Paper No. 8
Presentation Time: 10:15 AM
SUPRAREGIONAL SEISMITES IN TRIASSIC - JURASSIC BOUNDARY STRATA
The end-Triassic mass extinction event (201.564 Ma) was synchronous with the earliest volcanic phase during the emplacement of the Central Atlantic Magmatic Province (CAMP), a large igneous province (LIP) formed during the initial breakup of Pangea. Volcanic degassing of CO2
and other volatile gases, and/or thermogenic methane, from the CAMP is generally regarded as the main cause of the end-Triassic biotic crisis. However, while the episodic volcanism of this LIP lasted for ~600.000 years, the duration of the end-Triassic mass extinction event is estimated to <50.000 years. This, as well as the discrepancy in timing of recovery between the terrestrial and marine ecosystems, suggests a more complex scenario with both short- and long-term causes and feedback mechanisms that require further studies of the temporal succession of events in Triassic-Jurassic (TJ) boundary strata. A previously reported widespread single seismite layer from the UK has been suggested to have been caused by an extraterrestrial bolide impact. This, along with alledged but not confirmed records of Upper Rhaetian shocked quartz grains from Italy and Austria, and small Iridium anomalies below the TJ-boundary in Canada, have helped to keep an extraterrestrial bolide impact on the list of possible causes for the end-Triassic event.
Here we present soft-sediment deformations within both marine and terrestrial TJ-boundary strata of Denmark, Sweden and Germany that are interpreted as seismites (sensu stricto). These seismites are stratigraphically constrained by palynology and C-isotopes to the latest Rhaetian, and are synchronous to the single seismite layer from the UK. However, in the Danish and German Basins multiple levels of soft-sediment deformation, interbedded by undisturbed strata, have been identified. We discuss the temporal position of the seismites in regards to other end-Triassic events, and argue that their supraregional distribution in pre-TJ-boundary strata of NW Europe may be linked to intensified earthquake activity during CAMP rifting, rather than an extraterrestrial impact.