Concentric Impact Structures in the Paleozoic

Principal Investigators:
     Erik Sturkell, Gothenburg University, Sweden.
     Anette E.S. Högström, Tromsø University Museum, Norway.
     Jan Ove R. Ebbestad, Uppsala University, Sweden.

In 2009, CISP was one of two projects within the Swedish Deep Drilling Program (SDDP) that was granted funds for site investigations in the Swedish Research Council’s (VR) annual call for scientific projects.  The project received about 1/2 of the applied funding, for the period 2010 – 2012, although the funds were available until the end of 2013.
The main objectives of CISP have been fulfilled with great success (see summary under 2012), and has led to some quite revolutionary discoveries. The new facies distribution in the Siljan area revealed by Oliver Lehnert and his group and large scale tectonic implications should be mentioned.
As expected new research questions have arisen, and following the unsuccessful application to VR 2013 it was decided by the principal investigators, in understanding with co-workers, that future research under the umbrella of the new SSDP project should take different directions.
New proposals for pilot studies under CISP management will therefore not be made, and because the main objectives have been reached the CISP project is therefore declared ended. We, the principal investigators, are extremely thankful to everyone involved for their enthusiastic and engaging participation during these years. Even though CISP ceases, research will continue in the Lockne and Siljan craters, albeit regrouped and with different specific aims.

Large impact structures are a key to understanding a diverse set of scientific problems since they record essentials about the geological history where they occur. The ambition of CISP was to characterize the large Lockne and Siljan crater structures, with decisive features in common. The Siljan structure, the largest impact structure in Western Europe, and Lockne, which is the best accessible and studied impact formed in relatively deep sea, occurred at the supposedly Himalayan-type Caledonian mountain front in Sweden. Their development therefore expresses interaction between a gigantic over-thrust plate and Baltica through about 80 Ma. The most important apparent interaction was depressing Baltica’s west flank to form the trough where both craters formed. Another was tectonic stress that influenced shape and mineralization in the craters. It is all the more important to elucidate the less understood complications that can help to understand other craters. Major issues are the importance of basement lithology and structure, depth of water or sediment cover at the time of impact.
In addition to impact tectonics, the effect on life from the impact event can be studied in the Lockne area where records of post-impact re-colonization are found. The Siljan crater, with its renowned carbonate mud mounds, also contains unique sedimentological and palaeontological records preserved solely within the crater structure.

In 2009 CISP was one of two projects within the Swedish Deep Drilling Program (SDDP) that was granted funds for site investigations in the Swedish Research Council’s (VR) annual call for scientific projects.  The project received about 1/2 of the applied funding, for the period 2010 – 2012, although the funds were available until the end of 2013.
Dr. Erik Sturkell was the main applicant, with drs Jens Ormö (Centro de Astrobiología, Madrid, Spain), Christopher Juhlin (Uppsala University, Sweden), Reinhard O. Greiling (Karlsruhe Institute of Technology, Germany) and Anette Högström listed as co-workers. Administration of the project was handled by the principal investigators. The project was presented in the SDDP Science & Technology Plan in May 2010 (http://www.sddp.se/sciencetechnology), as well as in Högström et al. (2010).

Fig. 1 – Anette Högström sampling at the Nittsjö section 2010. Fig. 1 – Anette Högström sampling at the Nittsjö section 2010. The ditch was re-filled when sampling was done.

Objectives and progression
The initial objective of the VR-proposal in 2009 for the project CISP was to establish reliable geological parameters for the deeper drilling of the Lockne and Siljan impact structures under the SDDP umbrella (Högström et al., 2010a).
Planned analytical approaches towards reaching this objective were:

The Science and Technology Plan of SDDP lists 16 participants in CISP, which per 2011 was almost doubled.

