What caused the mass extinction?  A volcanic eruption.
Courtillot
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D015258:Acid Rain; D000538:Aluminum Silicates / Q000032:analysis / Q000737:chemistry; D000818:Animals; D005075:Biological Evolution; D000077215:Clay; D004391:Dust; D018534:Earth, Planet; D005580:Fossils; D019015:Geologic Sediments / Q000032:analysis*; D055593:Geological Phenomena; D005844:Geology; D017752:Greenhouse Effect; D007194:India; D007495:Iridium; D008280:Magnetics; D018543:Minor Planets; D010163:Paleontology; D018707:Volcanic Eruptions
D015258:Acid Rain; D000538:Aluminum Silicates; D004391:Dust; D007495:Iridium; D000077215:Clay