The Hilina Pali palaeomagnetic excursion and possible self‐reversal in the loess from western Ukraine

Abstract

nczyk, M.2018 (July): The Hilina Pali palaeomagnetic excursion and possible self-reversal in the loess from western Ukraine. Boreas, Vol. 47, pp. 954-966.A loess-palaeosol succession from the last glacial cycle was palaeomagnetically studied in the Rivne abandoned brickyard (western Ukraine). Two samples of undisturbed loess from the same depth of parallel sections display steep negative inclinations. These reversed directions in the loess dated at c. 18 ka may possibly be correlated with the Hilina Pali palaeomagnetic excursion. This is the first occurrence of the Hilina Pali in a loess sediment. Unfortunately, the loess with negative inclination does not form any continuous layer that could be suitable for studies of detailed features of geomagnetic field inversion. Another six samples from an illuvial horizon of the Holocene soil also showed negative inclinations and strongly deviated declinations. This part of the section does not represent, however, any palaeomagnetic excursion. The anomalous magnetization in maghemite-and titanomagnetite-rich sediment results most probably from self-reversal remagnetization. A new insight into palaeomagnetic excursions noted in loess, especially in its parts affected by pedogenic processes, is recommended.

Fluctuations of the Fennoscandian Ice Sheet recorded in the anisotropy of magnetic susceptibility of periglacial loess from Ukraine

“…However, a subordinate admixture of maghemite and hematite was also noted. On the plots presenting the ratio of saturation magnetization to saturation remanence and the ratio of coercivity of remanence to the coercivity most of the samples cluster in the pseudo-single-domain range but some of them are shifted right of the PSD range (Nawrocki et al 2018b). Because of this a certain addition of superparamagnetic and high-coercivity minerals is very likely (Dunlop & Carter-Stiglitz 2006).…”

Is the Hilina Pali ‘palaeomagnetic excursion’ becoming another example of the reinforcement syndrome? A comment inspired by Nawrocki et al. (2018)

“…Based on these two samples with steep negative inclinations, which are surrounded by neighbouring samples of exclusively normal polarity (and no intermediate directions, even in the more densely sampled profile), Nawrocki et al . () conclude that there must have been recording of the Hilina Pali excursion in isolated domains of loess due to discontinuous deposition. It must be pointed out, however, that the authors recognized a series of five correlatable features in inclination and declination above and below the two reversed samples, which implies that discontinuous deposition is coincident with the proposed excursion.…”

“…Using a combination of Optically Stimulated Luminescence (OSL) dating, mineral (rock) magnetism and palaeomagnetism, Nawrocki et al . () suggest that the Hilina Pali excursion (reviewed by Singer ) might have been recorded in loess profiles from western Ukraine, and dated it to c . 18 ka.…”

“…Thus, this comment on Nawrocki et al . () does not focus on a self‐reversing mechanism that might have produced reversed polarity ChRM directions in the palaeosol. Instead, it focuses on their report of ‘the first occurrence of the Hilina Pali [excursion] in a loess sediment’.…”

“…Nawrocki et al . () sampled an approximately 11‐m‐thick loess‐palaeosol section (Rivne ‘A’) at 5‐cm vertical increments, producing standard sized palaeomagnetic cylinder samples (25×22 mm). They found that a single sample (R117A) of loess located at a depth of 6.55 m with a steep negative ChRM inclination of −78° and an easterly declination (approximately 90°).…”