption>Figure F47. Interstitial water alkalinity, pH, chloride, bromide, sulfate, phosphate, ammonium, sodium, potassium, calcium, and magnesium concentration profiles.</figcaption></figure>

profile increases from the surface to a maximum concentration (33.7 mM) at 337 m, and below this depth calcium has a near-constant concentration. Changes in calcium concentration are mostly caused by carbonate diagenesis (i.e., dissolution and recrystallization of biogenic carbonate). The strontium profile in interstitial water is controlled by the dissolution of biogenic carbonate, so it is similar to the profile of calcium. Strontium concentrations increase from the subsurface to the maximum (440 µM) at 269 m and remain around 400 µM until the bottom of the hole (Table T16).

Dissolved Ba concentrations in the interstitial water are controlled by the formation and stability of the mineral barite (BaSO₄). Barium and sulfate concentrations are negatively correlated. In interstitial water Zone 1, the dissolved Ba concentration is very low (0.05 µM) and corresponds with the maximum in sulfate. In interstitial water Zones 2–4, Ba concentrations increase linearly to a maximum (2.49 µM) at the bottom of Hole U1501C at the same time sulfate concentrations decrease to a minimum.

In interstitial water Zone 1, degradation of organic matter releases B into the interstitial water (Li and Jiang, 2010), so the dissolved B concentrations increase with depth (Figure F48). In interstitial water Zone 2, the B profile is likely driven by clay mineral cation exchange (e.g., adsorption onto and desorption from clay minerals). Decreased B concentrations are observed in interstitial water Zones 2 and 3. Lithium is also easily adsorbed onto clay minerals such as kaolinite and smectite and/or other terrigenous sediments. Thereafter, in interstitial water Zone 1, the concentration of Li is lower than modern seawater (25 µM). In interstitial water Zone 2, Li concentrations increase gradually from 27 µM to a maximum (499 µM) and then decrease to lower concentrations in interstitial water Zones 3 and 4. The increases in Li concentration are possibly

due to the diagenetic release of Li from clay minerals and/or diffusion from Li-enriched deep fluids.

Silica concentrations in interstitial water Zone 1 are controlled by the dissolution of siliceous microfossils that release silica into interstitial water. In interstitial water Zone 2, peaks in Si, Fe, and Mn concentrations were observed between Sample 368-U1501C-21F-3, 0–10 cm, and Section 27F-2 at the same time as decreased Na, Cl, and Br concentrations. The changes in geochemical parameters are similar in character to those of the deeper fluids in Hole U1502A. The profiles of dissolved Fe and Mn change in a way similar to that of Si, perhaps because Fe and Mn are affected by the degradation of organic matter, which also occurs in surface sediments. At Site U1502, there was enrichment in Mg and Ca, but in Hole U1501C changes in Ca and Mg do not appear to be off-trend.

In summary, the most obvious changes in interstitial water chemical composition occur in Sections 368-U1501C-19F-3 through 27F-2 and deeper than 300 m. Fluid from these sections have similar geochemical parameters to the deep fluid from Hole U1502A, which is suggested to be influenced by the dissolution of mafic minerals within basalt. The fluid below 300 m corresponds to a boundary between lithostratigraphic Units I and Unit II. A sharp change in interstitial water chemistry at very shallow subseafloor depths suggests very rapid degradation of organic matter within the uppermost 16 m.

## Bulk sediment and rock geochemistry

We analyzed a total of 64 sediment samples from Holes U1501B, U1501C, and U1501D for major and minor element concentrations by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) (Table T17).
<figure><img src="image_261.png" /><figcaption>Table T16. Interstitial water minor elements, Hole U1501C. **View table in PDF format. Download table in CSV format.**</figcaption></figure>

<caption>Table T17. Major element oxide and minor element contents of sedimentary samples, Site U1501. **View table in PDF format. Download table in CSV format.**</caption>

Elemental compositions primarily reflect geological units and changes in lithology. Silica, aluminum, and calcium oxides are the major elements and typically account for greater than 90 wt% of the elemental composition of most lithologies (Figure F49). In lithostratigraphic Unit I, calcium oxide contents are high, and within the foraminifer-rich interval they exceed 40 wt% (consistent with the unit being a high-carbonate ooze, e.g., >50% carbonate). Within lithostratigraphic Units II and III, calcium (as carbonate) is less common and the units are predominantly siliciclastic with sharp distinctions between units that are mud-rich and the feldspathic, sandier lithologies toward the base of the hole. In lithostratigraphic Unit III, a steady decrease in potassium content reflects the upward transition from an orthoclase-rich to less orthoclase-rich sandstone. Sandstones at the top of lithostratigraphic Unit II are far muddier than those beneath, and the relatively increased potassium content is associated with increased aluminum content. Likely, these changes reflect an upward increase in clay content in lithostratigraphic Unit II. Such a progression is consistent with increased compositional maturity within the sediment, brought on by the transition from first- to second-cycle sediments (Suttner et al., 1981) (e.g., the breakdown and conversion of orthoclase to clay minerals during weathering in the sediment source). Within the basal part of lithostratigraphic Unit II, sodium and potassium are both high, which is also consistent with the presence of first-cycle feldspathic sediments.

Parameters previously proposed to represent sedimentological processes for the SCS were also evaluated (Clift et al., 2014). In detail, Figure F50 shows the depth profile of a parameter based on the major cations in smectite (Mg and Na) and illite (K). The variation of (Mg + Na)/K values reflects the different clay assemblages in the lithostratigraphic units. The Ti/Ca parameter has previously been used as a proxy of clastic flux (Clift et al., 2014), with Ti being dominated by the presence of heavy detrital minerals (e.g., rutile and titanite) and Ca by biogenic carbonate. The high peak in Ti/Ca depth profile (lithostratigraphic Subunit IA) is most possibly correlated with intensified clastic delivery from continents; furthermore, the high Ti/Ca with low Al/Si (low ratios of clay and quartz sand) values in Subunit IA (Figure F49) may indicate a high-energy transport regime during this period.

## Discussion of organic, formation water, and inorganic chemical results

The following synthesis is based on the geochemical data presented in the preceding sections. Based on the lack of methane generation and sulfate reduction and the fixation of sulfur as pyrite within sediments, aspects of early diagenetic environments at Site U1501 are atypical in comparison to other sites in the region (Li et al., 2015a). Deepwater marine mudstones do not regularly have high TOC values, largely because their depositional environments in general do not favor high rates of organic carbon preservation (Demaison and Moore, 1980). However, the low TOC values (<0.5 wt%) found in lithostratigraphic Subunit IIA are also at odds with nearby sites such as Site U1499. The low methane content of sediments and sulfate reduction profiles also differ markedly between the two sites; there is no evidence of a present-day sulfate-methane transition zone (SMTZ) at Site U1501 (Barnes and Goldberg, 1976). Figure F51 summarizes these features. Within lithostratigraphic Unit II,
<figure><img src="image_262.png" /><figcaption>Figure F49. (A) Major element oxide abundances and lithostratigraphic unit-normalized (B) CaO/SiO₂, (C) K₂O/SiO₂, and (D) Al₂O₃/SiO₂. B–D: solid black circles = Subunit IA, open circles = Subunits IB–IF, red circles = Unit II, green circles = Unit III.</figcaption></figure>

sulfate reduction is inhibited relative to Site U1499. Perhaps unsurprisingly, because sulfate is ultimately converted to pyrite, the main form in which pyrite is stabilized within sediments, the TS content of Unit I is mostly low, except for the topmost interval, where both iron and organic carbon contents are high.

Causes for inhibited pyrite formation and sulfate reduction might include a lack of iron, low organic matter content (organic matter serves as a reductant), and a dysoxic environment (Berner and Raiswell, 1984). Both factors are present at Site U1501, as can be seen in Figure F51. Iron, which is particularly noticeable in this

regard, has an inverse correlation to barite. Barite and thereby Ba can also serve as indicators for past redox boundaries in sediments (Torres et al., 1996). Barite precipitates and is fixed in sediment where sulfate is stable under oxic conditions, generally found above the SMTZ where sulfate is most abundant. The inversely varied Ba and Fe thus likely denote varying diagenetic conditions within the sediment column. Overall, this strongly indicates that Site U1501, situated at a basement high, has seen a substantial change in early diagenesis conditions during recent geological history.
Figure F50. Geochemical parameters correlated with sedimentological processes. A. (Mg + Na)/K ratio as proxy for smectite and illite. B. Ti/Ca ratio normalized by lithostratigraphic unit. Solid black circles = Subunit IA, open circles = Subunits IB-IF, red circles = Unit II, green circles = Unit III.

<figure><img src="image_263.png" /></figure>

Figure F51. Variations in diagenetic history, Site U1501. A. Interstitial water Zones 1–4 and redox state of early stage diagenesis (green = reducing, red = dys-oxic). B. Rescaled (from 0 to 1) interstitial water sulfate concentrations. AU = arbitrary units. C. Elemental and oxide abundances (Fe as Fe₂O₃). D. TOC and TS.

<figure><img src="image_264.png" /></figure>
# Physical properties

Sediment and rock physical properties were measured on cores from Holes U1501A (0–9.5 m), U1501B (0–9.5 m), U1501C (0–461.9 m), and U1501D (433.5–644.3 m). After cores reached thermal equilibrium with ambient temperature at ~20°C, gamma ray attenuation (GRA) density, magnetic susceptibility, and P-wave velocity were measured every 2 cm using the Whole-Round Multisensor Logger (WRMSL). After WRMSL scanning, NGR was measured on the whole-round sections with a counting period of 10 min and a measurement spacing of 10 cm. Thermal conductivity was measured next with a needle probe inserted into whole-round cores on unconsolidated sediments and with a puck probe on split section halves on hard rocks. Following core splitting, color reflectance and magnetic susceptibility measurements were taken from the archive halves using the point magnetic susceptibility (MSP) sensor on the Section Half Multisensor Logger (SHMSL). Discrete MAD measurements were obtained on every other section of the working halves. P-wave velocity was also measured on the working halves with the P-wave caliper (PWC) and P-wave bayonet (PWB) pulser-receiver systems of the Section Half Measurement Gantry (SHMG).

The following major physical property units were distinguished at Site U1501:

* PP Unit 1 (0–300 m),

* PP Unit 2 (300–450 m),

* PP Unit 3 (450–600 m), and

* PP Unit 4 (600–657 m).

These units are described below. The results from the WRMSL, SHMSL, SHMG, and discrete sample measurements are shown in Figure F52.

## Natural gamma radiation

The NGR intensity measured at an energy level characteristic for K, U, or Th is proportional to the content of that element in the sediment. These elemental proportions can help improve stratigraphic correlation and may be indicative of the geochemistry and mineralogy of the sediments (e.g., De Vleeschouwer et al., 2017). In general, the NGR count of sandstones increases with silt and shale content and a higher percentage of minerals other than quartz (Russell, 1944).

NGR values in PP Unit 1 are represented by two major intervals (Figure F53). The upper interval from the seafloor to ~65 m ranges from ~20 to ~50 counts/s and is associated with NGR values that peak around the middle of this depth range. The lower interval of PP Unit 1 has a similar but broader trend and ends at an abrupt increase in NGR values to ~60 counts/s at ~300 m. In PP Unit 2, NGR values vary rapidly, showing an overall increase followed by a decrease in values with depth to the top of PP Unit 3 at ~450 m. PP Unit 3 has a steady rise in NGR values and a sharp increase at ~600 m to ~80 counts/s that characterizes PP Unit 4.

Concentrations of K, U, and Th were estimated using the NGR counts and bulk density measurements for Hole U1501C according to the methods by De Vleeschouwer et al. (2017). The trends in the NGR counts are not as clearly expressed in the Th concentrations as

<figure><img src="image_265.png" /><figcaption>Figure F52. Physical properties, Holes U1501A and U1501B. cps = counts per second.</figcaption></figure>
<figure><img src="image_266.png" /><figcaption>Figure F53. Physical properties, Holes U1501C and U1501D. Note logarithmic scales used for magnetic susceptibility and P-wave velocity.</figcaption></figure>

they are in the K percent weight and U concentrations, which show very similar variations to the total NGR count values (Figure F54).

## P-wave velocity

In PP Unit 1, P-wave velocities gradually increase with depth from ~1450 to 1931 m/s, reflecting sediment compaction (Figure F53). P-wave velocities decrease sharply at the boundary between PP Units 1 and 2 to 1650 m/s. In PP Unit 2 (300–450 m), velocities increase again with depth but remain lower than 2000 m/s down-hole to ~450 m, where they spike to values of ~3500 m/s and higher. Scattered high velocity measurements continue to the bottom of PP Unit 3 (450–600 m), but they become the norm in PP Unit 4 (600–657 m), where they generally exceed ~3500 m/s.

## Thermal conductivity

In PP Unit 1, thermal conductivity increases gradually with depth from ~0.88 W/(m·K) near the seafloor to ~1.64 W/(m·K) at ~300 m (Figure F53). The increasing trend is interrupted at ~265 m by a slight reduction in thermal conductivity caused by poor connection between the core and the probe. Reliable measurements resumed below 267 m. A drop in thermal conductivity from 1.576 to 1.255 W/(m·K) occurs at the boundary between PP Units 1 and 2 (~300 m), followed by increasing trends in PP Unit 2. Thermal conductivity

is more variable in the lowermost section of PP Unit 2 and in PP Units 3 and 4 (440–622 m), where it ranges from ~1.350 to 3.600 W/(m·K).

## Density and porosity

In PP Unit 1, GRA and MAD bulk densities increase gradually from ~1.3 g/cm³ just below the seafloor to ~1.9 g/cm³ (Figure F55) at ~300 m. Dry density increases with depth from ~0.6 to ~1.5 g/cm³, and porosity decreases with depth from 80% to 45%, consistent with increasing compaction. At the boundary with PP Unit 2 (~300 m), bulk and dry densities abruptly decrease, whereas porosity increases up to 60%. Grain density remains constant at 2.7 g/cm³.

In PP Unit 2, bulk and dry densities slightly increase with depth from 1.7 to 2.0 g/cm³ and from 1.1 to 1.7 g/cm³, respectively. Scattered grain density values range from 2.6 to 2.9 g/cm³. Porosity decreases with depth from 60% to 40%. The boundary between PP Units 2 and 3 (450 m) is marked by an abrupt increase in bulk (2.0 to 2.7 g/cm³) and dry (1.7 to 2.7 g/cm³) densities. In PP Unit 3, densities vary, with an overall increasing trend toward the bottom of the unit. At ~600 m, corresponding to the transition between PP Units 3 and 4, bulk and dry densities increase rapidly from ~2.2 to >2.6 g/cm³ and from 2.0 to 2.5 g/cm³, respectively. In contrast, porosity at this depth decreases sharply from 20% to 5%.
Figure F54. NGR measurements, Hole U1501C. K, U, and Th concentrations are derived from NGR and GRA density measurements using method of De Vlee-schouwer et al. (2017).

<figure><img src="image_267.png" /><figcaption>Figure F55. GRA bulk density and MAD bulk density, dry density, grain density, and porosity, Holes U1501C and U1501D.</figcaption></figure>

<figure><img src="image_268.png" /></figure>

PP Unit 4 has an average bulk density of 2.6 g/cm³ and dry density of 2.5 g/cm³ (Figure F55). Grain densities and porosities in this unit fluctuate between 2.5 and 2.9 g/cm³ and 3% and 10%, respectively.

## Color reflectance spectrophotometry

L* values are higher in PP Unit 1, reflecting the higher concentration of biogenic carbonate in the uppermost 300 m. Reflectance

parameters a* and b* increase sharply from the seafloor to ~120 m to their highest values and then drop in similar fashion before ~180 m. Values remain low thereafter to the boundary with PP Unit 2. L* drops sharply at the boundary at ~300 m, marking the transition between PP Units 1 and 2 and reflecting the increase in clay in the formation (Figure F56). L*, a*, and b* values in PP Unit 2 show relatively constant trends with a variable range. The transition between PP Units 2 and 3 is characterized by a slight increase of L*
<figure><img src="image_269.png" /><figcaption>Figure F56. Sediment color reflectance parameters L*, a*, and b* and CaCO₃ content, Holes U1501C and U1501D.</figcaption></figure>

and b*. An abrupt increase in a* occurs at 600 m, coinciding with the change from glauconite sand to sandstone (see Lithostratigraphy). Below this depth, all reflectance values remain relatively constant.

## Magnetic susceptibility

Magnetic susceptibility rapidly increases from the seafloor to ~50 m and then gradually decreases downhole throughout the lower section of PP Unit 1 until abruptly increasing at the boundary between PP Units 1 and 2, coinciding with the change from nannofossil ooze to nannofossil-rich clay (see Lithostratigraphy). Magnetic susceptibility remains constant in PP Unit 2, with a slight decrease at the boundary between PP Units 2 and 3 (450 m) from 15 x 10⁻⁵ SI to 5 x 10⁻⁵ SI that is followed by an abrupt increase at the transition between PP Units 3 and 4. Magnetic susceptibility values in PP Unit 4 are relatively high, locally exceeding 500 x 10⁻⁵ SI (Figure F53).

