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Pelecypods from the Upper Eocene of East Poland

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The pelecypod assemblage from Upper Eocene sandy deposits of the vicinity of Siemień and Luszawa (eastern part of the Polish Lowlands) consists of 23 species. The majority of the species are typical of the Bartonian.
On December 26th, 2004, a tsunami hit the Andaman Sea coast of Thailand, leaving bimodal tsunami deposits in the coastal zone. Granite boulders and sandy tsunami deposits were investigated near Thap Lamu Navy Base in Phang Nga Province, Thailand. Boulders (< 2.5m³) were mostly scattered close to a tidal inlet on a flat plain elevated 1-2m above the high tide water level, reaching up to 140m inland. Most boulders had oyster shell remnants over their surface, which suggests that they were dragged from the nearby shore. The tsunami also brought a sheet of medium to coarse grained sand, with thickness ranging from a few mm up to 37cm. The distribution of deposits was mainly controlled by the existing topography. Another group of granite boulders was found between 150 and 300m from the coastline, at elevations of 2m and more. Their size reached 5.5m³. This second group of boulders may have been transported by an ancient tsunami.
The experiment, with the use of sand deposit from hygroarenal (shore sand beach wetted by lake waves) of the beach of eutrophic Lake Mikołajskie (Masurian Lakeland, Poland), was performed in order to test the hypothesis that shore sand deposit is the bank of resting forms of ciliate, rotifer and crustacean species. The experiment was conducted over a 38 days period in March-April 2004. Frozen sand taken in winter was exposed in aquariums filled with pre-filtered (GF/C) lake water in stable temperature (20ºC), oxygen saturation and 12:12 light/dark conditions. Samples (three replicates) were taken each day. A total number of 44 ciliate, 59 rotifer and 9 crustacean taxa were identified during the studied period. Resting forms of different species and/ or taxonomic groups developed in different time and it may be the result of different strategies in colonization of new habitats. Organisms forming resting cysts such as ciliates (11 species) and bdelloid rotifers appeared after the first day of the incubation whereas organisms hatching from resting eggs (monogonont rotifers and crustacea) were observed from the 2nd-3rd day of the experiment. The numbers of all the studied groups of organisms increased gradually and then strongly decreased indicating probably nutrient and/or organic matter limitation. The highest numbers of ciliates (731 ind. cm⁻² of sand) was found on the 5th day, rotifers (987 ind. 100 cm⁻²) on the 23rd day, cladocerans (60 ind. 100 cm⁻²) on the 21st day and copepods (30 ind. 100 cm⁻²) on the 33rd day of the experiment. The results of this study suggests that shore sand deposits being the temporal refugium for the small-bodied invertebrates transported here with the wave action may also play an important role as the transfer for their further dispersal in addition to postulated ways of expansions such as wind, rain, animals and surface runoff.
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