Astronomical time calibration of the Upper Devonian Lali section, South China

• Published in: Global and planetary change 2020-10, Vol.193, p.103267, Article 103267
• Main Authors: Ma, Kunyuan, Hinnov, Linda A., Zhang, Xinsong, Gong, Yiming
• Format: Article
• Language: English
• Subjects: Astronomical time scale; Cyclostratigraphy; Famennian; Hangenberg event; Kellwasser event; Sea level change
• ISSN: 0921-8181; 1872-6364
• DOI: 10.1016/j.gloplacha.2020.103267

The Late Devonian Period was a critical geological interval, affected by numerous significant global bio- and environmental events, including the Kellwasser, annulata and Hangenberg events, and a major climate transition leading to the Carboniferous ice ages. The timing and pattern of these events are unclear due to lack of the precise time scale. In this study, an analysis of calcium concentration series was carried out on the Upper Devonian cyclostratigraphic slope-facies of the Lali section, South China. Objective testing of the section indicates the presence of astronomical forcing: long orbital eccentricity, short eccentricity, obliquity, and precession index. Two independent astrochronologies were developed for the Ca series and compared with spectral analysis. The age of the Devonian–Carboniferous boundary (358.9 ± 0.4 Ma) was selected as an “anchor”, and an Astronomical Time Scale (ATS) was constructed from the late Frasnian to early Tournaisian based on 405-kyr cycles. The ATS indicates a duration of the Famennian Stage of 14.4 ± 0.28 myr, and assigns 373.3 ± 0.49 Ma to the Frasnian–Famennian boundary. The durations of the Famennian conodont zones are also indicated. The timing of Famennian bio- and environmental events also can be established by the ATS. The Upper Kellwasser horizon starts at 373.4 Ma and is constrained to a duration of 100-kyr; a sharp positive carbon isotope excursion CIE, +3‰ recognized across the Frasnian–Famennian boundary lasts 300 kyr. The Lower and Upper annulata events each last 50-kyr with positive CIEs; and the ages of two CIE peaks are 361.7 Ma and 361.3 Ma, respectively. Five transgressive events, including the Nehden, Enkeberg, Dasberg, Strunian, and Hangenberg transgressions occur at 370.6 Ma, 368 Ma, 360.4 Ma, 360.1 Ma, and 358.9 Ma, respectively. Five regressive events i.e., the linguiformis, prima, Condroz, velifer, and Derwer regressions occur at 373.4 Ma, 371 Ma, 369 Ma, 362.3 Ma, and 359.2 Ma, respectively. •Continuous calcium concentration series obtained from XRF have cyclic variations.•Two methods were used to test for astronomical forcing of the Ca concentration series.•Astronomical time scale indicate a 14.4 ± 0.28 myr duration for Famennian Stage.•Estimate the timing of major Late Devonian geological events and significant CIE peaks.•The duration of each Famennian conodont zone is estimated.