New Ordovician–Silurian drill cores from the Siljan impact structure in central Sweden: an integral part of the Swedish Deep Drilling Program

Analysis of borehole geophysical data from the Mora area of the Siljan Ring impact structure, central Sweden

“…We have used this as a basis for correlating the log response to lithology in the borehole (in some Igrene AB documents referred to as the Vattumyra 1 borehole) and use the results of this correlation for interpretation of the log response in the other three boreholes that were logged. After shifting the lithological column of Lehnert et al (2012) upwards by 5 m there is an excellent correlation between the natural gamma log and the core. The reason this shift is required is most likely due to different definitions of depth between the logging data and the core data.…”

“…The studies by Lehnert et al (2012) on the new Igrene AB drill cores have dramatically changed the established stratigraphic view of the successions within the ring. Their studies show that several facies belts existed, rather than the classical Ordovician carbonate succession separated by a stratigraphic gap from the Silurian shale dominated sequence.…”

“…4, for correlating the geophysical log response to the lithology. In that description the uppermost core consists of 47.8 m (taking into account the core description started at 14 m below the surface in Lehnert et al (2012)) of calcareous mudrock underlain by 36.6 m of shale. Below this a 27.2 m thick sandstone unit is present that is underlain by a 7.7 m thick layer of siltstone.…”

“…As stated earlier, we have used the core description of Lehnert et al (2012) from the Mora 001 borehole, shown in Fig. 4, for correlating the geophysical log response to the lithology.…”

“…Detailed descriptions of it can be found in the literature (e.g. Svensson, 1971Svensson, , 1973Wickman, 1981;Johansson, 1984;Grieve, 1988;Kenkmann and von Dalwigk, 2000;Reimold et al, 2004Reimold et al, , 2005Henkel and Aaro, 2005;Holm et al, 2011;Jourdan et al, 2012;Lehnert et al, 2012). It contains a central uplift that is about 20-30 km in diameter and is surrounded by a ring-shaped depression.…”