Ecological Assessment of Early Jurassic (Pliensbachian and Toarcian) Benthic Foraminifera from the Central High Atlas, Morocco

The Early Jurassic is an epoch of origination and proliferation; however, two extinction events punctuate the Early Jurassic: the Pliensbachian/Toarcian boundary event and the Toarcian Oceanic Anoxic Event (TOAE). The degassing of the Karoo-Ferrar large igneous province in the Early Jurassic is thought to be the catalyst for these two crises, which resulted in significant turnover of reef fauna. The Central High Atlas Mountains of Morocco provides a relatively continuous record of Tethys Ocean deposits, which provided optimal environments for the diversification of reef fauna.

Foraminifera are unicellular Protists; the phylum is highly diverse and can be found in a variety of marine environments. Foraminifera are particularly important for understanding climate in deep time; the diversity of benthic foraminifera indicate reef health, as these organisms have punctuated intervals of die-off that coincide with reef crises throughout the fossil record. Analyzing benthic foraminifera ecology from Pliensbachian and Toarcian reefs can provide for a better understanding of the severity of the late Early Jurassic extinction events.

In this study, we investigated foraminifera from several Pliensbachian and Toarcian reefs in Morocco (Glomospira sp., Glomospirella sp., Siphovalvulina sp., Siphovalvulina colomi, Siphovalvulina gibraltarensis, Haurania deserta, Placopsilina sp., Mesoendothyra sp., Everticyclammina praevirguliana, Nodosaria sp., Planisepta compressa, and members of either Vidalina or Ophthalmidium). Following the Pliensbachian/Toarcian boundary event, many large benthic foraminifera are lost locally from the assemblage (Mesoendothyra sp. and Everticyclammina praevirguliana); Hubert's PIE, used to calculate evenness, also declined across the boundary event. In contrast, the TOAE led to a decrease in the abundance of all previously observed clades, as foraminifera are highly infrequent and only include small disaster foraminifera (Glomospira sp., Placopsilina sp., Nodosaria sp., and Vidalina or Ophthalmidium). Analyzing these microfauna communities reveals the differential ecology of some extinct benthic foraminifera species, and provides evidence for the differentiation of these two extinction events.