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Strong storms cross the marine areas and contribute to the accumulation of specific sedimentary layers along the coasts, also known as "storm deposits". Other almost similar sedimentary structures which accumulate in the low-lying coasts hit by Tsunami waves are known as "tsunamites", Even though almost similar, these two types of structures also differ. Storm deposits are irregular and discontinuous, with lengths up to tens of meters, mainly spread between the fine- and stormy weather shoreline positions. Their structures generally show specific hummocky or swaley cross stratification. Tsunami-type layers form tabular sedimentary bodies up to 50 cms thick, consisting of coarse, poorly- or unsorted coarse sediments. Their on-shore limits are situated at longer distances when compared to those of the storm deposits - even over 1 km inland. The internal structure of the tsunami-type deposits usually is not very clear, while being rich in rock intraclasts (clay and limestone pebbles), some of them of exotic origin.
Classification of coarse deposits accumulated along the Romanian Black Sea coast into storm or tsunami deposits is a recent challenge to marine sedimentologists. Past studies identified coarse sedimentary layers accumulated in past and present lacustrine, coastal or inner shelf environments and considered these as storm deposits.
Recent researches on the same layers partially re-interpreted their formation mechanisms. Oaie et al (2006, 2007) describes discontinuous layers with centimetric thickness, generally consisting of shelly sands with limestone intraclasts, vegetation fragments, with unclear sedimentary structures. Samples taken from coastal lakes showed the existence of coarse layers (pebbles, sands, shells) intercalated in much finer sediments (silts, muds). Coarse-grained sediments accumulated on fine sand beaches are generally interstratified in the finer-grained and better-sorted sandy layers. Studies made on cores from 10 to 20 meters water depth at sea discovered relatively homogeneous, well sorted fine to medium grained sand layers with microfaunal contents typical to environments with different salinity levels. These were considered possible proofs of tsunami-type sedimentary structures accumulated in the recent geologic past.
Systematic studies made on present beach sediment structures showed that storm deposits only rarely exceeded 80 meters from the fair-weather position of the shoreline. So, even though relatively similar in their contents and structures, recent storm deposits from the Danube Delta beaches generally spread to the limit of the dune zone.
As a partial conclusion, at least a part of the coarse grained layers along the Romanian littoral may be due to tsunami type events.
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