TAXONOMIC ASSESSMENT OF EARLY JURASSIC MACROFAUNA FROM THE HIGH ATLAS MOUNTAINS OF MOROCCO

Marine communities in the Early Jurassic experienced varying degrees of biotic crises at the Pliensbachian/Toarcian boundary, ~183.5 million years ago, and during the Toarcian Oceanic Anoxic Event (TOAE), ~183 million years ago. Though not as severe as the biggest mass extinction events (e.g., the end-Permian), these events are thought to be caused by similar environmental stresses such as ocean warming, anoxia, and acidification, resulting from a Large Igneous Province eruption. Nevertheless, exact causes of the extinctions are debated, most likely due to limited data availability from shallow water carbonate strata from lower latitudes. Previous work from Lower Jurassic sections in the High Atlas of Morocco suggests that biotic changes in communities living in carbonate shelves were coincident with a two-phased carbonate factory collapse; however, the carbonate communities seemed to recover relatively quickly. Therefore, we will study the faunal composition of level-bottom communities before the extinctions and during the recoveries to assess how these communities responded to the environmental changes.

To investigate the cause and significance of the change in community dynamics across these two events, we quantify occurrences and abundances of different fauna from shallow marine carbonate strata in the Central High Atlas Mountains of Morocco. This study includes a preliminary assessment of the macrofauna sampled from different late Pliensbachian and early Toarcian localities. The macrofaunal groups studied herein include species of ammonites, bivalves, brachiopods, echinoids, and gastropods. Quantification of fossil invertebrate communities will allow analyses of long-term trends in community structure and provide data to assess the plausibility of local kill mechanisms. For example, if heat stress or ocean acidification are significant factors, we would see a significant loss of heat or lowered pH sensitive taxa. Quantification will also determine how the marine communities changed in response to environmental stressors at each event and what environmental or taxonomic factors dictated survival versus extinction. Broadly, community survival through smaller extinctions provide important data for survival strategies of organisms, which can be used for modern marine conservation.