On 11 February at 10:15 Kairi Põldsaar will defend her doctoral thesis "Soft-sediment deformation and gravity flow structures in the Lower Palaeozoic successions of the Baltic Basin" at Ravila 14a-1019.
Senior Reaserch Fellow Leho Ainsaar, Institute of Ecology and Earth Sciences Director, University of Tartu
Professor Antonius J. Van Loon, Geocom Consultants, Benitachell, Hispaania
Sand- and limestones in Estonia and Latvia contain ancient sedimentary structures that are triggered by earthquakes and tsunamis some 450 million years ago.
Kairi Põldsaar and her colleagues studied Kambrian and Ordovician (458-500 million years ago) sedimentary rocks of the Baltoscandian region. She describes in her doctoral thesis some specific rock structures which are caused by over 7 magnitude earthquake. At least once an ancient earthquake has triggered a tsunami wave, which in turn caused hundreds of kilometres large sediment avalanche in the deeper part of the sea.
This study is interesting because until so far it was a common belief amongst scientists that this region has been tectonically quiescent for over past 500 million years. Excluding some meteorite impacts, constant earthquake and tsunami fear has not been a problem for us, our ancestors, or even to ancient sea creatures long before the dinosaurs.
The studied structures belong to the category of the so called soft-sediment deformation structures. Such deformations form when the sediment is still soft. In right conditions, soft-sediment deformation structures can survive until lithification of the sediment and thus, preserve in rock record for hundreds and millions of years. Soft-sediment deformation is caused most often by liquefaction of water containing sands, in other words when the sediment obtains quick sand conditions. Most readily are liquefied for example coastal or sea bottom sands, or lake and river sediments. Liquefaction in nature is triggered by various high-energy processes – storms, tides, floods and landslides, but also of course earthquakes and tsunamis. Careful analysis of soft-sediment deformation structures, their geographical extent, morphology of the structures, and other criteria enable to conclude initial trigger of the liquefaction.
Results of the study by Põldsaar show that sedimentary structures preserved in the rock record can aid scientist to reconstruct geological events where we cannot go – such as in ancient past.