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IODP Expedition 393

South Atlantic Transect 2


Daily Science Report for 5 July 2022

Location:

  • Hole U1558D (30°53.7814′S, 24°50.4822′W, water depth 4334 mbsl)
  • Underway to Site U1583 (proposed Site SATL-33B)

Science Update: From midnight to 0330 h we disassembled the BHA and examined it for damage following yesterday’s operations to free the BHA from the casing, and we set aside the bottom three drill collars, one of which was slightly bent. We then secured the rig floor for transit and raised the thrusters, ending operations at Hole U1558D and Site U1558. We started the transit to Site U1583 (proposed Site SATL-33B) at 0530 h and by midnight the ship had completed 198 nmi of the 227 nmi voyage.

Cores U1558D-29R to 39R were described. They are sparsely to moderately plagioclase-olivine-phyric basalt, emplaced as pillow lavas with occasional sheeted flows, apart from a >3 m massive flow in Core 37R. Mottled to variolitic textures are more common than in the overlying basalts. There are occasional hyaloclastite-basalt clast interflow breccias.


Daily Science Report for 4 July 2022

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

Science Update: Core U1558D-39R penetrated from 365.4 to 370.2 mbsf and recovered 2.6 m (54%). This core reached 203.4 m into basement to meet our 200 m basement target depth for this site. At 0330 h we set back the top drive and pulled the bit up to 126.3 mbsf, observing 20,000 lb drag. At 0445 h we deployed the subsea camera to observe the bit release and guide reentry, in preparation for downhole logging. We pulled the bit out of the hole to 4317 mbsl, 17 m above seafloor. However, at 0615 h the drill pipe was observed by the subsea camera to be still inside the reentry cone, with the cone much higher up than it should be. The extra weight on the drill string confirmed that the cone and casing had been pulled out of the hole by the BHA. From 0730 to 0830 h we attempted unsuccessfully to free the casing by pushing into the seafloor. We brought the camera back up to the ship and from 1030 to 1100 h we attempted to free the drill string from the casing by rotation. A weight decrease of 30,000 lb was observed on the hook load indicator. The subsea camera was deployed again and at 1345 h we observed that the cone had fallen away and that some of the BHA drill collars appeared to be bent. We then pulled the camera and bit back up to the ship. By midnight the bit was at 449.5 mbsl.

Cores U1558D-22R to 28R were split and described. They contain sparsely plagiolcase phyric basalt with rare olivine and clinopyroxene phenocrysts.


Daily Science Report for 3 July 2022

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

Science Update: Cores U1558D-31R to 38R penetrated from 326.6 to 365.4 mbsf and recovered 16.3 m (42%). Cores U1558D-15R to 21R were split and described. They contain sparsely plagioclase-olivine-phyric pillow lavas. The science party worked on writing their results on the sediment sequence cored in Hole U1558F for the site report.


Daily Science Report for 2 July 2022

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

Science Update: Cores U1558D-22R to 30R penetrated from 282.9 to 326.6 mbsf and recovered 13.1 m (30%). Cores U1558D-12R to 15R were split and described. Core 12R contains moderately to highly plagioclase-olivine-clinopyroxene-phyric basalt pillow lavas. Section 13R-1 contains volcaniclastic breccia of broken pillow lavas and altered glass in a sediment matrix. Sections 13R-2 to 14R-2 are sparsely plagioclase-olivine-phyric pillow lavas with interpillow sediment and breccia. Core 15R contains the same basalt as the overlying unit but without interpillow sediment.


Daily Science Report for 1 July 2022

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

Science Update: Cores U1558D-15R to 21R penetrated from 244.1 to 282.9 mbsf and recovered 18.1 m (47%). Cores U1558D-8R to 11R were split and described. They are moderately plagioclase-olivine-clinopyroxene-phyric basaltic lavas, slightly to moderately altered.