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.
From 17th April to 6th June 2003 BGR conducted a marine geophysical cruise between 30°S and 38°S off the Atlantic coast of South Africa. The main research objective was to contribute to a better understanding of the initial breakup and the early opening of the South Atlantic. In continuation of our former work on the South Atlantic continental margins off Argentina, Brazil, Uruguay and Namibia marine geophysical research (multi-channel seismics, wide-angle refraction seismics, magnetics and gravity) was performed in cooperation with the Petroleum Agency South Africa (PASA). Multi-channel lines with a total lenght of 3,260 km, and additional 1,365km, with the other geophysical methods were acquired. Combined onshore/offshore refraction seismic work in cooperation with GeoForschungsZentrum Potsdam (Germany) and the Council for Geoscience (South Africa) was also part of the program.
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.
During cruise BGR79 from 29th June to 3rd September 1979 the Federal Institute for Geosciences and Natural Resources (BGR) carried out marine seismic reflection surveys in the three separate areas of the North Atlantic Ocean (Norwegian Sea, Scotian Basin, and U.S. East Coast Area) with S.V. EXPLORA. Simultaneously gravity, magnetic and reflection seismic data were recorded on parts of the lines. In addition, 66 sono-buoys were deployed for seismic refraction data recording on various seismic lines in all three areas. A detailed survey in the Norwegian Sea took place in the time from 29th June to 15th July, 1979 between the southern Vøring Plateau, the Jan Mayen Fracture Zone, the Møre Basin and the Faeroe-Shetland escarpment during leg 1 of cruise BGR79. The data showed that the Møre Basin contains a small sub-basin in the western part, the West-Shetland Basin. Further seaward, an outer high as well as a zone of intrusions were imaged.
The previous BGR-cruises with RV AURELIA in 2003 and 2004 and RV HEINCKE in 2005 and RV ALKOR in 2006 were designed to collect a grid of seismic MCS-data which should enable us to get a high-resolution overview over the upper 1-2 s TWT of the sediments of the German North Sea sector. The data format is Society of Exploration Geophysicists SEG Y. The aim of this cruise was a detailed survey in the north westernmost area of the German EEZ (exclusive economic zone), the so-called ‘Entenschnabel’ and additionally a mapping of special glacial structures off Sylt Island. The cruise was subdivided into two Legs. One outreaching additional aim was to extend the results from the previous cruises for the Late Tertiary and Quaternary sedimentary evolution into the ‘Entenschnabel’-area which was virtually unexplored by systematic shallow high-resolution seismics. During Leg 1 the BGR high-resolution multichannel seismic reflection system consisting of a GI-Gun (0.8 l) and a 500 m streamer with 36 channels and a shallow swath bathymetric system, type SIMRAD EM1200 by Kongsberg, Bergen, Norway were used. While the BGR-seismic system was used to observe the shallow subsurface down to 2 s TWT penetration depth, the swath bathymetric system was used to identify possible pockmark locations as well as sampling positions for the deployment of the BGR vibration corer during the succeeding Leg 2. All seismic records were processed onboard for the quality control and for a first interpretation loaded into GEOQUEST.
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.
The cruise BGR95 from 19th November to 28th December 1995 with M.S. AKADEMIK NEMCHINOV was designed to acquire new marine geophysical data for a better understanding of the geological processes and structural variations of the Cretaceous-aged oceanic crust of the Angola Basin in the South Atlantic regarding its reflectivity pattern, its shape of the basement surfaces and its crustal thickness. These evaluations were extended onshore to the ‘Damara Igneous Province’. The aim of this study was the investigation of the rift-related volcanic-magmatic processes accompanying the initial stage of the opening of the South Atlantic Ocean. The survey was a co-operation of BGR, Alfred Wegener Institute for Polar and Marine Research (AWI), GeoForschungsZentrum Potsdam, University of Göttingen and Johann Wolfgang Goethe-University Frankfurt/Main. The M.S. AKADEMIK NEMCHINOV generated the seismic signals by a tuned airgun array of 3260 cu.in. (= 53.4 l) together with two AWI owned large volume guns of 2 x 2000 cu.in. (= 65.6 l), recorded the MCS signals with a 3000 m streamer and controlled the shot releases for the ocean bottom hydrophones (OBH’s) and the onshore seismic stations (PEDAS). A total of 5,114 km of multichannel seismic reflection data in parallel with magnetic and gravity measurements have been collected onboard the M.S. AKADEMIK NEMCHINOV. 1069.4 km of the seismic work was done on 3 combined refraction/wide angle offshore and onshore traverses. The offshore part was recorded by 7 ocean bottom hydrophones (OBH) operated by the M.V. POLAR QUEEN (Reichert et al., 1996). The registration onshore Namibia was performed by 25 mobile seismic landstations (PEDAS) on each profile (Schulze et al., 1996). First results are described in the offshore and onshore reports of these investigations (Reichert et al., 1996, and Schulze et al., 1996). The data clearly show distinct series of the seaward dipping reflector sequences (SRDS) and isochronous variations in the accretion of the oceanic crust. The onshore and offshore registrations show deep arrivals from diving and refracted waves in a range up to 200 to 400 km.