## Red, green, blue

Red, green, blue (RGB) values show similar trends to the L* values throughout Holes U1501A–U1501D (Figures F56, F57). From the seafloor through the upper portion of PP Unit 1 (~95 m), RGB values increase from 100 to 160, whereas they remain constant and vary between ~140 and 160 in the lower portion of PP Unit 1. A marked decrease in RGB from 170 to 100 was observed at the boundary between PP Units 1 and 2 (Figure F57). RGB values in PP Unit 2 remain relatively constant at ~100, followed by another increase from 70 to 150 in PP Unit 4.

## Discussion and summary

Sediments recovered from Site U1501 are generally composed of both biogenic (calcareous or siliceous ooze) and terrigenous material dominated by either quartz or clay. Changes in sediment physical properties not only reflect relative amounts of these components but also their compaction/lithification state and may also be related to depositional environments. Overall, we found a strong correlation between the sediment physical properties and the designated lithostratigraphic units (Figure F53; see Lithostratigraphy). The GRA and bulk densities increase with depth, reflecting the in-

<figure><img src="image_270.png" /><figcaption>Figure F57. RGB values, Holes U1501C and U1501D.</figcaption></figure>

creasing compaction of sediments with depth. Porosity values are consistent with this trend and have an inverse relationship with density (Figure F55). The lowest porosities (about 5%) were encountered in sandstones from the lowermost section of Holes U1501C and U1501D and are related to diagenetic processes (i.e., lithification and cementation).

Similarly, a general increase in P-wave velocity at Site U1501 from 1451 m/s at the seafloor to 1931 m/s at 302 m (Figure F53) reflects sediment compaction. This increase is followed by a sharp decrease in velocity at 302.9 m to 1796 m/s, marking a distinct lithologic transition from nannofossil ooze to a sand layer overlying clays
(lithostratigraphic Units I to II; see Lithostratigraphy). Below this depth, P-wave velocities show a continuous trend of increasing values, with a second abrupt change from 1824 m/s at 446.7 m to 2453 m/s at 447.4 m that marks the change from an unconsolidated sand layer to a thin layer of sandstone (lithostratigraphic Subunits IIB to IIC). Rapid changes in velocities occur below this depth due to changes in lithology, with values ranging between 1760 and 5330 m/s. Below ~600 m, velocities lie in a narrower range and fluctuate between two sets of values, from as low as ~3491 m/s in a sand or silty sandstone layer to 4814 m/s in a grayish sandstone.

Thermal conductivity values show a general increase from ~0.88 W/(m·K) near the seafloor to ~3.60 W/(m·K) at ~662 m (Figure F53). The gradual increase in value at shallow depths is likely due to sediment compaction. A significant decrease in thermal conductivity between 294 and 304 m is associated with a major change from lithostratigraphic Subunits IE-IF to IIA.

Changes in NGR values are associated with the major lithologic boundaries, but there are also significant, well defined fluctuations at a much finer scale (Figure F53). NGR values are low in lithostratigraphic subunits with high calcium carbonate content such as Subunit IC, and values are high in subunits with low carbonate content such as Subunits IIA and IIB. NGR values show some of the strongest fluctuations of all of the physical properties measurements and reflect rapid changes in lithostratigraphic subunits below ~300 m.

Comparison between L\* values and lithologic content (Figure F56; see Lithostratigraphy) indicates that low L\* values (darker intervals) are well correlated with clay-rich strata, whereas high L\* values (lighter intervals) match well with carbonate-rich layers. There is also a close match between NGR and L\*; low L\* values (dark intervals) correlate with high NGR values and vice-versa because they both reflect the amount of clay minerals.

In Hole U1501C, the highest magnetic susceptibility values are between 25 and 95 m (Figure F53), corresponding to lithostratigraphic Subunits IB and IC, which are dominated by calcite-rich minerals. We suspect that the weak trend representing changes in paramagnetic clay minerals, compared to diamagnetic calcite, is overprinted by the presence of ferromagnetic minerals. One of the prominent peaks in magnetic susceptibility correlates with the ash layer found in the uppermost section of Hole U1501A. In Hole U1501D, extremely high magnetic susceptibility values within lithostratigraphic Subunits IIIA and IIIB correspond to layers of sandstone or sandstone with gravels.

## Downhole measurements

### Logging operations

After recovering the last RCB core from 644.3 m in Hole U1501D, a wiper trip was made to condition the hole for logging operations and the RCB drill bit was released at the bottom of the hole. The bottom of the drill pipe was raised to logging depth at 2971.8 m drilling depth below rig floor (DRF [I give the scale whether it's used again or not because some people will know the acronym better]), or 115.1 m below the seafloor (Figure F58). Rig-up for downhole logging started at 0400 h (local time; UTC - 8 h) on 24 April 2017. The modified triple combo tool string started downhole at 0705 h on 24 April. The upward pass of the triple combo run began at 0815 h and ended at 0905 h. Because a section of collapsed hole was identified during the triple combo run, the logging operation ended after completion of the run. Logging tools were rigged down at 1200 h. Heave conditions were less than ~0.2 m for the triple combo run; therefore, the active heave compensator was not used.

<figure><img src="image_271.png" /><figcaption>Figure F58. Logging operations summary, Hole U1501D.</figcaption></figure>

The modified triple combo tool string included the HNGS, HLDS, HRLA, and MSS (Figure F59). The centralized tools were run in the lower part of the tool string so it would be easier to lower the tool string past ledges than with an eccentricized tool (see Downhole measurements in the Expedition 367/368 methods chapter [Sun et al., 2018a]). The tool string encountered difficulty going down at approximately 173.3 m DSF and was unable to pass below 299.3 m DSF. The uphole log pass indicated a collapsed hole at ~156.3 m DSF based on the caliper curve. For safety reasons, no further attempts to descend below that undergauge spot were made. Because the interval of the collapsed hole was located only ~40 m below the bottom of the pipe, the originally planned FMS-sonic tool string was not run.

## Logging units

The triple combo run in Hole U1501D allowed us to define four logging units that are correlated with lithostratigraphic units (see Lithostratigraphy), lithology, and physical properties (see Physical properties) (Figure F60).

### Logging Unit 1: base of drill pipe to 190 m WSF

Logging Unit 1 is characterized by relatively high variability in the logs. For example, NGR values vary from ~38 to 70 gAPI. Excursions to lower and higher values also punctuate the magnetic susceptibility log. This logging unit corresponds to lithostratigraphic Subunits IA-ID.

### Logging Unit 2: 190-260 m WSF

Logging Unit 2 is characterized by relative homogeneity in the logs, without major excursions to higher or lower log values (e.g., magnetic susceptibility logs). It is also characterized by submeter-scale layering, which is particularly evident in the caliper and resistivity logs. This logging unit corresponds to the lowest part of lithostratigraphic Subunit ID and the upper part of Subunit IE.
<figure><img src="image_272.png" /><figcaption>Figure F59. Tools used in triple combo run, Site U1501. LEH-QT = logging equipment head-q tension, EDTC = Enhanced Digital Telemetry Cartridge.</figcaption></figure>

### Logging Unit 3: 260–275 m WSF

Logging Unit 3 shows relatively high variability in the logs similar to that in logging Unit 1. The NGR, density, and resistivity logs reveal higher amplitude variations than those in logging Unit 2. This logging unit corresponds to lithostratigraphic Subunit IE.

### Logging Unit 4: 275–300 m WSF

The upper part of logging Unit 4 (275–285 m WSF) corresponds to a section in the lower part of lithostratigraphic Subunit IE. This

logging unit does not exhibit any major excursions, similar to logging Unit 2. Although the bottom of the triple combo string reached 300 m WSF, the sensors did not reach the lower part of logging Unit 4 (285–300 m WSF), which corresponds to parts of lithostratigraphic Subunits IE and IF.

## Log data quality and lithology

Log data quality was affected by the large borehole diameter, which exceeded the 17 inch limit of the HLDS caliper arm for about half of the logged interval (Figure F60). Some particularly large caving was inferred at 115–190 and 260–275 m WSF, leading to uncertainty in some of the log values in those intervals. A major thin-bridged (narrow diameter) interval occurred at ~156.3 m WSF.

The downhole logs reflect the lithology at Site U1501. The clay-dominated sediments have high NGR readings because of high concentrations of K and Th in clay minerals, whereas the calcareous sediments have lower NGR and magnetic susceptibility because of a relative lack of radioactive and magnetic minerals. The same NGR and magnetic susceptibility signatures are also seen in the physical property measurements made on cores from Hole U1501C, which enables the downhole logs from Hole U1501D to be correlated to the core data from Hole U1501C.

Contrasts in NGR and magnetic susceptibility can be seen in the logs as a whole. In particular, the calcareous beds can be readily identified in the downhole logs with low NGR. Sand-rich beds can be difficult to identify because they tend to be only partially recovered in the cores and because they become easily washed out in the borehole, resulting in anomalous log data values. In fact, the best indication of sand layers in the logs may be the diameter of the borehole. Such washouts also have very low NGR values.

## Downhole temperature and heat flow

Four downhole temperature measurements were conducted in Hole U1501C using the advanced piston corer temperature tool (APCT-3). Temperatures range from 5.5°C at 47.3 m DSF to 12.4°C at 132.8 m DSF, giving a geothermal gradient of 81.4°C/km (Figure F61A). These measurements, together with the seafloor temperature of 1.2°C, indicate that temperatures increase linearly with depth.

Thermal conductivity under in situ conditions was estimated from laboratory-determined thermal conductivity from Hole U1501C using the method in Hyndman et al. (1974) (see Physical properties in the Expedition 367/368 methods chapter [Sun et al., 2018a]). Thermal resistance (Figure F61C) was then calculated by integrating the inverse of the in situ thermal conductivity over depth (Figure F61B). A heat flow of 100.1 mW/m² was obtained from the linear fit between temperature and thermal resistance (Figure F61D) (Pribnow et al., 2000). The geothermal gradient and heat flow at Site U1501 are comparable to the relatively high values observed in some ODP, Integrated Ocean Drilling Program, and IODP sites in this part of the SCS, including Sites U1432 (100.1 mW/m²) and U1499 (114 mW/m²). Together, these sites show that parts of the northern SCS margin have relatively high heat flow values (Li et al., 2010).
<figure><img src="image_273.png" /><figcaption>Figure F60. Downhole logs, Hole U1501D. HSGR = total spectral gamma ray, HCGR = computed gamma ray (U-free). Downhole logs were taken in Hole U1501D, and lithology and core recovery data are from Hole U1501C.</figcaption></figure>
<figure><img src="image_274.png" /><figcaption>Figure F61. Heat flow calculations, Site U1501. A. Sediment temperatures. B. Thermal conductivity data, Hole U1501C. C. Calculated thermal resistance. D. Bullard plot of heat flow calculated from a linear fit of temperature data.</figcaption></figure>

## Correlation to seismic data

We conducted two sets of analyses to correlate core measurements to the time-based seismic data at Site U1501. First, we analyzed core data and made a direct comparison with the seismic reflection profile. Second, we constructed synthetic seismograms using the Site U1501 core data and compared the results with the traces in seismic profiles. Preliminary calculations were done during the expedition using a combination of Matlab scripts and Matlab software.

### Velocity and density data and comparison with seismic reflectors

Whole-round core measurements, including P-wave velocity (PWL) and GRA density, were conducted from 0 to 457.7 m in Hole U1501C and from 433.5 to 643.5 m in Hole U1501D (Figure F62). P-wave velocity was also measured along the x-axis with the PWC system on working-half sections. MAD measurements were performed on discrete samples, one every other section. In addition, HLDS density measurements were obtained from downhole logging in Hole U1501D from 115 to 300 m (see Physical properties and Downhole measurements). After outliers were cleaned, the whole-round PWL data are in good agreement with the PWC velocities of core samples. The HLDS density values from downhole logging are also in good agreement with MAD data for intervals away from borehole enlargements (Figure F60).

Seismic velocity and density show significant variations in quality with depth, affecting calculations of TWT and synthetic seismograms. From 0 to ~450 m, PWC velocity is of excellent quality. From ~450 to ~608 m, PWC velocity is highly scattered. From ~608 to ~643.5 m, the number of PWC measurements is very limited, whereas the PWL data provide some constraints. For the density data, both the whole-round and discrete sample measurements provide excellent constraints in the 0–450 and 608–643.5 m intervals,

respectively. However, data recovery is poor at 450–608 m (Figure F62).

Site U1501 core measurements show distinct changes in physical properties and lithology in a number of depth intervals (see Physical properties). In general, these intervals correlate well with the depth intervals of strong amplitudes in the seismic reflection profile (Figure F62). Intervals with increasing velocity and density with depth often correlate with strong positive amplitudes in the seismic reflection profile, whereas decreases correspond to negative amplitudes. Such correlations are especially clear between the velocity and density profiles and the depth-converted seismic trace at Site U1501.

### Time-depth relationship

The PWC velocity measurements from Holes U1501C and U1501D were used to calculate the time-depth relationship (TDR) model of seismic waves. We first calculated a preliminary model of TDR that best fits the observed PWC velocity data, called “U1501_Preliminary_Model” (Figure F63). This model was calculated using data for the 0–450 m interval only, where PWC data are available. For the 450–608 m interval, the highly scattered PWC data do not provide reliable constraints on the TDR models.

At least three depth intervals at Site U1501 are associated with major changes in velocity and/or density and are assigned as reference points for correlation with the seismic reflection profile. The three depth intervals of the most prominent changes are at ~303 m (RP1), ~450 m (RP2), and ~600 m (RP3). RP1 and RP3 also correlate with the seismic sequence T60 boundary and with the seismic Tg reflector, respectively. These reference points are readily recognized in the drill core, lending further support to our models. With the additional constraints from these reference points and fitting the TDR using a polynomial function with depth, we constructed a new TDR model for Site U1501 called “U1501_modified_model” (Figure
<figure><img src="image_275.png" /><figcaption>Figure F62. Comparison of a subset of physical properties with seismic waveform (converted to depth scale using best-fitting TDR model) and seismic image (in timescale).</figcaption></figure>

F63). The modified TDR model with constraints of the three refer-ence points is, in general, in line with the preliminary TDR model.

We also compared our TDR models of Site U1501 with those of Sites 1148 (Shipboard Scientific Party, 2000), U1431 (Li et al., 2015b), U1499, and U1500 (see the Site U1499 and Site U1500 chapters [Sun et al., 2018b; Stock et al., 2018]). Our calculated TDR models for Site U1501 show substantial agreement with the TDR models of most of these drill sites, especially with the model of Site 1148 (Figure F64).

Using the best-fitting TDR model (U1501_modified_model), we were able to convert depth scale to timescale for all core measurements. Such conversion enabled us to display the core measurements directly on top of the time-based seismic sections, facilitating identification of correlated features, as illustrated in the example in Figure F65.
Figure F63. TDR curves, Site U1501. U1501\_preliminary\_model was primarily based on PWC velocity data for depths shallower than ~450 m, an interval where PWC data are available. U1501\_modified\_model was based on the preliminary model with additional constraints from three reference points (RP1-RP3).

<figure><img src="image_276.png" /></figure>

## Synthetic seismograms

To further illustrate the relationship between the core measurements at Site U1501 and the seismic reflection profile, the Seismic interpretation module in Petrel was used to compute synthetic seismograms based on the relevant core measurements. Synthetic traces were generated by convolving the reflectivity from the density of core samples and the smoothed velocities from the PWC together with the source wavelet that best fits the seismic data (Ricker 2_30 Hz; Figure F66).

Seismic impedance (SI) of a rock layer is the product of its average seismic velocity ($V_p$) and density ($\rho$) (i.e., SI = $V_p \times \rho$). The seis-

Figure F64. Site U1501 TDR curves, including U1501\_preliminary\_model and U1501\_modified\_model, compared to TDRs for Sites U1499, U1500, and 1148 (Li et al., 2008).

<figure><img src="image_277.png" /></figure>

mic reflection coefficient (RC), in turns, measures the change in the seismic impedance between two adjacent rock layers. Thus, we can expect greater amplitudes in the modeled seismogram for rock layers with larger RC values. The resulting synthetic seismogram shows strong reflectors at several depth intervals, including ~303 and 600 m, that are consistent with the observed seismic unconformities. The transition between lithostratigraphic Units II and III at 600 m, for instance, is marked by a sharp increase in density and velocity; the net result is a strong positive increase in impedance (Figure F66).
<figure><img src="image_278.png" /><figcaption>Figure F65. Seismic section at Site U1501 with thin strip of synthetic seismogram and lithostratigraphic units overlain at drill hole location. Also shown are selected core and downhole logging measurements converted to depth scale using best-fitting TDR model, including magnetic susceptibility (core), thorium (logging), uranium (logging), PWL (core), density (core and logging), and NGR (core and logging).</figcaption></figure>
<figure><img src="image_279.png" /><figcaption>Figure F66. Synthetic seismogram, Site U1501. Left to right: smoothed velocity and MAD density used in the calculation, resultant RC, real seismic traces with synthetic seismogram inserted in the center, and seismic source function "Ricker 2_30 Hz" used in modeling. TVD = true vertical depth from Petrel software.</figcaption></figure>
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## Site U1502¹

<figure><img src="image_280.png" /></figure>

Check for updates

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 U1502, northern South China Sea, continent-ocean transition zone, Ridge A, hyperextension, continental breakup, thinning, rifting, altered basalt, Cenozoic, prerift, red clay, greigite, agglutinated benthic foraminifers

## Site summary

### Background and objectives

Site U1502 (proposed Site SCSIII-17A; Sun et al., 2016) within the South China Sea (SCS) northern margin (Figures F1, F2) is located at 3764 meters below sea level (mbsl) on a prominent basement ridge (A) within the continent-ocean transition (COT) (Figure F3). Ridge A is one of four distinct basement highs found across the COT. The outer margin high (OMH) is the most landward of these highs and is followed seaward by the nearly parallel Ridges A, B, and C. A key objective of Expeditions 367 and 368 was to examine the nature of the crust within Ridge A. This ridge is considered to be a pivotal element in the transition from continental to oceanic crust. Hence, the main objective of Site U1502 was to drill through synrift deposits overlying an interpreted shallow-dipping (~20°) fault zone and into the crystalline basement below the fault. Information on the nature and age of the synrift deposits overlying the fault, as well as the nature and age of the overlying sediments and associated seismic unconformities, formed another target with the objective of constraining basin subsidence.

