Anisotropy of magnetic susceptibility and sedimentary cycle data from Permo-Carboniferous rhythmites (Paraná Basin, Brazil): a multiple proxy record of astronomical and millennial scale palaeoclimate change in a glacial setting

Abstract

In this study we examine glaciogenic rhythmites from the Late Palaeozoic Itararé Group, Paraná Basin, Brazil. We conduct spectral analysis on lithological cycle ('couplet') thickness series, and declination of maximum axis of anisotropy of magnetic susceptibility ellipsoidal tensor (K1) data. We tested the efficiency of K1 as a palaeoclimatic proxy. To constrain the timescale of harmonic features in the data, we analysed the couplet thickness spectra, converting the spectra to the time domain using an astronomical calibration based on Milankovitch frequency ratios. Comparison of the two rhythmites provides insights into their sedimentation rate evolution and cyclicity. Millennial-scale mechanisms of climatic origin influenced the deposition of both rhythmites, generating the lithological couplets, and are consistent with millennial-scale variations recognized as triggers for large-scale climatic changes during the Late Pleistocene. The common harmonic features in the couplet thickness and K1 spectra support the view that the azimuth of the K1 axis in sedimentary fabric is a useful palaeoclimatic proxy, reflecting sedimentation processes that were directly influenced by flow-induced, sediment transport, which is linked to external climate factors.

Orbital and Millennial‐Scale Cycles Paced Climate Variability During the Late Paleozoic Ice Age in the Southwestern Gondwana

“…The relatively long sedimentary succession studied here allows the recognition of reliable and stable sets of 100 kyr short‐eccentricity cycles within a cyclic and homogenous lithologic succession, which was a limiting factor of previous studies in high‐latitude successions (Franco et al, ; Silva & Azambuja Filho, ). Although individual lithological couplets were probably forced by millennial‐scale climate cycles (Franco et al, ; Franco & Hinnov, ), eccentricity appears to have played a major role in influencing orbitally paced glacial‐interglacial events at high latitudes during the LPIA, similarly to the pattern recognized in low‐latitude Carboniferous cyclothems deposits (e.g., Davydov et al, ; Montañez et al, ).…”

“…The cyclostratigraphy of Paleozoic rhythmites has been extensively studied, since their periodic nature may record changes in climate related to astronomical parameters such as millennial-scale cycles (e.g., Elrick & Hinnov, 2007;Franco et al, 2012). Rhythmites of the LPIA preserve astronomical cyclicities, although there are disagreements on which cycles controlled their deposition, leading to different estimates of sediment accumulation rates (SAR; Franco & Hinnov, 2013;Milana & Lopez, 1998;Silva & Azambuja Filho, 2005).…”

Magnetic methods and the timing of geological processes

“…Ellwood et al (2012a) develop obliquity-tuned 'floating timescales' for magnetic susceptibility variations along Middle Permian sections, Texas, to assess sedimentation rates and durations of geological events. Franco & Hinnov (2012) evaluate anisotropy of magnetic susceptibility in Brazilian Permocarboniferous glacial rhythmites as a palaeoclimate indicator. Finally, the cyclic Ordovician Kope Formation, USA, is evaluated for astronomical frequencies through analysis of a composite high-resolution magnetic susceptibility series (Ellwood et al 2012b).…”

Magnetostratigraphy and mid-palaeolatitude VGP dispersion during the Permo-Carboniferous Superchron: results from Paraná Basin (Southern Brazil) rhythmites

“…(2012) through the recognition of millennial‐scale variations, reminiscent of abrupt climate changes during late Quaternary time, which are recorded throughout both entire successions. Recently, Franco & Hinnov (2012) estimated the average sedimentation rates of the rhythmite successions, based on spectral analysis of lithologic cycle (‘couplet’) thickness series and declination of maximum axis of AMS ellipsoidal tensor (K1) data. Low frequency variations in the series were related by the method of ratios (Kruiver et al.…”