EXTINCTION-INDUCED CHANGES TO MOROCCAN REEF ECOLOGY IN THE EARLY JURASSIC

Mass extinctions in the early Mesozoic were foundational to the development of modern marine communities such as coral reefs. Two Early Jurassic extinctions, the Pliensbachian/Toarcian (Pl/To) boundary event and the Toarcian Oceanic Anoxic event (T-OAE), caused one of the most severe reef collapses of the Phanerozoic. Current research of the effects on shallow water reef ecosystems during these extinctions lacks the resolution necessary to either quantify the ecological changes they caused or determine how specific extinction drivers (e.g., acidification, ocean warming) influenced ecological shifts.

In the Central High Atlas Mountains of Morocco, we have been able to thoroughly sample reefal units from multiple locations and facies across the Early Jurassic. The Moroccan shallow water environments experienced severe carbonate factory collapses during both the Pl/To and the T-OAE. During these events, an increase in continental weathering caused thick siliciclastic deposits as well as a pause in reef growth. After each extinction, the biotic structural components of the reefs changed, giving insight on how extinction drivers impacted those taxa at the time of their onset. Following the Pl/To, there was a shift from a mix of coral-dominant and lithiotid bivalve-dominant reefs to predominantly lithiotid bivalve reefs. Following the T-OAE, lithiotids went extinct and coral-dominated reefs returned to the platform.

An ongoing quantitative point count analysis of more than 250 thin sections will allow us to determine more specific structural and ecological changes that occurred within reefs, as well as assess how the roles of certain taxa changed during this time. Occurrence and volumetric composition data will be used to quantify the differences in reef facies between time intervals. Detailed paleontological analyses of reefal compositional and structural change across these two extinctions will allow us to determine what role extinction drivers such as acidification, sediment influx, or rising ocean temperatures, played during each event and correlate those drivers with their effects on the faunal community and structure of the reefs.