## Contents

1. Site summary

7. Background and objectives

9. Operations

13. Lithostratigraphy

23. Igneous and metamorphic petrology

37. Structural geology

45. Biostratigraphy

49. Paleomagnetism

57. Geochemistry

62. Physical properties

67. Downhole measurements

71. Correlation to seismic data

75. References

## Operations

We conducted operations in two holes at Site U1502. Hole U1502A is located at 18°27.8720′N, 116°13.8381′E, at 3763 mbsl. Our operations in Hole U1502A were designed to provide information on formation characteristics and drilling conditions so that we could decide the length of casing to drill into the seafloor in deep-penetration Hole U1502B. Given this purpose and the amount of time to drill the second, deep hole, we did not core continuously in Hole U1502A. Instead, we drilled without coring from the seafloor to 375.0 m and cored with the rotary core barrel (RCB) system from 375.0 to 758.2 m, recovering 176.81 m (46%). Hole U1502B is located at 18°27.8798′N, 116°13.8409′E, at 3763.6 mbsl. In Hole U1502B, we drilled a reentry funnel and 727.7 m of 10¾ inch casing into the seafloor; cored with the RCB system through the sediment-basalt transition (727.7–739.16 m) and 180 m into the underlying basalt (739.16–920.95 m), recovering 128 m (70%); and collected downhole log data with the triple combo tool string and a check shot with the Versatile Sonic Imager (VSI) tool string.

<figure><img src="image_281.png" /></figure>

<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 U1502. *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.367368.106.2018*</footnote>

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

<footnote>MS 367368-106: Published 28 September 2018</footnote>

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

<figure><img src="image_282.png" /></figure>

## Lithostratigraphy

The sedimentary succession recovered at Site U1502 extends from the late Eocene to the late Miocene. The succession includes four sedimentary units (I and III–V) that are composed of mainly clay, nannofossil-rich clay, biosiliceous-rich clay, limestone, and clast-rich clay and two igneous units (II and VI) that are mainly composed of basalt. The base of the sedimentary succession is a sequence of clay and metasediments (dolomite marble and dolomitic limestone) that possibly forms the contact with a unit of altered basalt (Unit VI) (Figure F4).

Late Miocene to late Oligocene lithostratigraphic Unit I is divided into five subunits. Subunit IA (Hole U1502A = 375.00–486.82

Figure F2. Bathymetry with seismic lines, Site U1502. Site is not at exact crossing of seismic Lines 15ecLW7 and 15ecLW3. Common depth point (CDP) numbers are shown along seismic lines.

<figure><img src="image_283.png" /></figure>

m) is composed of dark gray, gray, dark greenish gray, and greenish gray silty clay, clay with nannofossils, and nannofossil-rich clay intercalated with dark grayish brown, grayish brown, and brown clay with nannofossils, with minor dark greenish gray sandy clay with calcite. Subunit IB (Hole U1502A = 490.20–599.57 m) is composed of alternating intervals of brown and greenish gray clay, silty clay, and clayey silt. Sandy intervals are rare. Recovery in Subunits IA and IB was very poor, which might be due to the occurrence of thick sand beds that were washed out. Subunit IC (Hole U1502A = 599.57–602.39 m) is composed of greenish gray and reddish gray foraminifer-rich clayey siltstone to sandstone with parallel laminations and convolute bedding, with thin layers of pinkish gray foraminiferal chalk. Subunit ID (Hole U1502A = 602.39–724.03 m) is mainly composed of alternating greenish and brownish gray and grayish brown clay, silty clay, clayey silt, and clay with silt (Cores 368-U1502A-25R through 32R), but brown colors dominate Cores 33R through 38R. Nannofossils are abundant within the lowermost ~4 m of this subunit. Subunit IE (Hole U1502A = 724.03–734.87 m; Hole U1502B; 727.79–727.96 m) is composed of brown nannofossil-rich clay with foraminifers and nannofossil-rich clay with pale green colored halos around fractures. The sediments of Unit I are interpreted as having been deposited in a deep-marine environment. Fining-upward intervals in Subunits IA–IC are interpreted as turbidites.

Unit II is a highly altered greenish gray basalt clast recovered from Hole U1502B at 727.96–728.04 m. The primary mineral phases are replaced by an alteration-mineral assemblage.

Unit III (Hole U1502A = 739.10–739.16 m; Hole U1502B = 728.04–733.82 m) is composed of brownish yellow, very hard, poorly sorted breccia. The granule- to pebble-size siliceous clasts consist of alteration minerals (Fe hydroxides) cemented by a matrix of annealed quartz in various grain sizes.

Unit IV (Hole U1502A = 739.16–747.20 m) consists of biosiliceous-rich silty clay. Diatoms, sponge spicules, and radiolarians are
Figure F3. 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 the COT. A large detachment fault ~150 km inland of the COT separates more stable crust landward from that of highly extended crust seaward. An OMH is a fairly consistent feature 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 (black) 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 = approximate location of normal polarity magnetic isochrons. MSB = midslope basin.

<figure><img src="image_284.png" /></figure>

abundant in the upper part, but the abundance of both nannofossils and diatoms decreases rapidly downhole from Section 368-U1502A-40R-1 to Section 40R-3. Pyrite occurs as centimeter-sized patches and along cracks. The layering in Unit IV is inclined and may be slightly deformed.

Unit V (Hole U1502A = 747.20–749.01 m; Hole U1502B = 733.82–739.16 m) is an interval of alternating metasediments (dolomite marble, dolomitic limestone, and clast-rich clay). The dolomite marble is dominated by very fine grained dolomite (~95%) with minor amounts of magnetite (~3%) and calcite (~2%). The annealing texture is equigranular and crossed by fine-grained dark gray bands. The presence of magnetite explains the extraordinarily high magnetic susceptibility of this unit. The gray, fine-grained dolomitic limestone in Hole U1502B is intercalated with well-consolidated, very dark greenish gray clay with 10%–15% igneous clasts. The sediment is partially overprinted with alteration caused by secondary high-temperature processes (e.g., hydrothermal fluid sediment interaction or contact metamorphism).

Unit VI (Hole U1502A = 749.01–750.67 m; Hole U1502B = 739.16–920.95 m) consists of highly altered basaltic breccia, brecciated basalt, pillow basalt, and sheet basalt. The unit is divided into two subunits. Subunit VIA is composed of highly altered basaltic breccia and brecciated basalt with minor sheet basalt, chert, and claystone and very minor pillow basalt. Subunit VIB is dominated by altered pillow basalt and sheet flows and is less brecciated than Subunit VIA.

## Igneous petrology

At Site U1502, we recovered two igneous lithologic units. Unit 1 (lithostratigraphic Unit II) is represented by just three small, aphanitic, fine-grained basalt fragments that contain rare plagioclase phenocrysts (Figure F5). Alteration of Unit 1 is intense, with most of the groundmass replaced by green clay minerals, clinozoisite, zeolites, and Fe (hydr)oxides.

Unit 2 (lithostratigraphic Unit VI) comprises a 182 m thick sequence of highly altered aphyric to highly plagioclase porphyritic basalts with minor chert (Figure F5). These basalts are divided into two igneous subunits (2a and 2b) based on flow morphology and alteration style: an upper brecciated and fractured massive lava flow sequence (Subunit 2a) and a lower sequence of interbedded pillow flows with lobate and sheet lava flows in which the alteration style is characterized by intense veining (Subunit 2b). Subunit 2a is characterized by highly altered breccia clasts of sparsely to moderately phyric basalt in a matrix of carbonates, epidote, chlorite, Fe (hydr)oxides, quartz, zeolite minerals, and clay minerals. The clasts show an alteration assemblage similar to the matrix, with remnant plagioclase and secondary pyrite. Subunit 2b consists of aphyric to highly plagioclase phyric (>30%) basalts with abundant chlorite and sulfides, as well as epidote, clay minerals, carbonates, zeolites, and opaque minerals.

All of Unit 2 has undergone some degree of hydrothermal alteration. This alteration varies from complete replacement of the rock,
<figure><img src="image_285.png" /><figcaption>Figure F4. Lithostratigraphic summary with simplified lithology and unit descriptions, Holes U1502A and U1502B.</figcaption></figure>

where the original composition and texture are difficult to deter-
mine, to replacement of mineral phases with little change to the tex-
ture. Glassy pillow rinds are completely replaced, and multiple
phases of veining and halos are ubiquitous throughout the rocks.
Three vein types were observed: (1) white to green to black silica-
epidote veins, (2) apple green pyrite-epidote veins, and (3) white sil-
ica and/or calcite veins. Sulfide mineralization (disseminated and

veined) is widespread throughout Unit 2 and is dominated by pyrite,
with minor sphalerite, chalcopyrite, and covellite.

Handheld portable X-ray fluorescence (pXRF) analyses show no
significant differences in contents of alteration-resistant elements
such as Ti and Zr within Unit 2, but Subunit 2a has lower MgO,
FeO, and MnO than Subunit 2b, which is consistent with the higher
degree of alteration. Subunit 2b is also strongly affected by second-
Figure F5. Lithostratigraphic summary of Holes U1502A and U1502B with main igneous lithologies and deformation structures. A. Highly plagioclase-phyric basalt with up to 50% plagioclase phenocrysts. B. Highly altered, sparsely plagioclasephyric pillow basalt with a well-preserved pillow. C. Moderately altered aphyric basalt flow with sparse vesicles. Note the change to a bluish gray color. D. Slump folds. E. Microfaults showing striations/slickensides on exposed surfaces. F. Distributed shear geometries with shear bands and tilted bedding. G. Brecciated basalt. H. Basaltic breccia. I. Network of composite epidote-rich veins.

<figure><img src="image_286.png" /></figure>

ary alteration, but areas of less intense alteration are indicated by higher magnetic susceptibility and high CaO and Fe₂O₃ contents. Unit 1 appears to be compositionally distinct from Unit 2 and has, for example, higher Ti/Zr ratios.

Structural geology

Deformation structures are scarce in Unit I above Core 368-U1502A-37R, with only a local, convolutely bedded sequence in Core 25R. Downhole from Core 37R at ~700 m, a gradual increase
in deformation structures was observed (Figure F5). Cores 37R through 39R are characterized by microfaults, as evidenced by downward-dip plunging striations and slickensides on exposed fracture surfaces, systematically associated with greenish halos. No deformation structures were encountered in Unit II. Unit III consists of extremely silicified breccia that was poorly recovered. The nature of this breccia, however, as sedimentary, tectonic, or hydrothermal remains unconstrained at the moment. In Unit IV, a small-scale transition from distributed to localized shear in unithilitified sediments was documented. No deformation structures were encountered in Unit V.

Unit VI is essentially composed of basalts that were heterogeneously affected by brecciation and veining associated with the circulation of hydrothermal fluids. Subunit VIA is dominated by brecciated basalt/basaltic breccia, whereas Subunit VIB comprises a rather coherent series of lava flows crosscut by a multistage network of polymineralic veins. The uppermost part of Unit VI contains severely fractured and fragmented basalt locally filled by fine-grained unconsolidated greenish rock. Subunit VIA is characterized by diverse brecciation horizons associated with veins and microcracks. Depending on the intensity of fragmentation and the clast/matrix ratio, the rocks are referred to as brecciated basalt or basaltic breccia. A typically observed feature is the jigsaw-puzzle structure, suggesting possible in situ fragmentation. Macro- and microscopic observations show that the breccia-clasts consist mainly of sparsely to moderately plagioclase phryic basalts that were hydrothermally altered to variable degrees. Thus, formation of such breccias likely involved fluid-assisted fracturing of basalt. In contrast, Subunit VIB is characterized by a progressive decrease of breccia horizons and the development of different vein types, almost always polymineralic. Notably, vein composition and their orientation changes through Subunit VIB. Although numerous small-scale veins often related with major veins were observed, three first-order vein types were categorized: (1) composite silica-rich veins, (2) composite epidotite-rich veins, and (3) composite carbonate- and/or silica-rich veins.

## Biostratigraphy

All core catcher samples from Hole U1502A and selected samples from Hole U1502B were analyzed for calcareous nannofossils, foraminifers, diatoms, and ostracods. Additional samples were taken from the working-half core intervals when necessary to refine the ages. The preservation of calcareous microfossils is mostly good to moderate in the upper sections (Cores 368-U1502A-2R through 13R) and moderate to poor in the lower sections (Cores 14R through 41R). Planktonic foraminifers and calcareous nannofossils are abundant to common in Cores 2R through 10R, 25R, and 37R through 39R and rare to barren in all other sections. Diatoms were only observed in Sections 40R-1 through 40R-3. In Hole U1502B, foraminifers were observed only in Section 3R-1 and are represented by well-preserved agglutinated deepwater taxa. Ostracods are extremely rare; single occurrences were observed only in three samples in Hole U1502A (Samples 3R-CC, 4R-CC, and 5R-CC).

Fourteen planktonic foraminifer and calcareous nannofossil biostratigraphic events were used to provide an age-depth model for Site U1502 from the late Oligocene to the late Miocene. The Pliocene/Miocene boundary is placed tentatively within Core 368-U1502A-2R, but it may be shallower than the cored section. The Miocene/Oligocene boundary was determined to lie between Samples 39R-CC and 40R-1, 7 cm. Sedimentation rates vary from ~10 mm/ky in the early-middle Miocene to ~39 mm/ky in the late Miocene.

No planktonic microfossils were found in Hole U1502B, but a sample from the sandy interval in Core 3R revealed abundant and diverse abyssal agglutinated benthic foraminifers. The composition of this agglutinated benthic foraminifer assemblage provides a possible age of late Eocene for this interval.

## Paleomagnetism

The magnetic behavior of sediments at Site U1502 correlates with their color (greenish gray or reddish brown). Reddish brown sediment shows alternating field (AF) magnetization indicative of magnetite or titanomagnetite and hematite (responsible for the color). In contrast, greenish gray sediment hosts magnetite or titanomagnetite and pyrrhotite. The predominance of steep normal inclinations (~75°; Figure F48) across all late Oligocene to late Miocene units (375.00–750.67 m) affects the superconducting rock magnetometer (SRM) section measurements and prevents any reliable magnetostratigraphy to be established for Holes U1502A and U1502B.

The basalt has natural remanent magnetization (NRM) intensity one order of magnitude higher than sediment. The main magnetically remanent phase is titanomagnetite, but its alteration produces maghemite or hematite. Magnetic susceptibility (κ) has a bimodal distribution with a median at $327 \times 10^{-6}$ SI. κ does not show any strong correlation with any chemical ($R^2$ = 0.343 for $Fe_2O_3$ wt%). Intervals of high κ might correspond to the bottoms of flows with a massive, less altered structure. Altered basalts have higher Koenigberger ratios ($Q_n$ = 1–10) than fresher basalts ($Q_n$ = 0.001–1). The mean dip of magnetic foliation is 8°.

Cores 368-U1502B-9R and 10R show less-pervasive drilling overprint, and two discrete samples show both a normal (soft) component and a reverse (hard) component, suggesting a possible reversal.

## Geochemistry

Site U1502 contains very low high-hydrocarbon gas abundances and total organic carbon (TOC), nitrogen, and sulfur contents, likely reflecting the poor preservation of organic matter. Instances of high carbonate content are associated with siderite, and on occasion this mineral comprises >50 wt% by mass of intervals in lithostratigraphic Subunit ID. The interstitial water at Site U1502 is enriched in Ca, Mg, and K and has notably high alkalinity but is depleted in Na, Cl, and Br. The linear increase of major anion and cation contents implies upward movement of fluid from deeper sediments. The hemipelagic sediments within Unit I have some similarities to the geochemical characteristics of the hemipelagic and pelagic units at Sites U1501 and U1505, but Site U1502 sediments are enriched in Fe, K, and clay concentrations, likely as a result of regions of increased alteration. All of the analyzed igneous rocks from Units II–VI are heavily altered, although samples from igneous lithologic Subunit 2b are altered to a lesser degree than those from Subunit 2a.

