title: Molar tooth carbonates and benthic methane fluxes in Proterozoic oceans.
abstract: 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.
authors.affiliation: 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.
authors.forename: Bing
authors.initials: B
authors.lastname: Shen
authors.affiliation: Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, Beijing 100871, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Dong
authors.affiliation: Department of Geosciences, Virginia Tech, Blacksburg, Virginia 24061, USA.
authors.forename: Shuhai
authors.identifier: http://orcid.org/0000-0003-4655-2663
authors.initials: S
authors.lastname: Xiao
authors.affiliation: 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.
authors.forename: Xianguo
authors.initials: X
authors.lastname: Lang
authors.affiliation: 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.
authors.forename: Kangjun
authors.initials: K
authors.lastname: Huang
authors.affiliation: Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
authors.forename: Yongbo
authors.initials: Y
authors.lastname: Peng
authors.affiliation: Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China.
authors.forename: Chuanming
authors.initials: C
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China.
authors.forename: Shan
authors.initials: S
authors.lastname: Ke
authors.affiliation: Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China.
authors.forename: Pengju
authors.initials: P
authors.lastname: Liu
mesh_terms: D002254:Carbonates / Q000737:chemistry*; D005580:Fossils; D008274:Magnesium / Q000032:analysis; D008697:Methane / Q000378:metabolism*; D008963:Molar / Q000737:chemistry*; D010084:Oxidation-Reduction; D013431:Sulfates / Q000378:metabolism*; D013440:Sulfides / Q000378:metabolism; D013460:Sulfur Isotopes / Q000032:analysis
chemical_list: D002254:Carbonates; D013431:Sulfates; D013440:Sulfides; D013460:Sulfur Isotopes; D008274:Magnesium; D008697:Methane