2010
In the initial year 2010, a general paper was published in where the project was presented (Högström et al., 2010a). During the autumn, field work was undertaken in the Siljan area near Nittsjö. Here a new section was measured of the Lower Palaeozoic sediments with a basal contact to the precambrian granites (Högström et al., 2010b). The field work was financed from sources outside CISP. The principal investigators are Oliver Lehnert (Friedrich-Alexander University Erlangen-Nürnberg, Germany), Ebbestad, Högström and Åsa Frisk (Fig. 1). Field work was also undertaken in Siljan by Holly Stein and Judith Hannah from the AIRIE Program (http://www.airieprogram.org/) at Colorado State University in partnership with the Geological Survey of Norway. This work is in collaboration with Jan Ove R. Ebbestad. The aim was to sample hydrocarbons and shales to better understand Re-Os fractionation between oil and shale on maturation. The field work was financed through grant support to the AIRIE Program. Previous preliminary studies from AIRIE include Stein et al. (2009a, b, c) and Zimmerman et al. (2009). A drilling down to 147 m was made in the Målingen structure in Lockne 2009 and 2010. This is a possible satellite crater to Lockne. The drilling was undertaken with sources outside CISP. Other field work consisted of geophysical surveys (magnetometry and gravimetry; Fig. 2). Results related to this work and other studies in Lockne were presented at meetings and in publications (Ormö et al., 2010a-d).

Fig. 2 – Fieldwork in the Lockne crater and in the possible satellite crater at Målingen. Fig. 2 – Fieldwork in the Lockne crater and in the possible satellite crater at Målingen located 12 km outside the Lockne structure. A) Gravity measurements performed in the autumn 2011. B) The crystalline impact breccia (Tandsbyn Breccia). C) Drilling in the centre of Målingen structure in the summer 2010. D) The drill-core recovered in Målingen, the hole finally reached almost 150 m.

2011
The main work performed during 2011 was the completion of two seismic lines on the west side of the Siljan structure. The principal investigator was Christopher Juhlin (Uppsala), and the work financed by CISP. The first line was 9 km and placed in an east-west direction just north of Mora. The second line was 12 km and placed in a north-south direction north of Orsa (Fig. 3). Each profile penetrated to about 2 km, and a number of good reflectors are evident. The seismic profile is being interpreted, and this will be the most important tool in determining the position of a deep drill hole. During field work at Nittsjö 2010, Högström and Ebbestad came in contact with personnel from the company Igrene (http://www.igrene.se/). In June 2011 Igrene extended an invitation to study three drill cores they had taken up in connection with their prospecting. Each core was about 600 m, penetrating the Palaeozoic succession and the underlying basement. The cores were taken at Solberga, Stumsnäs and Mora (Fig. 4). Oliver Lehnert, Stig Bergström (Ohio State University, Columbus, USA) and Jan Ove R. Ebbestad made initial investigations of the cores, which turned out to be extremely interesting (see Igrene’s newsletter linked here).

Fig. 3 – Map of the Siljan structure with inset showing the position of the seismic lines. Fig. 3 – Map of the Siljan structure with inset showing the position of the seismic lines in A) Mora area and B) Orsa area.

During October 2011 Lehnert, together with Guido Meinhold (University of Göttingen, Germany), continued a detailed logging of the core, sampling in detail for isotope- and biostratigraphy, geochemistry, thermal maturity, sediment provenance studies, and sedimentology (including detailed facies/microfacies studies). It seems that a palaeogeographical high existed to the west in Siljan, with a hiatus above the Holen Limestone. Preliminary graptolite identifications point to Silurian deposits following the Darriwilian Holen Limestone. The principal investigator is Lehnert. This work has been partly financed by CISP (Fig. 5). 

Fig. 4 – Map of the Siljan structure indicating sedimentological distribution and the position of the Ordovician carbonate mounds. Fig. 4 – Map of the Siljan structure indicating sedimentological distribution and the position of the Ordovician carbonate mounds. The three Igrene drill sites are indicated. Transpression ridges superimposed following the suggestion by Kenkman & von Dalwigk (2000). Map modified from Ebbestad & Högström (2007).

