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edicated to: My dear daughter Irina List of Papers This thesis is based on the following papers, which are referred to in the text by their Roman numerals. I Langinen A.E., Gee D.G., Lebedeva-Ivanova N.N. and Zamansky Yu.Ya. (2006). Velocity Structure and Correlation of the Sedimentary Cover on the Lomonosov Ridge and in the Amerasian Basin, Arctic Ocean. in R.A. Scott and D.K. Thurston (eds.) Proceedings of the Fourth International confer- ence on Arctic margins, OCS study MMS 2006-003, U.S. De- partment of the Interior, 179–188. II Langinen A.E., Lebedeva-Ivanova N.N., Gee D.G., Zamansky Yu.Ya. (2009). Correlations between the Lomonosov Ridge, Marvin Spur and adjacent basins of the Arctic Ocean based on seismic data. Tectonophysics, doi: 10.1016/j.tecto.2008.05.029. III Lebedeva-Ivanova N.N., Zamansky Yu.Ya., Langinen A.E., Sorokin M.Yu. (2006). Seismic Profiling across the Mendeleev Ridge at 82°N: Evidence of Continental Crust. Geophys. J. Int., 165, 527–544. IV Lebedeva-Ivanova N.N., Gee, D.G., Sergeyev M. Crustal structure of the East Siberian Continental Margin, Podvodnikov and Makarov basins based on wide-angle seismic data (TransArctic 1989–1991). Memoir series of the Geological Society of London "Arctic Petroleum Geology". (accepted) Reprints have been made with permission from the respective publishers. Contents Introduction...................................................................................................11 Outline of the thesis .................................................................................12 2. Background information about the Arctic Ocean....................................13 2.1 Morphology......................................................................................14 2.2 Gravity field data .............................................................................14 2.3 Magnetic field data ..........................................................................14 2.4 Previous research of the Amerasia Basin and the Lomonosov Ridge................................................................................................16 Seismic research...............................................................................16 Another geophysical experiment in the central Arctic...................19 Sampling of the bedrock and sedimentary cover ...........................19 2.5 The tectonic evolution of the Arctic Basin - different scenarios ...20 3. Methods....................................................................................................25 3.1 Seismic acquisition, data processing and modelling techniques......25 North Pole – 28 (NP-28) reflection seismic data (Paper II).............25 TransArctic 1989–1992 projects (Paper I and IV)...........................27 Arctic–2000 project (Paper III)........................................................32 HOTRAX seismic data over the central part of the Lomonosov Ridge........................................................................................32 3.2 Resolution and accuracy of seismic data and modelling ................38 Resolution and accuracy of reflected arrivals ..................................38 Estimation of the resolution and accuracy in refraction seismic.....40 4. Summary of Papers ..................................................................................49 Paper I: Velocity Structure and Correlation of the Sedimentary Cover on the Lomonosov Ridge and in the Amerasian Basin, Arctic Ocean. ..............................................................................................49 Paper II: Correlations between the Lomonosov Ridge, Marvin Spur and adjacent basins of the Arctic Ocean based on seismic data.......51 Paper III: Seismic Profiling across the Mendeleev Ridge at 82°N: Evidence of Continental Crust. ........................................................54 Paper IV: Crustal structure of the East Siberian Continental Margin, Podvodnikov and Makarov basins based on refraction seismic data (TransArctic 1989–1991). .......................................................56 5. The central part of the Lomonosov Ridge (HOTRAX) – first view ........59 The surrounding ridges ............................................................................59 The Intra Basin.........................................................................................63 6. Sampling the sedimentary cover and bedrock of the Arctic Basin. .........65 Summary in Swedish ....................................................................................72 Acknowledgments.........................................................................................74 References.....................................................................................................76 Abbreviations ACEX the Arctic Coring Expedition (IODP, Leg 302) AWI Alfred Wegener Institute bsl below sea level CMP common mid-point CDP common depth-point HOTRAX Healy-Oden Trans Arctic Expedition Hz Hertz, frequency units IBCAO International Bathymetric Chart of the Arctic Ocean IODP Integrated Ocean Drilling Program MCS multi channel seismic Moho Mohorovicic discontinuity ms milliseconds NMO normal moveout NP the ‘North Pole’ drifting ice-stations P-waves primary (compressional) waves RMS root-mean square s seconds SCICEX SCience ICe EXercises research program by U.S. Navy submarines S/N signal to noise S-waves secondary (shear) waves TRA shortening of the TransArctic project TWT two way travel time Figure 1 Introduction The Arctic Basin is one of the least explored regions on Earth, mainly due to thick multi-year ice cover. At the same time, it is enigmatic, complicated, largely unexplored and therefore debatable area, with considerable economic potential. That's why it is so attractive for research. The Arctic Basin is divided into the Eurasia and Amerasia basins, sepa- rated by the Lomonosov Ridge (Figure 1). The origin of the Eurasia Basin by sea-floor spreading is supported by a broad range of evidence and is not a subject for big debates. The origin of the Amerasia Basin still provides more questions than answers. The reflection and refraction seismic investigations, presented in this thesis, are mainly located in the Amerasia Basin and the central part of the Lomonosov Ridge (Figure 1). The Soviet NP–28, TRA(b), TransArctic 1989–1991 and Russian Arctic– 2000 reflection seismic research from drifting ice define the general charac- ter of the sedimentary cover over a large area of the Arctic Basin (Papers I and II). In addition, long-offset reflection seismic observations along the TRA(b) profiles provide information about the P-velocity characteristics of the sediments (Paper I). The main sedimentary units were identified over the research area based on these reflection seismic data. Available geological evidence from the Arctic margins and the results of the ACEX drilling of sediments on the central part of the Lomonosov Ridge allowed an estimation of the ages and composition of the identified sedimentary units. The interpretation of the Arctic–2000 (Paper III) and re-interpretation of the TransArctic 1989–1991 (Paper IV) refraction seismic data have been used for constraining models of the crust down to the mantle. These refrac- tion seismic data do not provide information about the low-velocity sedi- mentary units, but the interpretation of the refracted waves is strongly de- pendent on the latter. Therefore, incorporation of the sedimentary structure, defined by the reflection seismic research, was essential for the presented modelling. For interpretation of the derived crustal models, potential field data and geological evidence have also been incorporated. The HOTRAX expedition acquired reflection seismic data over the cen- tral part of the Lomonosov Ridge in 2005. The obtained seismic sections, included in this summary, illustrate the sedimentary cover and intra-crustal Figure 1. Bathymetric map of the Arctic Ocean and location of the seismic research presented in this thesis. TRA 89-92 (TransArctic project) and Arctic-2000 are crustal scale refraction seismic profiles. The TRA 90&91 and Arctic-2000 are also reflection seismic profiles as are NP-28, TRA(b), and HOTRAX. 11 reflectivity over an internal basin and surrounding ridges. Together with the ACEX results and sonobuoy velocity data, an interpretation of the tectonic history of this area has been suggested. Outline of the thesis Before summarizing the main aspects of the thesis research, general descrip- tions of the morphology