IODP Expedition 395C

Reykjanes Mantle Convection and Climate: Crustal Objectives

Daily Science Report for 30 June 2021

Location: Hole U1554F (60°7.5136′N, 26°42.1140′W; water depth 1870 mbsl; proposed Site REYK-6A)

Science Update: The BHA for drilling in the casing string was made up and the HRT running tool and reentry cone were assembled. At 0638 h, the HRT reentry system was deployed through the moonpool. The casing and drill string were run to a depth of 1552 mbsl and the subsea camera was deployed to observe the casing operations. The drill string continued to be lowered and at 1345 h Hole U1554F was spudded. As of midnight, the bit had advanced 275 m into the seafloor, with a target depth of 602 mbsf for the end of the casing.

The JRSO technical staff are processing the cores and samples in the laboratories. Cores 32X to 42X were measured using the SRM. Pore water and sediment chemistry measurements are ongoing.

Daily Science Report for 29 June 2021

Location: Hole U1554F (60°7.5133′N, 26°42.1337′W; water depth 1870 mbsl; proposed Site REYK-6A)

Science Update: The day began with pulling up the pipe from Hole U1554E. At 0245 h the bit cleared the rotary table, ending the hole. The ship was positioned over the Hole U1554F coordinates and the rig floor crew began assembling the casing and reentry system. The mudskirt of the reentry system was moved over the moonpool and the hydraulic release tool (HRT) was made up and racked in the derrick. A 602.3 m long casing string, composed of 52 joints of 10¾ inch casing, was assembled. The HRT was attached to the casing and lowered to the mudskirt. The HRT was then detached and put back into the derrick. A drilling assembly with a mud motor, underreamer, and bit was assembled and tested in the moonpool. The first mud motor rotated too freely and was replaced with a second mud motor. After successfully testing that the underreamer arms open appropriately, the crew began making up the BHA.

The JRSO technical staff are processing the cores and samples in the laboratories. Cores U1554E-24X to 31X were measured using the SRM. Pore water and sediment chemistry measurements are ongoing.

Daily Science Report for 28 June 2021

Location: Hole U1554E (60°7.5235′N, 26°42.1324′W; water depth 1870 mbsl; proposed Site REYK-6A)

Science Update: Downhole wireline logging continued with the triple combo tool string making two passes of the borehole. The tool string was able to descend to the base of the hole (~647 mbsf). The first attempt to pull the triple combo through the bit and into the drill pipe occurred at 0115 h. The lockable float valve (LFV) at the bit had closed, preventing the tool string from reentering the pipe. After several hours of pumping seawater and rotating the drill string, the triple combo was pulled past the LFV and the tools reached the surface at 0845 h. The FMS-sonic was assembled and deployed at 1120 h. A go-devil was attached to the top of the tool string to lock open the LFV. After two passes of the borehole, the FMS-sonic was unable to pass through the LFV and back into the pipe. After more pumping, the tools were successfully recovered and the FMS-sonic tool string reached the rig floor at 2055 h. Following logging operations the drill string was pulled out of the hole with the bit clearing the seafloor at 2210 h. The remainder of the day was spent pulling up the pipe and BHA.

The JRSO technical staff are processing the cores and samples in the laboratories. Cores 58X to 62X were split, imaged, and measured for point magnetic susceptibility and color reflectance. Cores 19X to 23X were measured using the SRM. The cores were sampled for paleontology and moisture and density analyses.

Cores 57X to 60X contain sediments that alternate between light green to dark gray with varying amounts of calcium carbonate and clay content. Sharp erosional contacts and burrows are observed in these cores. Core 61X transitions from the dark gray material to a light green and white nannofossil ooze. The basement was recovered in Core 62X and is composed of basalt alternating with carbonate. Pore water alkalinity decreases from 12.5 mM at ~350 mbsf to 2.3 mM at the base of the hole.

Daily Science Report for 27 June 2021

Location: Hole U1554E (60°7.5235′N, 26°42.1324′W; water depth 1870 mbsl; proposed Site REYK-6A)

Science Update: Coring continued in Hole U1554E from Core 56X to 62X (586.9–647.7 mbsf), with 50.5 m of core recovered (83%). Basement was encountered at ~647 mbsf while drilling Core 62X; the core contained 2.6 m of basalt interlayered with carbonate. After reaching the basement and a final depth of 647.7 mbsf, Hole U1554E was prepared for downhole wireline logging operations. The hole was cleaned and displaced with mud and the drill string pulled up to 72.8 mbsf. The triple combo tool string was made up and run in the hole at 2100 h.

