The Sonne Cruise SO122 was carried out by the Federal Institute for Geosciences and Natural Resources (BGR, Hannover) from 3rd August to 9th September 1997, in cooperation with GEOMAR (Kiel), the National Institute of Oceanography (NIO, Karachi) and the Hydrocarbon Development Institute of Pakistan (HDIP). During the joint project with R/V SONNE the Makran accretionary wedge off Pakistan should have been investigated in detail with multi-channel reflection seismics, magnetics and gravimetry. Intense fishery offshore Pakistan forced a change of the area of investigation to the south with the following objectives: investigation of the crustal structure and occurrence of the bottom simulating reflector (BSR) in the Makran accretionary wedge; investigation of the structure of the Murray Ridge System in order to reconstruct the geodynamic evolution of the eastern Indian Plate margin; determination of the origin of the crust underlying the Indus Fan and reconnaissance of the sedimentary history of the Indus Fan in order to reveal the uplift and erosion history of the Himalayas.
On the F.S. POLARSTERN cruise ANT-IV/3 (6th December, 1985 - 13th March, 1986) multichannel seismic measurements were carried out in parallel with magnetic and gravimetric measurements on 33 lines with a total length of 6,263 km. 3,350 km of the multichannel seismic lines have been processed aboard. The geophysical studies were designed to investigate the structure and geological development of the Weddell Sea continental margin from meridians zero to 60°W, and to define suitable and safe drilling locations for Leg 113 of the Ocean Drilling Program. The main results of the geophysical studies are: (1) The discovery of an approximately N50°E trending failed drift basin, following the trend of a negative magnetic anomaly and a positive gravity anomaly. (2) The discovery of two extensive wedge-shaped and symmetric basement units around a failed drift basin between longitudes 40°W and 20°W. The seismic characteristics, i.e. seismic velocities of 4 km/s and an internally divergent pattern of reflectors suggest that both wedges are formed from extrusive/intrusive volcanic rocks. (3) The confirmation of a major plate tectonic boundary trending approximately N80°E to N60°E, i.e. the EXPLORA-ANDENES escarpment. (4) The confirmation of a glaciogenic progradational wedge beneath the shelf of the Weddell Sea Embayment, made up of several thousand metres of sediments. (5) The definition of 13 suitable and safe drilling locations for ODP-Leg 113.
On the M/V Akademic Nemchinow multichannel seismic measurements were carried out on 34 lines with a total length of 4,000 km. The area covered was the Laptev Sea. The data format is Society of Exploration Geophysicists SEG Y.
The structure and tectonics of the Pacific margin of Costa Rica were studied by multichannel seismic measurements in parallel with gravity measurements and swathmapping from the Cocos Ridge to Nicoya Peninsula during R/V SONNE cruise SO81 legs 1 and 2 from 18th August to 15th September 1992. In addition geological sampling has been carried out. Dominant structural feature is the buried Costa Rica Terrrane (CRT), a complex and segmented, wedge-shaped unit characterized by relative high seismic velocities of 4 km/s. The thickness of this several tens of kilometres wide zone varies between 0.5 and 3 s (twt). The CRT forms the backstop against which the sediments of the subducting Cocos plate accrete resulting in accumulation of sedimentary mass beneath and in front of the CRT, as well as in simultaneous uplift and fracturing of the CRT. It appears that the distinct CRT is affected locally by raft tectonics, i.e. a form of thin-skinned extension by normal faulting from gravity sliding over a non-stretched oceanic crust. A unit is recognizable between the base of the CRT and the surface of the subducting oceanic crust on most of the seismic lines. This unit is thought to consist mostly of ductile pelagic to hemipelagic shales. Some segment boundaries of the CRT are associated with morphological furrows, 5 to 10 km wide and up to 30 km long running across the slope. We feel that the data acquired during SONNE cruise SO81, and the preliminary results at hand have already improved our knowledge on the geological processes of active continental margins. We are convinced that plausible concepts for the origin of tsunamis and asperities can be developed on the basis of the data collected during SONNE cruises SO81 and SO76. The research of both SONNE cruises are a contribution to the International Decade of Natural Desaster Reduction (IPNDR).
