International Ocean Discovery Program

IODP Publications

International Ocean Discovery Program
Expedition 395E Preliminary Report

Complete South Atlantic Transect Reentry Systems1

6 April–5 June 2021

Trevor Williams, Emily R. Estes, Bill Rhinehart, Rosalind M. Coggon, Jason B. Sylvan, Gail L. Christeson, and Damon A.H. Teagle

1 Williams, T., Estes, E.R., Rhinehart, B., Coggon, R.M., Sylvan, J.B., Christeson, G.L., and Teagle, D.A.H., 2021. Expedition 395E Preliminary Report: Complete South Atlantic Transect Reentry Systems. International Ocean Discovery Program.

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International Ocean Discovery Program (IODP) Expeditions 390C and 395E were implemented in response to the global COVID-19 pandemic and occupied sites proposed for the postponed Expeditions 390 and 393, South Atlantic Transect 1 and 2. Expedition 395E completed most of the preparatory work that Expedition 390C did not have time to complete. The overall objective of Expeditions 390C and 395E was to core one hole at each of the South Atlantic Transect sites with the advanced piston corer/extended core barrel (APC/XCB) system to basement for gas safety monitoring and to install a reentry system with casing through the sediment to a few meters into basement in a second hole.

Expedition 395E started in Cape Town, South Africa, and ended in Reykjavík, Iceland, after 20 days of on-site operations. We cored to basement at two new sites, U1560 and U1561, and completed reentry systems at three sites, U1556, U1557, and U1560. These operations will expedite basement drilling during the rescheduled Expeditions 390 and 393.

Hole U1560A (Proposed Site SATL-25A) lies in ~15.2 Ma crust and is composed of carbonate-rich sediments to 120 meters below seafloor (mbsf) and 2.5 m of underlying basalt. A reentry system was deployed in Hole U1560B to 122.0 mbsf. We then moved to the sites at the western end of the transect on ~61 Ma crust. In Hole U1557D, 10¾ inch casing was deployed to 571.6 mbsf to deepen the 16 inch casing that was deployed during Expedition 390C, and in Hole U1556B, a reentry system was deployed to 284.2 mbsf. The remaining operations time was insufficient to install a reentry system at the originally planned site, Proposed Site SATL-33B. Instead, we cored Hole U1561A (Proposed Site SATL-55A) to 47 mbsf. It is composed of red clay and carbonate ooze overlying 3 m of basalt.

The six primary sites of the South Atlantic Transect lie perpendicular to the Mid-Atlantic Ridge on the South American plate, overlying crust ranging in age from 7 to 61 Ma. Basement coring will increase our understanding of how crustal alteration progresses over time across the flanks of a slow/intermediate-spreading ridge and how microorganisms survive in deep subsurface environments. Sediment will be used in paleoceanographic and microbiological studies.