Shen Bing, Dong Lin, Xiao Shuhai, Lang Xianguo, Huang Kangjun, Peng Yongbo, Zhou Chuanming, Ke Shan, Liu Pengju
Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, Beijing 100871, China.
School of Earth and Space Sciences, Peking University, No.5 Yiheyuan Road Haidian District, Beijing 100871, China.
Nat Commun. 2016 Jan 7;7:10317. doi: 10.1038/ncomms10317.
Molar tooth structures are ptygmatically folded and microspar-filled structures common in early- and mid-Proterozoic (∼2,500-750 million years ago, Ma) subtidal successions, but extremely rare in rocks <750 Ma. Here, on the basis of Mg and S isotopes, we show that molar tooth structures may have formed within sediments where microbial sulphate reduction and methanogenesis converged. The convergence was driven by the abundant production of methyl sulphides (dimethyl sulphide and methanethiol) in euxinic or H2S-rich seawaters that were widespread in Proterozoic continental margins. In this convergence zone, methyl sulphides served as a non-competitive substrate supporting methane generation and methanethiol inhibited anaerobic oxidation of methane, resulting in the buildup of CH4, formation of degassing cracks in sediments and an increase in the benthic methane flux from sediments. Precipitation of crack-filling microspar was driven by methanogenesis-related alkalinity accumulation. Deep ocean ventilation and oxygenation around 750 Ma brought molar tooth structures to an end.
臼齿状构造是在早元古代和中元古代（约25亿至7.5亿年前）潮下序列中常见的、具有褶皱和微亮晶充填的构造，但在年龄小于7.5亿年的岩石中极为罕见。在此，基于镁和硫同位素，我们表明臼齿状构造可能形成于微生物硫酸盐还原作用和甲烷生成作用共同发生的沉积物中。这种共同发生是由元古代大陆边缘广泛存在的缺氧或富含硫化氢的海水中大量生成的甲基硫化物（二甲基硫和甲硫醇）驱动的。在这个共同发生区域，甲基硫化物作为一种非竞争性底物支持甲烷生成，而甲硫醇抑制甲烷的厌氧氧化，导致甲烷积累、沉积物中形成排气裂缝以及沉积物中底栖甲烷通量增加。裂缝充填微亮晶的沉淀是由与甲烷生成相关的碱度积累驱动的。大约7.5亿年前的深海通气和氧化作用使臼齿状构造终结。
