Abstract
The Nördlinger Ries and the Steinheim Basin are widely perceived as a Middle Miocene impact crater doublet. We discovered two independent earthquake-produced seismite horizons in North Alpine Foreland Basin deposits potentially related to both impacts. The older seismite horizon, demonstrated to be associated with the Ries impact, is overlain by distal impact ejecta in situ, forming a unique continental seismite-ejecta couplet within a distance of up to 180 km from the crater. The younger seismite unit, also produced by a major palaeo-earthquake, comprises clastic dikes that cut through the Ries seismite-ejecta couplet. The clastic dikes may have formed in response to the Steinheim impact, some kyr after the Ries impact, in line with paleontologic results that indicate a time gap of about 0.5 Myr between the Ries and Steinheim events. This interpretation suggests the Ries and Steinheim impacts represent two temporally separate events in Southern Germany that, thus, witnessed a double disaster in the Middle Miocene. The magnitude–distance relationship of seismite formation during large earthquakes suggests the seismic and destructive potential of impact-induced earthquakes may be underestimated.
Highlights
The Nördlinger Ries and the Steinheim Basin are widely perceived as a Middle Miocene impact crater doublet
The DREL components were ballistically transported over distances up to 180 km, deposited and preserved in the siliciclastic sediments of the North Alpine Foreland Basin
The DREL that caps the seismite unit (Figs. 2, 4, 5) provides compelling evidence that the Ries impact was the source for this seismic event, causing soft-sediment deformation within a radial distance of ~ 100 to 180 km from the impact site
Summary
The Nördlinger Ries and the Steinheim Basin are widely perceived as a Middle Miocene impact crater doublet. As described in this study, a laterally extensive seismite occurs in sandy deposits of the Upper Freshwater Molasse of pre-Ries age several tens of kilometres north of that line (near Biberach, Ochsenhausen, and Ravensburg) and is capped by a primary horizon of distal Ries ejecta in situ and undisturbed younger deposits.
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