Detection of diluted marine tertiary tephra by electron spin resonance and magnetic measurements

Abstract

SUMMARY Oligocene sediments from ODP leg 115 (South Indian Ocean), Site 709 and Site 711, have been investigated using electron spin resonance (ESR) and magnetic susceptibility measurements, to detect volcanic tephra layers of supposed Ethiopian traps origin. The results obtained at room temperature, without separating the volcanic material from the bulk sediment, show that the ash‐content strongly influences the lineshape and intensity of the ESR signal. As a result, the ESR alone, can be used as a powerful tool for characterizing the diluted ash‐content of marine sediments. We have also found a strong similarity between the ESR spectra of the same tephra layers from the two sites.

Study of a set of micrometeorites from Antarctica using magnetic and ESR methods coupled with micro-XRF

“…No specific additive line of dispersed Fe 3+ ions has been detected, at about B ¼ 160 mT (g ¼ 4.3), as sometimes seen in several glasses [10,11], clay minerals [12][13][14][15], tephra [16,17] and magnetofossils [18] which also present a large signal. The derivative lines give a direct access to the g-value at zero-crossing, which can be considered as the effective g-value of the samples, g eff .…”

“…As CS s-15 and s-47 present a strong ferrosilicate character and minimal values of the Ni/Cr ratio, their FMR response can be compared with that of a ferrosilicate tephra, free of Ni and Cr ions, largely studied under similar conditions in a previous work [16,17] (see Fig. 2).…”

Determining tephra fall deposit thickness in sedimentary record from magnetic susceptibility curve: Example of four Ethiopian tephras

“…Magnetic susceptibility measurements have been performed, as all laboratory measurements in the following, using an AGICO Kappabridge KLY 2 (0.4 mT) with a 920 Hz alternating magnetic field. A rock magnetism study combining low field magnetic susceptibility measurements, together with electron spin resonance (ESR) investigations have revealed μm sized titanomagnetite inclusions in glass shards [ Ananou et al , 2003]. Confirming that the volcanic material is responsible for the susceptibility peaks, it also suggests that part of the volcanic material that was left in the separated clay fraction is minimal, and have a magnetic susceptibility similar to the silt fraction.…”

“…In distal tephra fall deposits, dense particles such as large titanomagnetite grains are absent, since they have been removed from the volcanic plume. The distal volcanic material is mainly composed of glass shards, that can contain μm‐sized titanomagnetite inclusions [ Ananou et al , 2003]. Nevertheless, volcanic material may be magnetically indistinguishable from common sedimentary variations in coastal environments subjected to a significant detrital input.…”

Sediment−magnetic signature of the mid-Holocene paleoenvironmental change in the central Okinawa Trough

“…For instance, no distinct susceptibility peaks are observed in the core, which are typical of tephra material in marine sedimentary records (e.g., Ananou et al, 2003).…”