Holly Stein and Judith Hannah from the AIRIE Program at Colorado State University sampled the cores for Re-Os analyses (Fig. 5). The intent was to sample both hydrocarbon and the Fjäcka and Kallholn shales. No hydrocarbon of quantity suitable for sampling was found. Several sections of Fjäcka were sampled from Solberga #1 and Stumsnäs #1. The former contains a reddish brown shale, whereas the Stumsnäs is a black shale and is more promising for Re-Os geochemistry. A starter industry-based grant to look at Re-Os fractionation in oil and shale has been secured by Stein and Hannah. A second proposal pending with NSF will augment the industry-based study by building a picture of stratigraphic ages in the Siljan region for linking with the greater CISP geoscience community (Ebbestad is the primary external collaborator). The first Re-Os results on drill core demonstrate success. A supplementary contribution of CISP funds for the Re-Os study would strengthen efforts by Stein and Hannah to raise funds external to Sweden. 

Fig. 5 – Study and sampling of the Igrene cores. Fig. 5 – Study and sampling of the Igrene cores. A) Stig Bergström and Oliver Lehnert studying core sections, June 2011. B) Oliver Lehnert and Guido Meinhold sampling the Mora 1 core. October 2011. C) Judith Hannah, Mats Budh, Holly Stein and Paul Storm discussing geology. October 2011. D) The Igrene core storage, June 2011. All photos by Ebbestad.

During 2011 geophysical investigations have continued in the Lockne area, and field reconnaissance have been made to determine the location for two shallow drillings (50-60 m) to investigate the structural composition around the so called Tandsbyn Gully. A number of reports and papers related to the Lockne structure has been published (Asensio et al., 2011; Broman et al., 2011; Melero Asensio et al., 2011a-d, Ormö et al., 2011a, b). 

2012
One of the main objectives of the application to the Swedish Research Council in 2012 was to acquire reflection seismics in the Siljan area, and this has been achieved (Juhlin et al. 2012). Other analytical approaches like shallow geophysics (resistivity and gravity in Lockne) and AMS studies (anisotropy of magnetic susceptibility) on basement rocks (Melero Asensio et al. 2011a-e; Ormö et al. 2010a-d; Ormö et al. 2011a, b; Agarwal et al. 2012), study of fluid inclusions to determine composition of the fluids and constrain temperature and pressure conditions in shear zones relate to the cratering (Broman et al. 2011), and shallow drilling (Ormö et al. 2010c; Lehnert et al. 2012a-e) have also been fulfilled, analyses are still in progress on the wealth of data gathered. A new application for additional work was submitted in spring 2012. Despite a favourable review, this project was unfortunately not funded. Thus, major work on CISP will be suspended at the end of the year until further funding can be secured. We will try to keep continuity in the scientific work at a low level with remaining funds from the 2011 grant.

Below is a summary of activities:

The Siljan area

The Lockne area

Fig. 6 – Fieldwork 2012. Fig. 6 – Field work in the Lockne area 2012. A) Inspection of the railroad profile just west of the Ynntjärnen Lake, this locality displays three different breccias formed during the impact and directly after it. Large clasts of ejected crystalline impact breccia (Tandsbyn Breccia), the impact breccia in the sedimentary sequence (Ynntjärn Breccia), the coarse resurge breccia (Lockne Breccia) and the fine grained (finale) resurge deposits (Loftarstone). B) Drilling near Tandsbyn in the beginning of November 2012. C) The graduate student Irene with the gravimeter on a small island in the Näckten Lake. All photos by Sturkell.

General

2013
The original CISP project was stipulated to run between 2009 and 2012, with a proposal for continued studies of the Siljan and Lockne craters to determine the best position of deep coreholes was submitted to VR during the spring. Unfortunately, the proposal was turned down. Nevertheless, 2013 saw a number of new publications and continued studies on both craters.

2014
Presentations of results at several meetings, including the Nordic Geological Winter Meeting in Lund, where also the principal investigators made the executive decision to declare the scope of CISP fulfilled and develop further studies of the two craters independently.

Below is a summary of activities (2013-2014).

Lockne

Fig. 7 – Simplified geological mapFig. 7 – A simplified geological map of the Lockne crater, with the three-resistivity profiles made during the summer 2013.

