The Late Permian mass extinction, which eliminated ~90% of marine species, 70% of terrestrial vertebrate species, 30% of insect orders, and an indetermined percentage of terrestrial and marine plants, is the most devastating natural catastrophe in Earth’s history. In addition to commonly accepted factors such as asteroid impacts and volcanic eruptions, the emission of thermogenic greenhouse gases including CO2 and CH4 related to the emplacement of large igneous provinces (LIPs) is also considered as one of the important causes of the Late Permian mass extinction. However, most studies reported thus far are based mainly on indirect evidence or evidence solely derived from oil pyrolysis products including pyrobitumen and natural gas compositions. There is a lack of direct evidence on the timing of the oil pyrolysis event within the paleo-oil pools, and no attempt has been made to document the pyrolysis process in relation to the LIP-related hydrothermal fluid invasion.
A team led by Prof. Keyu Liu from China University of Petroleum (East China) in collaboration with scientists from Peking University, PetroChina and the Laoshan National Laboratory recently carried out an in-depth investigation on the pyrolysis process of a paleo-oil pool within the Ediacaran carbonate reservoirs in the central Sichuan Basin relating to the emplacement of the Emeishan Large Igneous Province (ELIP). Through detailed petrographic, fluid inclusion, and in situ geochemical analysis of hydrothermal minerals (including quartz and saddle dolomite), it was confirmed that the rapid pyrolysis of paleo-oil pools in the Ediacaran carbonate reservoirs occurred around 258.4±7.3 Ma, which is comparable to the eruption timing of ELIP. It is worth noting that this new geochronological result has shifted the widely accepted pyrolysis timing of paleo-oil pools in the Ediacaran carbonate reservoirs in the Sichuan Basin forward by at least 50 million years. The hydrocarbon-bearing fluid inclusions in the hydrothermal minerals recorded the entire pyrolysis process of paleo-oil pools, and the reservoir pressure experienced an initial rapid increase followed by a subsequent abrupt drop, indicating that massive over-pressured methane in the reservoir had been rapidly emitted into the atmosphere along faults or magmatic pipes, ultimately contributing to the end-Guadalupian extinction. This study highlights the significance of massive emission of thermogenic methane related to LIPs for climate change, carbon cycling, and biological evolution in Earth’s history.
Fig.1 (A&B) Geographic distribution of the Emeishan Large Igneous Province (ELIP) and location of the study area; (C) Burial history of the studied carbonate reservoir and inferred precipitation depth of the saddle dolomite (SA); and (D) Cross plot of reservoir pressure versus temperatures within the Ediacaran carbonate reservoir studied in the central Sichuan Basin.
The research results were recently published in Geology, a Nature-Index top journal in the field of earth sciences. The lead author of the paper is Dr. Peng Yang, a postdoctoral fellow at the School of Geosciences, China University of Petroleum (East China) while the corresponding author is Prof. Keyu Liu. Research collaborators include Prof. Zhijun Jin of Peking University, Drs. Xuesong Lu, Lili Gui and Junjia Fan of the Research Institute of Petroleum Exploration and Development, CNPC, Dr. Changwei Li of PetroChina Southwest Oil & Gas Field Company, Dr. Jianliang Liu and Shunyu Wang of China University of Petroleum (East China), and Dr. Yang Xu of the Laoshan National Laboratory.
CITATION：Peng Yang, Zhijun Jin, Keyu Liu*, Xuesong Lu, Changwei Li, Lili Gui, Jianliang Liu, Junjia Fan, Shunyu Wang, Yang Xu, 2024, Rapid pyrolysis of paleo-oil pools recorded by fluid inclusions in an Ediacaran carbonate reservoir, southern China: Implications for the end-Guadalupian mass extinction. Geology, https://doi.org/10.1130/G52452.1.
