Proceedings of the Ocean Drilling Program 174B Initial Reports

During Integrated Ocean Drilling Program (IODP) Expedition 336 to North Pond on the western flank of the Mid-Atlantic Ridge (8 Ma crust) in the late fall of 2011, borehole observatories were installed in IODP Holes U1382A and U1383C and Deep Sea Drilling Project Hole 395A. These borehole observatories are designed for long-term (multiyear) coordinated hydrogeological, geochemical, and microbiological monitoring and experimentation to understand the nature of life, fluid flow, and fluid-rock interactions in young and cool oceanic crust. Additional related activities during Expedition 336 included recovery of an instrument string that was deployed within an earlier generation of a circulation obviation retrofit kit (CORK) observatory in Hole 395A and preparation of IODP Hole U1383B, which was drilled, cased, and left open during Expedition 336, for a future deployment of a borehole observatory. A streamlined CORK observatory was deployed in Hole U1383B during a remotely operated vehicle-supported cruise in April 2012. An additional CORK servicing cruise is scheduled for 2013. Here, we summarize the observatory project goals and provide an overview of the design, construction, and deployment of these CORKs and related instrumentation during Expedition 336. We also summarize the project goals, design, and construction for the CORK-lite installation in Hole U1383B and discuss plans for its deployment. CORK servicing plans for 2012 and 2013 also are presented. Background, motivation, and overview Subseafloor observatoriesCirculation obviation retrofit kits (CORKs) (Davis et al., 1992) have been used in recent decades to isolate igneous basement from overlying sediments and seawater, allowing the borehole to return to its native hydrological and biogeochemical state . Initially, the principal function of CORKs was to monitor pressure and temperature in situ within single intervals within sealed boreholes (Davis et al., 1992). CORKs have evolved and become increasingly sophisticated, allowing fluid sampling for chemical analyses and biological sampling and experiments, all of which can be conducted at multiple sealed observatory intervals within basaltic basement K.J. Edwards et al. Design and deployment of borehole observatories Proc. IODP | Volume 336 2CORKs have become powerful tools for studying in situ hydrological, geochemical, and biological process in igneous oceanic crust.The principal driver for installation of CORK observatories during Integrated Ocean Drilling Program (IODP) Expedition 336 at North Pond was to study a section of young (8 Ma), cool (<20°C), "average" ridge flank in order to assess the role of microbiological processes in alteration of igneous oceanic crust. These observatories complement ongoing CORK observatory work being conducted in young and warm oceanic crust on the Juan de Fuca Ridge flank but target a crustal end-member that is more representative of global ridge flank conditions. Like the CORKs installed on the Juan de Fuca Ridge flank during IODP Expedition 327 , the Nor...

Section: North Pond Setting History Of Study and Initial Characterimentioning

confidence: 99%

Section: North Pond Upper Oceanic Crust Borehole Conditions and Cormentioning

confidence: 99%

Section: North Pond Upper Oceanic Crust Borehole Conditions and Cormentioning

confidence: 99%

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Design and deployment of borehole observatories and experiments during IODP Expedition 336, Mid-Atlantic Ridge flank at North Pond

Edwards¹,

Wheat²,

Orcutt³

et al. 2012

“…This initial CORK design was also used on the next four deployments (ODP Legs 156,168,174B,and 195) Becker, Malone, et al, 1998;Salisbury, Shinohara, Richter, et al, 2002). To minimize contamination with the casing, OsmoSamplers were attached to the thermistor cable during each expedition, with the exception of Leg 174B…”

Section: Initial Cork Designmentioning

confidence: 99%

Fluid sampling from oceanic borehole observatories: design and methods for CORK activities (19902010)

Wheat¹,

Jannasch²,

Kastner³

et al. 2011

Subseafloor borehole observatories ("CORKs") are currently the best mechanism by which fluids from subsurface hydrologic zones can be collected to evaluate the composition, evolution, and consequence of fluid circulation in oceanic crust. The fluidsampling capabilities of CORKs have evolved over two decades, spanning the Ocean Drilling Program and Integrated Ocean Drilling Program. The fluid-sampling system for the original CORK design consisted of a single polytetrafluoroethylene (PTFE) tube that connected to a valve at the seafloor and ended at depth in the formation. Through successes and disappointments coupled with community desires and efforts, significant iterations of CORK design and capabilities have led to the development of a range of crustal fluid-sampling systems. These iterations continue today with the development of new borehole capabilities, sensors, and samplers. This paper discusses these developments and transitions, highlighting the pros and cons of various designs, materials, and decisions. Although the evolution of CORK design has taken years because of the infrequency of CORK deployments and sample recovery operations, we as a community are now in a position to report on groundbreaking results that will enhance our understanding of subseafloor hydrogeology, crustal evolution, geochemical fluxes, microbial ecology, and biogeochemical processes, as indicated by the wealth of work referenced herein and by the complexity and flexibility of present and future designs.

“…Several expeditions have revisited Hole 395A for logging operations, packer testing, and borehole fluid sampling, including DSDP Leg 78B , ODP Leg 109 (Detrick, Honnorez, Bryan, Juteau, et al, 1988), ODP Leg 174B (Becker, Malone, et al, 1998), and the French DIANAUT expeditions (Gable et al, 1992). Temperature and flow logs acquired during Leg 78B indicated rapid fluid flow (~1000 L/h) into Hole 395A and low formation pressures, and this flow apparently continued for many years after drilling Gable et al, 1992).…”

Section: Background Geological Settingmentioning

confidence: 99%

Expedition 336 summary

Edwards¹,

Bach²,

Klaus³

2012

Integrated Ocean Drilling Program (IODP) Expedition 336 successfully initiated subseafloor observatory science at a young mid-ocean-ridge flank setting. All of the drilled sites are located in the North Pond region of the Atlantic Ocean (22°45′N, 46°05′W) in 4414-4483 m water depth. This area is known from previous ocean drilling and site survey investigations as a site of particularly vigorous circulation of seawater in permeable 8 Ma basaltic basement underlying a <300 m thick sedimentary pile. Understanding how this seawater circulation affects microbial and geochemical processes in the uppermost basement was the primary science objective of Expedition 336.