Previous   |    Next

doi:10.2204/iodp.proc.303306.208.2010

Methods and materials

Sediment was cored using the advanced piston coring system of the R/V JOIDES Resolution. The lithology at Site U1312 is composed of varying mixtures of biogenic and detrital components. Carbonate content of the sediment seems to be controlled by glacial and interglacial cycles. For example, the lightness record (L*) of sediment color from 0 to 40 meters below seafloor (mbsf) in Hole U1312B generally can be correlated to the global benthic δ¹⁸O stack (see the “Site U1312” chapter). A total of 105 U-channel subsamples (2 cm × 2 cm × 150 cm) were collected from splice sections from Holes U1312A and U1312B. The composite depth scale (mcd) was adopted as the depth scale of the spliced samples (see the “Site U1312” chapter). Splicing of the sections at Site U1312 was incomplete because of severe coring disturbances, especially in the interval between 65.24 and 74.5 mcd (Sections 306-U1312A-7H-5 through 8H-8). Because this situation prevented continuous interpretation of magnetic data downhole, magnetic measurements were made only in the interval between 0 and 65.24 mcd.

Natural remanent magnetization (NRM) of U-channel samples was measured using a 2G Enterprises horizontal cryogenic magnetometer at 1 cm intervals. Alternating-field (AF) demagnetization was carried out at 20, 25, 30, 35, 40, 45, 50, 60, 70, and 80 mT (Fig. F2). Subsequently, anhysteretic remanent magnetization (ARM) with a 100 µT biasing field and an AF demagnetization field of 80 mT was applied and then demagnetized at the same levels of NRM. Magnetic susceptibility (k) was measured at 1 cm intervals using a Bartington Instruments MS2 susceptibility meter with a 4 cm diameter loop sensor. Directions of NRM characteristic remanent magnetizations were calculated by principal component analysis (PCA) (Kirschvink, 1980). Data are available in NRM_PCA in “Supplementary material.”

Top of page   |    Previous   |    Next