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Milankovitch-scale paleoclimatic variability recorded in Permian loessite (south-central France)

We present the findings from our recent paper wherein rock magnetic data record discernible Milankovitch-scale paleoclimatic variability through the Permian Salagou Formation loessite (south-central France). Analysis and modeling of this stratigraphic series (~1000 m of magnetic susceptibility data measured with a portable magnetic susceptibility meter) shows a persistent 10-m-thick cyclicity inferred to represent orbital eccentricity-scale (~100 kyr) variability through the middle to late Cisuralian (ca. 285—275 Ma), and subordinate, higher-frequency cycles (3.3—3.5 and ~1.8 m-thick) that likely represent obliquity and precession-scale variability. Optimal sedimentation rates increase up-section, ranging between 9.4 cm/kyr and 13 cm/kyr. As evinced by laboratory rock magnetic data, the driver of the magnetic signal in the Salagou Formation is hematite, which has generally low magnetic enhancement compared to Eurasian Quaternary loess deposits. If the magnetic signal is pedogenic, then the ~10 m thick cyclicity may represent the thickness of loessite-paleosol couplets in the Salagou Formation. The predominance of hematite (as opposed to magnetite and maghemite) may be attributed to differing conditions of formation such as more arid and/or oxidizing climate conditions than in present Eurasia and/or post depositional oxidation of magnetite and maghemite. This work contributes to a growing evidence for astronomically-forced climate change in Permian loessite at low latitudes.


Lily S. Pfeifer (1), Linda Hinnov (2), Christian Zeeden (3), Christian Rolf (3) & Christian Laag (3,4)
University of Oklahoma, USA (1); Department of Atmospheric, Oceanic, and Earth Sciences, George Mason University, Fairfax, VA, USA (2); Leibniz Institute for Applied Geophysics, Hanover, Germany (3); Institut de Physique du Globe de Paris (IPGP), CNRS, Université de Paris, Paris, France (4)
GeoUtrecht 2020