## Physical properties

Physical property data acquired at Site U1502 include density, magnetic susceptibility, P-wave velocity, natural gamma radiation (NGR), color reflectance, and thermal conductivity (Figure F63). These data allow us to characterize four physical property (PP) units. PP Unit 1 (375–740 m) corresponds to the nannofossil-rich and biosiliceous-rich clay lithologies and exhibits small variations in NGR between 50 and 70 counts/s and uniformly increasing P-wave velocities with depth that average <2500 m/s. Unit 1 sediments have similar porosities to those recorded at nearby Sites U1499 and U1502.
U1500 in the same depth interval, suggesting the same compaction history. A significant increase in bulk density (up to 2.7 g/cm³) in Core 368-U1502B-3R is associated with strongly lithified limestone beds. Variations of high and low magnetic susceptibility values correspond to sediment color changes in Unit 1 and may be controlled by the amount of pyrrhotite within the sediments.

PP Unit 2 (740–750 m) in Hole U1502A is characterized by lower *P*-wave velocities and bulk densities and higher NGR than the strata above. Low densities and *P*-wave velocities found in Unit 2 reflect the clast-rich claystone from lithostratigraphic Unit V.

PP Units 3 and 4 represent the basaltic basement and are characterized by relatively low NGR (<10 counts/s), high densities, and *P*-wave velocities that vary over a broad range (3000–6000 m/s). The boundary between Units 3 and 4 is marked by an abrupt increase in density, *P*-wave velocity, and thermal conductivity and coincides with the change from igneous lithologic Subunit 2a to 2b. Prominent magnetic susceptibility peaks (up to 4000 × 10⁻⁵ SI) in Units 3 and 4 correspond to relatively less altered basalt. Thermal conductivity in Units 3 and 4 is variable but generally increases in line with decreasing porosity with depth.

## Downhole measurements

Wireline logging was conducted in Hole U1502B using a modified triple combination (triple combo) tool string and the VSI tool string. The modified triple combo tool string included the Hostile Environment Natural Gamma Ray Sonde (HNGS), Hostile Environment Litho-Density Sonde (HLDS), and Dipole Sonic Imager (DSI) for acoustic velocity. The triple combo run collected good data downhole from 875.3 m (~45 m above the bottom of Hole U1502B) and allowed us to define eight logging units, which correlate in great part to the lithostratigraphic units and core physical properties. Logging Units 1–5 are defined by data collected through the casing and drill pipe. Unit 6 data was collected outside the casing but inside the drill pipe, whereas data in Units 7 and 8 were collected in the open hole. For measurements inside the casing and/or drill pipe, only NGR and the associated K, Th, and U components provide meaningful data, although they are highly attenuated by the casing and/or drill pipe. Open borehole conditions from the bottom of the casing at 723 m to 875.3 m were generally good, with measured diameters from 12 to 14.5 inches. Log and core data generally show good agreement, and downhole measurements provide information in zones of poor core recovery in Hole U1502B. The log data exhibit increasing densities and *P*-wave velocities with depth. The amplitude of NGR increases gradually with depth throughout Units 1–3 (seafloor to ~630 m), with an interval of relatively constant values between 150 and 350 m. NGR values are lowest in Units 4–8 (~630–850 m).

The VSI tool string was run only inside the casing because the tool could not pass through an obstruction encountered at the end of the casing. Eight stations were attempted. The two deepest stations (at 715.1 and 695.2 m) are associated with large noise levels, which were possibly caused by poor mechanical coupling of the casing with the surrounding formation. The remaining upper six stations, located at 290.2, 350.3, 450.3, 550.1, 590.3, and 630.3 m, recorded good quality waveforms.

## Background and objectives

Site U1502 within the SCS northern margin (Figures F2, F6) is located at a water depth of 3764 m on a prominent basement ridge

Figure F6. 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 (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.

<figure><img src="image_287.png" /></figure>

<figure><img src="image_288.png" /></figure>

(Ridge A) within the seaward end of the COT. Ridge A is one of four distinct basement highs found across the COT (Figure F3). The OMH is the most landward of these highs (see the Site U1501 chapter [Larsen et al., 2018]) within the COT and is followed seaward by the nearly parallel Ridges A, B, and C. The crustal thickness
below Ridge A is significantly smaller (~8 km) than below the OMH (~15 km) and close to the thickness found ~6 km further seaward within the COT. The oldest interpreted seafloor-spreading magnetic anomaly seaward of Site U1502 is Chron C11n (~30 Ma), which runs parallel to Ridge A (Figures F1, F3) ~20 km to the south of the ridge.

Site U1499 was also drilled on Ridge A ~70 km west of Site U1502 and recovered a Neogene sediment section on top of the basin-wide Tg reflector. Below the Tg reflector, Site U1499 recovered Oligocene sediments (see the **Site U1499** chapter [Sun et al., 2018b]). The pre-Miocene sediments comprise sandstone, claystone, matrix-supported breccia, and gravel. They are interpreted to have a proximal source and to possibly reflect a tectonically active environment. True crystalline basement was not recovered at Site U1499 due to the collapse of Hole U1499B.

Site U1502 on Ridge A is located near the crossing of seismic Lines 15ecLW7 and 15ecLW3 (Figure F2, site specific bathymetry). Ridge A can be followed along the margins for more than 100 km (Figure F6). Before drilling, it was interpreted to be fault bounded (Figure F7, main line). The structure is narrower and steeper in this location than elsewhere along the ridge. Along strike, it forms an elongated local high on Ridge A (Figure F8, cross-line).

Figure F7. Original and predrilling interpretation of seismic dip Line 15ecLW7 crossing (projected) with seismic Line 15ecLW3 (red tick mark) (CDP distance = 6.25 m). Seismic stratigraphic Unconformities T30 (5.3 Ma), T32 (10.0 Ma), T60 (23.0 Ma), and T70 (33.9 Ma) and acoustic basement Unconformity Tg are shown (see Seismic stratigraphic framework in the Expedition 367/368 methods chapter [Sun et al., 2018a]). In places, there are clear but not extensively coherent seismic reflectors below Tg.

<figure><img src="image_289.png" /></figure>

This seismic line along the ridge also shows evidence of normal faulting. In general, however, the seismic reflectors do not show significant dip that would be indicative of major fault-block rotation. The one exception is the set of strong reflectors overlying the interpreted fault on the seaward flank of the ridge (Figure F7, main line). No 3-D interpretation of faults was possible.

The predrilling interpretation of the seismic unconformities (T30 to T70 and Tg reflector; see **Correlation to seismic data** in the Expedition 367/368 methods chapter [Sun et al., 2018a]) around Site U1502 is shown in Figure F7 (main line). This shows the regional T60 unconformity rising from the basin seaward of Ridge A, possibly present almost to the top of the structure, and reappearing on the landward side of the ridge. It is also possible, however, that the T32 unconformity has completely removed (eroded) the T60 unconformity across the ridge, in which case sediments of lower and middle Miocene age should be missing at this site. The high-amplitude, dipping reflectors at Site U1502 just below this unconformity were interpreted predrilling as synrift deposits of pre-T60 (~23 Ma) age, possibly sediments of the same age and nature as those recovered at Site U1499, and related to rifting. However, as detailed in this chapter, the high-amplitude reflector (Tg) represents the top of a sequence of seaward-dipping, submarine basaltic lava flows, implying that the structure is a seaward rotated fault block bounded entirely by landward-dipping normal faults.

A key objective of Expeditions 367 and 368 was to examine the nature of the crust within Ridge A. This ridge is considered a key element in the transition from continental to oceanic crust. Specific questions to be answered by drilling:

Figure F8. Original and predrilling interpretation of seismic strike Line 15ecLW3 crossing with seismic Line 15ecLW7 (red tick mark) (CDP distance = 6.25 m). See Figure F7 for description of seismic interpretations. Dashed lines = unconformities, red solid lines = faults.

<figure><img src="image_290.png" /></figure>
* Does it represent continental crust, and if so, does it represent upper or lower crust?

* Did tectonic exhumation reach into the lithospheric mantle, and did serpentinization take place?

* Or is the structure possibly partly or wholly of igneous origin (see the **Expedition 367/368 methods** chapter [Sun et al., 2018a]？)

Because Site U1499 failed to provide conclusive evidence of the nature of the crystalline basement of Ridge A, the key objective of Site U1502 was to drill through the interpreted fault zone and into the crystalline basement at this location on Ridge A. Information on the nature and age of interpreted synrift deposits overlying the fault forms a secondary objective, along with the nature and age of the overlying unconformities, their depositional environment, and the constraints they can offer on basin subsidence.

In this deep water, post-Miocene sediments were deposited below the carbonate compensation depth (CCD) and were therefore not a coring objective. Site operations were planned to drill without coring through the sediments postdating the T30 unconformity, core from there to basement in Hole A, drill in Hole B with casing almost to the T60 unconformity, and then core from there until conclusive results regarding basement were obtained (see **Operations**).

## Operations

We conducted operations in two holes at Site U1502 with the objective of sampling the lowermost sediment and underlying basalt. We successfully penetrated from the seafloor to the sediment/basalt contact at 728 m and 180 m into the underlying basalt. The sedimentary section was not continuously cored, and recovery in the cored intervals was highly variable and relatively low (46%). In contrast, core recovery in the basalt was significantly better (70%). Downhole logging was conducted in Hole U1502B with the triple combo and VSI tool strings.

Hole U1502A is located at 18°27.8720'N, 116°13.8381'E, at a water depth of 3763.2 m. Operations in Hole U1502A were designed to provide information on the formation characteristics and drilling

conditions so that we could decide the length of casing to drill into the seafloor at the second, deep-penetration Hole U1502B. Given this purpose and the amount of time needed to drill Hole U1502B, we did not core continuously in Hole U1502A. Instead, we drilled without coring from the seafloor to 375 m and RCB cored from 375 to 758.2 m, recovering 176.81 m (46%).

Hole U1502B is located at 18°27.8798'N, 116°13.8409'E, at a water depth of 3763.6 m. We conducted the following operations in Hole U1502B:

* Drilled a reentry funnel and 727.7 m of 10.75 inch casing into the seafloor,

* RCB cored the sediment sequence from 727.7 to 739.16 m (11.46 m cored; 3.55 m recovered; 31%),

* RCB cored 180 m into the underlying basalt (739.16–920.95 m; 128 m recovered [70%]), and

* Collected downhole log data with the triple combo and VSI tool strings.

Hole U1502A and U1502B coring summaries are presented in Table T1. A diagram of the reentry cone and casing in Hole U1502B is shown in Figure F9.

## Hole U1502A

The R/V JOIDES Resolution made the 36.5 nmi transit from Site U1501 to Site U1502 in 3.6 h, averaging 10.1 kt. The vessel arrived over the site coordinates at 2142 h on 24 April 2017. At 2240 h, an acoustic beacon was deployed approximately 100 m west of the site coordinates. Upon arrival at Site U1502, a new C-4 RCB bit with a mechanical bit release (MBR) was assembled onto the bottom of the bottom-hole assembly (BHA). The core barrel space out was checked, and the BHA was lowered to 161 mbl. The precision depth recorder measurement taken on arrival showed a calculated seafloor depth of 3768.4 m.

The bit was lowered to 3733 mbl, stopping every 20 stands to fill the pipe with water. The upper guide horn (UGH) was pulled, and the underwater camera system was deployed to the seafloor to observe the end of the pipe tag the seafloor. While the camera was being lowered, 115 feet of drill line was slipped and cut. After the

