During the period from 1974 to 2018 various cruises from BGR acquired seismic lines worldwide. The aim of these marine expeditions was a detailed survey of the geological structure.
The expedition PS155/1 started on August 5th, 2018 in Tromsø (Norway) and ended in Longyearbyen (Spitsbergen) on September 3rd, 2018. In the course of BGR’s GREENMATE project the geological development of the European North Atlantic and the northern and north eastern Greenland shelf was analyzed using various marine geophysical methods (seismics, magnetics, gravity, heatflow measurements) and geological sampling (gravity corer, box corer, multi-corer, dredge). Sampling of marine Shelf sediments was undertaken in close correspondence with co-users from Geomar (add-on project ECHONEG), aiming to reconstruct Holocene paleo environmental and climatic evolution. Using the ship’s helicopters, marine sampling was complemented by onshore sampling operations to extract geological material at selected near coastal locations. Other scientific project groups used the cruise PS115.1 as an opportunity to quantify marine mammals and sea birds and their statistical distribution in our research area as part of the long-term project (add-on project Birds& Mammals) and to gather additional meteorological data via radiosondes (add-on Project YOPP). Against all expectations, outstanding ice conditions along the northern coast of Greenland enabled us to carry out reflection seismic surveys north of 84°N at the southern tip of Morris Jesup Rise with a 3 km long streamer. Structural data of this particular region of North Greenland is of special importance for BGR’s project GREENMATE for reconstructing the continental margin evolution. A 100 km long refraction seismic profile was measured to complement the reflection seismic data. After completing this, scientific work was concentrated on the northeastern Greenland shelf area between 76°N and 82.5°N. Over the time of the cruise a total of 2500 km of reflection seismic profiles (2250 km measured with 3km streamer length) and 100 km of refraction seismic profile (using nine ocean bottom seismometers) were measured, accompanied by gravity and magnetic surveys and seven heat flow measurement stations. Along the shelf and deep-sea area 21 geological sampling sites were chosen, with all together one dredge (around 200 kg of sample), 16 gravity cores (total core length 65 m), 12 box corers and 6 multi-corer stations. Onshore sediment sampling was done at 11 sampling sites. Beside sediment sampling hard rock from near coastal outcrops was collected in a total amount of 250 kg that will be used for age dating. The entire science program was carried out under consideration of the highest ecological standards to protect marine mammals and to meet all environmental requirements of the permitting authorities. In addition to external marine mammal observers (MMO) various acoustic monitoring systems and AWI’s on board infrared detection system AIMMS monitored any activity of marine mammals in the ships perimeter, especially during seismic operations.
Reconnaissance surveys were carried out in 1974 within the framework of the BGR program "Geoscientific studies in the North Atlantic". The areas covered were the continental margin of Spitsbergen, the Barents Sea and the Norwegian continental margin. On the R/V LONGVA (10th August, 1974 - 10th September, 1974) multichannel seismic measurements were carried out on 40 lines with a total length of 8,091 km. The data format is Society of Exploration Geophysicists SEG Y.
In the time from 13th August to 13th September, 1989 a geophysical survey was carried out with S.V. PROSPEKTA in the Southeastern Newfoundland Basin and in the Sohm Abyssal Plain. Sixteen multichannel seismic lines with a total length of 3,568 km were surveyed. The general aim of the survey was to study the structure of the oceanic crust formed during the period from 150 to 80 m.y.B.P.. The results we found that the magmatic-volcanic activity at the Mesozoic Atlantic spreading center was episodic, and there was some form of magmatic-tectonic cycling in the Mid-Atlantic Ridge processes. Drastic changes of the oceanic crustal structure have been observed, and a volcanic basement unit characterized by an internally divergent pattern of reflection horizons having an eastward dip was found coinciding with magnetic anomalies M-4 to M-0. This body consists probably of basaltic flows and volcanic clastic rocks extruded near or above sea level, and it appears that this unit is continuous from the Eastern Newfoundland Basin to the New England Seamount Chain. A doubling of the oceanic crustal thickness occurs around M-10 and is present in the area of the young end of the series of magnetic M-anomalies. Doubling of the thickness of the oceanic crust is also present in the conjugate eastern central North Atlantic segment in the area of magnetic anomalies M-10 to about M-0.
Reconnaissance surveys were carried out in 1975 within the framework of the BGR program "Geoscientific studies in the North Atlantic". The data format is Society of Exploration Geophysicists SEG Y. The areas covered were the continental margin of Spitsbergen, the Barents Sea and the Norwegion continental margin. On the vessel LONGVA (30th August, 1975 - 29th September, 1975) multichannel seismic measurements were carried out on 37 lines with a total length of 2,815 km.
The BGR 1991 cruise with M.V. BIN HAI 511 was designed to study the variability of the oceanic crustal structure along flow-line profiles perpendicular to the ridge axis over Early Tertiary through Cretaceous old oceanic crust of the eastern Atlantic Ocean. Seismic data with a coverage of 3,000 % were acquired along four flow-line profiles with a total length of 4,194 km, and in addition 270 km of MCS data were collected during the period from 2nd October to the 3rd November 1991. The most intriguing new observation from the seismic flow-line profiles is the discovery of two huge oceanic crustal structures characterized by an internally divergent to planar pattern of reflectors having ubiquitous seaward dip. These remarkable structures were found within an about 1,300 km long oceanic crust segment of the eastern South Atlantic located between the Bode Verde Fracture zone in the north and the Rio Grande Fracture Zone in the south. These structures resemble the prominent wedges of seaward dipping reflectors on the widespread volcanic rifted continental margins described in the literature. They are interpreted to represent voluminous build-ups of layered extrusive rocks formed during three excessive episodes of volcanism that accompanied the Cretaceous opening of the South Atlantic. These episodes of excessive volcanism/magmatism are: An episode immediate prior to, and during the first stage of seafloor spreading in the South Atlantic, i.e. during about Hauterivian through about early Aptian; an episode of inferred subaerial and/or shallow marine volcanism along the central South Atlantic spreading ridge during the Albian; and an episode of inferred subaerial and/or shallow marine volcanism along the South Atlantic spreading ridge during latest Cenomanian/earliest Turonian through early Campanian.
