Diversity dynamics and mass extinctions of the Early-Middle Jurassic foraminifers: A record from the Northwestern Caucasus

The Early-Middle Jurassic foraminiferal assemblages of the Northwestern Caucasus, including a total of 315 species and 68 genera, were analysed to establish the principal diversity patterns at substage level of resolution. An overall conclusion is that the number of species varied significantly in contrast to the number of genera. The most diversified were Late Sinemurian-Pliensbachian, Late Toarcian-Early Aalenian, and Late Bajocian assemblages. Significant diversity drops have been documented in the Early Toarcian and in the Middle Aalenian. The first of them corresponds to the well-known mass extinction, which regionally was initiated in the Pliensbachian and terminated when rapid Late Toarcian diversification began. The second event could be considered as a regional evidence of a new mass extinction that appeared in the Middle Aalenian and was most likely associated with the Aalenian/Bajocian regional anoxic event also recorded in the Carpathian part of the Western Tethys. The most intense foraminiferal turnovers took place in the Toarcian, and in the Middle Aalenian-Early Bajocian. The Lazarus-effect in spite of its high value has not much influenced the estimation of principal diversity trends.