Lessons from an ancient coral reef refuge: Ecological and geochemical characteristics of a precarious Early Jurassic reef

The end-Triassic mass extinction event occurred 201.6 million years ago and is considered to be the second largest loss in biodiversity since the Cambrian. This event was catastrophic for reefs and reef-building organisms. Recovery of these ecosystems did not occur until the Pliensbachian stage of the Early Jurassic, ~11 million years after the extinction. The Telkwa reef, located in the Telkwa range of British Columbia, Canada, is one of the few coral reefs deposited prior to the recovery interval and is arguably the best-developed Sinemurian (Early Jurassic) coral reef deposit in the world. Moreover, this reef acted as a refuge to organisms that went extinct during the end-Triassic mass extinction. As the reef is part of the Stikinia Terrane, a volcanic arc located in the Panthalassic Ocean during the early Mesozoic, reef growth was punctuated by several periods of volcanism. The beds that flank either side of the reef are composed primarily of air-fall tuffs. The interbedding relationships between the limestone and volcaniclastic rocks are clearly visible, showing the complex history of this reef. This study aims to identify the geochemical and ecological characteristics that allowed these reef-building organisms to thrive despite hostile conditions induced by local volcanism and the end-Triassic mass extinction. Results show that erosion of newly deposited volcaniclastic rocks could have liberated trace element nutrients which may have led to the partial survivorship of reef-building organisms. Additionally, the partial eradication of reef-building organisms may have led to the decay of organic matter causing the liberation of organic nutrients which could have also influenced the partial survivorship of reef-building organisms.