Geoscience Reference
In-Depth Information
8.3.4 Reconstruction of Palaeocoastlines
The reconstruction of palaeocoastlines and bathymetry were based on GIS analysis,
from which interpolated surfaces of water levels were subtracted from the modern
DTM (Fig. 8.6 ) . The modern DTMwith a grid size of 20
20 m was generated using
the linear solution of the Natural Neighbour interpolation using different sources of
elevation data. Elevation data for the mainland were derived from the Estonian Basic
map on a scale of 1:10,000 (western part), the Soviet military topographic map on
a scale of 1:25,000 (eastern part) and the Baltic seabed from the bathymetric maps
on a scale of 1:50,000 (Estonian Maritime Administration 2001a - c , 2002a , b ) . All
maps were transformed into L-EST national reference system. The vertical datum
for the elevation data and DTM modelling was national height system BK77 based
on Kronstadt zero level.
DTM-based palaeoreconstructions have some limitations due to the impact of
deposition subsequent to the time being modelled. Therefore the thicknesses of
Holocene peat (Orru 1995 ) and gyttja (Veski 1998 ) deposits were removed from
the DTM before the palaeocoastline reconstruction.
×
Fig. 8.6 General cross-sections showing the principles of palaeoreconstructions. Topography
related to the isostatically deformed (uplifted) sea/lake water-level surface today ( a ) and during
sea/lake formation ( b )
8.4 Modelling Results
The distribution of the Baltic Ice Lake water-level surface isobases and shorelines in
the Pärnu area is presented in Fig. 8.7a-i for nine time slices since the deglaciation
of the area. The created spatial and temporal model made it possible to reconstruct
the palaeo-water levels and coastlines for the times for which coastal landforms
data are lacking, for instance the lowstands of the Ancylus Lake and Littorina Sea
(Fig. 8.7d , f , g ) , and to relate the palaeocoastlines with Stone Age settlement sites
in SW Estonia (Fig. 8.7d , f,i).
The main characteristics of interpolated water-level surfaces are summarized in
Table 8.2 . Calculated mean tilting gradients decrease exponentially over time as a
 
 
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