Millennial-scale climate cycles in Permian–Carboniferous rhythmites: Permanent feature throughout geologic time?

Abstract

Two late Paleozoic glacial rhythmite successions from the Itararé Group (Paraná Basin, Brazil) were examined for paleoclimate variations. Paleomagnetic (characteristic remanent magnetization, ChRM) and magnetic susceptibility (K z ) measurements taken from the rhythmites are interpreted as paleoclimatic proxies. Ratios of low-frequency components in the K z variations suggest Milankovitch periodicities; this leads to recognition of other, millennial-scale variations reminiscent of abrupt climate changes during late Quaternary time, and are suggestive of Bond cycles and the 2.4 k.y. solar cycle. We infer from these patterns that millennial-scale climate change is not restricted to the Quaternary Period, and that millennial forcing mechanisms may have been prevalent throughout geologic time.

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

“…For these PermoCarboniferous rhythmites, the similarities between the couplet thickness and K1 spectra, indicating common millennial-scale patterns, are also in accordance with those in K Z spectra for the same successions (Franco et al 2012a). The compatibility of harmonic features in the rhythmite couplet thickness sequences and K1 data support the view that K1 is an effective palaeoclimatic proxy for sedimentation influenced by sediment transport, which in turn is forced by climatic processes.…”

“…The IT and RS couplet thickness spectra are very similar to the characteristic remanent magnetization and bulk magnetic susceptibility spectra reported for these same rhythmites (Franco et al 2012a). The ratios of the very low frequency components were proposed to represent Milankovitch periodicities, with spectral peaks in the stratigraphic domain spectra compatible with those found in this study.…”

“…6a) displays highly visible cycling in contrast to subdued cycles in ChRM data from the same samples ( Fig. 2 in Franco et al 2012a). In the K1 stratigraphic spectrum (Fig.…”

“…What kind of perpetual harmonic phenomenon could cause the observed, repeated couplet lithologies -the almost constant, discrete thickness of dark lamina separating couplets -and the similarity in the harmonic process involved in the deposition of these rhythmites, separated by such large distances (c. 1000 km) and times (c. 10 million years)? For these same successions, Franco et al (2012a) reported harmonic features from a spectral analysis of bulk magnetic susceptibility and ChRM data series, for which they found evidence for a quasi-periodic c. 2.3-2.4 ka Halstatt cycle, as well as periodicities suggestive of DO and H events. This evidence -which is reinforced by the results of the present study -indicates the prevalence of these harmonic features in the palaeoclimate system throughout geological time; hence they are not restricted only to the Quaternary Period.…”

“…Franco et al (2011) argued for an annual scale for the millimetre-scale laminations in the IT and RS rhythmite sequences, and a multi-centennial to millennial scale for individual couplets. Analysis of ChRM directional series for both rhythmites in Franco et al (2012a) led to specific low-frequency astronomical calibrations based on the method of frequency ratios. This method was employed by Kruiver et al (2000), who posited that the frequency spacing of key spectral peaks of astronomically forced stratigraphic series, reported as 'wavelengths' in spatial units (e.g.…”