Mass wasting at continental margins on a global scale during the Middle
Ordovician has recently been related to high meteorite influx. Although
a high meteorite influx during the Ordovician should not be neglected,
we challenge the idea that mass wasting was mainly produced by meteorite
impacts over a period of almost 10 Ma. Having strong arguments against
the impact-related hypothesis, we propose an alternative explanation,
which is based on a re-evaluation of the mass wasting sites, considering
their plate-tectonic distribution and the global sea level curve. A
striking and important feature is the distribution of most of the mass
wasting sites along continental margins characterised by periods of
magmatism, terrane accretion and continental or back-arc rifting,
respectively, related to subduction of oceanic lithosphere. Such
processes are commonly connected with seismic activity causing
earthquakes, which can cause downslope movement of sediment and rock.
Considering all that, it seems more likely that most of this mass
wasting was triggered by earthquakes related to plate-tectonic
processes, which caused destabilisation of continental margins resulting
in megabreccias and debris flows. Moreover, the period of mass wasting
coincides with sea level drops during global sea level lowstand. In some
cases, sea level drops can release pore-water overpressure reducing
sediment strength and hence promoting instability of sediment at
continental margins. Reduced pore-water overpressure can also
destabilise gas hydrate-bearing sediment, causing slope failure, and
thus resulting in submarine mass wasting. Overall, the global mass
wasting during the Middle Ordovician does not need meteoritic trigger.
(C) 2010 International Association for Gondwana Research. Published by
Elsevier B.V. All rights reserved.