<table><caption>Table T1. Site U1502 core summary. DRF = drilling depth below rig floor, DSF = drilling depth below seafloor. Core type: R = rotary core barrel, numeric core type = drilled interval. (Continued on next two pages.) **Download table in CSV format.**</caption><thead><tr><th colspan="11">Hole U1502A</th><th colspan="6">Hole U1502B</th></tr><tr><th></th><th>Latitude:</th><th>Longitude:</th><th>Seafloor (drill pipe measurement below rig floor, m DRF):</th><th>18°27.8720'N</th><th>116°13.8381'E</th><th>Time on hole (days):</th><th>Total depth (drill pipe measurement from rig floor, m DRF):</th><th>Distance between rig floor and sea level (m):</th><th>Total penetration (drilling depth below seafloor, m DSF):</th><th>Total core recovered (m):</th><th>Core recovery (%):</th><th>Drilled interval (m):</th><th>Total cores (no.):</th><th>18°27.8798'N</th><th>116°13.8409'E</th></tr><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 type</th><th>Mud pumped (bbl)</th><th>Driller's notes</th><th></th><th></th></tr></thead><tbody><tr><td>368-U1502A-</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>1</td><td>1</td><td>0</td><td>375.0</td><td>375.0</td><td>*****Drilled interval*****</td><td></td><td></td><td>4/25/2017 00:00</td><td>150</td><td>Nonmagnetic</td><td>135</td><td></td><td></td></tr><tr><td>2</td><td>R</td><td>375.0</td><td>384.6</td><td>9.6</td><td>1.81</td><td>1.81</td><td>19</td><td>4/26/2017 01:05</td><td></td><td>Nonmagnetic</td><td></td><td></td><td></td></tr><tr><td>3</td><td>R</td><td>384.6</td><td>394.2</td><td>9.6</td><td>0.85</td><td>0.85</td><td>9</td><td>4/26/2017 02:30</td><td></td><td>Nonmagnetic</td><td>15</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 type</th><th>Mud pumped (bbl)</th><th>Driller's notes</th></tr></thead><tbody><tr><td>4</td><td>R</td><td>394.2</td><td>403.8</td><td>9.6</td><td>0.47</td><td>0.47</td><td>5</td><td>4/26/2017 03:35</td><td>15</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>5</td><td>R</td><td>403.8</td><td>413.4</td><td>9.6</td><td>0.05</td><td>0.05</td><td>1</td><td>4/26/2017 05:45</td><td></td><td>Nonmagnetic</td><td>15</td><td></td></tr><tr><td>6</td><td>R</td><td>413.4</td><td>423.0</td><td>9.6</td><td>0.64</td><td>0.64</td><td>7</td><td>4/26/2017 06:50</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>7</td><td>R</td><td>423.0</td><td>432.6</td><td>9.6</td><td>0.05</td><td>0.05</td><td>1</td><td>4/26/2017 07:50</td><td>15</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>8</td><td>R</td><td>432.6</td><td>442.2</td><td>9.6</td><td>0.14</td><td>0.14</td><td>1</td><td>4/26/2017 09:15</td><td></td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>9</td><td>R</td><td>442.2</td><td>451.8</td><td>9.6</td><td>8.02</td><td>8.02</td><td>84</td><td>4/26/2017 11:00</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>10</td><td>R</td><td>451.8</td><td>461.4</td><td>9.6</td><td>7.01</td><td>7.01</td><td>73</td><td>4/26/2017 13:00</td><td>15</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>11</td><td>R</td><td>461.4</td><td>471.0</td><td>9.6</td><td>9.15</td><td>9.15</td><td>95</td><td>4/26/2017 15:30</td><td></td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>12</td><td>R</td><td>471.0</td><td>480.6</td><td>9.6</td><td>9.23</td><td>9.23</td><td>96</td><td>4/26/2017 17:55</td><td>20</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>13</td><td>R</td><td>480.6</td><td>490.2</td><td>9.6</td><td>6.27</td><td>6.27</td><td>65</td><td>4/26/2017 20:10</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>14</td><td>R</td><td>490.2</td><td>499.8</td><td>9.6</td><td>7.06</td><td>7.06</td><td>74</td><td>4/26/2017 22:35</td><td>20</td><td>Nonmagnetic</td><td>20</td><td>Drilling break at 497 m</td></tr><tr><td>15</td><td>R</td><td>499.8</td><td>509.3</td><td>9.5</td><td>0.90</td><td>0.90</td><td>9</td><td>4/27/2017 00:30</td><td></td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>16</td><td>R</td><td>509.3</td><td>518.9</td><td>9.6</td><td>0.35</td><td>0.35</td><td>4</td><td>4/27/2017 02:20</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>17</td><td>R</td><td>518.9</td><td>528.6</td><td>9.7</td><td>0.75</td><td>0.75</td><td>8</td><td>4/27/2017 04:10</td><td>20</td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>18</td><td>R</td><td>528.6</td><td>538.2</td><td>9.6</td><td>6.06</td><td>6.06</td><td>63</td><td>4/27/2017 06:00</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>19</td><td>R</td><td>538.2</td><td>547.8</td><td>9.6</td><td>0.00</td><td>0.00</td><td>0</td><td>4/27/2017 07:45</td><td></td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>20</td><td>R</td><td>547.8</td><td>557.3</td><td>9.5</td><td>0.00</td><td>0.00</td><td>0</td><td>4/27/2017 09:25</td><td>20</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>21</td><td>R</td><td>557.3</td><td>566.9</td><td>9.6</td><td>0.01</td><td>0.01</td><td>0</td><td>4/27/2017 11:15</td><td></td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>22</td><td>R</td><td>566.9</td><td>576.4</td><td>9.5</td><td>0.00</td><td>0.00</td><td>0</td><td>4/27/2017 01:05</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>23</td><td>R</td><td>576.4</td><td>585.9</td><td>9.5</td><td>0.42</td><td>0.42</td><td>4</td><td>4/27/2017 15:10</td><td></td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>24</td><td>R</td><td>585.9</td><td>595.5</td><td>9.6</td><td>3.05</td><td>3.05</td><td>32</td><td>4/27/2017 17:05</td><td></td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>25</td><td>R</td><td>595.5</td><td>605.0</td><td>9.5</td><td>7.00</td><td>7.00</td><td>74</td><td>4/27/2017 19:20</td><td></td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>26</td><td>R</td><td>605.0</td><td>614.6</td><td>9.6</td><td>1.31</td><td>1.31</td><td>14</td><td>4/27/2017 21:05</td><td>20</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>27</td><td>R</td><td>614.6</td><td>624.2</td><td>9.6</td><td>0.01</td><td>0.01</td><td>0</td><td>4/27/2017 22:55</td><td>40</td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>28</td><td>R</td><td>624.2</td><td>633.8</td><td>9.6</td><td>2.98</td><td>2.98</td><td>31</td><td>4/28/2017 00:55</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>29</td><td>R</td><td>633.8</td><td>643.4</td><td>9.6</td><td>9.66</td><td>9.66</td><td>101</td><td>4/28/2017 03:30</td><td></td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>30</td><td>R</td><td>643.4</td><td>653.0</td><td>9.6</td><td>9.87</td><td>9.87</td><td>103</td><td>4/28/2017 05:50</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>31</td><td>R</td><td>653.0</td><td>662.5</td><td>9.5</td><td>9.75</td><td>9.75</td><td>103</td><td>4/28/2017 08:10</td><td></td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>32</td><td>R</td><td>662.5</td><td>672.1</td><td>9.6</td><td>9.37</td><td>9.37</td><td>98</td><td>4/28/2017 10:15</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>33</td><td>R</td><td>672.1</td><td>681.7</td><td>9.6</td><td>6.98</td><td>6.98</td><td>73</td><td>4/28/2017 13:10</td><td></td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>34</td><td>R</td><td>681.7</td><td>691.3</td><td>9.6</td><td>7.22</td><td>7.22</td><td>75</td><td>4/28/2017 15:20</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>35</td><td>R</td><td>691.3</td><td>700.9</td><td>9.6</td><td>7.55</td><td>7.55</td><td>79</td><td>4/28/2017 17:30</td><td></td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>36</td><td>R</td><td>700.9</td><td>710.4</td><td>9.5</td><td>9.56</td><td>9.56</td><td>101</td><td>4/28/2017 19:35</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>37</td><td>R</td><td>710.4</td><td>720.0</td><td>9.6</td><td>9.22</td><td>9.22</td><td>96</td><td>4/28/2017 22:00</td><td></td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>38</td><td>R</td><td>720.0</td><td>729.6</td><td>9.6</td><td>8.32</td><td>8.32</td><td>87</td><td>4/29/2017 01:00</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>39</td><td>R</td><td>729.6</td><td>739.1</td><td>9.5</td><td>5.27</td><td>5.27</td><td>55</td><td>4/29/2017 03:30</td><td></td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>40</td><td>R</td><td>739.1</td><td>748.7</td><td>9.6</td><td>8.43</td><td>8.43</td><td>88</td><td>4/29/2017 05:40</td><td></td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>41</td><td>R</td><td>748.7</td><td>758.2</td><td>9.5</td><td>2.02</td><td>2.02</td><td>21</td><td>4/29/2017 09:40</td><td></td><td>Nonmagnetic</td><td>30</td><td></td></tr><tr><td colspan="12">Hole U1502A totals (excluding drilled interval):</td></tr><tr><td>368-U1502B-1</td><td>1</td><td>0</td><td>727.7</td><td>727.7</td><td colspan="5">****Drilled interval****</td><td>5/4/2017 03:00</td><td>1225</td><td>Nonmagnetic</td><td>20</td></tr><tr><td>2</td><td>R</td><td>727.7</td><td>733.7</td><td>6.0</td><td>0.84</td><td>0.85</td><td>14</td><td>5/4/2017 04:15</td><td>35</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>3</td><td>R</td><td>733.7</td><td>738.7</td><td>5.0</td><td>2.71</td><td>2.71</td><td>54</td><td>5/4/2017 07:40</td><td>110</td><td>Nonmagnetic</td><td>15</td><td></td></tr><tr><td>4</td><td>R</td><td>738.7</td><td>748.3</td><td>9.6</td><td>2.60</td><td>2.60</td><td>27</td><td>5/4/2017 11:30</td><td>135</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>5</td><td>R</td><td>748.3</td><td>757.9</td><td>9.6</td><td>1.75</td><td>1.75</td><td>18</td><td>5/4/2017 17:40</td><td>240</td><td>Nonmagnetic</td><td>15</td><td></td></tr><tr><td>6</td><td>R</td><td>757.9</td><td>767.5</td><td>9.6</td><td>8.80</td><td>8.80</td><td>92</td><td>5/4/2017 23:10</td><td>230</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>7</td><td>R</td><td>767.5</td><td>777.1</td><td>9.6</td><td>4.48</td><td>4.48</td><td>47</td><td>5/5/2017 03:25</td><td>170</td><td>Nonmagnetic</td><td>15</td><td></td></tr><tr><td>8</td><td>R</td><td>777.1</td><td>786.7</td><td>9.6</td><td>3.41</td><td>3.41</td><td>36</td><td>5/5/2017 08:15</td><td>200</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>9</td><td>R</td><td>786.7</td><td>791.3</td><td>4.6</td><td>2.48</td><td>2.48</td><td>54</td><td>5/5/2017 12:05</td><td>135</td><td>Nonmagnetic</td><td>15</td><td></td></tr><tr><td>10</td><td>R</td><td>791.3</td><td>796.3</td><td>5.0</td><td>4.19</td><td>4.19</td><td>84</td><td>5/5/2017 15:55</td><td>140</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>11</td><td>R</td><td>796.3</td><td>800.9</td><td>4.6</td><td>2.88</td><td>2.88</td><td>63</td><td>5/5/2017 19:30</td><td>120</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>12</td><td>R</td><td>800.9</td><td>805.9</td><td>5.0</td><td>3.55</td><td>4.205</td><td>71</td><td>5/5/2017 23:50</td><td>165</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>13</td><td>R</td><td>805.9</td><td>810.5</td><td>4.6</td><td>4.90</td><td>5.20</td><td>107</td><td>5/6/2017 04:25</td><td>175</td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>14</td><td>R</td><td>810.5</td><td>815.5</td><td>5.0</td><td>4.72</td><td>4.72</td><td>94</td><td>5/6/2017 09:00</td><td>190</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>15</td><td>R</td><td>815.5</td><td>820.1</td><td>4.6</td><td>4.62</td><td>4.62</td><td>100</td><td>5/6/2017 12:40</td><td>125</td><td>Nonmagnetic</td><td>15</td><td></td></tr><tr><td>16</td><td>R</td><td>820.1</td><td>825.1</td><td>5.0</td><td>3.96</td><td>3.96</td><td>79</td><td>5/6/2017 16:40</td><td>145</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>17</td><td>R</td><td>825.1</td><td>829.6</td><td>4.5</td><td>3.75</td><td>4.70</td><td>83</td><td>5/7/2017 00:20</td><td>135</td><td>Nonmagnetic</td><td></td><td>Deplugger run</td></tr><tr><td>18</td><td>R</td><td>829.6</td><td>834.6</td><td>5.0</td><td>4.48</td><td>4.86</td><td>90</td><td>5/7/2017 03:50</td><td>115</td><td>Nonmagnetic</td><td>15</td><td></td></tr><tr><td>19</td><td>R</td><td>834.6</td><td>839.2</td><td>4.6</td><td>4.60</td><td>4.98</td><td>100</td><td>5/7/2017 07:30</td><td>125</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>20</td><td>R</td><td>839.2</td><td>844.2</td><td>5.0</td><td>2.03</td><td>2.22</td><td>41</td><td>5/7/2017 12:50</td><td>145</td><td>Nonmagnetic</td><td>40</td><td></td></tr><tr><td>21</td><td>R</td><td>844.2</td><td>846.8</td><td>2.6</td><td>3.04</td><td>3.48</td><td>117</td><td>5/7/2017 16:50</td><td>80</td><td>Nonmagnetic</td><td>45</td><td></td></tr><tr><td>22</td><td>R</td><td>846.8</td><td>850.3</td><td>3.5</td><td>0.19</td><td>0.25</td><td>5</td><td>5/9/2017 09:40</td><td>95</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>23</td><td>R</td><td>850.3</td><td>853.8</td><td>3.5</td><td>3.21</td><td>3.53</td><td>92</td><td>5/9/2017 13:00</td><td>95</td><td>Nonmagnetic</td><td>25</td><td></td></tr><tr><td>24</td><td>R</td><td>853.8</td><td>858.4</td><td>4.6</td><td>3.10</td><td>3.65</td><td>67</td><td>5/9/2017 16:50</td><td>110</td><td>Nonmagnetic</td><td>25</td><td></td></tr><tr><td>25</td><td>R</td><td>858.4</td><td>863.4</td><td>5.0</td><td>3.53</td><td>3.90</td><td>71</td><td>5/10/2017 12:05</td><td>105</td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>26</td><td>R</td><td>863.4</td><td>868.0</td><td>4.6</td><td>4.34</td><td>4.57</td><td>94</td><td>5/10/2017 16:10</td><td>135</td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>27</td><td>R</td><td>868.0</td><td>873.0</td><td>5.0</td><td>4.39</td><td>5.15</td><td>88</td><td>5/10/2017 20:20</td><td>95</td><td>Nonmagnetic</td><td>20</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 type</th><th>Mud pumped (bbl)</th><th>Driller's notes</th></tr></thead><tbody><tr><td>28</td><td>R</td><td>873.0</td><td>877.6</td><td>4.6</td><td>1.50</td><td>1.94</td><td>33</td><td>5/10/2017 23:40</td><td>100</td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>29</td><td>R</td><td>877.6</td><td>882.6</td><td>5.0</td><td>2.25</td><td>2.70</td><td>45</td><td>5/11/2017 02:50</td><td>80</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>30</td><td>R</td><td>882.6</td><td>886.6</td><td>4.0</td><td>3.85</td><td>4.39</td><td>96</td><td>5/11/2017 06:35</td><td>120</td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>31</td><td>R</td><td>886.6</td><td>892.1</td><td>5.5</td><td>4.64</td><td>5.01</td><td>84</td><td>5/11/2017 10:50</td><td>140</td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>32</td><td>R</td><td>892.1</td><td>896.1</td><td>4.0</td><td>4.05</td><td>4.41</td><td>101</td><td>5/11/2017 14:45</td><td>120</td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>33</td><td>R</td><td>896.1</td><td>901.6</td><td>5.5</td><td>5.09</td><td>5.26</td><td>93</td><td>5/11/2017 19:15</td><td>140</td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>34</td><td>R</td><td>901.6</td><td>905.7</td><td>4.1</td><td>3.75</td><td>4.13</td><td>91</td><td>5/11/2017 22:50</td><td>105</td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>35</td><td>R</td><td>905.7</td><td>911.2</td><td>5.5</td><td>5.10</td><td>5.13</td><td>93</td><td>5/12/2017 02:00</td><td>105</td><td>Nonmagnetic</td><td></td><td></td></tr><tr><td>36</td><td>R</td><td>911.2</td><td>915.8</td><td>4.6</td><td>3.75</td><td>4.16</td><td>82</td><td>5/12/2017 05:30</td><td>105</td><td>Nonmagnetic</td><td>20</td><td></td></tr><tr><td>37</td><td>R</td><td>915.8</td><td>920.8</td><td>5.0</td><td>5.04</td><td>5.15</td><td>101</td><td>5/12/2017 09:45</td><td>135</td><td>Nonmagnetic</td><td>20</td><td></td></tr></tbody><tfoot><tr><td colspan="12">Hole U1502B totals (excluding drilled interval):</td></tr><tr><td colspan="12">193.1</td><td>131.57</td><td>140.425</td><td>68.14</td></tr></tfoot></table>

<figure><img src="image_291.png" /><figcaption>Figure F9. Hole U1502B reentry system and casing.</figcaption></figure>

slip and cut operations were completed, the bit was spaced out to 3750.7 m and slowly lowered until it was observed that the bit had tagged the seafloor. Seafloor was determined to be at 3763.7 m. The bit was again spaced out to 3750.7 m, and the top drive was picked up. The UGH was raised, and the underwater camera was recovered at 1215 h. A center bit was dropped, and drilling in Hole U1502A started at 1300 h on 25 April. The hole was advanced without coring to 375 m in 18 h. The center bit was removed, and an RCB core barrel was dropped to begin coring operations. One of the main objectives in Hole U1502A was to RCB core to a depth in the formation that would provide a stable casing set point for the next hole.

Cores 2R through 7R were drilled very quickly and had little recovery. This low-recovery area was interpreted as an unconsolidated sand interval. Penetration rates slowed for Cores 8R through 14R, with the bit taking approximately 15,000 lb of weight during coring operations. Recovery improved through this mudstone interval but dropped off in what was interpreted as another unconsolidated sand interval from 499.5 to 585.9 m (Cores 15R through 23R). A second mudstone interval was sampled with very good recovery from Core 24R at 585.9 m to Core 39R at 739.1 m. The last 2 m of

the following core, Core 40R, drilled very slowly, indicating a major change in formation. One more core was drilled to confirm the continuity of the formation change. At that point, coring in Hole U1502A was terminated in favor of continuing to core in a cased hole. The drill string was pulled to the surface, clearing the seafloor at 0330 h on 30 April and ending Hole U1502A and beginning Hole U1502B.

Total time spent on Hole U1502A was 125.25 h (5.2 days). A total of 40 RCB cores were taken over a 383.2 m interval with 176.81 m of recovery (46%). One interval was drilled without coring from the mudline to 375.0 m.

## Hole U1502B

We secured the RCB components of the BHA and prepared the rig floor for reentry and casing operations. The vessel was offset to the coordinates provided from the science office, and the UGH was removed and laid out to the drill collar racks.

The hydraulic release tool (HRT) was made up to a landing stand and racked back in the derrick. The prepared mud skirt was moved onto the moonpool doors and centered underneath the rotary table. After rigging up to run 10¾ inch casing, 62 joints of 10¾ inch casing (723.7 m) were run through the mud skirt. The landing stand was picked up, and the casing was lowered to the moonpool and latched into the mud skirt. The adapter flange was unbolted, and the landing stand was pulled back to the rig floor and racked back in the derrick.

The bit, bit sub, underreamer, and mud motor were assembled, and a pump-in sub was connected to the top of the mud motor. The mud motor and underreamer were function tested in the moonpool with good results. The remainder of this drilling stinger was assembled. The landing joint was again picked up, and the mock hanger and HRT were attached to the top of the casing and mud skirt. The adapter flange was bolted up and tightened with a torque wrench to the recommended torque. The reentry funnel was picked up in the moonpool and securely welded to the mock hanger.

The drilling and casing assemblies were lowered to the seafloor, stopping every 20 stands to secure the drill string and fill it with water to prevent collapse from differential pressure. After running in to 3744 m, the subsea camera was lowered to the bottom of the pipe to observe the drilling activity. While the camera descended, the top drive was picked up and the rig was serviced. The drill string was spaced out, and slow circulating rates were recorded. Drilling the casing into Hole U1502B started at 3763.7 mbl at 1255 h on 1 May 2017. Drilling continued until the 723.7 m long casing string had
been fully drilled into the seafloor and the mud skirt landed on the seafloor. The go-devil was inserted into the drill pipe and pumped down to release the casing at 2220 h on 2 May. The drill string was released from the casing assembly, and the bit and underreamer were pulled back through the casing and back to the rig floor. The bit cleared the seafloor at 0115 h on 3 May. The remainder of the drill string was pulled back to the rig floor, and the bit cleared the rotary table at 1130 h on 3 May.

After the tricone bit was removed, the mud motor and under-
reamer were flushed with freshwater and laid out. The UGH was
reinstalled, and the drill floor was reassembled. The RCB outer core
barrel was set up in the rotary table, and the core barrels were
spaced out to the outer core barrel. The remainder of the RCB BHA
was made up, and the bit was lowered to 3732 m. The subsea cam-
era system was deployed and run to near bottom in preparation for
reentering Hole U1502B to begin coring operations. While the sub-
sea camera was lowered to the seafloor, 115 feet of drill line was
slipped and cut. After a 3.5 h search, we found the Hole U1502B re-
entry cone and reentered the hole at 0400 h on 4 May. The camera
was then pulled back to the surface and secured.

The bit was lowered through the casing until it encountered fill at 715.3 m, 12.4 m above the total depth of the hole. The top drive was picked up, a core barrel was dropped, and the hole was washed and reamed to bottom. A 20 bbl mud sweep was circulated to help clean cuttings from the hole. Once the hole was clean, RCB coring began from 727.7 m and continued through Core 21R at 846.8 m. While cutting Core 21R, the driller noticed some excessive torque while on bottom. With 48.8 h on the bit, it was decided to pull out of the hole for a bit change. The bit was found to be in relatively good condition.