The BGR Antarctic cruise 1996 from 29th December 1995 to 6th February 1996 with M.S. AKADEMIK NEMCHINOV was designed to acquire new marine geophysical data for a better understanding of the geological processes, timing, occurrence and location of rifts of the initial break-up of southern Gondwanaland. A total of 3,836 km of multichannel seismic reflection data have been collected in the areas of the Cosmonaut Sea, the Astrid Ridge, the Lazarev Sea and the southern Agulhas Plateau in parallel with magnetic and gravity measurements. In addition magnetic and gravity measurements were carried out on transit. Major new observations of the collected MCS data include: (1) Volcanic rocks play a major part in the construction of the Astrid Ridge and also of the Agulhas Plateau. (2) The early opening of the Lazarev Sea was associated with excessive volcanism resulting in the emplacement of a voluminous volcanic body characterized by an internally divergent pattern of seaward-dipping reflectors. (3) The Astrid Fracture Zone continues in form of a sediment-filled basement depression flanked by distinct basement highs into the Lazarev Sea, and apparently swings to the west parallel to the coast of Queen Maud Land. (4) The thickness of sediments in the Cosmonaut Sea overlying oceanic crust of inferred Early Cretaceous age is in excess of 4s (twt), i.e. about 6,000 m. Three regional seismic markers of inferred Cretaceous, Late Eocene-Oligocene and Middle Miocene ages subdivide the sedimentary column.
A geophysical reconnaissance survey was carried out in the Labrador Sea and Davis Strait between July and September 1977 by BGR. The data format is Society of Exploration Geophysicists SEG Y. The survey was executed on the research vessel MS Explora. The seismic, magnetic and gravity data from 5931 line-kilometers on 21 lines were recorded on magnetic tape. A 24-fold coverage technique was used with 48 seismic channels (traces), with a 2400m streamer cable, and 23.45 l airgun array. A full integrated computerized satellite navigation system (INDAS III) served as positioning system. Based on a preliminary interpretation of the seismograms, the Labrador Sea was devided into an eastern (Greenland) and western (Canadian) area, seperated by the Mid Labrador Ridge. Within the eastern part of the Labrador Sea the Pre-Cenozoic sediments show three distinct layers, traceable over the entire Greenland area of the sea. In the Cenozoic layer olisthostromes occur. The highest apparent velocity determined from sonobuoy data was 9.26 km/sec. The calculated refractor lies at a depth of approximately 13 km. The seismic section from the sediments on the Canadian side of the Labrador Sea show a uniform series of thick sediments below the Cenozoic cover. The highly disturbed basement is often masked by the multiple reflections from the seafloor. Statements about the nature and structure of the basement can only be made after processing data.
The Scientific staff and crew onboard CCGS Louis S. St. Laurent (LSL) returned September the 10th, 2001 from a scientific expedition to the Nares Strait, the northernmost waterway connecting the Arctic and Atlantic oceans. The data format is Society of Exploration Geophysicists SEG Y. The ice conditions in the strait required the support of Canada's largest ice breaker. The ship was a versatile platform for 34 scientists to accomplish their marine investigation. The LSL has a history of supporting international scientific expeditions including an oceanographic transect of the Arctic Ocean in 1994 and a biological study of the Canadian Arctic Islands in 1999. Germany (Bundesanstalt für Geowissenschaften und Rohstoffe, BGR) and Canada (Geological Survey of Canada) undertook a 5-week scientific cruise to study and explore the geological structure and evolution of the Nares Strait. The primary objective was the study of structural features relating to the formation of the Arctic Ocean and, in particular, the study of the Wegener Fault. This fault is a linear boundary between Greenland and Ellesmere Island which was noted by the German scientist Alfred Wegener in 1915 and later became the subject of a major scientific controversy. The co-operative cruise, which was planned over a period of 2 years, provided the basis for a wide range of scientific investigations, from marine seismic work and climate change studies through airborne magnetic investigations to geodetic survey measurements and geological sampling onshore. Systematic geophysical offshore studies in this key area had not been undertaken before. Where towing of seismic equipment was not possible because of ice coverage, magnetic maps were made using a helicopter-borne magnetic sensor system. Sediment and water samples taken during the cruise provide information on changes in climate and sea ice cover from the last ice-age to the present. An 11 m-long sediment core from outer Jones Sound is the longest core ever taken in the Canadian Arctic channels and holds clues to the detailed climate history of northern Baffin Bay.
