TERMINATION OF SUPERANOXIA AND CHERT GAP AFTER THE END-PERMIAN MASS EXTINCTION: CONSTRAINTS FROM ASTRONOMICAL TIME SCALE OF DEEP-SEA SEQUENCE IN JAPAN

After the severest mass extinction event in the Phanerozoic, the biotic and environmental recovery from the extinction at the Permian/Triassic boundary, such as productivity collapse, long-lasted oceanic anoxia, and carbon cycle perturbation, is considered to have been required ~ 5 Myr, covering the entire Early Triassic. However, the lack of their high-resolution age constraints prevented to reconstruct their temporal and causal linkage. Here we present the astronomical time scale for the Early to Middle Triassic pelagic sequence in Japan. The pelagic sequence in Japan shows the drastic change in color from red to grey or black and the decrease in the biogenic silica content across the P/T boundary, called “Superanoxia” and “Chert gap”, respectively, although their paleoceanographic/paleoclimatic interpretations are still debated (Isozaki, 1997; Sakuma et al., 2012). To construct the astronomical time scale for this sequence, the Lower Triassic to Lower Jurassic bedded chert sequence in the Inuyama area, Japan have been used primary based on the recognition of ~ 20 kyr precession cycle of chert-shale couplet with fine-tuning by the 405 kyr eccentricity cycle in chert bed thickness variation (Ikeda et al., 2010). Our astronomical time scale of the Inuyama bedded chert was anchored at the end-Triassic mass extinction interval within ~ 0.02 Myr resolution (e.g. Carter and Hori, 2005), which were dated at 201.36±0.13 Ma of U-Pb age in shallow marine sequence (Schoene et al., 2010). Based on our astronomical time scale, the termination of “Chert gap” was corresponding to the beginning of the Spathian gradual positive carbon isotope excursion and the vegetation recovery (e.g. Galfetti et al., 2007). This timing is consistent with the interpretation of “Chert gap” as the result of increased eolian dust flux related with the devastating terrestrial ecosystems, which is supported by the extremely high sedimentation rate during “Chert gap” (Sakuma et al., 2012). The termination of “Superanoxia” was corresponding to the terminations of the carbon isotope perturbation and the minimum of the 3.6 Myr eccentricity cycle (Galfetti et al., 2007; Ikeda et al., 2010). The coincidence suggests their possible linkage through global carbon cycle and possible impact of astronomical forcing on the biotic and environmental recovery.