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Microbes, mud and methane: cause and consequence of recurrent E arly J urassic anoxia following the end‐ T riassic mass extinction
Author(s) -
Schootbrugge Bas,
Bachan Aviv,
Suan Guillaume,
Richoz Sylvain,
Payne Jonathan L.
Publication year - 2013
Publication title -
palaeontology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.69
H-Index - 63
eISSN - 1475-4983
pISSN - 0031-0239
DOI - 10.1111/pala.12034
Subject(s) - photic zone , anoxic waters , extinction event , phytoplankton , organic matter , isotopes of carbon , oceanography , geology , paleontology , total organic carbon , environmental science , ecology , biology , nutrient , biological dispersal , population , demography , sociology
The end‐ T riassic mass extinction ( c . 201.6 Ma) was one of the five largest mass‐extinction events in the history of animal life. It was also associated with a dramatic, long‐lasting change in sedimentation style along the margins of the T ethys O cean, from generally organic‐matter‐poor sediments during the T riassic to generally organic‐matter‐rich black shales during the J urassic. New core material from G ermany provides biomarker evidence of persistent photic‐zone euxinia during the H ettangian, the onset of which is associated with a series of both negative and positive carbon isotope excursions. Combined inorganic and organic geochemical and micropalaeontological analyses reveal strong similarities between the H ettangian and the better‐known T oarcian anoxic event. These events appear to be the most clearly expressed events within a series of anoxic episodes that also include poorly studied black shale intervals during the S inemurian and P liensbachian. Both the H ettangian and T oarcian events are marked by important changes in phytoplankton assemblages from chromophyte‐ to chlorophyte‐dominated assemblages within the E uropean E picontinental S eaway. Phytoplankton changes occurred in association with the establishment of photic‐zone euxinia, driven by a general increase in salinity stratification and warming of surface waters. For both events, the causes of large negative carbon isotope excursions remain incompletely understood; evidence exists for both variation in the δ 13 C of atmospheric CO 2 and variation in the sources of organic carbon. Regardless of the causes of δ 13 C variability, long‐term ocean anoxia during the E arly J urassic can be attributed to greenhouse warming and increased nutrient delivery to the oceans triggered by flood basalt volcanism.