Physical properties evaluation at Site 1115 included nondestructive measurements of bulk density, bulk magnetic susceptibility, natural gamma ray, and P-wave velocity on unsplit cores using the MST. Discrete measurements of longitudinal and transverse P-wave velocities and index properties were collected on split cores. Depending on the level of sediment induration, thermal conductivity was measured from either unconsolidated whole cores or discrete rock slices. Measurements of compressive strength and undrained shear strength were taken until the level of consolidation became too high.
Bulk densities at Site 1115 were derived from both gamma-ray attenuation porosity evaluator (GRAPE) measurements conducted on unsplit cores and discrete mass and volume measurements. Composite profiles of these independently-derived bulk densities indicate a similar trend in the two data sets (Fig. F49). The GRAPE bulk densities exceed the index properties values above 226 mbsf (APC cores). This discrepancy was also observed at Site 1109 (see "Density and Porosity" in the "Site 1109" chapter), and no obvious explanation has been found. The GRAPE bulk densities agree reasonably well with the index properties measurements between 226 and 290 mbsf (XCB cores), and are generally less than index properties values below 290 mbsf (RCB cores). For RCB cores, GRAPE underestimation of bulk density may be related to small core diameters. Corrections were attempted at a previous site (see "Density and Porosity" in the "Site 1109" chapter), but could not fully account for the discrepancy. Because of these discrepancies and the large scatter in the GRAPE data, our discussion will focus primarily on the discrete bulk density measurements. GRAPE data from the MST measurements can be found on the accompanying LDEO CD-ROM, and the discrete density data are compiled in Table T11.
Bulk density increases rapidly from 1.50 to 1.60 g·cm-3 in the upper 60 m (Fig. F49), which contain the nannofossil ooze of lithostratigraphic Unit I and the upper part of the nannofossil-rich silty clay of lithostratigraphic Unit II. Below 60 mbsf, bulk densities decrease slightly with depth down to 200 mbsf, with no significant variation observed at the boundary (~150 mbsf) between lithostratigraphic Unit II and lithostratigraphic Unit III, which is a calcareous silty clay. Between 200 and 410 mbsf, bulk densities increase to 1.70 g·cm-3 and then remain relatively constant to slightly decreasing. Exceptions to the general trend are observed in GRAPE values and in one index property sample at 251 mbsf. High-density spikes are observed in the logging data at 246, 248, and 256 mbsf. These spikes are associated with elevated photoelectric effect (PEFL) values, which suggest increased calcium carbonate content (see "Downhole Measurements"). However, measured calcium carbonate content was similar to surrounding sediments (see "Organic Geochemistry"), and no unusual lithology was noted in this core (see "Lithostratigraphy").
At ~410 mbsf, the bulk densities jump to ~1.80 g·cm-3. This discontinuity is located slightly above the boundary between lithostratigraphic Unit IV (calcareous sandy silty claystone) and Unit V (silty sandstone). Below 410 mbsf, bulk densities generally increase steadily to 1.90 g·cm-3 at 550 mbsf. This interval contains the siltstones and sandstones of lithostratigraphic Units V, VI, and VII. Large scatter is present between 560 and 650 mbsf, which probably results from the highly variable sediments of lithostratigraphic Units VIII, IX, X, and XI. Densities range from 1.70 to 2.50 g·cm-3, the latter of which is the highest density measured at Site 1115. Below 650 mbsf, bulk densities steadily increase from 2.10 to 2.15 g·cm-3 at the base of the hole.
A profile of the grain densities with depth indicate discontinuities at ~230 and ~440 mbsf (Fig. F50). Grain densities average ~2.65 g·cm-3 between the seafloor and 230 mbsf, where grain densities suddenly decrease to 2.60 g·cm-3. Between 230 and 440 mbsf, grain densities increase to values of ~2.65 to 2.70 g·cm-3 within the calcareous silty claystones of Unit IV (Fig. F50). At 440 mbsf, grain densities are sharply offset to <2.60 g·cm-3 and then increase to 2.70-2.75 g·cm-3 at the base of Hole 1115 (Fig. F50). Large scatter in grain densities is observed between 560 and 610 mbsf. This latter interval corresponds to lithostratigraphic Units V through XII, but exceptionally high grain densities of up to 2.80 g·cm-3 are found in the conglomerates and sandstones of lithostratigraphic Units IX and X (see "Lithostratigraphy"). High grain densities may reflect the presence of igneous clasts within the conglomerates. No geologically realistic reason has been found for outlier values of 2.95-3.00 g·cm-3 in Units IV and XII, leaving experimental or instrumental error as the most likely explanations.
