Abstract
AbstractFine‐grained magnetic particles in deep‐sea sediments often statistically align with the ambient magnetic field during (and shortly after) deposition and can therefore record geomagnetic reversals. Correlation of these reversals to a geomagnetic polarity time scale is an important geochronological tool that facilitates precise stratigraphic correlation and dating of geological records globally. Sediments often carry a remanence strong enough for confident identification of polarity reversals, but in some cases a low signal‐to‐noise ratio prevents the construction of a reliable and robust magnetostratigraphy. Here we implement a data‐filtering protocol, which can be integrated with the UPmag software package, to automatically reduce the maximum angular deviation and statistically mask noisy data and outliers deemed unsuitable for magnetostratigraphic interpretation. This protocol thus extracts a clearer signal from weakly magnetized sediments recovered at Integrated Ocean Drilling Program (IODP) Expedition 342 Site U1406 (Newfoundland margin, northwest Atlantic Ocean). The resulting magnetostratigraphy, in combination with shipboard and shore‐based biostratigraphy, provides an age model for the study interval from IODP Site U1406 between Chrons C6Ar and C9n (∼21–27 Ma). We identify rarely observed geomagnetic directional changes within Chrons C6Br, C7r, and C7Ar, and perhaps within Subchron C8n.1n. Our magnetostratigraphy dates three intervals of unusual stratigraphic behavior within the sediment drifts at IODP Site U1406 on the Newfoundland margin. These lithostratigraphic changes are broadly concurrent with the coldest climatic phases of the middle Oligocene to early Miocene and we hypothesize that they reflect changes in bottom water circulation.
Highlights
Since the 1960s, the geomagnetic polarity time scale (GPTS) has become established as a widely applied tool for the development of accurate age models and global stratigraphic correlations
One major obstacle to develop reliable magnetostratigraphic chronologies of these important geological events is the occurrence of very low natural remanent magnetization (NRM) intensities that is sometimes present in deep-sea sequences
Oligocene to Miocene sediment drift deposits of the Newfoundland margin recovered from Integrated Ocean Drilling Program (IODP) Expedition 342 Site U1406, where the NRM intensity measured shipboard is in the range 1024 to 1025 A/m after 20 mT peak alternating field demagnetization (Norris et al, 2014)
Summary
Since the 1960s, the geomagnetic polarity time scale (GPTS) has become established as a widely applied tool for the development of accurate age models and global stratigraphic correlations. Oligocene to Miocene sediment drift deposits of the Newfoundland margin recovered from Integrated Ocean Drilling Program (IODP) Expedition 342 Site U1406, where the NRM intensity measured shipboard is in the range 1024 to 1025 A/m after 20 mT peak alternating field demagnetization (Norris et al, 2014). This weak magnetization, together with lower measurement sensitivity and incomplete shipboard demagnetization protocols, precluded the construction of a full and rigorous magnetostratigraphy in certain intervals, most notably around the OMT. The resulting magnetostratigraphy allows us to identify rarely observed polarity changes (e.g., Channell et al, 2003, 2013; Lanci et al, 2005) and firmly places IODP Site U1406 in a global chronostratigraphic framework of middle Oligocene to early Miocene climate and oceanographic records
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