Relative Paleointensity Record of Integrated Ocean Drilling Program Site U1396 in the Caribbean Sea: Geomagnetic and Chronostratigraphic Observations in the Pliocene

• Published in: Geochemistry, geophysics, geosystems : G3 Vol. 22; no. 7
• Main Authors: Hatfield, R. G., Stoner, J. S., Fraass, A. J.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01.07.2021; Wiley
• Subjects: Benthos; Drill string; Drilling; Geomagnetic field; inclination anomaly; IODP; Magnetic data; Magnetic field; Magnetic fields; New records; Ocean floor; Oceans; Palaeomagnetism; paleomagnetic; Paleomagnetic studies; Paleomagnetism; Pliocene; Polarity; Quaternary; relative paleointensity; Resolution; RPI; Sediment; Sediments; Stratigraphic correlation; Stratigraphy; Caribbean Sea; Caribbean area
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2021GC009677

Continuous sedimentary records of paleomagnetic directional variability and relative paleointensity (RPI) provide valuable information on the evolution of the geodynamo while also facilitating stratigraphic correlation and age control. While the Quaternary RPI record has received much attention, Pliocene records are relatively rare. Here, a u‐channel paleomagnetic study from Integrated Ocean Drilling Program (IODP) Site U1396 in the Caribbean Sea refines the shipboard‐derived polarity stratigraphy and generates an RPI and directional record extending back 4.5 Ma. Rock magnetic data reveal changes in magnetic coercivity around 2.1 Ma that influences the quality of the paleomagnetic record; while the older record is well‐resolved and passes RPI quality criteria, much of the younger section does not. To facilitate the development of the RPI record, spike noise associated with discrete intervals of volcanogenic sediments are filtered from the data set. The resulting record passes RPI reliability criteria between 0–0.6 Ma and 2.1–4.5 Ma and represents the highest resolution RPI record extending into the early Pliocene. We use this record to refine the existing benthic δ18O chronology and open the door to high‐resolution RPI chronostratigraphies during the Pliocene. Although we find no evidence for a previously observed increase in magnetic field intensity after ∼4 million years ago, we do observe an asymmetrical form to RPI in the normal polarity intervals of the Gauss chron. We also find a polarity bias in inclination that cannot be simply explained by a drill string overprint, suggesting polarity‐driven field asymmetries that are particularly pronounced during the Pliocene. Plain Language Summary As sediments slowly accumulate on the ocean floor past variations in magnetic field intensity and direction are recorded. While we have a relatively good record of intensity variations over the last 2–3 million years, we know little about earlier time intervals. Here, we reconstruct past magnetic (or paleomagnetic) variations over parts of the last 4.5 million years using a sediment core from the Caribbean Sea collected by the Integrated Ocean Drilling Program. A deterioration in the quality of the paleomagnetic signal occurred about 2.1 million years ago, however, prior to that time, the sediments preserve a high fidelity paleomagnetic record at a temporal resolution higher than any previously obtained. Good agreement to existing data from 2.1 to 3 million years ago builds confidence in the quality of our new observations. Although we find no evidence for a previously observed change in magnetic field intensity at around 4 million years ago, differences in mean inclination during normal as compared to reverse polarity intervals are observed, suggesting field asymmetries during this time interval. The unparalleled quality and length of our new record means we can now begin to define characteristic geomagnetic field behavior during times rarely observed. Key Points Rock and paleomagnetic filtering provide a more robust estimate of relative paleointensity (RPI) that is used to refine the Integrated Ocean Drilling Program Site (IODP) U1396 δ18O chronostratigraphy IODP Site U1396 provides the longest, highest‐resolution, independently dated record of RPI to establish characteristic Pliocene behavior Plio‐Pleistocene inclination anomaly contains a strong polarity bias and RPI asymmetry may be a characteristic feature of the Gauss chron