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KRIEGERS FLAK OWF GEOPHYSICAL SURVEY RESULTS 16 Figure 10-1 Interpreted depth below seabed (DBS) in m of Holocene Marine 1 (HM1) unit Figure 10-2 Interpreted depth below seabed (DBS) in m of the Holocene Marine 2 & 3 (HM2+3) unit Figure 10-3 Representative of the Holocene Units, Seismic Section, Line 6104900 KF_OWF_Geophysical_Survey_Results_v4.docx
KRIEGERS FLAK OWF GEOPHYSICAL SURVEY RESULTS 17 10.2 Pleistocene Units Pleistocene units are sedimentary deposits from the geological epoch which lasted from about 2.6 million to 12 thousand years ago, spanning the world's recent period of repeated glaciations. The Pleistocene is at the site sub-divided into three geological units. The base of the lowermost glacial unit, Lower Till (LT), which also is the top of the Cretaceous Chalk unit, is primarily picked from the multichannel sparker data set whereas the rest of the units primarily are picked from the pinger data set. The Flow Till unit (FT) is present in the record infilling the irregular/undulating till unit which lies beneath. The base of the unit is consequently highly irregular (Figure 10-7) and the unit is missing above the glacial highs. Unit thickness varies between 0m and c. 9m and variations mainly follow the topography of the base. The unit that comprises diamict, and probably also sorted sediments was deposited during and after the last deglaciation of the area and is consequently less consolidated than the underlying tills that have been subject to ice preloading. An example of the Flow Till unit is seen in Figure 10-4. The Upper Till unit (UT) unit is in contrast to the FT unit and is clearly depicted in the geophysical record. The unit is likely to comprise glacial till of predominantly clay with gravel, cobbles and boulders but also occurrences of silt and sand including those derived from melt water. The base of the unit is undulating and irregular, representing an old glacial landscape formed by glaciers and comprising the underlying Lower Till. The top of the larger hills have been eroded by later aquatic erosion but the depth below seabed map in Figure 10-8 newer the less show a clear pictures of this glacial landscape with large (now eroded) hills, large depressions and smaller elongated ridges. The thickness of the unit ranges from 0m to c. 23m and thickness variations both reflect the irregular base, the infilling geometry of the unit and the erosive top in areas of formerly large glacial hills. The Internal Reflector within the UT (UTi) is concentrated within the topographic lows of the LT relief, and cannot be observed extensively across the entire site. The reflector is prominent and therefore likely to represent a change in sediment. Taking in to consideration that the UT unit is a diamict the unit underlying the UTi horizon could be representative of a lens of sediment of more uniform grain size. Given the rather high stratigraphic position within the Pleistocene deposits the Kriegers Flak Clay is not the most likely candidate but it can’t be complete rules out. An example of the Upper Till internal reflector is seen in Figure 10-5. The Lower Till unit (LT) directly overlies the top of the Cretaceous Chalk. The Lower Till unit can be observed exposed at the seabed towards the perimeter of the Kriegers Flak and this is clearly seen in the seabed features datasets (Figure 7-1) through the coarsening of sediments and increased number of boulders. As mentioned above the top of the unit forms an old glacial landscape although the tops of the larger hills have been removed by later erosion. Overall the base is a gentle, sub-horizontal surface but in this surface a network of larger and smaller channels are cut, the deepest of them more than 50m deep (Figure 10-9). The age of the channels is unknown but they are probably filled with sediments comparable to those of unit LT and channels and channel fill are consequently included in unit LT. Outside the channels the unit is generally c. 10-30m thick but over the channels the thickness is up to 90m and the total thickness range is 0-90m. Outside the channels variations in thickness are controlled by the unit top, the old glacial landscape. The unit comprises glacial till and meltwater deposits from a number of ice stream advances and it includes Eemian marine clay and probably also the Kriegers Flak Clay. Both of these clay units are probably present as dislocated rafts and lenses rather than as uniform in situ layers. An internal reflector within the LT unit (Horizon A) is intermittently observed across the site, in particular where the Holocene sediment cover is thin. When observed it is generally of a low amplitude and not easily discerned in the record. The horizon does mark a slight reduction in the intensity of the bounding units. KF_OWF_Geophysical_Survey_Results_v4.docx
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