Dr Mike Simms will be presenting a School's Seminar at the University of Glasgow, School of Geographical and Earth Sciences. The Title will be Extreme sedimentology: A giant meteorite impact in the Mesoproterozoic of NW Scotland.
Extreme sedimentology: A giant meteorite impact in the Mesoproterozoic of NW Scotland
Mike Simms (National Museums Northern Ireland)
Friday 12th April at 16:00 in the East Quadrangle Lecture Theatre
Abstract: Many commonplace sedimentological processes or events can be observed in the field or reproduced in the laboratory. Others, such as tsunamis, are rare and unpredictable events where chance observations by non-specialists may be as important as years of research by experts. Still other events are so rare that they have never been witnessed by humans and can only be investigated long after, and so extreme that we are still far from understanding them in detail. One such ‘ extreme sedimentary event’ is found in the Mesoproterozoic Stoer Group of north-west Scotland, where the 5-10 metre thick Stac Fada Member is now generally recognised as an ejecta deposit from the hypervelocity impact of a kilometre-scale meteorite. Just a narrow elongate outcrop of the ejecta deposit survives today, but it exemplifies the extreme processes involved in the emplacement of impact ejecta. The Stac Fada Member is similar to previously documented impact ejecta deposits in some respects, but unique in others. The impact occurred into a heterogeneous landscape of basement (Lewisian) inliers and thick (km-scale) waterlogged fluvial sediments, which strongly influenced the nature and distribution of the ejecta deposit. Large-scale sedimentary structures within the Stac Fada Member suggest that its source – the impact crater - lay to the east of the Stoer Group outcrop. The presence of a deep gravity low beneath the Moine Thrust at Lairg, due east of the Stoer Group outcrop, suggests that the crater itself may still survive.