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doi:10.2204/iodp.sp.302.2004
PROPOSED DRILL SITES (Table T1)
Successful drilling in the Arctic requires contingency planning. Sites are identified that span a large region of the Lomonosov Ridge to ensure that drilling can take place in one area should ice conditions preclude drilling operations in another. These areas are defined as the operational priority contingency areas (PCAs) within which the scientific priorities can be achieved. Because the PCAs are distributed over a 360 nm long and 40 nm wide corridor along the crest of the Lomonosov Ridge, they provide options should any single area have severe ice conditions. Severe ice conditions can occur within our study corridor, but during summer months, it is highly unlikely that more than one area would have severe conditions at any one time. Thus, the first site drilled will be in the PCA (Figure F1) that has suitable ice conditions to achieve the highest science priority possible and subsequent site selections will follow the same strategy.
There are five primary drill sites identified on the Lomonosov Ridge (Figure F1) to recover sequences that address our three priority objectives.
The first primary site (LORI-13A; Figures F1, F2, F4) is required to ensure recovery of a complete stratigraphic sediment record and to meet the highest priority paleoceanographic objective, a high-resolution long-term (50 Ma) climate history of the central Arctic Ocean; and the tectonic objective. It is proposed to drill and sample to a maximum penetration of 480 m to recover the complete hemipelagic sediment sequence (450 m) and 30 m of acoustic basement (bedrock). Because of the different objectives, it is proposed to drill three holes at this site, one APC/XCB/RCB hole to full penetration and two APC/XCB holes to recover multiple sections of the sediment sequence to ensure complete recovery for construction of a composite section (see Site Summary Forms). It is also proposed to wireline log the deepest hole at this site after completion of the coring. A similar strategy will be employed at all other cored sites.
Should drilling or coring result in unexpected problems at LORI-13A, two separate alternate sites have been approved: LORI-08A (Figures F1 and F3) for completing the primary paleoceanographic objective (I), and LORI-14A (Figures F1, F2 and F4) for completing the tectonic objective (III). It is proposed to drill and sample three APC/XCB holes to a maximum penetration of 450 m at LORI-08A to recover the hemipelagic sediment sequence. At LORI- 14A, it is proposed to drill and sample a single RCB hole to 200 mbsf to meet the tectonic objectives, where the transition between the oldest part of the hemipelagic sediment sequence and acoustic basement can be reached at a penetration depth of 176 m.
The second science priority is the recovery of a shorter-term climate history that will link the Neogene history of the Arctic Ocean to that of the North Atlantic Ocean at a sub-millennial scale resolution. For this objective, Site LORI-06A (Figures F1 and F5) has an expanded Neogene sediment section and it is proposed to drill and sample three APC/XCB holes to EPSP approved depths. An alternate site to this one, Site LORI-12A (Figures F1 and F5) is located more than half a degree north so that it could be drilled, should the local ice conditions at LORI-06A be severe or if drilling difficulties are encountered. This site is interpreted to have an expanded Neogene sediment section, similar to the primary site.
Should the ice conditions prevent drilling at Site LORI-13A and its alternates, the primary paleoceanographic objectives can also be met by drilling either at Site LORI-10A (Figures F1 and F6) or at Site LORI-05A (Figures F1 and F6). At these sites the drilling strategy is identical and it is proposed to drill and sample three APC/XCB holes to EPSP-approved depths. One hole at each site will also be targeted for logging. The tectonic objective could be achieved within another priority contingency area at Site LORI-04A (Figures F1 and F7) that is situated over a culmination of old sediments and/or basement below the regional unconformity within 200 m of the seafloor. Therefore, it is proposed to drill and sample a single RCB hole to EPSP-approved depths. Should drilling difficulties be encountered at any of these three primary sites, alternate sites can be drilled at any point within a limited range along the seismic line (see Site Summary Forms).