The drill string was pulled inside the casing before setting back
the top drive. Overpull of 60,000 lb was noted between 740.3 m and
the casing shoe. The bit was then raised to the mouth of the reentry
cone, and the vibration isolated television (VIT) camera was run to
the seafloor to verify the condition of the base and cone. The cone
was visible but was below the sediment surface. Seawater was circu-
lated in a successful attempt to clear the funnel of cuttings, and the
VIT camera was retrieved to the moonpool. The bit was then re-
trieved to the surface, clearing seafloor at 0600 h and the rotary ta-
tle at 1345 h on 8 May 2017.

A new 9⅞ inch C-7 RCB bit and an MBR were installed in the BHA, and the bit was run back to seafloor, followed by the subsea camera, for reentry. The cone was clearly visible, and Hole U1502B was reentered at 0240 h on 9 May. The camera was recovered, and the bit was lowered to 728.3 m, ~1.5 m below the casing shoe. The top drive was picked up, and a center bit was dropped. The hole was then washed to total depth, with the fill holding 10,000 lb weight on bit from 733.3 to 770.3 m.

A mud sweep was circulated, and the center bit was retrieved prior to resuming coring operations. Coring continued to 858.4 m, at which depth the low clutch diaphragm failed for the second time during the expedition at 0115 h on 10 May. The bit was pulled inside the casing and up to 715.3 m, and the drill pipe was hung off the elevators. The clutch diaphragm was replaced, and the drill string was lowered again by 0945 h on 10 May. While running in the hole, the driller noticed a spike in pressure, and a deplugger was dropped to clear any obstruction in the bit. The deplugger was retrieved, and a center bit was deployed so that the bit could be worked to the bottom of the hole. Before reaching the total depth of the hole, 3 m of fill was cleared. The center bit was then recovered, and coring resumed from 858.4 m (Core 25R) to a final depth of 920.8 m (Core

37R). Recovery was generally high over this interval (82%–101%), except for Cores 28R and 29R, which recovered only 33% and 45% and had higher rates of penetration of 2.76 and 3.75 m/h, respectively. The hole was then prepared for logging operations by circulating a high-viscosity mud sweep and performing a wiper trip. The bit was then released in the bottom of the hole. The end of pipe was raised to a logging depth of 747.3 m to ensure that the logging tools could bypass obstructions encountered by the bit when reentering the hole below casing.

Downhole logging

Two logging tool strings were deployed in Hole U1502B: a mod-
ified triple combo and the VSI. The triple combo tool string was
then rigged up, zeroed, presurvey calibrated, and deployed in the
hole with the following tools:

• DSI,

• HLDS with source,

• HNGS,

• Enhanced Digital Telemetry Cartridge (EDTC), and

• Logging Equipment Head (model QT) (LEH-QT).

The string made it into the open hole without any issue, but it stopped at a maximum depth of 4639 m wireline depth below rig floor (WRF), roughly 45.5 m higher than the driller's total depth. Based on an unexpected drop in gamma ray readings through casing, this obstacle was believed to be fill from above that had slumped and fallen to the bottom of the hole.

The repeat pass was taken from that depth up to the point where the logging head was just outside the pipe. The tool was then returned to maximum depth, which remained firmly at 4639 m WRF. The main log started there and continued up past the seafloor to provide a continuous gamma ray log of the entire interval. The caliper was closed at 4549 m to facilitate pipe entry, which was accomplished without any problems. The tools were pulled to surface with ease until the final joint of pipe at the top.

With the EDTC already sticking out of the top of the pump-in
sub during the process of pulling the tool up to remove the density
source, a large overpull was observed, causing the tension alarms to
trip and disable winch function. Several attempts were made to free
the tool, but they only resulted in it becoming too stuck to move up
or down significantly. An alternate plan to disconnect the first joint
of drill pipe to permit access to the tool inside and then disassemble
whichever portion was free to move was successful, and the radio-
active source was rigged down along with the majority of the string.
The portion remaining stuck in the top single consisted only of the
LEH-QT and EDTC, which were extracted relatively quickly and
easily from the bottom of that single using an air tugger.

There was no sign of damage to the tool string itself, nor was
there any sign of a problem in the affected joint of pipe. The cause of
the problem could have been a fragment of shear pin from coring or
some other small debris such as a pebble or shear pin, but these
items were never located. The string was safely rigged down with
only ~30 min of additional time required. The wireline was ex-
tracted from the traveling blocks to facilitate pulling the pipe up to
approximately 69 mbsl for the seismic run, and wireline operations
were paused for that action.

The VSI string was rigged up, zeroed, presurvey calibrated, and lowered in Hole U1502B with the VSI, EDTC, and LEH-QT. While pulling up the pipe, the drill crew observed that the hole was beginning to flow and made an unplanned break in the tripping operation
to pump down some seawater and stop the flow. Once the flow was halted, the seismic string was rigged up and lowered inside the hole without finishing the pull-out because the pipe was already at 4023 mbsl (259 m) and sufficiently high to avoid any major complication with the seismic experiment and because it was getting too late to raise the pipe any higher and still have sufficient time to finish the survey before dark.

The tool was rigged up as quickly as was safe and was run in the hole at a somewhat accelerated rate to make as much use as possible of the remaining daylight. The depth was correlated and adjusted to be on-depth in real time using a distinct gamma ray peak at 4413 meters below rig floor (mbrf) (corrected depth based on field pick of sea bed; raw depth of 4411.3 mbrf on main pass of first run). With the seismic tool on-depth, several attempts were made to get out of the casing and down to the bottom of the hole so that the deepest requested stations for the survey could be recorded, but the tool appeared to be hanging up on a ledge and was unable to pass into the open-hole section.

With very little daylight remaining, the open-hole stations were canceled in order to concentrate on getting as many of the cased-hole stations as time would permit. In all, eight stations were attempted, all in casing. Of those, the deepest two did not produce any useful signal, but the upper six all resulted in good seismic arrivals. The seismic survey was concluded roughly at sunset, and the tool was pulled out of the hole and rigged down in the usual manner. The heave compensator was not required for any portion of the logging because the total heave was just ±2 inches throughout the entire operating time.

The logging equipment was then rigged down, and the crew began recovering the drill string. The bit cleared the seafloor at 2235 h on 13 May. The beacon was recovered at 0015 h on 14 May, and the vessel began moving toward Site U1503 in dynamic positioning mode. The bit cleared the rotary table at 0445 h on 14 May, ending Hole U1502B and Site U1502.

Total time spent on Hole U1502B was 337.25 h (14.1 days). A total of 36 RCB cores were taken over a 193.1 m interval in Hole U1502B with 126.94 m of recovery (66%). There was one drilled interval from the mudline to 727.7 m, with 10¾ inch casing installed to 723.7 m. The triple combo string collected data in the open hole between 747.3 and 875.3 m, and the VSI logging experiment was conducted only inside casing between 259 and 629 m.

## Lithostratigraphy

We examined the lithostratigraphy of Holes U1502A (Figure F10) and U1502B (Figure F11) and defined six lithostratigraphic units and seven subunits 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]). Four units (I, III, IV, and V) are sedimentary, and two units (II and VI) are igneous. Units II and III were only recovered in Hole U1502B, and Unit IV was only recovered in Hole U1502A. Several of the subunits exhibit gradual changes, complicating a clear definition of their boundaries. The precise depth of boundaries between certain lithostratigraphic subunits within the intervals of poor core recovery is difficult to determine. The boundaries were refined using physical property measurements (e.g., changes in 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 carbonate measurements (Figure F56).

The sedimentary succession recovered at Site U1502 extends from the early Oligocene to the late Miocene (see Biostratigraphy), includes four units (I, III, IV, and V), and comprises mainly clay, nannofossil-rich clay, biosiliceous-rich clay, limestone, and clast-rich clay. The two igneous units (II and VI) are composed of highly to moderately altered basalt, basaltic breccia, and brecciated basalt. The base of the sedimentary succession is a sequence of clay and metasedimentary rocks (dolomite marble and dolomitic limestone) that form the contact above a unit of altered basalt (Unit VI). Unit I is dominated by clay and silty clay with varying amounts of nannofossils and foraminifers. The base of Unit I is defined at the base of the clay interval that has millimeter-sized pale green nodules. The contacts between Units II, III, and IV were not recovered. Unit II is a basalt clast. Unit III is silicified breccia. Unit IV consists of biosiliceous-rich silty clay transitioning downhole into silty clay barren of siliceous microfossils. Unit V is an interval of alternating metasedimentary rocks, including epidote-rich metaclaystone and dolomite marble. Unit VI consists of highly to moderately altered basaltic breccia, brecciated basalt, pillow basalt, and sheet basalt. Unit I is divided into five subunits, and Unit VI is divided into two subunits, described below.

## Unit description

### Unit I

Intervals: 368-U1502A-2R-1, 0 cm, to 39R-CC, 19 cm; 368-U1502B-2R-1, 0–26 cm

Depths: Hole U1502A = 375.00–734.87 m; Hole U1502B = 727.79–727.96 m

Age: Miocene

### Lithology and sedimentary structures

Unit I is dominated by clay, silty clay with varying proportions of nannofossils, clay-rich nannofossil ooze, minor sandy clay with calcite, nannofossil-rich clay with foraminifers, and sandy silt. The unit is divided into five subunits, IA–IE, based on slight lithologic variation. Recovery within the upper part of Unit I is very poor.

### Bulk mineralogy

The bulk mineralogy results of XRD analyses are listed in Table T2. Unit I sediments in Hole U1502A are composed mainly of quartz, plagioclase, K-feldspar, siderite, clay minerals (smectite, illite, kaolinite and chlorite), and halite, as well as minor amounts of calcite and dolomite. The relative content of minerals changes significantly downhole (Figure F12). Siderite is a major component of the sediments and has a relatively high content (average ~39%) throughout Subunits IA–IC and the upper part of Subunit ID (410–680 m) but is almost absent in the lower part of Subunit ID between 680 and 750 m, except for an interval with an abnormally high content (~15%) at about 734.8 m. In Subunits IA and IB, the abundance of siderite corresponds well to the alternation of greenish gray (lower siderite) and brownish gray (higher siderite) layers. Other minerals, including quartz, plagioclase, smectite, and halite, show the reverse trend to siderite, possibly because of a dilution effect. K-feldspar and chlorite decrease downhole, whereas illite and kaolinite increase. Calcite and dolomite are rare, except for exceptionally high abundances in Subunits IC and IE.
<figure><img src="image_292.png" /><figcaption>Figure F10. Lithostratigraphic summary, Hole U1502A.</figcaption></figure>

## Subunit IA

Interval: 368-U1502A-2R-1, 0 cm, to 13R-5, 79 cm

Depth: 375.00-486.82 m

Age: late Miocene

Subunit IA spans the uppermost 111.82 m of Unit I and comprises dark gray, gray, dark greenish gray, and greenish gray silty clay; clay with nannofossils; and nannofossil-rich clay intercalated

with dark grayish brown, grayish brown, and brown clay with nannofossils. There is also minor dark greenish gray sandy clay with calcite. The lithologies are dominantly dark gray and dark greenish gray in the upper cores (375.15-432.67 m). Intervals that fine upward are common (Figure F13). The lithology changes downhole (442.2-486.82 m) to more greenish gray, dark grayish brown, and rarely brown lithologies. Lithologic variations are not directly tied to color boundaries, and some burrows extend across areas of con-
<figure><img src="image_293.png" /><figcaption>Figure F11. Lithostratigraphic summary, Hole U1502B.</figcaption></figure>

trasting color. The clay contains varying amounts of nannofossils, as well as foraminifers in some intervals. The terrigenous component is mainly quartz and clay, with lesser feldspar and rare singular volcanic glass shards. Most lithologies have calcite or dolomite crystals, as well as accessory glauconite, pyrite, and iron oxide grains in the more brownish lithologies.

Bioturbation is heavy throughout most of Subunit IA, with *Planolites* and *Chondrites* as the main ichnospecies (Figure F13). Recovery between 375 and 445 m was very poor, possibly because sand layers were washed out.

The boundary between Subunits IA and IB is defined by the absence of nannofossils in Subunit IB.
<caption>Table T2. Mineral percentages, Hole U1502A. View table in PDF format. Download table in CSV format.</caption>

Figure F12. Bulk mineralogy data from shipboard XRD analysis, Holes U1502A and U1502B. Units IV and V are plotted based on depth and not stratigraphic order. The incorrect stratigraphic order of these units is due to overlap of Holes U1502A and U1502B.

<figure><img src="image_294.png" /></figure>

## Subunit IB

Interval: 368-U1502A-14R-1, 0 cm, to 25R-3, 109 cm

Depth: 490.20–599.57 m

Age: late Miocene

Subunit IB is 109.37 m thick and composed of alternating intervals of brown and greenish gray clay, silty clay, and clayey silt. Sandy intervals are rare. Two intervals of (light) greenish gray calcareous ooze occur in intervals 14R-1, 23–57 cm, and 15R-1, 63–69 cm (Figure F14). In general, the lithology (clay dominated) does not change across color boundaries, and some burrows extend across areas of contrasting color. Intervals that fine upward are common in the greenish gray layers. The sediment is dominated by clay minerals, quartz, feldspar, and authigenic siderite, as well as traces of pyrite.

Bioturbation is heavy in Subunit IB. Recovery was poor, which might be due to the presence of unconsolidated sand beds between the clay intervals.

The boundary between Subunits IB and IC is marked by a distinct change in lithology and in the consolidation and bedding structure of the sediments. Subunit IB is overall massive and well consolidated, whereas Subunit IC is laminated and lithified.

## Subunit IC

Interval: 368-U1502A-25R-3, 109 cm, to 25R-5, 91 cm

Depths: 599.57–602.39 m

Age: late Miocene

Subunit IC is 2.82 m thick and coarser grained than the other subunits of Unit I. The dominant lithology is greenish gray and reddish gray foraminifer-rich clayey siltstone to sandstone with some thin layers of pinkish gray foraminiferal chalk (Figure F15). Foraminifers make up 25%–30% of Subunit IC, and foraminifer tests are

<figure><img src="image_295.png" /><figcaption>Figure F13. Bioturbation and burrows, Subunit IA. A. Dark grayish brown clay with nannofossils and greenish gray clayey silt that fines upward. B. Intercalated dark gray silty clay with nannofossils and grayish brown clay with silt. C. Dark grayish brown clay with nannofossils and greenish gray silty layer (368-U1502A-12R-1A, 64–73 cm).</figcaption></figure>

embedded within a matrix of nannofossil-rich micritic calcite. The subunit consists of several layers that are characterized by erosive
and inclined bottom contacts and upward fining. Within these intervals, the sediments show parallel laminations and convolute bedding.

In contrast to the subunits above and below, Subunit IC is only slightly bioturbated. The contact with Subunit ID was not recovered but was interpreted on the basis of a change in the lithology from lithified foraminifer-rich siltstone to greenish gray clay.

## Subunit ID

Interval: 368-U1502A-25R-CC, 91 cm, to 38R-3, 131 cm

Depth: 602.39–724.03 m

Age: late to early Miocene

Subunit ID is 121.64 m thick and mainly composed of clay, silty clay, clayey silt, and clay with silt. The sediment has alternating colors from greenish and brownish gray to grayish brown between Cores 25R and 32R. Brown colors dominate in Cores 33R through 38R, and greenish gray colors only occur along fractures and burrows (Figure F16). The sediments are well consolidated and slightly laminated. Clay minerals are abundant, and quartz is common. Glauconite, pyrite, and siderite are rare to common.

Subunit ID is heavily bioturbated, and some thin yellowish layers contain abundant diagenetic siderite (e.g., Core 33R; Figure F16).

The boundary between Subunits ID and IE is characterized by the appearance of abundant nannofossils and foraminifers in Subunit IE, accompanied by a slight change in color from darker to lighter brown.

## Subunit IE

Intervals: 368-U1502A-38R-3, 131 cm, to 39R-CC, 19 cm; 368-U1502B-2R-1, 0–26 cm

Depths: Hole U1502A = 724.03–734.87 m; Hole U1502B = 727.79–727.96 m

Age: early Miocene

Subunit IE is 10.84 m thick and composed of brown nannofossil-rich clay with foraminifers and nannofossil-rich clay. Pale green colors are restricted to halos around fractures (Figure F17) and are not related to a change in lithology. The sediment contains abundant clay minerals and, commonly, quartz and calcite. Pyrite was found in patches throughout the subunit. At the base of Unit I, within Core 368-U1502A-39R, are single, green, up to centimeter-size concretions (various green alteration minerals, including epidote) with black rims. The number of concretions increases downhole.

Unit II (igneous rock) was not recovered in Hole U1502A, and only a clast (fall-in) of Unit III was recovered in the uppermost few centimeters of Core 40R at the top of Unit IV. The boundary between Units I and IV is marked by a change in color from brown to dark greenish gray, a change in lithology from nannofossil-rich clay to biosiliceous clay, and an increase in NGR. However, there is a ~5 m gap in recovery between Cores 39R and 40R (see Operations). The contact between Units I and II was not recovered in Hole U1502B, but the lithology changes from sediment to igneous rock (Figure F18).