The main purpose of the cruise SO75 from 14th October to 12th November 1991 was to test the new instrumentation of the SONNE and the ship itself for the needs of marine geophysics. The second purpose was the investigation of the crustal structure of the Atlantic Ocean from the Madeira-Torre Rise to the continental slope of Portugal which is conjugate to the margin off Newfoundland being investigated by a previous BGR cruise (Hinz et al., 1989). Methods used were multichannel reflection seismics, gravimetry, magnetics, swath echosounding and sediment echography. The test of the ship and its result is discussed in a separate technical report (Roeser et al., 1991). On two lines crossing the Madeira-Torre Rise we have observed seaward dipping reflector sequences. Their position is conjugate to similar features observed off Newfoundland. Magnetic models for one line show a strong magnetization of the whole reflector sequence. Thus, in analogy to the drilled dipping reflector sequence on the Vøring Plateau, it is likely that it mainly consists of lava flows which were extruded subaerially or in shallow water. In contrast to the dipping reflector sequences found earlier, the newly detected sequences are far away from continental crust. Presumably, at the time of their formation the Midatlantic Ridge was subaerial. Geometrical constraints indicate a compressional regime for the eastern part of the Azores-Gibraltar Fracture Zone. Most prominent expression of this is the Gorringe Bank. Our seismic line across it indicates an overthrusting of oceanic crust, however, it does not show any evidence for a Benioff zone. Therefore, only a small amount of oceanic crust can be subducted until now. We have observed compressional features also in the Tagus Abyssal Plain. Our lines north of the Azores-Gibraltar Fracture Zone did not confirm the weak indications for a continuation of the magnetic anomaly M0 across the fracture zone. The present platetectonic models for this area require therefore a modification. For the definition of the ocean-continent transition in the Iberia Abyssal Plain and for the investigation of the nature of the crust near the transition zone 6 ODP drillsites have been proposed. In response to a request by R.B. Whitmarsh from the Institute of Oceanographic Sciences at Wormley, Godalming, we have carried out the required ODP Site Survey.
The MSM67 SEGMENT research cruise was carried out between August 31st and October 4th 2017 aboard the research vessel MARIA S. MERIAN. Survey MSM67 SEGMENT it is intended to study the architecture of the rifted continental margin off East Greenland around the Jan Mayen fracture zone. Key issues to be addressed are margin segmentation and the location of the continent-ocean transition (COT). Both subjects are highly debated. Symmetric segmentation of conjugate margins has significant implications on our general understanding of continental rifting processes, and a margin-parallel COT off East Greenland would indicate an N-S opening in the Norwegian/Greenland Sea. The latter challenging most publications on the early evolution of the North Atlantic. A major open question is also the timing, duration and distribution of magmatism that resulted in the formation of the North Atlantic large igneous province. Previous suggestions of very short (~3 Myr) periods of intense magmatism have been challenged and a much longer duration and/or a post-breakup origin are under discussion. Here, we want to establish the amount of post-breakup magmatism as evident in high-velocity lower crust and test the dependence of magmatism with distance from the proposed hot-spot under Iceland and the influence of major fracture zones on volcanism.
A geophysical reconnaissance survey across oceanic fracture zones has been carried out by the BGR in the eastern North Atlantic using S.V. PROSPEKTA. The geophysical measurements, including multichannel seismic reflection profiling, magnetics and gravity were concentrated on three oceanic crustal areas of Mesozoic crust which are crossed by the Hayes Fracture Zone, the Atlantis Fracture Zone and the Kane Fracture Zone respectively. 24 geophysical lines with a total length of 5,362 km have been measured during the time period from 25th October to 4th December 1985. Besides intracrustal seismic events a deep coherent seismic event is often recognizable in the monitor records between 10 - 12 s (TWT) along several lines, which probably is a reflection from the crust-mantle boundary.
In May/June 2001, as part of the expedition NARES I, an aeromagnetic survey was carried out in the area of the eastern Kane Basin in cooperation with the Canadian GSC, in addition to the survey over the Robeson Channel and parallel to marine geophysical investigations with the Canadian icebreaker Louis S. St. Laurent. Another survey, NARES II, was conducted from Alexandra Fiord in 2003 and covered coastal areas of Ellesmere Island and the western Kane Basin. The aim of the research was to detect and localize the Wegener Fault, a transform fault between Ellesmere Island and NW Greenland, which is closely linked to the opening of the North Atlantic and the Arctic Ocean. The helicopter-borne magnetic surveys NARES I + II (Kane Basin) were carried out with a flight line spacing of 2 km, and control profiles were flown every 10 km. During the two expeditions, 11806 km of line data were collected (3573 km in 2001, and 8333 km in 2003), covering an area of approximately 20000 km². The aeromagnetic data were recorded by a magnetometer, which was towed approx. 25 m beneath the helicopter.
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