Global mass wasting at continental margins during Ordovician high meteorite influx

A large body of evidence exists for the break-up of an asteroid in the Middle Ordovician period (around 470 million years ago) and the rapid delivery of meteorites to the Earth, most notably recorded in meteorite-rich strata in Sweden(1-6). The large number of meteorites at a single locality, spanning a relatively short time interval, implies a meteorite flux two orders of magnitude greater than at present(7). Here I survey published data to show that the deposition of Middle Ordovician sedimentary megabreccias-consisting of large rock fragments dispersed in a fine matrix-was coincident with the high meteorite flux. The widespread distribution of such deposits reflects downslope movement of sediment and rock at continental margins on a global scale. My calculations show that this process could have been triggered by the seismic activity and destabilization of sediment slopes resulting from the high influx of meteorites. If so, the anomalous occurrence of megabreccias in the geological record may provide evidence for other episodes of enhanced meteorite delivery to the Earth.