The field activity in the Lockne crater (and surroundings) and its doublet crater the Målingen structure was performed in July, by the Madrid, Gothenburg and Karlsruhe groups. The Madrid and Gothenburg groups worked together with the following sub-projects:

Fig. 8 – Field measurementsFig. 8 – Eric Hegardt with the resistivity instrument at profile 1.
Fig. 9 – Geological mapFig. 9 – Geological map of the Lockne area with location of the suspected Proterozoic shear zone (black line), sample locations for 2012 and 2013 sampling campaigns (map kindly provided by E. Sturkell, University of Gothenburg).

Work done on Lockne Crater in 2013 by Greilings group
The aim of this year’s study was to further increase our understanding of the effects of impact cratering on microstructural and rock magnetic properties of the target crystalline basement rocks. Orientated hand samples from the crystalline basement rocks (metavolcanic, granite and dolerite) were collected during field work in summers of 2012 and 2013 (Fig. 9). At least five cores were drilled from each hand sample for anisotropy of magnetic susceptibility (AMS) studies. Magnetic mineralogical studies like temperature dependent magnetic susceptibility (?-T), isothermal remnant magnetisation (IRM) acquisition, hysteresis and back field were also performed. Polished thin sections were prepared along the magnetic foliation and in a direction perpendicular to it for investigating effects of impact on microscopic scale. These investigations were performed under transmitted and reflected light microscopy and scanning electron microscopy (SEM). In order to identify the magnetic minerals, the thin sections were coated with a ferrofluid (produced by Institut für Angewandte Polymerchemie, FH Aachen), which is a colloidal solution of ultrafine magnetite particles. This ferrofluid sticks on the grains that generate a magnetic field giving them a brownish red colour. SEM studies were carried out with LEO 1530 of Gemini instrument and the secondary (SE) and backscattered (BSE) electrons were recorded along with energy-dispersive X-ray spectroscopy (EDX) for a qualitative elemental analysis.

From our studies so far we can conclude that the metavolcanics have the highest P’ (magnetic anisotropy) and magnetic susceptibility but lack any impact related deformational structures. AMS fabrics of these metavolcanics do not show any impact overprint. The granites have the lowest P’ and magnetic susceptibility and the magnetic fabrics are carried entirely by paramagnetic phases. They have microfabrics indicating some recrystallization of the quartz subfabric, which should have resulted in higher P’. We conclude that the low P’ in granite is due to impact related fracturing on a microscale. The dolerites have shallow dipping magnetic foliations and kmax axis, which is interpreted as a magmatic fabric. They have not suffered any post magmatic ductile deformation. Impact related brittle microfracturing is observed in granites and dolerites. These microfractures have two subsets. While the first subset is radial to the impact crater the other is concentric, similar to those developed in impact cratering experiments. Unlike the experimental studies, where radial fractures are more frequent than the concentric fractures outside the crater rim, our results show that in the Lockne area both radial and concentric micro-fractures are equally frequent.

Based on the results an abstract titled ‘Evolution of magnetic fabrics before and after the impact in the Lockne Crater, Sweden.’ has been published in Geophysical Research Abstracts. Vol. 15, EGU 2013-622, 2013. EGU General Assembly 2013. And a manuscript titled ‘Effects of cratering on crystalline target rocks: microstructural and magnetic fabric studies in the Lockne impact crater’ has been submitted in Geological Magazine.

Siljan crater

Fig. 10 – At the core storageFig. 10 – Guido Meinhold in the core storage of Igrene AB in Mora, logging.
Fig. 11 – At the core storageFig. 11 – Oliver Lehnert in the core storage of Igrene AB in Mora, taking sediment samples for geochemical analyses.

 Current research in the ‘Siljan Ring’:
To support our hypotheses on the geodynamic evolution of the Siljan area in the frame of the Caledonian foreland basin development we have started studies on geochemistry and biomarkers in the organic-rich, fine-grained Upper Ordovician and Silurian siliciclastics. This will be completed by palynofacies research in the Silurian units in the near future (Vivi Vajda and Kristina Mehlqvist, Lund) to distinguish between marine conditions and brackish to lacustrine environments at certain times.

