Archive | 2021
Data report: moisture and density analysis and ultrasonic velocity, Hole U1513E, IODP Expedition 369
Abstract
In this data report, we present postcruise petrophysical measurement results for Hole U1513E. During International Ocean Discovery Program (IODP) Expedition 369, five holes were drilled at Site U1513 on the Naturaliste Plateau offshore southwest Australia. The last and deepest hole, U1513E, recovered a volcanic sequence (Lithostratigraphic Unit VI) consisting of basalt flows, dolerite dikes, and volcaniclastic beds. Because of time constraints, moisture and density (MAD) measurements were not possible on board for Hole U1513E. To obtain bulk (wet), dry, and grain density and porosity data, we performed the MAD analysis on 25 core samples collected from Hole U1513E after the expedition. Among these samples, five were selected to measure ultrasonic velocity and dynamic Poisson’s ratio. Six additional samples from Hole U1513D were analyzed to compare with shipboard data to validate the postcruise measurements. The results are compatible with shipboard data in individual lithologic units. Samples of relatively fresh rocks show bulk and dry density values near 2.5 g/cm3 and porosity near 10%, whereas altered basalts and volcaniclastics exhibit lower values of bulk and dry density and higher values of porosity. Grain density varies between 2.6 and 3.3 g/cm3. S-wave velocity ranges from 934 to 3135 m/s, which accompanies variable dynamic Poisson’s ratio between 0.1 and 0.35. Introduction During International Ocean Discovery Program (IODP) Expedition 369, five holes (U1513A–U1513E) were drilled at Site U1513 on the eastern flank of the Naturaliste Plateau offshore southwest Australia (Figure F1A). The site is near Deep Sea Drilling Project (DSDP) Site 258, which was drilled during Leg 26 (Davies et al., 1974). The deepest hole, U1513E (33°47.6190′S, 112°29.1204′E), reached 770.27 m core depth below seafloor, Method A (CSF-A) (Huber et al., 2019b). Holes U1513E and U1513D penetrated through a volcaniclastic-rich sedimentary sequence (Lithostratigraphic Unit V) and recovered a volcanic sequence (Lithostratigraphic Unit VI) (Figure F1B). The volcaniclastic-rich sequence (235 m thick) consists of sandstone, siltstone, and silty claystone layers containing abundant volcanic clasts and lithic fragments (Lee et al., 2020). The volcanic sequence (cored thickness = 82.2 m) is composed of basaltic flows (Lithologic Units 1, 3, 5, 7, and 9) and volcaniclastic beds (Lithologic Units 2, 4, 6, and 8) cut by multiple dolerite dikes (Tejada et al., 2020). Because of time constraints during Expedition 369, it was not possible to finish shipboard core descriptions and the moisture and density (MAD) analysis for Hole U1513E. After the expedition, Cores 369-U1513E-2R through 9R were reexamined at the Kochi Core Center, Japan. A modified volcanic stratigraphy based on descriptions of petrological and mineralogical characteristics and lithologic boundaries was established for the volcanic sequence at Site U1513 (Figure F1B). The data were reported and studied in Lee et al. (2020) and Tejada et al. (2020). The studies helped us to select core samples that were used for the postcruise MAD analysis to obtain bulk (wet), dry, and grain density and porosity data for Hole U1513E. Among the samples, five were selected to measure ultrasonic velocity and dynamic Poisson’s ratio. Additional samples from Hole U1513D were also analyzed to compare with shipboard data to validate the postcruise measurements. In this data report, we present our postcruise petrophysical measurement results of the volcanic sequence in Hole U1513E. E.Y. Lee and I. Song Data report: moisture and density analysis and ultrasonic velocity, Hole U1513E Materials and methods Moisture and density measurements During Expedition 369, shipboard MAD measurements for the volcanic sequence (Lithostratigraphic Unit VI) in Hole U1513D were performed on 16 core samples collected from the working-half sections of Cores 369-U1513D-66R through 75R. The standard IODP MAD procedures (ASTM International, 1990; Blum, 1997) were applied to analyze the hard rock samples from Hole U1513D (Huber et al., 2019a). The measured wet mass, dry mass, and dry volume of each sample were used to determine bulk (wet) density, dry density, grain density, and porosity. Salt precipitation in pore space during the drying process was included in the wet mass and dry volume values. The shipboard MAD data were described in Huber et al. (2019b) and are available at https://web.iodp.tamu.edu/LORE. The postcruise MAD analysis was completed at the Korea Institute of Geoscience and Mineral Resources (KIGAM), Republic of Korea. MAD instrumentation, measurements, and analysis followed shipboard procedures as much as possible, except for a few minor procedural differences. For saturation, we placed the samples in individual plastic vials that were filled with distilled water (density = ~1.0 g/cm3) instead of seawater (density = ~1.024 g/cm3). Thus, the mass and volume of salt were not evaluated and are not considered for MAD calculations in this report. Because of their very low values, however, only slight differences are observed, which is supported by a good comparison between shipboard and postcruise MAD data using samples from Hole U1513D (Table T1). The vacuum chamber (Model OV-12; Figure F2A) was used to saturate pore spaces. The vacuum pump removed air from the chamber to a pressure of ~50 kPa below atmospheric pressure. These samples were kept under saturation for ~24 h with the vacuum maintained in the chamber. After removal from the saturator, the samples were patted dry with a paper towel, and their wet masses were immediately determined using the Mettler-Toledo electronic balance (Model XS404SV; Figure F2B). The samples were then dried in an oven for ~24 h at 100°–110°C and measured for dry mass using the electronic balance after cooling in a desiccator. Dry sample volume was determined with a five-celled helium gas pycnometer (Model Pentapyc 5200e; Figure F2C). Volume measurement was preceded by five purges of the sample chamber with helium. The data from the five measurement cycles of each sample were averaged to determine dry volume and grain density (see MAD_DATA in Supplementary material). The measured values were used to calculate bulk density, dry density, porosity, and other parameters (Table T1) following the standard IODP MAD calculations (Blum, 1997; Huber et al., 2019a). To conduct the postcruise MAD analysis for Hole U1513E, dozens of core samples were collected from Cores 396-U1513E-2R through 9R. Among them, 25 samples were carefully selected from what were deemed suitable conditions because shipping induced fragmentation of some samples. A total of 12 samples were from dolerite dikes, 9 samples were from basalt flows, 3 samples were from volcaniclastic beds in the volcanic sequence, and 1 sample was from the volcaniclastic-rich sequence (Table T1). Six samples from Hole U1513D were also analyzed alongside to compare with shipboard data. Ultrasonic measurements During Expedition 369, P-wave velocity was determined by measuring the time required for a compressional wave to travel a specific distance through a core section. The velocity measurement was performed using Panametrics-NDT Microscan delay line transducers for selected positions on the working-half sections (Huber et al., 2019a). A total of 27 data sets of P-wave velocity were acquired for the volcanic sequence in Hole U1513D (Figure F3E), and 99 data sets were acquired for Hole U1513E (Figure F4E), all of which can be accessed at https://web.iodp.tamu.edu/LORE. Figure F1. A. Map of submarine Naturaliste Plateau and Mentelle Basin offshore southwest Australia (modified from Borissova, 2002; Huber et al., 2019b) showing location of Site U1513, adjacent DSDP Site 258, and IODP Sites U1514–U1516. FZ = fracture zone. B. Lithostratigraphy at Site U1513 with Lithostratigraphic Units I–VI. Lithologic (volcanic) units of Lithostratigraphic Unit VI in Holes U1513E and U1513D are shown (revised from Huber et al., 2019b; Tejada et al., 2020).