Guillaume Delpech

Eruptive history of the Karoo lava flows and their impact on early Jurassic environmental change

This paper reports new paleomagnetic and geochronologic data from a ~1500 m-thick composite section belonging to the Drakensberg group, the thickest remnant of the Karoo lavas in Northern Lesotho. Flow-by-flow analysis of paleomagnetic directions reveals twenty-one magnetic directional groups (DG), corresponding to single eruptive events (SEE), and sixteen individual lava flows. The new age determinations of lava flows range from 180.1 ± 1.4 to 182.8 ± 2.6 Ma. These data, combined with previous results allow us to propose that the main part of the Drakensberg group and the Karoo intrusive complex dated around 181-183 Ma may have been erupted over a period as short as 250 kyr, and may have coincided with the two main phases of extinction in the Early Toarcian. This scenario agrees well with the discontinuous rhythm of environmental and biotic perturbations in the late Pliensbachian-Toarcian interval.