In general, porosity profiles reflect a combination of loading history and lithostratigraphic effects such as variability in sediment strength, degree of pore filling by cementation, or permeability differences that affect dewatering rates. Several of these factors are observed at Site 1115. Typically, seafloor porosities of marine oozes are high, as previously measured at Site 1109 (~80%; see "Density and Porosity" in the "Site 1109" chapter). For homogeneous sediments that are not overpressured, porosity loss follows an exponential relationship (e.g., Terzaghi, 1925; Athy, 1930). In contrast, the porosities from Site 1115 show unusually low values (65%-70%) at the seafloor, and decrease only slightly within the uppermost ~140 m (Fig. F51). This profile may reflect surficial erosion, as indicated by the >120 ka age for Core 180-1118-1H (see "Biostratigraphy").
Distinct zones of relatively high porosity are found between 140 and 240 mbsf and between ~320 and 420 mbsf. From 200 to 450 mbsf, a high sedimentation rate of ~284 m/m.y. has been estimated (see "Biostratigraphy"). This sedimentation rate may contribute to undercompaction and anomalously high porosities within the lower interval (300-420 mbsf). Above 200 mbsf, sedimentation rates are lower (~63 m/m.y.) and would not be as likely to result in undercompaction.
The lower boundaries (~240 and 420 mbsf) of the two high-porosity intervals are near discontinuities in the grain density profile (~230 and 440 mbsf), suggesting a mineralogic control on porosity. The IW silica data indicate elevated values between ~210 and 420 mbsf (see "Inorganic Geochemistry"). These data suggest that the decrease in pore space below 420 mbsf may be related to cementation of sediment with silica, which would increase average grain density and decrease pore space.
Porosities are extremely scattered between 560 and 620 mbsf. Low porosities probably reflect low-porosity igneous clasts within the conglomerates of Units IX and X. At 572 mbsf, an unconformity is present (see "Biostratigraphy"). If the amount eroded were greater than the present overburden, a jump to lower porosities would be expected at the unconformity. Because the porosity profile is not significantly offset across this boundary (Fig. F51), it is reasonable to assume that erosion did not exceed 572 m of thickness, the depth of the uncomformity.
Compressional wave velocity was measured on whole cores using the MST P-wave logger (PWL). On split cores, the PWS1 probe was used to measure longitudinal (z) velocities and the PWS2 and PWS3 probes were used to measure transverse (y and x, respectively) velocities, with the split core remaining in the core liner. When the degree of sediment induration was sufficient, or hard rock samples were recovered, the PWS3 probe was used to measure both the longitudinal and transverse velocities. The PWL yielded poor quality results, and thus this discussion will be limited to PWS velocity data. From Cores 180-1115A-1H to 180-1115B-7H, velocity measurements were taken in the z and y directions. Insufficient sediment induration precluded measurement in the x direction. From Cores 180-1115B-8H to 11H, the x, y, and z velocities were routinely measured. From Cores 180-1115B-12H to 180-1115C-1R, because of the degree of sediment induration, only the x velocity was measured. From Core 180-1115C-2R to the bottom of the hole, the level of induration was sufficient for ~10-cm3 cubes to be cut from the cores, thereby allowing for velocity to be measured in the transverse and longitudinal directions. The PWL data are presented in Table T12.
From the seafloor to 405 mbsf, velocities increase gradually from ~1550 to 1850 m·s-1 (Fig. F52). This depth range includes lithostratigraphic Units I, II, III, and IV (see "Lithostratigraphy"). A single spike in the velocity at 293 mbsf corresponds to a thin dolomite-rich layer (see "Lithostratigraphy"). Within lithostratigraphic Units IV, V, and VI (405-505 mbsf), velocities average ~1850 m·s-1. From 505 to 620 mbsf, velocities show an increase in scatter, with some velocities exceeding 3000 m·s-1, and three values exceeding 4500 m·s-1. These depths correspond to the variable lithologies of Units VII through X. From 660 mbsf to the base of Hole 1115C (lithostratigraphic Units XI and XII), velocities gradually increase from 2350 to 2600 m·s-1, with outliers occasionally exceeding 4000 m·s-1.
