Site U1526

Abstract

This work is distributed under the Creative Commons Attribution 4.0 International (CC BY 4.0) license. Contents 1 Background and objectives 3 Operations 4 Lithostratigraphy 9 Biostratigraphy 11 Paleomagnetism 14 Structural geology 16 Geochemistry 18 Physical properties 20 Core-seismic integration 25 References L.M. Wallace et al. Site U1526 IODP Proceedings 3 Volume 372B/375 Operations Transit to Site U1526 The vessel arrived at Site U1526 at 1700 h (UTC + 12 h) on 22 April 2018. Upon arrival, the thrusters were lowered, and the dynamic positioning (DP) system was engaged. Hole U1526A A rotary core barrel (RCB) bottom-hole assembly (BHA) was assembled, and the drill string was lowered to the seafloor. Hole U1526A (39°1.3203ʹS, 179°14.7594ʹE; 2890.1 meters below sea level [mbsl]; Table T1) was spudded at 0150 h on 23 April 2018. Cores 1R-14R advanced from 0 to 83.6 meters below seafloor (mbsf) and recovered 29.26 m (35% recovery). Nonmagnetic core barrels were used for all cores. At the completion of coring, the drill bit was partially raised from the seafloor, and the ship returned to nearby Site U1520. Hole U1526B On 2 May 2018, we returned to Site U1526 following an 8 h transit from Site U1520 in DP mode. The ship was offset 20 m westnorthwest from Hole U1526A, and Hole U1526B (39°1.3146ʹS, 179°14.7481ʹE; 2888.4 mbsl) was spudded at 2015 h on 2 May. Advanced piston corer (APC) Cores 1H-4H and extended core barrel (XCB) Core 5X advanced from 0 to 33.5 mbsf and recovered 31.56 m (94% recovery). Nonmagnetic core barrels were used for all APC cores. The total time spent at Site U1526 was 2.88 days.

Expedition 372B/375 summary

“…LWD data acquired during Expedition 372 at Sites U1518 and U1520 documented sediment properties and structure and characterized stress orientations through analysis of wellbore failures at Site U1518 (see the Site U1518 and Site U1520 chapters [Saffer et al, 2019;Barnes et al, 2019c]). Coring during Expedition 375 aimed to collect key samples and data sets for sediment/rock physical properties, pore fluid composition, and downhole temperature with a focus on hydrogeology and fault mechanical processes.…”

“…Site U1518 is located on the lower continental slope near the trench and ~73 km from shore at ~2630 m water depth (Figures F2, F3; Table T1) (see the Site U1518 chapter [Saffer et al, 2019]). This site is located on the forelimb of an anticline formed by an active thrust, the Pāpaku fault, which branches from the plate interface ( Figure F2).…”

“…Broad facies-level comparisons (i.e., packets of beds at a 10+ m scale) can be made between the lithostratigraphy defined from core descriptions and the provisional log-based stratigraphy defined in Holes U1518A and U1518B (see Logging while drilling in the Site U1518 chapter [Saffer et al, 2019]) ( Figure F6). Six logging units were defined for Site U1518 during Expedition 372.…”

“…Fractures were observed at various depths in the Site U1518 LWD resistivity image logs acquired during Expedition 372 (see Logging while drilling in the Site U1518 chapter [Saffer et al, 2019]). Significant fracture clusters were observed between 170 and 230 mbsf, between 315 and 321 mbsf (at a comparable depth, although slightly deeper than those observed in the main fault zone in Hole U1518F; Figure F8), and between 436 and 444 mbsf.…”

“…The primary drilling objective at Site U1526 was to sample the thin sediment cover (~30 m) and ~100-150 m of underlying volcaniclastics or basement on the western flank of Tūranganui Knoll seamount at 2908 m water depth (Figures F2, F3; Table T1) (see the Site U1526 chapter [Wallace et al, 2019]). The scientific aim of coring was to characterize the seamount's composition, physical properties, extent of alteration and hydration, and structure and hydrogeology prior to transport into the SSE source region.…”