A publication of the biogeochemistry results is in preparation by Ulrich Berner (Statoil, Bergen, Norway), O. Lehnert and G. Meinhold. The geochemical data from Solberga 1 suggesting ‘lacustrine’ to brackish and marine palaeoenvironmental conditions for the Silurian shales are comparable to biomarker data from samples of crude oil and bitumen stored in large pores and vugs in the Ordovician carbonate succession (with the bulk concentrated in the voids in the Upper Ordovician mound facies) in the eastern part of the Siljan Ring (Ahmed et al. 2014). This recent study on seep oil and bitumen also displays different source characteristics for these hydrocarbons expelled from the Lower Palaeozoic shales and confirms that the Upper Ordovician and Silurian organic-rich sediments represent the source rock for oil and bitumen in the Siljan Ring. Biomarker studies showing lacustrine to brackish conditions for the sedimentation of the younger Silurian siliciclastic succession in the Mora area clearly support a depositional model for these deposits in a backbulge basin of the Caledonian foreland basin system.

A set of papers on stable isotope, K-bentonites, sedimentological and biostratigraphic studies is in preparation by Oliver Lehnert and Guido Meinhold and their cooperation partners.

Future studies in the Siljan crater:
Europe’s largest impact structure and its fill is not yet well studied and understood. Many questions arose from our investigations in the framework of CISP and some ideas on sedimentological models developed. The timing of the development of the backbulge basin formation, a tracing of the forebulge in the area and effects of the Caledonian movements in the sedimentary record of the platform to the east (regional vs global sea-level changes) still need to be investigated. Detailed investigations of additional drill cores are essential with respect to the understanding of the geological history along the western margin of Baltica. A detailed stratigraphic framework is needed for the comparison of geodynamic processes related to the Ordovician foreland basin evolution in this area with the record in the Föllinge Basin to the northwest in Jämtland and the Oslo Region, Norway, to the southwest.
A team conducted by Mikael Calner, Oliver Lehnert, Chris Juhlin, Jan Ove Ebbestad and Guido Meinhold is planning to propose a new drilling project in connection with a shallow seismic program focussed on the Siljan impact structure in 2015 under the framework of SSDP.

 

 

The CISP working group

Logotypes of participating institutes and companies.

Prof. Erik Sturkell, Gothenburg University, Sweden.
Dr. Anette S.E. Högström, Tromsø University Museum, Norway.
Prof. Stig M. Bergström, The Ohio State University, USA.
Dr. Mikael Calner, Lund University, Sweden.
Dr. Jan Ove R. Ebbestad, Uppsala University, Sweden.
Dr. Oliver Lehnert, Friedrich-Alexander University Erlangen-Nürnberg, Germany.
Dr. Jens Ormö, Centro de Astrobiología, Madrid, Spain.
Prof. Christopher Juhlin, Uppsala University, Sweden.
Prof. Reinhard O Greiling, Karlsruhe Institute of Technology, Germany.
Dr. Gudio Meinhold, Göttingen University, Germany.
Prof. Holly Stein, Colorado State University, USA.
Prof. Judith Hannah, Colorado State University, USA.
Dr. Jörg Maletz, Frei University Berlin, Germany.
Prof. Lars Holmer, Uppsala University, Sweden.
Prof. Risto Kumpulainen, Stockholm University, Sweden
Dr. Paula Lindgren, Stockholm University, Sweden.
Prof. Warren Huff, University of Cincinnati, USA.
Prof. Sven Egenhoff, Colorado State University, USA.
Dr. Arne Thorshøj Nielsen, Natural History Museum of Denmark.
Dr. Yutaro Suzuki, Shizuoka University, Japan.
Dr. Olga Bogolepova, CASP, England.
Dr. Jaak Nolvak, Tallinn University, Estland.
Dr. Thijs Vandenbroucke, Gent University, Belgium.
Dr. Åsa. M. Frisk, Zurich University, Switzerland
Dr. Arzu Arslan, Göttingen, Germany
Dr. Ulrich Berner, Bundesanstalt für Geowissenschaften und Rohstoffe, Hannover, Germany

 

References

Ahmed, M., Lehnert, O., Fuentes, D., Sestak, S., Meinhold, G. & Gong, S. 2012. Biomarker evidence for the origin of seep oil and solid bitumen from the Late Devonian Siljan impact structure, Sweden. 17th Australian Organic Geochemistry Conference: Biogeochemistry from Deep Time through Petroleum Resources to Modern Environments. Abstract. Macquarie University, Sydney, New South Wales, Australia, 2nd - 5th December 2012.

