2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 278-11
Presentation Time: 10:50 AM


FU, Wanlu1, JIANG, Da-yong1, MONTANEZ, Isabel2, MEYERS, Stephen R.3 and MOTANI, Ryosuke4, (1)Geology, Peking University, Beijing, 100871, China, (2)Department of Earth and Planetary Sciences, University of California, Davis, One Shields Dr., Davis, CA 95616, (3)Department of Geoscience, University of Wisconsin, 1215 West Dayton St, Madison, WI 53076, (4)Department of Geology, University of California, Davis, CA 95616, wanlufu@pku.edu.cn

Systematical carbon isotope analysis of Majiashan section in Chaohu, South China was conducted from mid-Smithian through Spathian at ~10-cm stratigraphic resolution. Three major δ13Ccarb shifts are similar to the global time-equivalent δ13Ccarb records and are potentially correlated to changes in water column stratification and oceanic circulation conditions. To further constrain the observed δ13Ccarb variations and the chronology of the marine reptile beds, we performed astrochronologic testing on the high-resolution δ13Ccarb data.

The results of e-ASM show strong astronomical signal in the δ13Ccarb data, including a pronounced 405-kyr rhythm, similar to younger geological records. Frequency domain minimal tuning was applied to generate a floating astronomical time scale. Available geochronology is used to calculate the approximate duration of the interval and to assess the potential time scale of the observed oscillations in the δ13Ccarb data. Astrochronologic results provide a good basis for developing a nominal astronomical time scale (ATS). The Smithian-Spathian boundary (SSB) in the Chaohu area, characterized by the shift of δ13Ccarb from negative values to positive values, has an age of 250.2 Ma that compares well with the radioisotopic date. The first stratigraphic occurrence of the air-breathing marine top predator, Chaohusaurus (248.8 Ma) constrains the post-extinction recovery duration to 3.35 My.

The persistent eccentricity cyclicity in the Majiashan δ13Ccarb indicates eccentricity-controlled redistribution of carbon between the carbon reservoirs. Increased short-term δ13Ccarb variability (phases 5 and 6), synchronous with the time interval of abundant and diversified Mesozoic marine reptiles in mid-Spathian, potentially reveals changes in oceanic circulation that represent an interaction of astronomical influence and secular ocean evolution following the end-Permian extinction.