Cambrian millennial-scale climate cycles paced by Milanković forcing

Abstract

Millennial-scale climate variability is a prominent feature of the late Cenozoic high-resolution climate records and is closely linked to ice sheet dynamics and changes in ocean-atmosphere systems. However, while quasi-cyclic millennial-scale climate proxy variability is observed in much older strata, the origins of these cycles in deep time remain uncertain. To better understand the nature and evolution of millennial-scale cycles close to the equator, high-resolution physical property records of the Global Stratotype Section and Point (GSSP) for the Wuliuan Stage (Middle Cambrian, ∼510 Ma) in South China were utilized to conduct a cyclostratigraphic analysis. An ∼1 Myr-long astronomical time scale across the Stage 4-Wuliuan was developed by astronomical tuning of natural gamma-ray data to the ∼100-kyr short eccentricity cycle. We report semi-precession cycles of 7.9–11.7 kyr, which were associated with the twice passage of a precipitation maximum across the site in the inner tropics, consistent with the paleogeographical location of South China block near the equator. Furthermore, our results suggest that millennial-scale cycles are influenced by obliquity, precession and semi-precession at least in this case. Millennial-scale cycles also can be directly generated by the harmonization between fundamental Milanković cycles. These results describe one of the oldest known geological candidates for sub-Milanković scale climate change modulated by astronomical climate forcing.