Agarwal, A., Lied, P., Srivastava, D., Kontny, A., & Greiling, R. 2013. Evolution of magnetic fabrics before and after the impact in the Lockne Crater, Sweden. Geophysical Research Abstracts 15, EGU General Assembly 7–12 April, Vienna.

Angerer, T. & Greiling, R. 2012. Fabric evolution at basement–cover interfaces in a fold-and-thrust belt and implications for de´collement tectonics (Autochthon, Lower Allochthon, central Scandinavian Caledonides). International Journal of Earth Sciences (Geolgische Rundschau) 101, 1763–1788.

Arslan, A., Meinhold, G. & Lehnert, O., 2013. Tectonic structures in the Stumsnäs 1 core from the southern Siljan Ring, central Sweden: Ordovician sediments sandwiched between Proterozoic basement slivers. GFF, doi: http://dx.doi.org/10.1080/11035897.2013.809016.

Arslan, A., Meinhold, G., Lehnert, O., 2013. Tectonic structures in the Stumsnäs 1 core of the southern Siljan Ring, south-central Sweden. – Insights from Geochemistry. IODP/ICDP Colloquium, Freiberg, Germany, 25th – 27th March 2013. Abstractband: 27-28.

Asensio, I., Martín-Hernández, F., and Ormö, J., 2011. Evidence of ferrichromite of extraterrestrial origin by means of rock magnetic studies from the Loc-9 drill core (Lockne crater, Sweden). American Geophysical Union Fall Meeting, 5-9 December, San Francisco, USA.

Berner, U., Lehnert, O. & Meinhold, G., 2013a. Fluid Migration in Ordovician and Silurian Rocks of the Siljan Impact Structure (Sweden) – Insights from Geochemistry. IODP/ICDP Colloquium, Freiberg, Germany, 25th – 27th March 2013. Abstractband: 40-41

Berner, U., Lehnert, O. & Meinhold, G., 2013b. Hydrocarbon potential of Ordovician and Silurian rocks, Siljan Region, Sweden. DGKM Meeting, Abstract. Celle, Germany, 18th – 19th April 2013.

Berner, U., Lehnert, O. & Meinhold, G., 2013c. Depositional environments of Ordovician and Silurian sediments of the Siljan impact structure (Sweden) – Insights from organic geochemistry. In Lindskog, A. & Mehlqvist, C. (eds): Proceedings of the 3rd IGCP 591 Annual Meeting – Lund, Sweden, 9-19 June 2013: 47-48; Lund University.

Broman, C. Sturkell. E. & Fallick, A.E. 2011. Oxygen isotopes and implications for the cavitygrown quartz crystals in the Lockne impact structure, Sweden, GFF 133, 101-107.

Ebbestad, J.O.R  & Högström, A.E.S. 2007. Ordovician of the Siljan District, Sweden. In Ebbestad, J.O.R., Wickström, L.M. & Högström, A.E.S. (eds.) WOGOGOB 2007. 9th meeting of the Working Group on Ordovician Geology of Baltoscandia. Field guide and Abstracts. SGU Rapporter och meddelanden 128, 7-26.

Högström, A.E.S., Sturkell, E., Ebbestad, J.O.R., Lindström, M., and Ormö, J., 2010a. Concentric Impact Structures in the Palaeozoic of Sweden – the Lockne and Siljan craters. GFF 132, 65–70.

Högström, A.E.S., Ebbestad, J.O.R. & Frisk, Å.M. 2010b. Om ett dike i Siljansringen ur ett historiskt klimatperspektiv. Geologiskt Forum 68, 20–23.

