IODP Expedition 393

South Atlantic Transect 2

Daily Science Report for 30 June 2022

Location: Hole U1558D (30°53.7814′S, 24°50.4822′W, water depth 4334 mbsl)

Science Update: Cores U1558D-9R to 14R penetrated from 205.3 to 244.1 mbsf and recovered 23.9 m (66%). Core U1558D-7R was split and described. Sections U1558D-7R-1 to 7R-3 contain highly plagioclase-olivine-clinopyroxene-phyric basaltic pillow lavas, which are moderately to highly altered but with frequent fresh glass pillow margins. Sections U1558D-7R-4 to 7R-6 contain fewer phenocrysts and have a less obvious pillow morphology than the overlying lavas.

Daily Science Report for 29 June 2022

Location: Hole U1558D (30°53.7814′S, 24°50.4822′W, water depth 4334 mbsl)

Science Update: Cores U1558D-4R to 8R penetrated from 166.5 to 205.3 mbsf and recovered 23.6 m (61%). The sediment/basement contact was determined to be at 166.8 mbsf based on an abrupt slowing of the rate of penetration at that depth. Cores U1558D-2R to 6R were split and described. Cores 2R to 3R are nannofossil chalk with clay. Cores 4R to 6R are highly plagioclase-olivine-clinopyroxene-phyric basaltic pillow lavas, moderately to highly altered but with frequent fresh glass in pillow margins.

The science party met for presentations on the results from Hole U1559B.

Daily Science Report for 28 June 2022

Location:

Hole U1558F (30°53.7923′S, 24°50.4757′W, water depth 4337 mbsl)
Hole U1558D (30°53.7814′S, 24°50.4822′W, water depth 4334 mbsl)

Science Update: We completed disassembly of the BHA at 0035 h, ending operations at Hole U1558F. We then made up the RCB BHA and lowered it down to Hole U1558D, where a reentry system had been installed during Expedition 390C in November 2020. Guided by the subsea camera video feed, the ship maneuvered over the hole and the bit reentered Hole U1558D at 1505 h. We lowered the bit to the depth of the existing hole, 150 mbsf, and started coring at 1845 h. Cores U1558D-2R to 3R penetrated from 150 to 166.5 mbsf and recovered 3.27 m (20%). These cores contain sediment. The depth of the basement contact is expected to be between 159 and 176 mbsf, the depths of the contact at Holes U1558A and U1558F, respectively.

Cores U1558F-16F to 24X were split and described. Cores 16F to 20X are nannofossil ooze, Cores 21X to 22X are nannofossil chalk with clay in some layers, and Cores 23X to 24X are nannofossil chalk with clay. The lowermost 10 cm of Core 24X is basalt. Cores 16F to 24X are earliest Oligocene to middle Eocene in age.

Daily Science Report for 27 June 2022

Location: Location: Hole U1558F (30°53.7923′S, 24°50.4757′W, water depth 4337 mbsl)

Science Update: Cores U1558F-16F to 24X penetrated from 110.4 to 177.2 mbsf and recovered 60.0 m (90%). After a drillover on Core 19F we switched to XCB drilling for the rest of the hole. We contacted basement in Core 24X at 176 mbsf, drilled 1.2 m further in an effort to recover the uppermost basement rocks, and then ended the hole. Basement depth in Hole U1558F is 17 m deeper than the basement depth in Hole U1558A, indicating that there is steep basement topography at this site. At 1415 h we started to pull the BHA up to the ship and by midnight we had begun disassembling the BHA. Cores U1558F-6H to 15F were split and described. Core 6H is nannofossil ooze with clay and Cores 7H to 11F alternate between nannofossil ooze and nannofossil ooze with clay. Cores 12F to 15F are nannofossil ooze. Cores 6H to 15F are Oligocene in age.

Daily Science Report for 26 June 2022

Location:

Hole U1558E (30°53.7922′S, 24°50.4822′W)
Hole U1558F (30°53.7923′S, 24°50.4757′W, water depth 4337 mbsl)

Science Update: We lowered the bit to 4319 mbsl but bad weather delayed the start of Hole U1558E, and we waited until ship heave was starting to subside. At 0440 h we started Hole U1558E, but the core barrel was full and did not recover a mudline so we offset 10 m to the east and at 0610 h started Hole U1558F. Cores U1558F-1H to 15F penetrated from 0 to 110.4 mbsf and recovered 104.5 m (95%). Whole-round samples were taken for microbiological studies and oxygen content was measured by needle probe soon after the cores were recovered. Cores U1558F-1H to 5H are clayey nannofossil ooze. Core 1H contains a hiatus or condensed interval and Cores 2H to 5H are early Miocene to late Oligocene in age.

