Site U1512

Abstract

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Salient Changes of Earth's Magnetic Field Toward the End of Cretaceous Normal Superchron (CNS)

“…The stepwise demagnetization results show that secondary overprints can be removed at ∼10 mT or slightly higher and the high-stability components exhibit normal magnetic polarities that are interpreted to be in the Cretaceous Normal Superchron C34n (Huber et al, 2019) (Figure 2b). The downcore median destructive field (MDF) (Figure 2d), an alternating-field (AF) at which the remanence intensity decays to one half of the NRM, ranges from 10 to 25 mT and implies low-coercivity magnetic minerals as major magnetic remanence carriers (Liu et al, 2012;Thompson et al, 1980).…”

“…The MDF distributions show that the most frequent occurrence of MDFs is in the range of ∼13–18 mT (Figure 3d). MS values of archive halves range from −0.6 to 253.6 instrument units (IU) (Huber et al., 2019). MS roughly reflects variations in magnetic minerals concentration (Thompson et al., 1980).…”

“…The archive halves of the U1512A cores were measured during the expedition (Huber et al., 2019). Magnetic susceptibility (MS) was measured every 2.5 cm on whole‐round sections at 21,060 stratigraphic levels with the whole‐round multisensor logger.…”

“…For this study, we focus on the lithologically homogenous subunit IIb, that is, the 85–700 m CSF‐A interval of the U1512A cores, that was accumulated relatively rapidly from ∼94 Ma to ∼85 Ma (Huber et al., 2019; Watkins & Guerra, 2020) (Figure 2a). Thus, the studied U1512 cores potentially document semi‐continuous, detailed geomagnetic field behavior of the ∼94 Ma to ∼85 Ma interval, which encompasses both high and low variability stages of the CNS, in the high‐latitude southern hemisphere.…”

“…Thus, the studied U1512 cores potentially document semi‐continuous, detailed geomagnetic field behavior of the ∼94 Ma to ∼85 Ma interval, which encompasses both high and low variability stages of the CNS, in the high‐latitude southern hemisphere. In this study, we analyze the high‐resolution paleomagnetic measurements of the archive‐half sections of the subunit IIb obtained during the expedition (Huber et al., 2019) and collected additional 145 discrete cubic samples (2.2 × 2.2 × 2.2 cm 3 ) from the working‐half sections to conduct further in‐depth analysis of the magnetic properties of the subunit IIb.…”