## Unit II

Interval: 368-U1502B-2R-1, 26–34 cm

Depth: 727.96–728.04 m

Age: early Miocene or older

Figure F14. A. Color change from greenish gray to brown in Subunit IB.

B. Close-up image (red square in A) of calcareous ooze and silty clay to clay.

C. Smear slide image showing siderite-rich clay of Subunit IB.

<figure><img src="image_296.png" /></figure>

Unit II is a ~10 cm clast of greenish gray basalt with an equigranular texture (Figure F18). The basalt is highly altered, and most of the primary mineral phases are replaced by an alteration assemblage. Plagioclase laths as large as 3 mm make up approximately 1% of Unit I. The groundmass is intersertal with possible altered olivine, clinopyroxene, and/or altered glass between a felt of plagioclase crystals. The plagioclase has swallow-tail and bow-tie textures, indicating quenching.

The contact with Unit III was not recovered but is marked by a change in lithology (Figure F18).

## Unit III

Intervals: 368-U1502A-40R-1, 0–6 cm (fall-in); 368-U1502B-2R-1, 34 cm, to 3R-1, 12 cm

Depths: Hole U1502A = 739.10–739.16 m; Hole U1502B = 728.04–733.82 m

Age: Miocene/Oligocene boundary

Unit III is composed of a brownish yellow, silicified, very hard, poorly sorted breccia (Figures F18, F19). The average grain size is granule, and maximum clasts are pebble sized. The clasts consist of alteration minerals (Fe hydroxides) cemented by a matrix of annealed quartz in various grain sizes (see Structural geology for interpretation of textures).
Figure F15. Dominant lithology of Subunit IC is greenish gray and reddish gray foraminifer-rich clayey siltstone to sandstone with some thin layers of pinkish gray foraminiferal chalk. A. Greenish and reddish clayey siltstone and pinkish gray foraminiferal chalk. Red square = parallel laminations and convolute bed-ding, green square = color change is interpreted as fluid interaction. B. Clayey siltstone with abundant foraminifers. C. More clay-rich upper part of Subunit IC.

<figure><img src="image_297.png" /></figure>

In Hole U1502A, Unit III is represented by a single clast (fall-in) in the uppermost centimeters of Core 40R (Figure F20), whereas in Hole U1502B, an interval of 0.63 m (interval 2R-1, 34 cm, to 3R-1, 12 cm) was recovered (Figure F19). The contact with the underlying Unit IV was not recovered in Hole U1502A but is indicated by a change in lithology from poorly sorted silicified breccia to dark greenish gray biosiliceous clay. Unit IV was not recovered in Hole U1502B.

## Unit IV

Interval: 368-U1502A-40R-1, 6 cm, to 40R-6, 83 cm

Depth: 739.16–747.20 m

Age: late Oligocene

## Lithology and sedimentary structures

Unit IV is 8.1 m thick and was recovered only in Hole U1502A. The unit is dominated by dark greenish gray biosiliceous clay (Fig-
Figure F16. Subunit ID is dominated by sediment with greenish and brownish gray and grayish brown colors from Cores 368-U1502A-25R through 32R and brown colors from Cores 33R through 38R. A. Brownish clay with greenish halos along fractures. Red square = 38R-1, 91–106 cm. Subunit ID is heavily bioturbated. B. Yellowish layers contain abundant diagenetic siderite. C. Siderite-rich clay.

<figure><img src="image_298.png" /></figure>

ure F20). The amount of nannofossils decreases rapidly within Section 40R-1, and diatoms, sponge spicules, and radiolarians are abundant. Diatom abundance decreases significantly from Section 40R-1 to Section 40R-3. The calcareous nannofossil abundance is rare to barren in Unit IV. Pyrite occurs in centimeter-sized patches and along cracks (Figure F20).

Unit IV is heavily bioturbated and, in the upper section, contains the same green concretions found in the lower part of Subunit IE. The layering in Unit IV is inclined (~20°) and slightly deformed (see Structural geology).

The bottom contact of Unit IV is irregular and subhorizontal, and the boundary is characterized by a lithology change from dark greenish gray, well-consolidated, biosiliceous clay to light gray, lithified marble. The boundary between Units IV and V is associated with a distinct increase in magnetic susceptibility in Unit V (see Physical properties).

## Bulk mineralogy

One XRD sample from Unit IV (Table T2) indicates that the bulk mineralogy of the sediments is quartz, plagioclase, K-feldspar,

Figure F17. A. Subunit IE sediments are brown nannofossil-rich clay with foraminifers and clay with nannofossils. Pale green colors are restricted to fractures and are not related to a change in lithology. B. Nannofossil-rich clay with foraminifers (cross-polarized light [XPL]). C. Greenish clasts/concretions in the lower part of Subunit IE. The material is soft and easily scratched with a fingernail. D. Green concretions in brown clay. Green minerals are probably alteration sheet silicates. Thin section was made from a fall-in clast.

<figure><img src="image_299.png" /></figure>

and clay minerals (smectite, illite, and kaolinite), as well as minor amounts of halite and dolomite. No siderite, calcite, or chlorite were detected in the XRD sample. Apart from the absence of these minerals, Unit IV has a very similar mineral assemblage to Unit I but with slightly more abundant smectite (Figure F12).

## Unit V

* Intervals: 368-U1502A-40R-6, 83 cm, to 41R-1, 31 cm; 368-U1502B-3R-1, 12 cm, to 4R-1, 46 cm

* Depths: Hole U1502A = 747.20–749.02 m; Hole U1502B: 733.82–739.16 m

* Age: unknown (at least pre-late Oligocene, possibly late Eocene)

Unit V is 1.82 m thick in Hole U1502A when calculated using the curated section lengths; however, only 43 cm of rock was recovered. In Hole U1502B, 3.05 m was recovered. The unit is composed of massive, light gray dolomite marble and meta claystone in Hole U1502A and dolomitic limestone intercalated with clast-rich clay and sandstone in Hole U1502B (Figures F21, F22).

The dolomite marble in Hole U1502A is very fine grained, equigranular with an annealing texture, and crossed by fine dark gray bands. The marble is dominated by dolomite (~95%), with minor amounts of magnetite (~3%) and calcite (~2%) (Figure F22). The calcite occurs in enclaves, whereas magnetite forms dark gray bands or occurs as singular grains within the dolomite marble and limestone. The presence of magnetite explains the high magnetic susceptibility of this unit.
Figure F18. A. Subunit IE and Units II and III. The brown clay with green concretions of Subunit IE is not in contact with Unit II (altered basalt); contact between Units II and III was not recovered. Unit III is brownish yellow silicified breccia. Overall recovery of Core 368-U1502B-2R was only 14%. B. Unit II basalt with plagioclase and alteration minerals (e.g., epidote). C, D. Silicified breccia. Texture is interpreted as cataclastic, and matrix is rich in recrystallized annealed quartz.

<figure><img src="image_300.png" /></figure>

The gray, fine-grained dolomitic limestone in Hole U1502B is intercalated with a well-consolidated, very dark greenish gray clay with 10%–15% igneous clasts (Figure F21). The clay is composed of clay minerals, calcite, feldspar, quartz, and pyrite in decreasing order of abundance. Abundant benthic agglutinated foraminifer tests occur in Section 3R-1 (see Biostratigraphy). Gray, coarse-grained dolomitic sandstone occurs at the base of Unit V and is lithified and well sorted.

The boundary between Units V and VI is characterized by a change in lithology from (meta)sedimentary dolomite marble, dolomitic limestone, clay, and sandstone to igneous Unit VI (Figure F22).

Figure F19. A, B. Brownish yellow silicified breccia, Unit III. C. Silicified breccia with possible foraminifer tests filled by Fe hydroxides and quartz. D. Matrix of Unit III dominated by secondary quartz.

<figure><img src="image_301.png" /></figure>

## Unit VI

Intervals: 368-U1502A-41R-1, 31 cm, to 41R-CC, 18 cm; 368-U1502B-4R-1, 46 cm, to 37R-4, 141 cm

Depths: Hole U1502A = 749.01–750.67 m; Hole U1502B = 739.16–920.95 m

Age: Unknown (at least pre-late Oligocene, possibly Eocene)

Unit VI consists of highly to locally moderately altered basalt. The unit is divided into two subunits, VIA and VIB. The upper part of Hole U1502A (interval 41R-1, 30–62 cm) is greenish gray, highly altered, and heavily fractured, possibly due to drilling disturbance (Figure F23). Interval 41R-1, 62–90 cm, is light greenish gray, lithified, brecciated, fine-grained rock with phenocrysts of plagioclase. From Section 41R-1, 90 cm, downhole, the rock is still heavily but less altered. The rock is light gray and coarser grained with subrounded amygdules as large as 0.5 cm in diameter. Reddish iron oxides are common and occur as single crystals and along fractures, together with rare sulfides. Fragments show yellowish concentric alteration horizons. All basalt in Hole U1502A is within Subunit VIA.

Unit VI was recovered in Hole U1502B from Section 4R-1, 46 cm, downhole to 920.95 m. Unit VI is divided into two subunits, VIA (Section 4R-1, 46 cm, to 12R-1, 105 cm) and VIB (Section 12R-1, 105 cm, to 37R-4, 141 cm). The basalt is heavily altered and fractured, and veins with quartz, carbonates, epidote, and sulfides are common. Highly fractured, matrix-supported intervals and intervals with a mixture of basaltic and sediment clasts are described as basaltic breccia (Figure F23). Intervals that are fractured but clast supported are described as brecciated basalt. Fractured basalt without any matrix between the basaltic fragments is described as basalt (with optional prefixes for phrytic basalts).

Subunit VIA is composed of highly altered basaltic breccia and brecciated basalt with infrequent sheet basalt, chert, and claystone
Figure F20. Unit IV is dominated by dark greenish gray biosiliceous clay. A. Dark greenish gray biosiliceous silty clay. Red square = location of B. B. Pyrite occurs as centimeter-sized patches and along cracks. C, D. Biosiliceous silty clay with sponge spicules. Diatom abundance decreases significantly in Sections 368-U1502A-40R-1 through 40R-3, whereas sponge spicules and radiolarians are present throughout Unit IV.

<figure><img src="image_302.png" /></figure>

and very minor pillow basalt. The basaltic breccia in Sections 4R-1 through 6R-2 is a mixture of light gray and greenish gray claystone and basaltic clasts in an altered matrix (e.g., Section 6R-1; Figure F23). Chert and claystone layers and clasts were recovered between the brecciated basalt and basaltic breccia in Sections 6R-3 through 7R-2. No sedimentary clasts were recovered from Section 7R-2 downhole. From Core 11R downhole, pillow lavas were recovered in between the sheet lava flows and the basalt is locally less altered (moderately highly altered) and less brecciated.

The boundary between Subunits VIA and VIB is placed at the base of a fine-grained interval (12R-1, 105 cm), which might be a tectonic or hydrothermal breccia (see **Structural geology**). This interval also marks the boundary between the basaltic breccia and brecciated basalt of Subunit VIA and the more coherent sheet and pillow flows in Subunit VIB. Veins are more localized and larger in Subunit VIB, crosscutting the complete length of core sections (e.g., Sections 13R-3 and 14R-1).

The lithology of Unit VI basalt is described in more detail in **Igneous and metamorphic petrology**, and its structures are described in more detail in **Structural geology**.

# Discussion

## Depositional environment of Unit V

Unit V is composed of dolomite marble and limestone intercalated with clast-rich clay. Although the sediment is overprinted by

Figure F21. Unit V is composed of dolomite marble, dolomitic limestone, and clay. A. Dolomitic limestone intercalated with clast-rich clay. B. Fine-grained dolomite limestone with magnetite enclaves. C. Epidote veins. D. Close-up image (red square in A) of clast-rich clay that contains igneous clasts (368-U1502B-3R-2, 64–74 cm). E. Clay (XPL).

<figure><img src="image_303.png" /></figure>

secondary high-temperature processes (likely hydrothermal fluid sediment interaction or possibly contact metamorphism), it still retains primary sedimentary bedding and bioturbation features. The clay lithology and presence of deep-water benthic agglutinated foraminifers (see **Biostratigraphy**) indicate the unit was deposited in a deep abyssal environment.

## Depositional environment of Unit IV

Unit IV is composed of dark greenish gray biosiliceous clay (Figure F20), and calcareous nannofossils are rare. The lower part of the unit (Section 368-U1502A-40R-6) is barren of diatoms, but their abundance increases with time, and diatoms are abundant at the top of the unit (Section 40R-1). Sponge spicules occur throughout the unit. The lower part of Unit IV is slightly deformed and interpreted as being postdepositional (see **Structural geology**).

Comparing the dominantly calcareous microfossil assemblage in the early to late Miocene Unit I with the dominantly biosiliceous microfossil assemblage in Unit IV may either indicate deposition of
Figure F22. Contact between Unit V and Subunit VIA, Hole U1502A. A. Contact of light gray dolomite marble (Unit V) and greenish gray altered basalt (Unit VI). B. Fine-grained dolomite marble with calcite patches. The marble is dominated by dolomite (~95%) with minor amounts of magnetite (~3%) and calcite (~2%). C. Altered basalt showing plagioclase and alteration minerals.

<figure><img src="image_304.png" /></figure>

Unit IV in deeper water or the existence of a shallower CCD during its time of deposition (see **Biostratigraphy**).

## Depositional environment of Unit I

Lithostratigraphic Unit I (late Miocene-late Oligocene) at Site U1502 was deposited in a deep-marine environment. The dominant lithologies in Unit I are clay and silty clay with nannofossils and nannofossil-rich clay, which are interbedded with centimeter-scale silt layers and rarely foraminifer-rich siltstone. There are variable amounts of foraminifers in all lithologies.

Some thin silty beds and thick silty laminae in Unit I (Sections 368-U1502A-9R through 33R; ~440–680 m) have upward fining and erosive bottom contacts that are interpreted as fine-grained (mostly Bouma sequence) turbidite deposits. Similar beds were observed at Site U1499.

Subunit IC comprises an approximately 3 m thick foraminifer-rich siltstone interbedded with foraminiferal sand. The subunit has parallel lamination and convolute bedding, which we interpret as evidence of downslope slumping of slightly to moderately consolidated sediments on the continental slope.

Site U1502 is located at the boundary between the lower continental slope and the deep-sea basin, and a similar depositional environment probably existed during the deposition of Unit I. This environment is very prone to redeposition of sediment by sediment-

Figure F23. Basaltic breccia, brecciated basalt, and sedimentary rocks, Subunit VIA. A. Basaltic breccia with sediment clasts. B. Claystone and chert intervals within the brecciated basalt. C. Brecciated basalt with dolomitic matrix and basaltic clasts. Location of D is marked on the image. D. Thin section (TS) 34 showing (left) dolomitic matrix around basalt clasts and (right) euhedral dolomite and epidote with high interference colors.

<figure><img src="image_305.png" /></figure>

gravity processes, including slides, slumps, debris flow, and turbidity currents. Sea level change and tectonic uplift are two important mechanisms that may trigger sediment gravity flows.

According to the preliminary age model of Site U1502 (see **Biostratigraphy**), the variation in sedimentation rate correlates well with the lithologic change from Subunit IE to Subunit IA. Between the early Oligocene and middle Miocene (~30–15 Ma), the sedimentation rate was very low (~1 cm/ky). Sediment from this interval has a low siderite abundance and a monotonous reddish-brown color, likely indicating an oxidizing environment (Subunits ID and IE; 670–740 m). The sedimentation rate increases to ~3.9 cm/ky between the middle and late Miocene (~15–6 Ma), consistent with the many thin turbidite beds (Subunits IA–ID; 440–670 m). Here, the sediment is also siderite rich.

Unit I has likely been affected by diagenetic processes. For example, the decrease in the abundance of nannofossils within Subunit ID correlates with an increase in the abundance of single calcite crystals in the sediment. This correlation may indicate that the nannofossils have been dissolved and redeposited as crystalline calcite during diagenesis. Alternately, the decrease may simply indicate a decrease in the overall nannofossil abundance.

A striking feature of Unit I is the alternation of brownish gray to greenish gray intervals along the core. This alternation is most pronounced in Subunits IA–ID (e.g., Cores 368-U1502A-9R through 31R; Figure F14), where the alternations occur as thick, approximately bedding-parallel bands, typically 10–50 cm long, with some crosscutting relations between the color change and the bedding.
The number of greenish gray intervals decreases downhole, and Cores 34R through 39R are dominantly brownish in color. In these lower sections, greenish gray intervals usually crosscut the bedding (Figures F16, F17).

The color change from brownish gray to greenish gray sediment within Subunit IE and the lower part of Subunit ID (Cores 34R through 39R) is evidently related to secondary processes because it occurs along faults, fractures, and silty beds and in burrows (Figure F16). Halos of greenish sediment around these features do not extend more than a few centimeters, and the color change is most likely the result of interaction of the oxidized sediment with reducing fluids. Boundaries between the color bands from Subunit IA through the upper part of Subunit ID (Cores 9R through 31R) cross-cut biogenic features such as burrows and are sometimes discordant to bedding. However, the boundaries are most often approximately parallel to the bedding. An association of greenish gray sediment with thin silt beds was interpreted as turbidites. Therefore, the cause of the color change in the upper part of the core may be related to (secondary) diagenetic fluids, differences in the input of derived matter associated with turbidites (e.g., Wilson et al., 1986), changes in bottom water conditions (e.g., Dean et al., 1989), or allo-cyclic change such as climate (e.g., Gardner et al., 1982).