Daily Science Report for 25 June 2022

Location:

Underway to Site U1558 (proposed Site SATL-43A)
Site U1558 (30°53.77′S, 24°50.49′W, water depth 4337 mbsl)

Science Update: The ship completed the final 114 nmi of the 508 nmi voyage to Site U1558 (proposed Site SATL-43A). In November 2020, Expedition 390C cored Hole U1558A to recover sediment down to the basement interface at 159 mbsf and installed a reentry system in Hole U1558D. Holes U1558B and U1558C were the locations of unsuccessful attempts to install the reentry system. At 1130 h we arrived on site and lowered the thrusters. In preparation for Hole U1558E, we made up the advanced piston corer/extended core barrell (APC/XCB) BHA and lowered it down to 4310 mbsl. At 2300 h we picked up the top drive, and pumped down a pipecleaning device to clean the inside of the pipe. The science party worked on Site U1559 reports.

Daily Science Report for 24 June 2022

Location: Underway to Site U1558 (proposed Site SATL-43A)

Science Update: The ship completed 269 nmi for a total of 394 nmi of the 508 nmi voyage to Site U1558. COVID-19 mitigation protocols were lifted at 0700 h. The science party met in the conference room for presentations to review operations at Hole U1559B and plan for the next site, Site U1558. We completed sampling of the Hole U1559B cores for shipboard measurements.

Daily Science Report for 23 June 2022

Location:

Hole U1559B (30°15.6336′S, 15°2.0941′W, water depth 3055 mbsl)
Underway to Site U1558 (proposed Site SATL-43A)

Science Update: Core U1559B-13R penetrated from 104.1 to 107.9 mbsf and recovered 0.34 m (9%). Core 13R contains sparsely plagioclase phyric microcrystalline basalt with rare olivine and clinopyroxene phenocrysts. One core piece has a glassy rim. At 0300 h we stopped coring because of the slow penetration rate and because the bit was wearing down. We pulled the bit out of the hole and raised it to the ship. The rig floor crew disassembled the BHA and secured the rig floor for transit, ending operations at Hole U1559B at 1235 h. We raised the thrusters and were underway to Site U1558 at 1242 h. By midnight, the ship had completed 125 nmi of the 508 nmi voyage. COVID-19 mitigation protocols continue to be followed.

Daily Science Report for 22 June 2022

Location: Hole U1559B (30°15.6336′S, 15°2.0941′W, water depth 3055 mbsl)

Science Update: Cores U1559B-9R to 12R penetrated from 92.9 to 104.1 mbsf and recovered 5.13 m (46%). Cores U1559B-9R to 12R contain relatively fresh microcrystalline to fine grained sparsely plagioclase phyric basalt, with rare fresh olivine. Cores 11R and 12R also contain rare clinopyroxene phenocrysts. COVID-19 mitigation protocols continue to be followed.

Daily Science Report for 21 June 2022

Location: Hole U1559B (30°15.6336′S, 15°2.0941′W, water depth 3055 mbsl)

Science Update: Cores U1559B-5R to 8R penetrated from 73.5 to 92.9 mbsf and recovered 5.67 m (29%). The cores are half-length and the average rate of penetration is ~1.1 m/h. Cores U1559B-5R to 8R contain relatively fresh microcrystalline to fine grained sparsely plagioclase phyric basalt, with rare fresh olivine phenocrysts, and rare clay and carbonate veins. All shipboard personnel took their second-to-last COVID-19 antigen test of the mitigation period, and COVID-19 mitigation protocols continue to be followed.

Daily Science Report for 20 June 2022

Location: Hole U1559B (30°15.6336′S, 15°2.0941′W, water depth 3055 mbsl)

Science Update: At the start of the day we were preparing to reenter Hole U1559B. A “pig” was pumped down the drill pipe to clean out any debris from the inside, and the bit depth was set for reentry. We reentered the hole at 0143 h and washed down to 58.9 meters below seafloor (mbsf), the depth the hole had reached when casing was installed in it during Expedition 390C. The subsea camera was pulled back up to the ship. At 0430 h we began coring with the rotary core barrel (RCB) system. Cores U1559B-2R to 4R advanced from 58.9 to 73.5 mbsf and recovered 1.68 m (12%). The cores are half-length and Core 2R was empty. Cores 3R and 4R contain slightly altered basalt pieces, some with euhedral plagioclase phenocrysts. COVID-19 mitigation protocols continue to be followed.

Daily Science Report for 19 June 2022

Location:

Underway to Site U1559 (proposed Site SATL-13A)
Hole U1559B (30°15.6336′S, 15°2.0941′W, water depth 3055 mbsl)

Science Update: The ship transited 135 nmi and arrived at Site U1559 at 1220 h, completing its 1713 nmi voyage from Cape Town, South Africa. We lowered the thrusters and switched from cruise mode into DP mode. Operations started on the rig floor with assembly of the bottom-hole assembly (BHA). At 1630 h the BHA was complete and we started adding drill pipe to lower the bit down through the water column. At 2130 h the bit reached 2482 meters below sea level (mbsl) and we deployed the subsea camera in preparation for reentry into Hole U1559B. By midnight we had lowered the bit to 3031 mbsl and picked up the top drive. COVID-19 mitigation protocols continue to be followed.