The JRSO technical staff are processing the cores and samples in the laboratories. Cores 56X to 62X were run through the whole-round physical properties tracks and Cores 44X to 57X were split, imaged, and measured for point magnetic susceptibility and color reflectance. Cores 14H to 18X were measured using the SRM. We are collecting routine samples for interstitial waters, gas, microbiology, paleontology, and moisture and density analyses.

The cores contain dark gray clay and silt with dropstones, and pyritized gastropods are present. Core 56X contains a formation change to lighter material with soft sediment deformation and erosional surfaces. The XCB cores have prevalent biscuiting from the coring process.

Daily Science Report for 26 June 2021

Location: Hole U1554E (60°7.5235′N, 26°42.1324′W; water depth 1870 mbsl; proposed Site REYK-6A)

Science Update: Coring at Hole U1554E continued from Core 42X to 55X (451.1–586.9 mbsf), with 102.35 m of core recovered (75%). XCB coring will continue until the basement is reached, which is estimated at 700 mbsf.

The JRSO technical staff are processing the cores and samples in the laboratories. Cores 35X to 55X were run through the whole-round physical properties tracks and Cores 25X to 43X were split, imaged, and measured for point magnetic susceptibility and color reflectance. Cores 9H to 13H were measured using the SRM. We are collecting routine samples for interstitial water, gas, microbiology, paleontology, and moisture and density analyses.

The cores contain dark gray clay and silt with dropstones, and pyritized gastropods are present. The XCB cores have prevalent biscuiting.

Daily Science Report for 25 June 2021

Location: Hole U1554E (60°7.5235′N, 26°42.1324′W; water depth 1870 mbsl; proposed Site REYK-6A)

Science Update: Coring at Hole U1554E continued with Core 17H at a depth of 208.8 mbsf. After the core barrel was shot, it could not be pulled out of the sediment using the core winch line. The barrel was drilled over using the drill string to free the core. Following Core 17H, the XCB system was deployed. Cores 18X to 41X were collected (218.3–451.1 mbsf) with 98% core recovery. The Co-Chief Scientists and Expedition Project Manager hosted a review meeting of Site U1555 for the science party. The meeting reviewed the site operations, coring results, and some of the datasets.

The JRSO technical staff are processing the cores and samples in the laboratories. Cores 12H to 34X were run through the whole-round physical properties tracks and Cores 10H to 24X were split, imaged, and measured for point magnetic susceptibility and color reflectance. Cores 4H to 8H were measured using the SRM.

Catwalk sampling for interstitial pore water and microbiology began at Core 31X (~350 mbsf). The overlying sedimentary section will be sampled for these analyses during Expedition 395 when a sailing science party is available to assist with the measurements.

The cores contain dark gray clay and silt with intervals that are light gray and light greenish gray. The APC cores display mottling and bioturbation. Dropstones are occasionally observed. Foraminifers and biogenic silica can be seen in the split core sections using a hand lens. The XCB cores have prevalent biscuiting.

Following 14 d of isolation at sea, shipboard COVID-19 safety protocols were lifted at 1000 h.

Daily Science Report for 24 June 2021

Location: Hole U1554E (60°7.5235′N, 26°42.1324′W; water depth 1870 mbsl; proposed Site REYK-6A)

Science Update: The vessel arrived at Site U1554 early in the day. The ship’s thrusters were lowered at 0124 h and the vessel switched to dynamic positioning mode at 0136 h. The BHA and drill string were made up and run to the seafloor. At 0754 h Hole U1554E was spudded and drilled without recovery to 66.3 mbsf, based on initial coring operations conducted during Expedition 384 in July 2020. Coring using the APC advanced from 66.3 to 208.8 mbsf (Cores 2H–16H). A total of 148 m of sediment was cored, with 104% core recovery. The cores were expanding upon arrival on the core receiving platform. Formation temperature measurements using the APCT-3 tool were collected on Cores 2H, 5H, 8H, and 11H.

The JRSO technical staff are processing the cores and samples in the laboratories. Cores 2H to 11H were run through the whole-round physical properties tracks and Cores 2H to 9H were split, imaged, and measured for point magnetic susceptibility and color reflectance. Cores 2H to 3H were measured using the SRM. Methane concentrations increased downhole from 0 to 11,000 ppm.