Huff, W., Lehnert, O. & Meinhold, G., 2013a. Paleozoic K-bentonites in drill cores from the Siljan impact structure. In Lindskog, A. & Mehlqvist, C. (eds): Proceedings of the 3rd IGCP 591 Annual Meeting – Lund, Sweden, 9-19 June 2013: 132-134; Lund University.

Huff, W., Lehnert, O. & Meinhold, G., 2013b. Paleozoic K-bentonites in drill cores from the Siljan impact structure, Sweden. Geological Society of America, Abstracts with Programs; Boulder.

Juhlin, C., Sturkell, E., Ebbestad, J.O.R., Lehnert, O., Högström, A. E. S. & Meinhold, G. 2012: A new interpretation of the sedimentary cover in the western Siljan Ring area, central Sweden, based on seismic data. Tectonophysics Onlinedoi>10.1016/j.tecto.2012.08.040

Kenkmann, T. & von Dalwigk, I., 2000: Radial transpression ridges: A new structural feature of complex impact craters. Meteoritics and Planetary Science 35, 1189–1202.

Lehnert, O., Meinhold, G. Bergström,  S.M., Calner, M. Ebbestad, J. O. R., Egenhoff, S. Frisk, Å.M., Högström, A.E.S. & Maletz. J., 2012a. The Siljan Meteorite Crater in central Sweden – an integral of the Swedish Deep Drilling Program (SDDP). ICDP (International Continental Scientific Drilling Program) DFG Schwerpunktkolloquium, March, 7 - 9. Abstracts: 102-103; Geomar (Kiel, Germany).

Lehnert, O., Meinhold, G. Bergström,  S.M., Calner, M. Ebbestad, J. O. R., Egenhoff, S. Frisk, Å.M., Högström, A.E.S. & Maletz. J,.  2012b. The Siljan Ring in central Sweden - a window into the Palaeozoic history of Baltoscandia. General Assembly 2012 of the European Geosciences Union (EGU), Vienna, Austria, 22 – 27 April 2012.

Lehnert, O., Meinhold, G. Bergström,  S.M., Calner, M. Ebbestad, J. O. R., Egenhoff, S. Frisk, Å.M., Högström, A.E.S. & Maletz. J.,  2012c. The Siljan Impact Structure - an important integral for reconstructing the early Palaeozoic history of Baltoscandia. GV and SEDIMENT Meeting September 23-28, 2012, Hamburg.

Lehnert, O., Meinhold, G., Bergström, S.M., Calner, M., Ebbestad, J.O.R., Egenhoff, S.,  Frisk, Å.M., Hannah, J.L., Högström, A. E. S., Huff, W.D., Juhlin, C., Maletz, J., Stein, H.J., Sturkell, E. & Vandenbroucke, T.R.A. 2012d: New Ordovician-Silurian drill cores from the Siljan impact structure in central Sweden an integral part of the Swedish Deep Drilling Program. GFF 134, 87–98.

Lehnert, O., Meinhold, G., Arslan, A., Ebbestad, J.O.R. & Calner, M., 2013. Ordovician stratigraphy and sedimentary facies of the Stumsnäs 1 core from the southern Siljan Ring, central Sweden. GFF, DOI: http://dx.doi.org/10.1080/11035897.2013.813582.

Lehnert, O., Meinhold, G., Arslan, A., Berner, U., Calner, M., Huff, W.D., Ebbestad, J. O., Joachimski, M. M., Juhlin, C. & Maletz, J., 2013. The Siljan impact structure of south-central Sweden: an unique window into the geologic history of western Baltoscandia. IODP/ICDP Colloquium, Freiberg, Germany, 25th – 27th March 2013. Abstractband: 120-123.

Lehnert, O., Calner, M., Ahlberg, P., Ebbestad, J. O. R., Harper, D.A.T & Meinhold, G., 2013. Palaeokarst formation in the early Palaeozoic of Baltoscandia – evidence for prominent sea-level changes in a shallow epicontinental sea. In Lindskog, A. & Mehlqvist, C. (eds): Proceedings of the 3rd IGCP 591 Annual Meeting – Lund, Sweden, 9-19 June 2013: 169-171; Lund University.

