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doi:10.2204/iodp.proc.327.106.2011

Lithostratigraphy

Note: This section was contributed by Sarah-Jane Jackett (Integrated Ocean Drilling Program, Texas A&M University, 1000 Discovery Drive, College Station TX 77845, USA).

Five holes were cored at Site U1363 in the vicinity of the Grizzly Bare outcrop. Four lithostratigraphic units were recognized (Fig. F3).

Unit 1 is composed of hemipelagic mud (clayey silt to silty clay), thin-bedded turbidites (sand-silt-clay), and thick-bedded medium sand turbidites. The hemipelagic mud is generally homogeneous, with local clay-rich color bands and zones of bioturbation. The mud increases in carbonate component downhole, especially calcareous nannofossils. Turbidite characteristics include sharp and erosional bases, which regularly contain a high percentage of foraminifers, normal/fining-upward grading sequences, color banding, and gradational tops. Beds of clayey silt to silty clay are generally <10 cm in thickness, whereas sand beds have a maximum thickness of 1–5 m. Medium-grained sand flow-in at the base of APC cores is common.

Unit 2 is composed of beds of silt and sandy silt intercalated with hemipelagic mud deposits (silty clay to clayey silt). Silt beds range from 1 to 5 cm in thickness, with sharp bases, normal/fining-upward grading, and gradational tops. Characteristic features include silt and fine sandy-silt laminae, slightly darker clay-rich bands, and carbonate-rich mud with foraminifers. This unit has a higher percentage of mottling from bioturbation relative to Units 1 and 3. Beds assigned to Unit 2 were probably deposited by thin, fine-grained turbidity currents. As with Unit 1, flow-in at the base of APC cores is common.

Unit 3 is composed of hemipelagic carbonate-rich claystone rich in foraminifers and nannofossils. This unit displays some brown color variations that probably were imparted by low-temperature alteration with underlying crustal rocks.

Unit 4 represents the basement at Site U1363 (see “Petrology”). Depths to basement in all holes at Site U1363 are summarized in Table T2 on the basis of a combination of core recovery and “tagged” depths identified by the driller.

Reflectance spectroscopy and colorimetry data were collected with the SHMSL to provide a high-resolution record of color variations. These data are displayed in the Site U1363 visual core descriptions in “Core descriptions.”

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