Multi-staged reef recovery following the Pliensbachian/Toarcian boundary event (Early Jurassic) in the Moroccan Central High Atlas

At the end of the Pliensbachian Age (Early Jurassic), eruptions of the Karoo Large Igneous Province dramatically changed global climates and led to a collapse of carbonate factories in shallow marine environments. In the High Atlas Basin of Morocco, an influx of siliciclastic sediment and nutrients from the Anti Atlas Mountains poisoned shallow water ecosystems just after the Pliensbachian/Toarcian boundary; reefs built by corals, sponges, microbialites, and the distinctive Lower Jurassic lithiotid bivalves were wiped out. Folslowing the initial extinction and carbonate collapse, a multi-phased recovery of reef communities is documented in the early Toarcian. This high-resolution study takes advantage of the uniquely expanded stratigraphic record in the Moroccan Central High Atlas Mountains to document the phases of reef recovery as conditions steadily improved after the Pliensbachian/Toarcian boundary event. Lithiotid bivalves recovered first, as they were able to tolerate high turbidity and eutrophication; they built bioherms and biostromes along with small corals and other bivalves. Frequently found within submarine channels, lithiotids reappeared as soon as the carbonate factory recovered and established themselves as the main reef builders across the region. As ocean conditions continued to improve, waters became less turbid and more oligotrophic. Subsequently, sponges, microbialites, and corals were able to reestablish patch reefs on middle to outer ramp environments. Sponge, coral, and microbialite patch reefs became the predominant reef types until the collapse of the carbonate factory at the onset of the Jenkyns Event. This work highlights the nuanced community recovery during the dynamic environmental changes that occurred as conditions stabilized following the environmental perturbations at the start of the Toarcian. High-resolution documentation of reef recovery stages following major geological climate changes provides key insight for future patterns of reef rehabilitation.