Meinhold, G., Wengler, M. & Lehnert, O., 2013. Geochemical comparison of Silurian sandstones from the Mora 001 core of the Siljan Ring structure with the Mesoproterozoic Dala Sandstone Formation of central Sweden. In Lindskog, A. & Mehlqvist, C. (eds): Proceedings of the 3rd IGCP 591 Annual Meeting – Lund, Sweden, 9-19 June 2013: 214-216; Lund University.

Melero Asensio, I., Martín-Hernández, F., and Ormö, J., 2011a. Rock-Magnetic Properties of Drill Core LOC-9 from the Lockne Crater, Sweden. LPS XLII. Houston, USA. #1463

Melero Asensio, I., Martín-Hernández, F., and Ormö, J., 2011b. Rock magnetic properties of drill core LOC-9 from the Lockne crater, Sweden. European Geosciences Union General Assembly, 3-8 April, Vienna, Austria. #9131.

Melero Asensio, I., Ormö, J., and Sturkell, E., 2011c.Preliminary Geophysical Survey of the Målingen Structure, Sweden. LPS XLII. Houston, USA. #1542

Melero Asensio, I., Ormö, J., and Sturkell, E., 2011d. Preliminary geophysical survey of the Malingen structure, Sweden. European Geosciences Union General Assembly, 3-8 April, Vienna, Austria. #9148.

Melero Asensio, I., Ormö, J., and Sturkell, E., 2011e. Geophysical survey of the proposed Målingen marine-target crater, Sweden. Fragile Earth - Geological Processes from Global to Local Scales and Associated Hazards, 4-7 September, Munich, Germany.

Ormö, J., Hill, A., and Self-Trail, J.M. 2010a. A chemostratigraphic method to determine the end of impact related sedimentation at marine-target impact craters (Chesapeake Bay, Lockne, Tvären).  Meteoritics and Planetary Science 45, 1206–1224.

Ormö, J., Sturkell, E., and Lepinette, A., 2010b. Geological and numerical evidence for a crater bound sedimentary impact breccia lining the basement crater at the Lockne impact structure. LPS XLI. Houston, USA.

Ormö, J., Sturkell, E., Melero Asensio, I., and Frisk, Å., 2010c: Preliminary results from the 2009 and 2010 core drillings of the Målingen structure, a probable doublet to the Lockne marine-target impact crater, central Sweden. Geological Society of America Annual Meeting, Denver, USA.

Ormö, J., Lepinette, A., Sturkell, E., Lindström, M., Housen, K.R., and Holsapple, K.A. 2010d. Water resurge at marine-target impact craters analyzed with a combination of low-velocity impact experiments and numerical simulations” In: R.L., Gibson, and W.U., Reimold (Eds.) “Large Meteorite Impacts and Planetary Evolution IV”. Geological Society of America Special Paper 465, 81–101.

Ormö, J., King, D. T., Jr., Sturkell, E., and Lepinette, A., 2011a. Catastrophic water movements at marine impact events. Fragile Earth - Geological Processes from Global to Local Scales and Associated Hazards, 4-7 September, Munich, Germany.

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Stein, H., Yang, G., Hannah, J.L., Zimmerman, A., and Egenhoff, S., 2009b. Re-Os fractionation on instantaneous maturation at the Siljan meteorite impact site, central Sweden: Geochimica et Cosmochimica Acta, v. 73, no. 13, p. A1268.

Stein, H., Zimmerman, A., Yang, G., Hannah, J., and Egenhoff, S. (2009) Hydrocarbon maturation and Os mixing on bolide impact at the Frasnian-Famennian boundary: Geophysical Research Abstracts, v. 11, European Geosciences Union (EGU), EGU2009-11085-1 (electronic).

Zimmerman, A., Yang, G., Stein, H.J., Hannah, J.L., and Egenhoff, S. (2009) Out of this world crude oil – separating meteoritic and hydrocarbon Re-Os components:  Geochimica et Cosmochimica Acta, v. 73, no. 13, p. A1536.