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Site NNB-01A

Priority: 1
Position: 45°24.3'N; 44°47.1'W
Water Depth: 4559 m
Sediment Thickness: 2080 m, from stacking and wide-angle velocity models
Target Drilling Depth: 2180 mbsf
Approved Maximum Penetration: 2500 mbsf; drill without coring to 800 mbsf

Seismic Coverage: Ewing 00-07 line 2 MCS; SP 28433 (CMP 228470) (see Figs. F3, F5, F7)


  1. Primary objective: Composition and igneous/tectonic history of basement. The nature of the U reflection and the composition and origin of the high-velocity interval between U and basement. Subsidence history of the stratigraphic sequence immediately above reflection U.
  2. Secondary objective: Age of a prominent reflection (horizon Au?) which marks the initiation of abyssal current-controlled deposition in the basin, implications for a northern Atlantic gateway, and sedimentary characteristics of subsequent current-controlled sedimentation. Stratigraphic sequence development compared to development of synchronously deposited, formally defined formations that are widely developed in the western North Atlantic.

Operational Program: See "Primary Site: Proposed Site NNB-01A" section and Table T1. Drill-in a reentry cone with ~80 m of 20-in casing. Drill without coring from 80 to 800 mbsf and install 16-in casing to ~775 mbsf. RCB coring 800 mbsf down to ~1375 mbsf and then set a 133/8-in casing liner to ~1350 mbsf. RCB core from ~1375 mbsf down to basement (~2080 mbsf) and possibly into the upper few tens of meters of basement, hole conditions permitting, before setting a 103/4-in casing liner to ~2080 mbsf. Then basement will be penetrated 100–200 m, depending on hole and drill-bit conditions as well as time available (see Table T1). Logging will be conducted in each of the cored sections and will consist of three runs (triple combo and FMS-sonic tool strings and WST). After the primary deep objectives have been achieved, if time permits, we will core the upper ~800 m of section in order to obtain a complete sedimentary record at this site.

Logging and Downhole: Three logging runs (1) triple combo tool string, (2) FMS-sonic tool string, and (3) checkshot with WST. Core orientation and temperature tools if alternate plan for shallow coring occurs.

Nature of Rock Anticipated: From top to base: clays, silty clays, and claystones (equivalent to Blake Ridge formation); siliceous and/or cherty claystones (equivalent to Bermuda Rise formation); multicolored claystones ± limestones (equivalent to Plantagenet formation); black shales (equivalent to Hatteras formation); possible limestone beds (?Blake-Bahama formation).

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