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Paper No. 76-25
Presentation Time: 9:00 AM-5:30 PM
ON THE TIMESCALE CONTROVERSY OF THE SPATHIAN SUBSTAGE (EARLY TRIASSIC) IN SOUTH CHINA
Recently published inconsistent astronomical time scales of the Spathian substage at Chaohu section in South China highlights difficulties in astrochronology (1.4 myr in Li et al., 2016 and 2.89 myr in Fu et al., 2016 for the Spathian duration). Here, we revisit Spathian paleoclimate series of Chaohu section to seek reconciliation between these two proposed scales. Constraints on the Spathian-Anisian boundary at Chaohu are lacking; this hinders confidence in estimating the Spathian duration. Quantitative matching of measured gamma ray series between Chaohu and Guandao sections suggests that the basal Anisian occurs in the lowermost Dongma’anshan Formation at Chaohu. The evolutionary average spectral misfit metric for the δ13Ccarb and gamma ray series of the upper Nanlinghu Formation at Chaohu suggests three accumulation rate solutions for the late Spathian. Option #1 indicates a 1.4 myr duration for the Spathian substage (i.e., option #1 in Li et al., 2016); option #2 indicates a 2.74 myr duration (i.e., option #2 in Li et al., 2016, and similar to the 2.89 myr in Fu et al., 2016); and option #3 indicates a 3.14 myr duration. Radioisotope dating using latest EarthTime protocols and tracer suggests a 4.6 myr duration for the Early Triassic Epoch (Burgess et al., 2014; Lehrmann et al., 2015; Ovtcharova et al., 2015). The astronomically constrained total duration for the combined Griesbachian, Dienerian and Smithian is 3.7 myr. This, together with the 1.4 myr Spathian duration in the Germanic Basin, indicates that option #1 is the most reliable solution for the Spathian time scale, i.e., the duration of the Spathian substage is 1.4 myr.
References: Burgess et al., 2014. Proc. Natl. Acad. Sci. doi: 10.1073/pnas.1317692111; Fu et al., 2016. Sci. Rep. doi: 10.1038/srep27793; Lehrmann et al., 2016. J. Asian Earth Sci. doi: 10.1016/j.jseaes.2015.04.030; Li, M., et al., 2016. Earth Plant. Sci. Lett. doi: 10.1016/j.epsl.2016.02.017; Ovtcharova et al., 2015. Earth-Sci. Rev. doi: 10.1016/j.earscirev.2015.03.006.