IODP Expedition 390C

South Atlantic Transect Reentry Systems

Daily Science Report for 31 October 2020

Location: Hole U1556A (30°56.5244′S, 26°41.9472′W, water depth 5006.4 m, proposed Site SATL-53B)

Science Update: Cores U1556A-24X through 29X advanced from 216.0 to 273.6 m below seafloor (mbsf) and rec overed 39.85 m (69%). Core 30X encountered a hard layer that decreased the rate of penetration dramatically. Upon recovery, this layer was confirmed to be basement, which was determined to be at 278 mbsf. Cores 31X to 32X attempted additional coring of the altered basalt basement material. By midnight, we had recovered 3.13 m from a total advance into basement of 4.3 m (72.8%). The sediment/basement interface in Core 30X had the lowest recovery of basement (23%) but once fully into basement, we experienced higher recovery.

Cores U1556A-1H through 29X have been split and measured on the track systems. In addition, we took 1–2 whole-round samples per core for chemical analysis of interstitial waters. No core description will occur during Expedition 390C.

The Staff Scientist communicated with the Co-Chief Scientists in order to revise operations plans as basement was found to be deeper than predicted from the seismic data.

Daily Science Report for 30 October 2020

Location: Hole U1556A (30°56.5244′S, 26°41.9472′W, water depth 5006.4 m, proposed Site SATL-53B)

Science Update: Cores U1556A-16H advanced from 142.0 to 151.40 m below seafloor (mbsf). A strong overpull prompted an overdrill of Core 16H to release it from the formation before it could be recovered. We then changed to the extended core barrel (XCB) coring system using the polycrystalline diamond compact (PDC) cutting shoe. Cores U1556A-17X through 23X advanced to 216.0 mbsf and recovered 39.68 m (61.4%). Average rate of penetration was 11.5 m per hour for these XCB cores.

Daily Science Report for 29 October 2020

Location: Hole U1556A (30°56.52′S, 26°41.94′W, water depth 5006.4 m, proposed site SATL-53B)

Science Update: Cores U1556A-2H through 15H advanced from 9.0 to 142.0 m below seafloor (mbsf) and recovered 136.71 m (103%). All cores were oriented with the Icefield MI-5 core orientation tool. Formation temperature measurements were taken on Cores 4H, 7H, 10H, and 13H with the advanced piston corer temperature tool (APCT-3). Cores 11H to 13H were partial strokes due to the stiffness of the sediment but had good recovery; Cores 14H and 15H were full strokes.

Standard shipboard analyses are being conducted by JRSO staff for safety purposes and to capture ephemeral properties of the cores. The Expedition 390 and 393 science parties will describe the cores and conduct additional analyses during the expeditions.

Daily Science Report for 28 October 2020

Location: Hole U1556A (30°56.52′S, 26°41.94′W, water depth 5006.4 m, proposed site SATL-53B)

Science Update: The JOIDES Resolution arrived at Site U1556 (proposed Site SATL-53B) at 0206 h, completing the 3608 nmi transit from Las Palmas, Canary Islands, and switched from cruise mode to dynamic positioning mode at 0230 h. The advanced piston corer/extended core barrel (APC/XCB) bottom-hole assembly was made up and deployed. We lowered the drill bit to 5006 m below sea level (mbsl), then pumped a “pig” (pipe cleaning device) through the drill string to remove rust. At ~2200 h, the sinker bars and core orientation tool were installed and the core barrel was lowered. We spudded Hole U1556A at 2300 h. Mudline Core U1556A-1H arrived on deck at 2335 h and recovered 9 m. This established a seafloor depth of 5006.4 mbsl.