The multidisciplinary marine geoscientific expedition ARK-25/3 was focused on the Greenland part of northern Baffin Bay and was aimed to acquire new geoscientific data to be used for modelling the evolution of the Greenland continental margin and its hydrocarbon prospective. The data format is Society of Exploration Geophysicists SEG Y. The cruise was performed under the direction of the Federal Institute for Geosciences and Natural Resources Hannover in cooperation with the Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven. Using 70 days of ship time onboard the research icebreaker R/V POLARSTERN a comprehensive data set was acquired along profiles extending from the deep oceanic basin in the central part of North Baffin Bay onto the Greenland continental margin in an area which was bordered by the Kane Basin in the North and Disko Island in the South. By means of multi-channel seismic, wide angle seismic, gravimetric and magnetic methods the structural inventory of the crust in the NW Baffin Bay was investigated. Additionally, heat flow data and sediment cores were collected along lines crossing the Greenland continental margin. The cores were extracted for geochemical and geomicrobiological analysis to be used for basin modelling, studying the hydrocarbon potential, and the hydrocarbon degradation by microorganisms under polar conditions. Geological sampling in the coastal area was done between Melville Bay and Washington Land. The collected rock material will be used to derive constraints on the erosion history of the coastal area. Aeromagnetic data was acquired covering a substantial part of the marine survey area to investigate magnetic signatures of the oceanic crust and the continental margin. This report summarizes the working programme and contains the documentation of acquired data and first results of the expedition.
In July/August 1988 a seismic reconnaisance survey was carried out with F.S. Polarstern on the perennially ice covered East Greenland shelf between latitudes 73°N and 81°N. The data format is Society of Exploration Geophysicists SEG Y. 14 reflection seismic lines with a total length of 2.016 km and 12 sonobuoy refraction profiles were recorded. The following results were obtained: •On the wide Holm Land shelf province north of 79°N three possible Cretaceous rift basins were observed. •A buildup of layered extrusive basaltic rocks forming a wedge of seaward dipping reflectors underlies the Holm Land continental slope. •On the Northeastern Greenland shelf province the existence of a wide sedimentary basin was demonstrated north of 76°N. •South of 76°N four volcanic structures from the continent to ocean were observed: The zone of Early Tertiary plateau basalts (zone I) that occur landward of an escarpment, a flat lying basaltic flow unit immediately seaward of the escarpment (zone II), an elongate wedge of seaward dipping reflectors (zone IIIa), a basaltic flow unit which in places shows seaward dipping beds of short length (zone IIIb), and the oceanic crust. •Dyke swarms and intrusions of inferred Neogene age were recognized at several locations.
In September 1993, the Federal Institute for Geoscience and Natural Resources (BGR) has carried out in cooperation with Sevmorneftegeofizika (SMNG), Murmansk a 2D-seismic survey of the eastern part of the Laptev Sea shelf. The data format is Society of Exploration Geophysicists SEG Y. During the survey with a total length of 3189 km the 70 km wide New Siberian Basin and two other basins were mapped. In the central part of the New Siberian Basin, a Tertiary sediment thickness of more than 4 km overlying older sediments was observed. Further to the east, a large area covered by lava flows of unknown thickness was investigated. There are no indications of a propagation of real seafloor spreading into the Laptev Shelf and thus the Asian continental crust. Therefore seafloor spreading seems impossible at total spreading rates below 0.7 cm/year, at least for crust of the character which is present here.
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