FUNCTIONAL DIVERSITY OF LOWER JURASSIC MACROFAUNAL COMMUNITIES FROM MOROCCO

The Pliensbachian/Toarcian boundary event (~183.5 million years ago) and the Toarcian Oceanic Anoxic Event (TOAE, ~183 million years ago) represent two of the most severe environmental perturbations of the Lower Jurassic Epoch, leading to marine ecosystem disruption and biotic crises. Previous work on the Lower Jurassic biotic crises have regarded warming-induced anoxia as the primary driver for the TOAE extinctions, and the two events (i.e., the stage boundary and TOAE) are often considered to be causally linked. Recent studies, however, show elevated extinction rates in well oxygenated basins, such as the Iberian Basin in Spain and the High Atlas Basin in Morocco. Furthermore, subtle differences in environmental conditions between the two events have been identified at multiple localities.

The Lower Jurassic environmental perturbations had severe ecological impacts on the diversity and the functioning of marine macrofaunal communities. So far, there have been no quantitative studies on the Lower Jurassic macrofauna in the Moroccan mixed carbonate-siliciclastic ecosystems. Additionally, it is not clear what were the most important extinction drivers in this well-oxygenated ecosystem and how community structure changed. In this study, we report quantitative paleoecological data about the marine level-bottom communities and their survival and extinction dynamics from the Central High Atlas Basin of Morocco. We collected macrofaunal samples from the late Pliensbachian- Toarcian strata, capturing the boundary event and the TOAE. Following taxonomic identification, macrofaunal functional diversity are documented based on their inferred lifestyle, and niches were assigned based on the Bambachian ecospace classification scheme. The studied faunal groups include ammonites, bivalves, brachiopods, echinoids, and gastropods. Functional diversity determines how organisms operate in a community; thus, assessing the ecospace shifts provides data about how marine communities changed in response to environmental stressors (increased temperature or acidification) and what dictated survival versus extinction. Our quantified data shows that the marine communities structure changed substantially across the stage boundary and TOAE most likely due to multiple kill mechanisms, such as ocean warming and acidification.