The Ediacaran Period (635–538 Ma) was a critical period in the Earth's habitability evolution. However, the precision of the Ediacaran timeframe significantly lags behind that of the well-anchored astronomical time scales established for the most recent periods. This hinders global stratigraphic correlations and subdivision of the Ediacaran System as well as generating controversies about the tempo of deep-ocean oxygenation and eco-evolutionary dynamics. Cyclostratigraphy enables the construction of high-resolution astrochronology for deep-time sediments through a workflow that identifies geological imprints of Milanković cycles and uses specific orbital forcing cycles as the metronome for time-depth calibration.
Recently, Professor WANG Wei from the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGPAS), together with XUE Naihua, a double PhD student from the Vrije Universiteit Brussel (VUB) and the University of Münster, worked with an international research team to establish the longest continuous astronomical time scale (ATS) for the Ediacaran Period to date (635.1 ± 0.6 Ma to 568.3 ± 6.8 Ma), based on drilled core around the Jiulongwan section in Yichang, South China. This ATS provides a series of new age constraints for Ediacaran geochemical perturbations and fossil assemblages, revealing significant temporal heterogeneity of the Shuram carbon isotope excursion, as well as a coupling relationship between carbon isotope fluctuations and the second-order sea-level oscillations in the inner-shelf basin of South China. The related paper was recently published in the international academic journal Precambrian Research.
This research utilized multi-proxy analyses (meter-scale δ13Ccarb analysis, gamma ray (GR) logging with 5-cm measuring interval, and millimeter-scale X-ray fluorescence (XRF) core scanning) and a sedimentation-rate-dependent meshing scheme (recurrence analysis) (Fig.1) to establish continuous astronomical time scale across long temporal spans. In addition, the study comprehensively considered the uncertainties of the absolute age anchor, long eccentricity term, and astronomical tuning within each segment, as well as error accumulation and propagation, ultimately providing an age model with quantified uncertainty assessment.
Based on astrochronology, new age constraints have been provided for the major carbon isotope perturbations and fossil assemblages recorded in the inner-shelf basin of South China: EN3/DOUNCE triggered ≤ 584.2 ± 5.2 Ma, lasting 12.2 ± 1.4 Myr–15.9 ± 1.7 Myr; EN2/BAINCE: ≤ 599.5 ± 3.2 Ma to ≤ 593.2 ± 4.0 Ma; the nadir of the WANCE ≤ 613.9 ± 2.0 Ma; large acanthomorphic acritarchs: 632.5 ± 0.48 Ma to ≤ 584.2 ± 5.2 Ma; Lantian biota: ~616 Ma to ~593 Ma; Weng'an biota: ≤ 613.9 ± 2.0 Ma to ≤ 584.2 ± 5.2 Ma; Miaohe biota: <568.3 ± 6.8 Ma to ~550 Ma (Fig.2).
Most studies assumed and/or highlighted the isochronism of the Shuram excursion occurs in South China, Oman, northwestern Canada and other locations. The newly established astrochronology would highlight a novel perspective on the temporal heterogeneity of this the Shuram excursion. Compared to the Shuram excursion recorded in open-ocean settings, the Shuram excursion of South China exhibits temporal heterogeneity in terms of potentially earlier onset, prolonged duration. Especially, the Shuram excursion in South China occurred with a moderate trigger tempo (dropping to the nadir form 0‰ around 4.2 ± 0.4 Myr) that is approximately 3.5 times longer than the trigger tempo of the Shuram excursion reported in Oman (Fig.2). Future research on the trigger mechanisms and biogeochemical perturbations of the Shuram excursion should account for the spatiotemporal heterogeneity in δ13C variations.
To further investigate the potential drivers of temporal heterogeneity in Ediacaran shallow-marine carbon cycle perturbations, the research team reconstructed ~67-Myr relative sea-level changes in the inner-shelf basin of South China using lithological encoding, astronomically calibrated sedimentation rates, and time-domain ρ1 (lag-1 autocorrelation coefficient) modeling. The research found that the carbon isotope negative excursions in the South China Basin are highly coupled with the "M"-shaped secondary sea-level changes (Fig.3). The ρ1 modeling together with sedimentological and lithological evidence effectively indicates large-scale sea-level oscillations, offering a possible dynamic mechanism for the fundamental carbon-isotope framework of the Ediacaran Period. The sea-level-paced dynamics of the Shuram excursion in South China is compatible with the previous hypothesis of sedimentology and paleogeography, carbon isotope, atmospheric and oceanic redox conditions, phosphorus cycling, and continental weathering.
This research was supported by: Strategic Priority Research Program of Chinese Academy of Sciences, National Key Research and Development Program of China, National Natural Science Foundation of China, VUB Strategic Research program, CycloNet: European Cyclostratigraphy Network, and China Scholarship Council.
Reference: Naihua Xue, Wei Wang*, David De Vleeschouwer, Chengguo Guan, Mingsong Li, Meng Wang, Xunlai Yuan, Philippe Claeys, Astrochronology of the Ediacaran Period reveals the temporal heterogeneity and sea-level pacing of Shuram excursion. Precambrian Research 445 (2026) 108222. https://doi.org/10.1016/j.precamres.2026.108222.
Fig.1 Composite stratigraphic profiles of the Doushantuo Formation in the Wuhe drill core. (a) δ13C (‰, VPDB) profile aligned with high resolution lithology. (b) Gamma-ray logging curve. (c) Recurrence plot of Gamma-ray. (d) Determinism (DET) of recurrence analysis.
Fig.2 Astronomicallycalibrated δ13C (‰, VPDB) profile of South China accompanying sedimentation rate, Ediacaran fossil zonation of South China, and ρ1 model of the astronomically tuned gamma-ray series.
Fig.3 A 3D conceptual model for depicting the dynamics of the EN3/DOUNCE in South China, paced by the second-order sea-level oscillations.
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