A comparison between transverse and longitudinal velocities indicates that velocities are isotropic above 520 mbsf (Fig. F53). Below this point there is a fair degree of scatter, which reduces below 660 mbsf. The predominance of positive anisotropies below 660 mbsf coincides with lithostratigraphic Unit XI, which consists of sandstone, packstone, siltstone, and silty claystone (see "Lithostratigraphic Unit XI"). Here, the transverse velocity is almost always greater than the longitudinal velocity.
Thermal conductivity measurements at Site 1115 show an overall increase with depth, ranging from ~0.95 W·m-1·ºC-1 near the seafloor to ~1.15 W·m-1·ºC-1 at the base of Hole 1115C (Fig. F54). Measurements could not be taken between 240 and 280 mbsf, where sediments were too indurated for needle-probe insertion and too soft for half-space measurements. A full compilation of the data is presented in Table T13.
Some intervals indicate slight deviation from the downhole increase with depth. Thermal conductivity decreases slightly below 120 mbsf, which correlates well with the top of a zone of high porosity (see above). Conversely, sediments that are thermally more conductive (e.g., siltstones and sandstones of Units V and VI) are found between 420 and ~510 mbsf, where lower porosities were observed (Fig. F54). Large scatter is observed between 550 and 620 mbsf (Units VIII-XI; see "Lithostratigraphic Unit VIII," "Lithostratigraphic Unit IX," "Lithostratigraphic Unit X," and "Lithostratigraphic Unit XI") which is also consistent with the porosity data.
Split cores from Holes 1115B and 1115C were subjected to undrained shear strength and unconfined compressive strength tests using the motorized miniature vane-shear device and the pocket penetrometer, respectively. Below 240 mbsf, strength parameters could not be measured as a result of incipient induration. The data are presented in Figure F55 and Table T14.
Undrained shear strength (Su) was measured in the uppermost ~60 mbsf of the sedimentary succession drilled (i.e., within the nannofossil oozes and clays of lithostratigraphic Unit I). The data show an increase with depth, rising from ~5kPa at the seafloor to around 80 kPa at 60 mbsf (Fig. F55). Unconfined compressive strength (2 Su) increases along a similar trend as the undrained shear strength, starting from near zero strength at the seafloor (Fig. F55). At ~200 mbsf, values between 180 and 220 kPa are reached. The state of sediment consolidation can be estimated by comparing the range of strengths measured relative to normally consolidated sediment, expressed as the ratio of undrained strength (Su) to effective overburden stress (P0'). Normally consolidated sediments show Su/P0' values of 0.2 (e.g., Mesri, 1975), as shown by the dashed line in Figure F55. It can be seen that the data from Site 1115 plot slightly below this line, suggesting slight underconsolidation.
To evaluate the nature and origin of the magnetic mineralogy for the recovered Site 1115 sediment, the magnetic susceptibility, natural gamma ray (NGR), and remanent intensity were compared (Fig. F56). All magnetic susceptibility data can be found with the MST measurement data set (in ASCII format) on the accompanying LDEO CD-ROM. For the entire section, there exists a direct correlation between the susceptibility and the remanent intensity. From this we can infer that, in general, the mineralogy controlling the magnetic susceptibility is the same as that controlling the remanent magnetic intensity. Further, the correlation between NGR variations and the magnetic susceptibility suggests that the clays and sands containing radioactive material also are rich in ferromagnesium minerals.
A more detailed comparison between the lithology and grain-size distribution with the susceptibility indicates that there is no clear relationship between either grain size or the main lithostratigraphic boundaries. Nevertheless, the magnetic susceptibility as a function of depth has a number of clear trends. In particular, there is a first-order difference between the high-amplitude susceptibility variations within the upper part of the section (50-220 mbsf) and the low-amplitude variations within the middle part of the section (220-420 mbsf). The transition occurs within lithostratigraphic Unit III, which is characterized by abundant volcaniclastic sands. In contrast, lithostratigraphic Unit II is dominated by ashes. Likewise, grain sizes between 25 and 140 mbsf are associated with high-frequency, fine-grained distal turbidites whereas the section between 140 and 380 mbsf comprises high-frequency, proximal turbidites (see "Lithostratigraphy"). Again, no simple relationship exists between grain-size distribution and the trends in the susceptibility.