From 19th November to 19th December 2004 BGR conducted a marine geophysical cruise between 34°S and 36°S off Uruguay and between 46°S and 50°S off Argentine. The main research objective was to contribute to a better understanding of the initial breakup and the early opening of the South Atlantic. In continuation of our former work on the South Atlantic continental margins off Argentina, Brazil, Uruguay, Namibia and South Africa marine geophysical research (multi-channel seismics, refraction-/wide-angle reflection seismics, magnetics and gravity) was performed in close cooperation with the Argentine and Uruguayan authorities Comisión Nacional del Límite Exterior de la Plataforma Continental (COPLA) of Argentina and Servicio de Oceanograficia, Hidrograficia y Meteorologia de la Armada (SOHMA) of Uruguay. Multi-channel seismic lines with a total length of 3,754 km and additional 3540 km with the other geophysical methods were acquired . Along two lines refraction-/wide-angle reflection seismic work was carried out. The preliminary analyses of the new seismic data show different images of the crustal structures between Uruguay and southern Argentine with regard to the distribution and volume of offshore volcanic rocks (seaward dipping reflector sequences, SDRS) along the South American Atlantic margin. On the northern profiles between 34°S and 36°S one single well developed wedge of SDRS is present. Although the landward termination (‘feather edge’) on most of the lines is masked by multiples the average total width of the wedge across the margin seems to be 90 – 100 km and is very constant for this margin segment. This is strong contrast to the results from former cruises (BGR87, SO85 and BGR98) which covered the area between 38°S and 45°S. There, the SDRS showed distinct multiple wedges which in some places extend over 120 km across the continental slope. The investigation of the sedimentary section yielded that in the area off Uruguay widespread bottom simulating reflectors (BSR) are present. This indications for stable gas hydrates cover a total area of 7000 km2. One major aim of the cruise was to cover the transition between a volcanic passive margin and a non-volcanic passive resp. sheared margin. This was accomplished in the southern part of the investigated area. Two EW-trending profiles across the Argentine shelf into the Argentine Basin still show indications for SDRS but these structures are only 25 – 30 km wide. The profiles which extend from the NE to the SW crossing the Agulhas-Falkland Fracture Zone (AFFZ) onto the Falkland Plateau show the typical trend of a sheared margin. At the northern rim of the Falkland Plateau a set of small pre-rift half grabens were found indicating pre-rift extensional tectonic phases. The magnetic data in the area off Uruguay show lineations which are preliminary interpreted as chrons M0 to M3. This might indicate that the first (oldest) oceanic crust was created at a time around the magnetic polarity reversal between the normal interval M4 and the reversed interval M3 (126-127 Ma). Together with existing data from previous cruises this indicates that the breakup of the South Atlantic started further South because there magnetic chrons back to M9 (130 Ma) were identified. In the southernmost part of the margin at 47°S only the magnetic lineations M0 to M4 were identified in the oceanic domain Nevertheless, it is likely that between M4 and the assumed position of the continent ocean boundary/transition (COB/COT) older oceanic crust exists that for some reasons does not show correlatable lineations. The the free-air gravity map is dominated by the main topographic and structural features in the survey area. Rifted continental margins are characterized by prominent free-air gravity anomalies elongated parallel to the ocean-continent transition. The continental slope is considerably steeper in the North off Uruguay than in the South and thus the gravity high is much more pronounced in the North than in the South. The simple Bouguer anomaly map also shows the difference between the more gentle and wider continental slope in the South and the steeper slope in the North. The lowest Bouguer gravity values are found in the area of the basins on the continental shelf. Especially the Salado Basin in the prolongation of the Rio de la Plata and the Colorado Basin at about 40°S are indicated by Bouguer gravity anomaly highs. The interpretation by forward density modelling shows, however, the presence of SDRS units in the North of relative high density in the area of the continental slope. Whereas the modelling shows no indications for such volcanic bodies in the South. Although the MCS data indicate a small SDRS wedge but this body may be too small to cause an anomaly.From 17th April to 6th June 2003 BGR conducted a marine geophysical cruise between 30°S and 38°S off the Atlantic coast of South Africa. The main research objective was to contribute to a better understanding of the initial breakup and the early opening of the South Atlantic. In continuation of our former work on the South Atlantic continental margins off Argentina, Brazil, Uruguay and Namibia marine geophysical research (multi-channel seismics, wide-angle refraction seismics, magnetics and gravity) was performed in cooperation with the Petroleum Agency South Africa (PASA). Multi-channel lines with a total lenght of 3,260 km, and additional 1,365km, with the other geophysical methods were acquired. Combined onshore/offshore refraction seismic work in cooperation with GeoForschungsZentrum Potsdam (Germany) and the Council for Geoscience (South Africa) was also part of the program.
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.
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