### Interpretation of Units II–VI

The interpretation of Units II and VI is given in **Igneous and metamorphic petrology**, and the interpretation of Unit III is given in **Structural geology**.

## Igneous and metamorphic petrology

At Site U1502, we recovered two igneous lithologic units (Figures F10, F11). Three small, altered basalt fragments were recovered in interval 368-U1502B-2R-1, 26–34 cm (727.96–728.04 m), and they represent igneous Unit 1, which corresponds to lithostratigraphic Unit II (see **Lithostratigraphy**). Hole U1502A terminated in highly altered basalt that comprises the upper part of igneous lithologic Unit 2 (corresponding to lithostratigraphic Unit VI; see **Lithostratigraphy**). This unit was drilled from 749.0 to 750.7 m with a total recovered core length of 1.7 m. A more complete section of igneous lithologic Unit 2 was drilled in Hole U1502B below 739.16 m. This sequence of strongly (hydrothermally) altered aphyric to highly plagioclasephyric basalts has a total drilled thickness of 181.79 m. These basalts are divided into two igneous lithologic subunits, 2a and 2b, based on flow morphology and alteration style (Figure F24). Subunit 2a contains an upper sequence of brecciated and fractured massive lava flows (739.16–801.95 m), and Subunit 2b contains a lower sequence of interbedded pillows with lobate and sheet lava flows (801.95–920.95 m).

The igneous lithologic units were described macroscopically and microscopically from thin sections (see **Igneous and metamorphic petrology** in the Expedition 367/368 methods chapter [Sun et al., 2018a]). Chemical analyses were carried out by inductively coupled plasma–atomic emission spectroscopy (ICP-AES) and the handheld pXRF to check for any major compositional changes, both primary and from the alteration process. Alteration assemblages were recognized through a combination of hand specimen examination, thin section examination, and XRF and XRD data.

### Igneous lithologic Unit 1 (lithostratigraphic Unit II)

Interval: 368-U1502B-2R-1, 26–34 cm

Depth: 727.96–728.04 m

Thickness: 0.08 m

Lithology: altered basalt

Age: early Miocene–late Oligocene or older

The greenish gray basalt of igneous lithologic Unit 1 is altered, and an assemblage of alteration minerals has replaced most of the primary mineral phases (Figure F18B). The aphanitic, fine-grained basalt is nonvesicular to moderately vesicular and contains rare (as large as 6 mm) plagioclase phenocrysts. Alteration of the unit is intense, with less than 50% of the primary crystals remaining, which makes it difficult to determine the primary phases that were originally present. Thin section observations indicate a primary mineralogy of plagioclase with a potential assemblage of pyroxene and Fe-Ti oxides ± mesostasis. The texture is equigranular, and plagioclase laths as large as 1 mm make up approximately 40% of the unit. The groundmass is intersertal with possible altered pyroxene, olivine, and altered glass between a felt of tightly woven, quench-textured plagioclase crystals (Figure F18B). The groundmass is replaced by green clay minerals, clinozoisite, zeolites, and Fe (hydr)oxides. Zeolites radially fill pore space, which may represent original vesicularity.

The contacts with lithostratigraphic Units I and III were not recovered due to low overall recovery in this core (2R; Figure F18A).

### Igneous lithologic Unit 2 (lithostratigraphic Unit VI)

Intervals: 368-U1502A-41R-1, 31 cm, to 41R-CC, 18 cm;

368-U1502B-4R-1, 46 cm, to 37R-4, 141 cm

Depths: Hole U1502A = 749.01–750.67 m; Hole U1502B = 739.16–920.95 m

Thickness: Hole U1502A = 1.71 m; Hole U1502B = 181.79 m

Lithology: highly altered, aphyric to highly plagioclasephyric pillow and sheet basalt, brecciated basalt, and basaltic breccia

Recovery: 75%

Age: late Oligocene–late Eocene or older

Igneous lithologic Unit 2 (lithostratigraphic Unit VI) encompasses a sequence of basaltic breccia, brecciated basalt, pillow basalt, and sheet-flow basalts that range from aphyric to highly plagioclasephyric volcanics and minor chert (Figure F25). The entire section of igneous rock recovered in Hole U1502B has undergone some degree of hydrothermal alteration within the temperature range representative for zeolite to greenschist facies conditions (200°–500°C). This alteration varies from complete replacement of the rock, where the original composition and texture are difficult to determine, to replacement of mineral phases with little change to the texture. Glassy pillow rinds are completely replaced, and multiple phases of veining and halos are ubiquitous throughout the rocks.

Igneous lithologic Unit 2 is divided into two subunits based on morphological character and alteration style (Figure F24). Subunit 2a, in Cores 368-U1502B-4R through 12R, is dominantly basaltic breccia and brecciated basalt (e.g., interval 5R-CC, 19–29 cm) with strong carbonate alteration forming a matrix between the basalt clasts (Figures F25, F26). Subunit 2b is moderately to highly altered and less brecciated than Subunit 2a. It comprises pillow lavas alternating with sheet flows. The change between both subunits is gradual, but the boundary was placed at the base of interval 12R-1, 64–105 cm, which was interpreted as hydrothermal breccia and possibly represents a fault gouge (see **Structural geology**).
<figure><img src="image_306.png" /><figcaption>Figure F24. Lithostratigraphic summary of igneous lithologic Unit 2 showing lithology, lava flow type, and igneous Subunits 2a (basaltic breccia and brecciated basalt) and 2b (interbedded pillow lava and massive/sheet lava flows), Hole U1502B. Intervals of highly (>10% plagioclase phenocrysts) and very highly (>20% plagioclase phenocrysts) phyric basalts, pillow or chilled margins, and intervals sampled for bulk rock ICP-AES analysis are also shown.</figcaption></figure>

## Igneous lithologic Subunit 2a (lithostratigraphic Subunit VIA)

Intervals: 368-U1502A-41R-1, 31 cm, to 41R-CC, 18 cm; 368-U1502B-4R-1, 46 cm, to 12R-1, 105 cm

Depths: Hole U1502A = 749.01–750.67 m; Hole U1502B = 739.16–801.95 m

Lithology: highly altered, brecciated basalt, and basaltic breccia

Age: late Oligocene–late Eocene or older

Igneous Subunit 2a is composed of pale green, yellowish, light gray, light greenish gray, and greenish gray highly altered basaltic breccia and brecciated basalt, with minor sheet basalt, chert, and claystone and very minor pillow basalt (Core 368-U1502B-11R) (Fig-

ure F25). The color change along the core in Hole U1502B is mostly subtle, from pale green or yellowish at the contact with lithostratigraphic Unit V (Figure F22) to light greenish gray to greenish gray without an apparent relationship to flow structure. The basaltic breccia in Sections 4R-1 through 6R-3 is a mixture of predominantly basaltic clasts and subordinate light gray and greenish gray claystone and chert in an altered matrix (e.g., Section 6R-1; Figure F23).

The basaltic breccia and brecciated basalt differ in the proportion of matrix and arrangement of clasts (Figure F25). The clasts are either sparsely to moderately porphyritic basalt with altered plagioclase phenocrysts (2%–15%) in an altered groundmass of plagioclase and alteration minerals or aphyric with a groundmass of
Figure F25. Lithologies, Hole U1502B. A. Fractured and highly altered basalt with reddish, yellowish, and light green alteration colors and spots of iron (hydr)oxide, igneous Subunit 2a. B. Highly altered brecciated basalt with jigsaw arrangement of clasts and a matrix of carbonate and clay minerals, Subunit 2a. C. Highly altered basaltic breccia. Clasts are angular and have random, sometimes matrix-supported texture. Matrix is largely made up of dolomite with calcite, albite, clay minerals, quartz, and minor epidote. Rare clasts of fine-grained sedimentary rock occur in some sections. D. Highly plagioclase phytic basalt with up to 50% phenocrysts. Veins of calcite, epidote, and green sheet silicate minerals are also visible. E. Highly altered, moderately plagioclase phytic basalt lobate flow with sparse amygdules filled with green sheet silicate. Pillow margins visible in 19R-3, 70–114 cm (shown in D). F. Highly altered, sparsely plagioclase phytic pillow basalt with a well-preserved pillow that has a very fine grained dark greenish margin and alteration zones that parallel the pillow margin. Pipe vesicles and fractures are perpendicular to the pillow margin. Veins filled with epidote, chlorite, silica, and minor carbonate and pyrite cut the pillow. G. Moderately altered, aphyric basalt flow with sparse vesicles. Note the change to a bluish gray color.

<figure><img src="image_307.png" /></figure>

plagioclase and alteration minerals. The groundmass comprises variably altered plagioclase partially replaced by a combination of albite, sericite, calcite or dolomite, clinozoisite, zeolite minerals, Fe hydroxides, and clay minerals, with a felty, intersertal, often tightly interwoven texture (Figure F27B). Plagioclase phenocrysts have a similar alteration assemblage. Potential former interstitial pyroxene may contain some relict fresh areas but is largely replaced by chlorite, zeolite minerals, epidote-group minerals, and clay minerals, with accessory pyrite. The basalt clasts vary from nonvesicular to having approximately 10% amygdules. The amygdules are dark to light green and filled with carbonate, epidote, zeolite minerals, and pyrite (Figure F28B). The matrix of the breccia and veins that cut the brecciated basalt are dominantly pale green-gray to yellowish and reddish brown and consist largely of carbonate (likely dolomite or siderite) crystals with lesser calcite, epidote, chlorite, Fe (hydr)oxides, quartz, zeolite minerals, and clay minerals (Figure F28).

## Igneous lithologic Subunit 2b (lithostratigraphic Subunit VIB)

Interval: 368-U1502B-12R-1, 105 cm, to 37R-4, 141 cm
Depth: 801.95–920.95 m

Lithology: highly to moderately altered pillow basalt, lobate basalt, and sheet basalt

Age: late Oligocene–late Eocene or older

Igneous Subunit 2b is composed of (light) greenish gray and bluish gray, highly to moderately altered pillow basalt and sheet basalt, with minor lobate basalts and brecciated basalt (Figure F25). Pillow basalt is recognized by pillow rims and chilled margins in the cores (e.g., interval 19R-1, 117–128 cm; Figures F29, F30). Some pillows show pipe vesicles that are perpendicular to the pillow rim. No glass is preserved in the basalt. The altered pillow rims, which may originally have been glass, are dark greenish gray and completely altered to chlorite, calcite, epidote, zeolite minerals, Fe hydroxides, and clay minerals (Figure F29). Pillow rims are interpreted as having been glassy prior to alteration due to their extremely fine grain size, variolitic texture (variolites are millimeter sized), and different alteration style compared to the pillow cores. Some pillow rims are plagioclase phytic, with often better-preserved plagioclase than in the adjacent basalt. One thin section of a pillow rim has quench-texture plagioclase laths in an altered groundmass with relict perlitic cracking (Figure F29). Alteration minerals highlight the perlitic cracks. The perlitic cracking and quench textures also indicate that
Figure F26. Representative minerals and textures in veins and areas of alteration, igneous Subunit 2b. A. Calcite (Cal)-rich vein crosscutting altered basalt with plagioclase (Pl) and clay minerals (XPL). B, C. Composite epidote (Ep)-rich vein with chlorite (Chl) crosscut by calcite vein, both crosscutting altered basalt with plagioclase, chlorite, and clay minerals (B: plane-polarized light [PPL]; C: XPL). D–F. Highly altered basalt crosscut by vein with an assemblage of epidote, quartz (Qtz), pyrite (Py), plagioclase, clay minerals, and zeolite minerals (D: PPL; E: XPL; F: reflected light). G, H. Highly altered basalt with an assemblage of plagioclase, chlorite, pyrite, clay minerals, and zeolite minerals (G: PPL; H: XPL). I. Altered plagioclase phenocryst, partially replaced with veins of calcite, chlorite, and epidote in an altered groundmass of plagioclase, chlorite, epidote, clay minerals, and zeolite minerals (XPL).

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the pillow rims were glassy prior to alteration. Very thin (<1 mm) carbonate veins occur mostly parallel to the pillow margin within the altered glass (e.g., interval 17R-1, 33–43 cm).

Sheet flows were recognized by the absence of pillow or intrusive margins. Rare flow boundaries are defined by chilled margins and areas of brecciation and drilling-induced fragmentation that may be brecciated flow tops. Depending on the degree of alteration, the basalt is greenish gray (high alteration) to bluish gray in some intervals and patches (e.g., interval 35R-3, 103–120 cm) that we interpret as less altered (consistent with thin section observations).

Subunit 2b basalt varies from sparsely to highly plagioclasephyric (e.g., interval 19R-3, 35–41 cm), partially reflecting glomero-porphyritic assemblages, with only minor intervals of equigranular and aphyric texture (Figure F25). The texture and petrography (Figure F27C–F27J) of Subunit 2b is similar to the clasts in the Subunit 2a breccia and brecciated basalt. Subunit 2b includes intervals with

as much as 50% tabular to equant plagioclase phenocrysts (e.g., interval 15R-1, 104–111 cm; Figure F25D). Chlorite and sulfides are more abundant in thin sections of Subunit 2b, and several of the samples are also high in epidote (Figure F26G–F26I). Pseudomorphs, replaced by a brown mineral with first-order interference colors, probably a clay mineral such as saponite, may represent either olivine or filled vesicles (Figure F27E). Interstitial areas that may have been glass now show an amorphous gray, isotropic mineral and opaque minerals (Figure F27I, F27J). Carbonate and zeolite minerals occur in the groundmass, but they are not as abundant as in Subunit 2a. Veins are filled with dark and apple green minerals (chlorite and epidote), carbonates (dolomite, calcite, and siderite), zeolite minerals, pyrite, quartz, and secondary feldspar (Figures F28, F31).

The coarse-grained basalt flow in Sections 37R-2 and 37R-3 contains several thin (0.5–1.5 cm wide), fine-grained gray basaltic
Figure F27. Representative minerals and textures, igneous lithologic Units 1 and 2. A. Altered basalt with an intersertal, tightly interwoven texture, Unit 1 (PPL). Plagioclase laths (Pl) are partly altered and display quench textures (e.g., swallow-tail). Interstitial material consists of secondary minerals (clay and zeolite minerals and Fe [hydr]oxides). B. Very fine grained altered basalt with intersertal texture, Subunit 2a (XPL). Plagioclase laths are partly altered and display quench textures (e.g., swallow-tail and sheath). Interstitial material consists of secondary minerals (clay and zeolite minerals and Fe [hydr]oxides). C, D. Highly to moderately altered, highly plagioclasephyric basalt with intersertal texture, Subunit 2b (C: PPL; D: XPL). Plagioclase phenocrysts (Pl) are relatively fresh. Interstitial material between altered plagioclase grains in the groundmass is an assemblage of epidote, sericite, chlorite, carbonate, clay minerals, and opaques (Op). E, F. Sparsely plagioclasephyric (Pl) basalt with intersertal groundmass of altered plagioclase and an alteration assemblage that includes chlorite, epidote (Ep), sericite, quartz, zeolite minerals, and minor pyrite and chalcopyrite, Subunit 2b (E: PPL; F: XPL). Regular areas of chlorite and zeolite minerals may be pseudomorphs after a ferromagnesian mineral or amygdules (former olivine [Ol]/vesicle). G, H. Highly altered, highly plagioclasephyric basalt with intersertal texture, Subunit 2b (G: PPL; H: XPL). Interstitial material between altered plagioclase grains is an assemblage of epidote, sericite, chlorite (Chl), carbonate, clay minerals, and pyrite. Note the thin rims on the twinned plagioclase phenocrysts (Pl). I, J. Fine and even-grained, moderately altered, sparsely plagioclasephyric (Pl) basalt, Subunit 2b (I: PPL; J: XPL). Quench-textured plagioclase and an interstitial assemblage of chlorite (Chl), epidote (Ep), clay minerals, and minor pyrite.

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veins with irregular margins (intervals 37R-2, 134–137 cm; 37R-3, 0–2 cm; and 37R-3, 3–10 cm). Analyses using the pXRF show that, relative to the coarse-grained host lava, these veins have lower TiO₂ (1.1 wt% versus 1.7 wt%) and Ni (20 ppm versus 40 ppm), as well as higher Zr (400 ppm versus 170 ppm). These data indicate that the veins have more evolved compositions than the host lava and therefore may represent segregation veins that formed just prior to final solidification of the flow.

## Veins and alteration

The pervasive greenish gray color of the samples indicates that the basalt is altered from its original mineralogy (e.g., Figure F29). Plagioclase, as phenocrysts and in the groundmass, appears only partially altered in some thin sections (Figures F27, F26), and XRD indicates that it is labradorite (Figure F32). XRD data also indicates abundant albite, and therefore in some sections the plagioclase may now be albitized. The plagioclase is sericitized or altered to clay minerals in other thin sections. Some relict areas of pyroxene may