Second-order trends are represented by the relatively high amplitude susceptibility variations of the shallow-marine, lagoonal, and fluvial deposits of lithostratigraphic Units VII, VIII, and IX, and the outer neritic and upper bathyal calcareous sandstones and siltstones of the forearc lithostratigraphic Units X, XI, and XII. Presumably, the extreme anoxic environment within the brackish lagoons and swamps were conducive to formation of iron sulfides and clays (e.g., pyrite and smectite; see "Lithostratigraphy").
The NGR emissions were recorded for all cores at Site 1115, as part of the continuous MST measurements. Because K, U, and Th are the principal sources of NGR and often preferentially bind to clay particles, an increasing NGR count typically correlates to an increasing clay/shale content. In contrast, sand-prone and calcium carbonate units are usually characterized by low NGR counts. However, this usual relationship has been confounded by the presence of radiogenic sands and clays within the basin, which are being produced from the erosion or alteration of volcaniclastic, igneous, and metamorphic terranes. Composite NGR data from Site 1115 are presented graphically in Figure F56, and all NGR data can be found with the MST measurement data set (in ASCII format) on the accompanying LDEO CD-ROM.
The NGR data are approximately constant between the seafloor and 100 mbsf, and correlate with the nannofossil ooze of lithostratigraphic Unit I and the upper part of lithostratigraphic Unit II (see "Lithostratigraphic Unit I" and "Lithostratigraphic Unit II"). Between 100 and 180 mbsf, the NGR count gradually increases from 10 to 20 counts/s, after which the count remains fairly constant to slightly decreasing until ~400 mbsf. This second interval corresponds to lithostratigraphic Units II and III. These units are characterized by clays containing ash layers and clays with volcaniclastic sands, respectively. From 400 to 470 mbsf the NGR count increases gradually to 30 counts/s within the silty sandstone of lithostratigraphic Unit IV. There is an abrupt increase in NGR count to an average of 45 counts/s within Unit V, comprising sandy siltstone and silty sandstone, before tailing off to ~5 counts/s at 660 mbsf. Throughout lithostratigraphic Unit XII, NGR count remains scattered tightly below 6 counts/s. The correlation of high NGR count with sandstone is not typical, and thus may be indicative of provenance and again is symptomatic of radiogenic sands within the basin. It is important to note that the discontinuities observed in the NGR (180 and 400 mbsf) are similar to those observed in magnetic susceptibility (220 and 410 mbsf), and in porosity.
Given only the shipboard analyses, the general NGR trends are difficult to explain in terms of either grain size or lithostratigraphic variations. For example, in the interval 200-400 mbsf, both relatively thick clays and sands (e.g., at 197-207 and 417-426 mbsf, respectively) have an identical NGR count of 20 counts/s. Individual spikes superposed on the general trend increase the NGR count by 10-15 counts/s and tend to be correlated with volcaniclastic sands. In contrast, the NGR maxima between 480 and 520 mbsf are associated with the relatively "clean" neritic sands and carbonaceous siltstones of lithostratigraphic Units VI and VII (see "Lithostratigraphic Unit VI" and "Lithostratigraphic Unit VII").
Magnetic susceptibility and NGR were used to correlate between Holes 1115A, 1115B, and 1115C (Figs. F57, F58). Interhole correlation is based on recognizing characteristic features in the data sets. Magnetic susceptibility and GRAPE density proved difficult in correlating between Holes 1115B and 1115C because of (1) a major data gap within the overlap zone, and (2) the lack of distinguishing features outside of the data gap. Figure F57 shows a magnetic susceptibility peak at 2.0 mbsf in both Holes 1115A and 1115B. A second peak, correlating with an ash layer, is present at 3.9-4.1 mbsf in Hole 1115A and 3.75-4.1 mbsf in Hole 1115B. Within the lower part of the section, an offset of 15-20 cm is suggested, whereas there is minimal offset in the upper section between the two holes. The ~20-cm offset in the upper part of the section is consistent with the lithostratigraphy. With respect to Holes 1115B and 1115C, Figure F58 shows correlation between two minima (shown by dashed lines) and correlation between a series of small NGR peaks, numbered 1 to 6 for Hole 1115B and 1' to 6' for Hole 1115C, superposed onto a relatively long wavelength low between 287.5 and 289.5 mbsf. The correlation suggests that an offset of 0.3-0.7 m exists between Holes 1115B and 1115C.