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At Site M0066, two holes were drilled: Hole M0066A to a total depth of 28 mbsf, and Hole M0066B to a total depth of 27.85 mbsf. Open holing of the upper 2 mbsf at this site was necessary because of possible contamination with hazardous materials. Between ~2 and 15 mbsf, core recovery by piston coring was approximately 80%–85% in each of the holes. Deeper than ~15 mbsf, coring advanced using primarily the nonrotating core barrel in Hole M0066A with reduced recovery and a combination of nonrotating core barrel, push coring, and piston coring in Hole M0066B, resulting in 100% recovery in the interval between 20 and 27 mbsf (see “Operations”). In both holes, coring terminated in a massive glauconitic sand unit.

Lithostratigraphic divisions (Units I–IV; Fig. F1) are based on descriptions of the cut face of the split core and observations from smear slides (see “Core descriptions”). The stratigraphy of the upper ~9 mbsf (Unit I) shows similarities to that recovered from Sites M0064 and M0065.

Unit I

Subunit Ia

  • Intervals: 347-M0066A-2H-1, 0 cm, to 2H-2, 142 cm; 347-M0066B-2H-1, 0 cm, to 3H-1, 26 cm
  • Depths: Hole M0066A = 2.0–4.92 mbsf; Hole M0066B = 2.0–5.56 mbsf

Subunit Ib

  • Intervals: 347-M0066A-2H-2, 142 cm, to 4H-1, 0 cm; 347-M0066B-3H-1, 26 cm, to 5H-1, 0 cm
  • Depths: Hole M0066A = 4.92–8.6 mbsf; Hole M0066B = 5.56–9.6 mbsf

Unit I comprises dark grayish brown to dark gray laminated silty clay and silty fine sand with dispersed clasts. The clay is rhythmically laminated by color and texture on a centimeter scale, with lamina thickness decreasing downhole from 4–10 cm at the top of Subunit Ia to 2–3 cm thickness at the bottom of Subunit Ia and throughout Subunit Ib. Lamination is planar, parallel, and inclined. The grayish brown Subunit Ia is separated from the dark gray Subunit Ib by a 2–8 cm thick dark brown lamina. Color contacts between subunits are sharp and steeply inclined (Fig. F2). Dispersed gravel-sized rock clasts are present near the base of Subunit Ib.

The sediments were deposited in a glaciolacustrine depositional environment.

Unit II

  • Intervals: 347-M0066A-4H-1, 0 cm, to 9N-1, 0 cm; 347-M0066B-5H-1, 0 cm, to 8N-1, 0 cm
  • Depths: Hole M0066A = 8.6–15.2 mbsf; Hole M0066B = 9.6–15.4 mbsf

This unit consists of grayish brown parallel-bedded massive medium sand with centimeter- to decimeter-scale laminated silt and clay interbeds. Glauconite is a common component of the sand.

This unit was probably deposited in a glaciofluvial depositional environment. The glauconite was likely reworked from local bedrock.

Unit III

  • Intervals: 347-M0066A-9N-1, 0 cm, to 13N-1, 81 cm; 347-M0066B-8N-1, 0 cm, to 12H-1, 0 cm
  • Depths: Hole M0066A = 15.2–19.51 mbsf; Hole M0066B = 15.4–19.4 mbsf

Unit III is clast-rich muddy diamicton and clayey silt with dispersed clasts. Clast sizes are up to several centimeters with a high abundance of granule-sized clasts. Rare color banding and wispy lamination is present.

This unit represents deposition in an ice-proximal environment. The color banding, changes in clast abundance, and wispy laminations are consistent with a glaciolacustrine or glaciomarine depositional environment.

Unit IV

  • Intervals: 347-M0066A-13N-1, 81 cm, to end of hole; 347-M0066B-12H-1, 0 cm, to end of hole
  • Depths: Hole M0066A = 19.51–28.00 mbsf; Hole M0066B = 19.4–27.25 mbsf

This unit comprises parallel-bedded dark greenish gray massive medium sand. Centimeter- to decimeter-scale interbeds of clay and partly laminated silt are found interbedded with the sand. Glauconite is common in the sand fraction.

These sediments were probably deposited in a fluvial or glaciofluvial depositional environment. The glauconite could be reworked from local bedrock.