doi:10.2204/iodp.proc.324.106.2010
Physical properties
Volcanicalstic sediments and basalts in Hole U1349A were characterized for physical properties as described in "Physical properties" in the "Methods" chapter. Core sections with continuous intervals longer than 8 cm were run through the Whole-Round Multisensor Logger for measurement of gamma ray attenuation (GRA) density and magnetic susceptibility. Data from whole-round measurements were filtered to remove data associated with gaps and small pieces as described in "Physical properties" in the "Methods" chapter. Sections longer then 50 cm were measured with the Natural Gamma Radiation Logger. Thirty-two discrete, oriented cubic samples were cut from the working half of the cores for measurement of moisture and density (MAD) properties as well as compressional (P-wave) velocities in three directions.
Whole-Round Multisensor Logger measurements
Magnetic susceptibility
Results of whole-round magnetic susceptibility measurements are shown in Figure F60. Distinctive magnetic susceptibility signatures are observed within all of the Hole U1349A stratigraphic units (see "Sedimentology"). Unit II and Subunit IIIa are claystone-sandstones with a large proportion of volcaniclastics. These units are characterized by magnetic susceptibilities of <1000 x 10–5 SI. Subunit IIIb consists of volcaniclastic conglomerate. Section 324-U1349A-7R-1 of the conglomerate contains the highest magnetic susceptibility readings measured during Expedition 324. The signal of almost 4000 x 10–5 SI corresponds to a large basaltic clast, which, upon thin section investigation, was found to contain abundant groundmass magnetite (see "Igneous petrology").
The top of the basaltic basement was encountered in Section 324-U1349A-7R-1 at 96 cm (165.1 mbsf), denoting the top of the vesicular basalts making up Unit IV. The upper 26 m of this unit (from Section 7R-1 to 10R-5) is characterized by low magnetic susceptibility. This interval has an overall red appearance and contains abundant hematite (see "Igneous petrology" and "Paleomagnetism"). Hematite, although magnetic, has less susceptibility than magnetite, and this may explain the lower readings measured in this interval. From Core 324-U1349A-11R to 13R, magnetic susceptibility increases (average = 1000 x 10–5 SI), reaching values >2000 x 10–5 SI. Unit V commences at 221.7 mbsf and is composed of autobrecciated basalts. The brecciated material composing Cores 324-U1349A-14R through 16R has very low magnetic susceptibility readings (average = 105 x 10–5 SI).
Gamma ray attenuation bulk density
The results for GRA bulk density measurements from Hole U1349A are shown in Figure F60. Volcaniclastic sandstones, claystones, and lapillistones of Unit II and Subunit IIIa have low GRA densities of ~1.8–2.0 g/cm3. The rest of the hole has GRA densities >2.0 g/cm3, remaining fairly uniform with an average of 2.2 g/cm3 in igneous material. The autobrecciated basalts of Unit V show increased variation in GRA density. This is not surprising, given the heterogeneous clast type and distribution observed in this unit (see "Sedimentology" and "Igneous petrology").
Natural Gamma Ray Logger
Measurements of natural gamma radiation (NGR) are shown in Figure F60. Counts per second range from 1 cps to almost 40 cps throughout the hole, with an average of 13.8 ± 12.5 cps (2σ). The range of counts per second is slightly lower but still comparable to the altered basalts of Hole U1346A (~22 cps). Gamma spectra from Hole U1349A indicate that counts dominantly result from the 40K decay chain. Excursions to high NGR counts occur in sedimentary Unit II and Subunit IIIa. In general, the vesicular basalts of Unit VI and the upper part of brecciated basalts in Unit V (above 225 mbsf) have higher (10–15 cps) counts than the lower autobrecciated basalts of Unit V (5–10 cps). The lower counts found in the middle and lower sections of Unit V (below 225 mbsf) are consistent with low K2O values, some of which were below the detection limit of ICP measurements (see "Geochemistry").
Moisture and density
Summaries of bulk density, dry density, grain density, void ratio, water content, and porosity measurements on discrete samples are listed in Table T7. Densities and porosities are shown in Figure F61 and display a good negative correlation. Bulk density ranges from 2.06 to 2.34 g/cm3 in Unit II and Subunit IIIa. Density increases in the igneous material of Units IV and V to values between 2.16 and 2.96 g/cm3, averaging 2.63 ± 0.34 g/cm3 (2σ). The density measurements of autobrecciated material in Unit V are more variable than those found in the vesicular basalts of Unit IV, in keeping with the heterogeneous nature of this unit (see "Sedimentology" and "Igneous petrology").
Porosities in the upper sedimentary units are high (between 20% and 40%). Throughout the vesicular basalts of Unit IV, porosity decreases (1.5%–15.8%), with an average of 9.2% ± 8.0% (2σ). The lowermost autobrecciated basalts of Unit V once again display variation, with porosity ranging from 8.0% to 33.5%.
Compressional (P-wave) velocity
Downhole variation of compressional wave velocity is shown in Figure F61 and listed in Table T8. Figure F62 illustrates the negative correlation of P-wave velocity with porosity and positive correlation of P-wave velocity with bulk density. There was no significant anisotropy observed in the samples. Figure F62 depicts the generally lower densities and P-wave velocities and higher porosities of the sedimentary units (Unit II and Subunit IIIa) compared with the igneous material from Units IV and V. The vesicular basalts of Unit IV have downhole velocities ranging between 4.3 and 7.1 km/s, similar to those found in igneous material at the other Expedition 324 sites. There is one outlier in Figure F62 from Core 324-U1349A-10R. This sample lies off the trend to lower P-wave velocities for a given density and porosity. Visual examination of the sample did not reveal any obvious reason for the discrepancy.
Thermal conductivity
Thirty-seven measurements of thermal conductivity were performed on material recovered from Hole U1349A. The results are summarized in Table T9 and displayed in Figure F63. Thermal conductivity in sedimentary Unit II and Subunit IIIa was generally lower than measured in igneous material and ranged from 1.01 to 1.57 W/(m·K). The igneous material of Unit IV had an average thermal conductivity of 1.80 ± 0.36 W/(m·K) (2σ; N = 22). The autobrecciated basalts of Unit V showed a decrease in thermal conductivity compared to Unit IV, averaging 1.36 ± 0.31 W/(m·K) (2σ; N = 10). This is plausibly due to the higher porosity of this unit, since thermal conductivity of rock is greater than pores filled with air or water.