Figure F8. Shipboard paleomagnetic data and initial interpretations of inclination clusters of the Oligocene–Cretaceous from Holes 1257A, 1257B, and 1257C. Magnetic inclinations from long-core measurements from Hole 1257A are a 21-point moving average after AF demagnetization at 15 or 20 mT. Magnetic inclinations from Holes 1257B and 1257C are from intact blocks (excluding measurements in 5 cm of the end of each blocks) after 15-mT demagnetization. The inclination data exclude measurements near the background noise limit of the cryogenic magnetometer (<3 x 10–5 A/m); therefore, measurements with intensities <5 x 10–5 A/m are not considered reliable. In addition, the upper 20 cm of each core that commonly displays spurious high-intensity magnetization or downhole contamination and the upper 5 cm of each section that is influenced by magnetization carried by the blue-colored end cap are excluded. The displayed inclinations are either 3-point running means (solid circles), 2-point means (open circles), or single-level data (open triangles) (from the central portion of blocks between 10 and 15 cm long or from isolated levels in a larger block in which the adjacent measurements were <5 x 10–5 A/m). The magnetic intensity column is from Hole 1257A and includes NRM (small orange circles = 21-point running mean) and after 15-mT demagnetization (small black circles; large blue circles = 101-point log-mean average). Magnetic susceptibility in Hole 1257A, obtained using a magnetic susceptibility core logger (MSCL), is shown by green circles in the rightmost column. Shipboard assignment of polarity zones was based on clusters of magnetic inclinations from intact blocks (right of the polarity zone column), as delimited by the thin lines. Black/dark gray (if less certain) = positive inclinations (originally considered to be normal polarity zones); white/light gray (if less certain) = negative or mixed inclinations (originally considered to be reversed polarity zones). Cross-hatched = uncertain inclination characteristics or gaps in data coverage. The shipboard interpretations of polarity zones were not always supported by analyses of magnetic characteristics during progressive thermal demagnetization of minicores (Fig. F9). F = foraminifers, N = nannofossils, R = radiolarians. (This figure is available in an oversized format.)

Figure F8. Shipboard paleomagnetic data and initial interpretations of inclination clusters of the Oligocene–Cretaceous from Holes 1257A, 1257B, and 1257C. Magnetic inclinations from long-core measurements from Hole 1257A are a 21-point moving average after AF demagnetization at 15 or 20 mT. Magnetic inclinations from Holes 1257B and 1257C are from intact blocks (excluding measurements in 5 cm of the end of each blocks) after 15-mT demagnetization. The inclination data exclude measurements near the background noise limit of the cryogenic magnetometer (<3 x 10^–5 A/m); therefore, measurements with intensities <5 x 10^–5 A/m are not considered reliable. In addition, the upper 20 cm of each core that commonly displays spurious high-intensity magnetization or downhole contamination and the upper 5 cm of each section that is influenced by magnetization carried by the blue-colored end cap are excluded. The displayed inclinations are either 3-point running means (solid circles), 2-point means (open circles), or single-level data (open triangles) (from the central portion of blocks between 10 and 15 cm long or from isolated levels in a larger block in which the adjacent measurements were <5 x 10^–5 A/m). The magnetic intensity column is from Hole 1257A and includes NRM (small orange circles = 21-point running mean) and after 15-mT demagnetization (small black circles; large blue circles = 101-point log-mean average). Magnetic susceptibility in Hole 1257A, obtained using a magnetic susceptibility core logger (MSCL), is shown by green circles in the rightmost column. Shipboard assignment of polarity zones was based on clusters of magnetic inclinations from intact blocks (right of the polarity zone column), as delimited by the thin lines. Black/dark gray (if less certain) = positive inclinations (originally considered to be normal polarity zones); white/light gray (if less certain) = negative or mixed inclinations (originally considered to be reversed polarity zones). Cross-hatched = uncertain inclination characteristics or gaps in data coverage. The shipboard interpretations of polarity zones were not always supported by analyses of magnetic characteristics during progressive thermal demagnetization of minicores (Fig. F9). F = foraminifers, N = nannofossils, R = radiolarians. (This figure is available in an oversized format.)