All APC cores from Holes 1222A and 1222B that did not show a large drilling-related disturbance were measured on the shipboard pass-through cryogenic magnetometer. Natural remanent magnetization (NRM) was measured at 5-cm intervals in each core section, followed by three steps of alternating-field (AF) demagnetization up to a maximum peak field of 20 mT. In addition to whole long-core measurements, discrete samples were taken from Hole 1222A to carry out more detailed progressive demagnetization and rock-magnetic analysis.
The NRM intensities were in the order of 10-1 to 10-2 A/m and decreased to ~10-2 to 10-3 A/m after partial AF demagnetization (Fig. F6). The drilling-induced overprint was mostly removed by AF demagnetization at 10 mT. Yet, a large group of ChRM directions show relatively high magnetic inclinations after blanket demagnetization, especially in the most clay-rich lithologic units. The cause of the steep inclinations is unclear and might be indicative of unrecognized deformation caused by drilling. We noticed that cores (e.g., 199-1222A-4H) with bedding features or burrows show that the sediment has been deformed near the core wall edges or "core liner."
The paleomagnetic data from lithologic Subunit IA down to ~40 mbsf are not interpretable except for the very top of Hole 1222A. Core 199-1222A-4H displays a subvertical magnetic inclination, which is clearly not a record of the paleomagnetic field. We suspect that core deformation is responsible for such a distribution of magnetization directions. Other cores from both Holes 1222A and 1222B also show variable degrees of disturbance, mostly related to flow-in, and have not been considered for further paleomagnetic analysis.
Sediments in lithologic Subunit IB provided identifiable paleomagnetic polarity reversals. A preliminary correlation of the magnetic stratigraphy to the geomagnetic polarity timescale is shown in Figure F7. At the very top of the section, we were able to identify the bottom of polarity Chron C1n (Brunhes). Stratigraphically downward, we identify Chrons C6Cn to (?)C12n. A long reversed-magnetization chron at the bottom of the section (~67 to 75 mcd) (Fig. F7) could represent Chron C18r, as Zone RP15 (middle Eocene) is found starting at ~66 mcd (see "Radiolarians" in "Biostratigraphy") and downhole.