Paleoecological Patterns of Reef Death and Possible Causes for the Carbonate Collapse at the End-Triassic Mass Extinction

During the Middle and Late Triassic (247 to 200 mya) there was prolific reef growth by sponges and scleractinian corals, but at the end of the Triassic, an extinction event eradicated half the species on Earth and 20% of marine families, including reef builders. The end-Triassic extinction is one of the largest and least understood mass extinctions of the Phanerozoic, as well as one of the most severe reef crises. Although no consensus exists regarding its cause, a number of theories have been proposed, including, but not limited to: climate change, ocean acidification, ocean anoxia, and productivity collapse. Currently, the most popular theory posits that carbon dioxide levels increased in the Late Triassic (possibly due to Central Atlantic Magmatic Province volcanism), heating the globe, and causing ocean stratification, a scenario that is consistent with many of the previously mentioned kill-mechanisms.

Coral reefs are extraordinarily sensitive to environmental perturbations, and so the interactions of ancient reef organisms and their ecosystems provide important clues to understanding extinctions, as well as factors controlling reef growth and ecology. In this study, eastern Panthalassic reefs located in Nevada and Oregon (Norian, 217-204 mya), and the Yukon Territory, Canada (Rhaetian, 204-200 mya) were visited, and their paleoecology assessed using quadrate analyses and line intercept transects where applicable. These detailed results of reef paleoecology before the end-Triassic extinction provide valuable information regarding environmental conditions and stresses, which can be used to determine the factors controlling the collapse of these carbonate ecosystems. Today, reefs are undergoing major die-off, commonly attributed to elevated nutrients, ocean acidification, climate change, and other factors comparable to proposed conditions in the Late Triassic. The thorough understanding of analogous reef crises can provide valuable information pertinent to the current crisis with respect to the cause, severity, and extent of a forthcoming extinction.