Logging Plan | Table of Contents


The establishment of a sea-level curve for the Miocene in the Coral Sea region is critically dependent on determining the facies and age of the MP2 and MP3 platforms of the Marion Plateau (Figs. 2, 10). Typically, precise dating of warm shallow-water carbonate platforms is difficult because of the broad stratigraphic range of larger foraminifers and diagenetic alteration of the sediments. Therefore, the drilling strategy described here involves paired holes chosen so that one is located within predicted shallow-water facies and a second is located downslope to obtain correlative facies in which planktonic forms are preserved for high resolution dating. Five primary and 10 contingency sites are proposed according to this strategy and defined on multichannel seismic lines collected in 1999 (Tables 1, 2; Figs. 11-34 and Site Summary section).

Primary Sites
The operational time estimates indicate that the five highest priority sites can be cored and logged in the time allocated for Leg 194 (Table 2). These include two platform sites (Sites CS-01 and 06), two sites to sample the adjacent paleoslope sediments (Sites CS-02 and 05), and a distal site (Site CS-10) to acquire a high-quality biostratigraphy that can be correlated to the other sites using high-resolution seismic data. The platform sites will first be penetrated to basement using the advanced hydraulic piston corer and the extended core barrel (APC/XCB) (e.g., Site CS-01) and/or the rotary core barrel (RCB) where the formation is too indurated (e.g., Sites CS-01 and 06). In an attempt to achieve better recovery in reefal carbonate intervals of interest (maximum 300 m per site), we plan to deploy the developmental advanced diamond core barrel (ADCB; see below). All sites are to be drilled to basement (including up to one barrel of basement rock) to form a facies transect from a position within the shallow facies of MP2, across the platform edge, and downslope to platform MP3. Sites between the two shallow phases of platform facies are designed to establish whether lowstand signals can be detected in slope sediments (Sites CS 03A and CS-05A). If such signals can be seen, it may be possible to establish rates as well as amplitudes of sea-level fluctuations.

The order of operations will greatly depend on weather conditions. Should conditions be favorable after transit from Townsville (1.2 days) and the Hydrate Autoclave Coring Equipment (HYACE) tests (2 days, see below), sites would be drilled in the following order: CS-01A, CS 02A, CS-06, CS-05, and CS-10A. After completing operations, including potential contingency plans (see below), there will be an 8-day transit to Guam.

Contingency Sites/Holes
Should time be available after completing operations at the five primary sites, the following contingency plans will be evaluated and ranked depending on available Leg 194 results. Three types of contingency plans have been developed:

  • Additional sites: (in order of priority) CS-08A, CS-03A, CS-12A, CS-09A, CS-11A, CS-13A, CS-14A, CS-15A, CS-16A, and CS-17A.
  • Third holes to improve stratigraphic coverage: CS-10A, CS-02A, CS-05A.
  • Additional ADCB coring: Site CS-06A to recover the upper reefal carbonate interval and also Site CS-12A, if it is drilled.

  • All primary and some contingency sites have been approved by the Pollution Prevention and Safety Panel (PPSP). Sites CS-03A, CS-05A, CS-06A, and CS-09A are located within the Great Barrier Reef Marine Park. As such, it is imperative that care be taken during coring to prevent impacts on the reef ecosystems. All Leg 194 shipboard operations will follow the guidelines established by the Great Barrier Reef Marine Park Authority (GBRMPA) for scientific research within park boundaries.

    As the site survey seismic data was collected using differential Global Positioning System (GPS) navigation, it is not expected that we will have to use the JOIDES Resolution to collect survey data prior to drilling Leg 194 sites.

    Advanced Diamond Core Barrel (ADCB) Coring System
    The ADCB coring system was designed to improve core recovery in indurated sediments and rocks by using a diamond-impregnated drill bit that cuts a core by grinding instead of chipping as does the conventional RCB system. The outer diameter and cutting area of the ADCB are smaller than those of the conventional RCB system (outer diameter = 7.5 in vs. 9.875 in), which potentially increases the penetration rates. In addition, circulation around the freshly cut core is better constrained, and flushing away recovered core material is minimized. The recovered ADCB core has a larger diameter than conventional RCB cores (3.345 in vs. 2.312 in), which results in greater recovery in friable sediments while also increasing available material for analysis.

    Because this tool is still in development, there are a few operational limitations. First, only 300 m of smaller diameter drill pipe needed for the ADCB has been purchased by ODP to date. This means to core an interval greater than 300 m, the drill string needs to be tripped to the surface, a RCB bit must be deployed to ream the hole to the bottom of the first 300-m interval, and the pipe must be tripped again to deploy the next ADCB bit to continue coring. Second, the logging tools cannot be deployed through the ADCB bit. Thus, if downhole logging is desired, an additional pipe trip is needed to deploy the logging bottom-hole assembly (BHA). Third, as the diamond coring bit is more susceptible to wear, a pipe trip may also be required to change the bit before 300 m are penetrated. In addition, core splitting, sampling, and archiving issues have not been addressed for the larger core diameter and would have to be optimized during the cruise.

    The ADCB system will be deployed for the first time on Leg 193. Since the recovery of reefal carbonates has traditionally been difficult with the ODP arsenal of tools, and because the recovery of these lithologies is a primary Leg 194 objective, the use of this system will be important for Leg 194. Deployment of this developmental tool at one or two sites is therefore an essential use of Leg 194 operational time. Unless some fatal flaws are discovered during Leg 193, the ADCB will be used at the first site to evaluate the usefulness of this tool in these sediments. Subsequent deployments will only occur if operational time does not exceed the time estimates and if coring results are truly superior to those obtained with the RCB system.

    HYACE Testing
    In July 2000, two days were added to the original Leg 194 operations schedule to accommodate feasibility tests of the developmental HYACE tool, which is a gas hydrate sampling and monitoring system. The HYACE was modified from the ODP Pressure Core Sampler (PCS) at the Technische Universität Berlin with support from the European Commission and from ODP. The tests will be carried out at the very beginning of the leg at one of the designated contingency sites. At least five dedicated personnel will sail for these tests. Since a full technical and scientific staff is needed during the scientific operations of Leg 194, the HYACE test personnel will be replaced by ODP technical staff arriving with a boat from shore two days into the cruise.

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