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KRIEGERS FLAK OWF GEOPHYSICAL SURVEY RESULTS 4 4. GEODESY 4.1 Horizontal Datum To generate a regular gridded coordinate system (easting and northing) across the site, a project geodesy is assigned. The client specification for the site assumes a global spheroid of the shape depicted by the WGS84 model and the assigned zone in which the work is conducted is UTM32N. Any co-ordinates stated within this report are referenced to this geodesy. 4.2 Vertical Datum The vertical reference system for the survey is DVR90, which is represented by the DKGEOID02 geoid model. All bathymetric and sub bottom horizon elevations stated in this report are relative to DVR90. KF_OWF_Geophysical_Survey_Results_v4.docx
KRIEGERS FLAK OWF GEOPHYSICAL SURVEY RESULTS 5 5. GEOLOGICAL HISTORY Except for the lowermost geological unit, Cretaceous Chalk (C) that was deposited in an intracontinental sea during the Late Cretaceous, the geology of Kriegers Flak is the result of Pleistocene glaciations and the basin history of the Baltic Sea Basin during the Late Pleistocene and the Holocene. The site area was covered by ice streams a number of times during the Elsterian, Saalian and Weichselian glaciations. The ice streams and their melt-water with associated debris eroded the chalk surface and deposited glacial till and glacigenic (deglaciation and melt-water) sediments. The glaciers also caused glaciotectonic deformation of older glacial/glacigenic deposits and the Cretaceous basement. Saalian glacial till and deglaciation deposits are known from outcrops in the southern part of the island of Zealand and the island of Møn (e.g. Houmark-Nielsen, 1994, Ref. 8; Damholt, 2005, Ref. 9) west of the site. Saalian (and possibly also older) glacial and glacigenic deposits and (possibly dislocated) Eemian marine clay form part of the Lower Till unit (LT). This unit probably also includes some Weichselian glacial and glacigenic deposits, while at least the youngest Weichselian glacial and glacigenic deposits are included in the Upper Till unit (UT). Following the Eemian a fall in the global sea-level caused regression in the site area in the Early Weichselian. During deglaciation isostatic depression caused by the weight of the ice-sheet allowed an inflow of marine waters into the Baltic Sea Basin. In the Swedish part of Kriegers Flak an up to 10m thick partly marine, partly lacustrine clay succession, the Kriegers Flak Clay was deposited (Anjar et al., 2010, Ref. 13; Anjar et al., 2012,Ref. 12). The clay that includes thin beds of gyttja and peat is overconsolidated by later ice load (Klingberg, 1998, Ref. 14). The clay may be present in situ or dislocated in the Lower Till unit and/or in the Upper Till unit. Blanking caused by gas/peat/gyttja recorded in the Upper Till unit may originate from the Krigers Flak Clay. During the Late Weichselian the site area was overrun by at least three ice-streams, partly separated in time by periods of ice-free conditions (Kjær et al., 2003, Ref. 15; Houmark-Nielsen & Kjær, 2004, Ref. 16). These ice-streams again caused erosion, glaciotectonic deformation and deposition of glacial and glacigenic deposits. In the site area deposits from the three ice-streams are probably included in the Upper Till unit. In the site area glaciotectonic deformation probably caused the overall geometry of the area with glacial highs (formed by Lower Till unit) and intermediate lows filled with Upper Till unit, late glacial and Holocene deposits. However, it is unclear whether this glaciotectonic deformation should be ascribed to the first Late Weichselian ice stream (Weichselian Main Advance) or an older ice stream. A multistage deformational history is also possible. It is not clear if deglaciation took place under aquatic or subaerial conditions. However, during and following deglaciation the site area was subject to redeposition, possibly including solifluction under periglacial conditions causing the formation of the Flow Till unit (FT) that covers the irregular glacial topography in lower parts of the site area. Alternatively the Flow Till unit was deposited primarily as a deglaciation deposit during deglaciation under aquatic conditions (in the early Baltic Ice Lake). In both cases the unit will comprise normal consolidated diamicton with interbedded lenses and stringers of sorted materials. Hereafter the site area was subject to the complex late glacial and Holocene sea-level and lake-level history of the Baltic Sea Basin. This history is synthesized in Björck (1995), Ref. 17 with minor corrections in e.g. Björck et al. (2008), Ref. 18 . Following deglaciation the area was covered by the Baltic Ice Lake, which transgressed the area c. 12 thousand years ago. The Early Holocene saw a new transgression, the Ancylus Transgression c. 9.5 thousand years ago reaching levels similar to those of the Baltic Ice Lake transgressions. The highstand lasted c. 300 years and was followed by c. 1,000 years of dry land until the area c. 8 thousand years ago was transgressed by the Littorina Sea that reached levels near present day sea-level c. 7 thousand years ago (Christensen, 1995, Ref. 19). KF_OWF_Geophysical_Survey_Results_v4.docx
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