A geomagnetic record over the last 3.5 million years from deep‐tow magnetic anomaly profiles across the Central Indian Ridge

Abstract

Abstract. High-resolution records of the geomagnetic field intensity over the last 4 Myr provided by paleomagnetic analyses of marine sediments have shown the occurrence of shortlived low field intensity features associated with excursions or short polarity intervals. In order to evaluate the ability of marine magnetic anomalies to record the same geomagnetic events, we have collected six deep-tow (-500 m above the seafloor) and several sea surface magnetic anomaly profiles from the Central Indian Ridge across the Brunhes, Matuyama, and Gauss chrons (i.e., from the ridge axis to anomaly 2A). After removal of topography, latitude, and azimuth effects, we converted distances into time sequences using well-dated polarity reversal anomalies as tie points. We calculated the average signal to test the robustness of the short-wavelength anomalies. The resulting stacked profile is very similar to stacked sea surface and downward continued profiles from the Central Indian Ridge, the East Pacific Rise, and the Pacific-Antarctic Ridge. Our results suggest that in addition to polarity reversals, to previously suggested geomagnetic events (subchrons or excursions) within the Brunhes and Matuyama chrons. A new small-scale magnetic anomaly, likely generated by several closely spaced geomagnetic field intensity variations represent the major contributor to the detailed shape of recent marine magnetic anomalies in investigated areas. We observe a dense succession of microanomalies that are correlated excursions (Ontong Java 1 and 2, and Gilsa), is found after the Olduvai chron. The near-bottom results support the existence of three geomagnetic features between the Gauss-Matuyama boundary and Olduvai. They also suggest three geomagnetic events during the C2A. I n subchron within the Gauss chron. This study emphasizes the potential of deep-tow magnetic surveys in detecting fluctuations in geomagnetic field intensity and, in particular, short-lived excursions, a poorly constrained part of the geomagnetic field temporal variation spectrum.

Geomagnetic field variations between chrons 33r and 19r (83–41 Ma) from sea-surface magnetic anomaly profiles

“…Most tiny wiggles thus appear to be due to geomagnetic intensity variations [6]. A similar conclusion is also suggested by recent deep-tow magnetic measurements which revealed a detailed pattern of micro-anomalies that correlates very well with paleointensity fluctuations inferred from magnetostratigraphic studies ( [34], for the Brunhes period; [35,36] for the Brunhes and Matuyama periods; [37,28] for chron 5n.2n).…”

Identification of the magnetization low of the Lucky Strike hydrothermal vent using surface magnetic data

“…The two short-wavelength magnetic anomalies within Brunhes epoch (B2 and B4 of Pouliquen et al [2001]) were important to enhance the fit between the regional magnetic model and observations.…”

“…Magnetization across a segment follows the polarity reversal scale of Cande and Kent [1995]. Within the Brunhes epoch, short-wavelength magnetic anomalies (corresponding approximately to B2 and B4 of Pouliquen et al [2001]) were also considered.…”

The Cretaceous opening of the South Atlantic Ocean

“…Although geomagnetic reversal-related anomalies are the most prominent magnetic signature of the oceanic crust, past changes in the strength of the dipolar geomagnetic field are also recorded, resulting in globally correlatable wiggles within geomagnetic chrons (Bouligand et al, 2006;Cande and Kent, 1992;Granot et al, 2012;Pouliquen et al, 2001). Two globally traceable magnetic anomalies from the CNS (Granot et al, 2012) are used here to define internal ages within the South Atlantic quiet zones: the oldest is a long-wavelength wiggle (Anomaly Q2, 108 ± 1 Myr ago) and the youngest (Anomaly Q1, 92 ± 1 Myr ago) is a short-wavelength wiggle, which is followed by subdued magnetic anomalies toward the younger end of the quiet zones.…”