In the southwestern part of the Sulu Sea and in the southeastern part of the South China Sea, between NW Palawan and the northwestern part of the Reed Bank the Federal Institute for Geosciences and Natural Resources (BGR), Hannover carried out the geophysical survey BGR84 from 11th October, 1984 to 23rd November, 1984. This work was done in close cooperation with the Bureau of Mines and Geosciences (BMG), Manila, using the German seismic vessel EXPLORA chartered from PRAKLA-SEISMOS GmbH, Hannover. Multichannel reflection seismic measurements were carried out on 40 lines with a total length of 4,467 km simultaneously with magnetic measurements on 19 lines with a total length of 3,047 km. The Oligocene to lower Miocene Nido-carbonates of the South China Sea that have been proven during the SONNE cruises SO-23 and SO-27 beneath the allochthonous and chaotically deformed complex which was overthrusted from the Sulu Sea terrane, could be correlated up to the Balabac Straits. The three major unconformities of the Sulu Sea, unconformity A (Early Pliocene), unconformity B (mid Middle Miocene) and unconformity C (lower Middle Miocene) have been correlated over extensive areas by tying into the Sulu Sea well Coral-1. In the Sulu Sea reflection horizon C forms the top of a chaotic bedded rock complex and presumably represents an equivalent to the unconformity "Red" of the South China Sea, in the west of Palawan. There, the unconformity "Red" forms the surface of a highly deformed rock complex which has been interpreted as an allochthonous mass accumulation (HINZ, 1983; HINZ & SCHLÜTER, 1985). It is assumed that pronounced magnetic anomalies, approximately 140 - 160 km off NW Palawan as well as a change in the reflection seismic pattern of the acoustic basement, associated with diapiric structures which are interpreted as intrusions represent the ocean-continent boundary in this part of the South China Sea. In the Reed Bank area the basement type which is interpreted as continental crust (transitional crust?) extends as far as 160 km to the northwest, towards the South China Sea Basin. The northern part of the Reed Bank is characterized by intense downfaulting and rotated fault blocks with reef complexes ontop. In contrast to results from the Dangerous Grounds of the previous SONNE cruises, the deeper lying coherent reflections could be recognized in the monitor records off the northwestern Reed Bank area. It might be that these parts of the Reed Bank block consists of metamorphized and/or highly consolidated rocks of pre-Tertiary age which originally formed part of the Chinese back country, and which was effected by previous orogenies prior to the rifting of the proto-China continental margin.
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 the scope of International Geoscientific Programs and in close cooperation with PETRONAS, Malaysia, and in agreement with the Bureau of Mineral Resources (BMR) and the Bureau of Energy Development (BED), Manila, the Federal Institute for Geosciences and Natural Resources (BGR) carried out a geophysical survey on the continental margin off Sabah during the period from 20th July to 10th August, 1986, and in the Northwestern Sulu Sea during the period from 12th August to 28th August, 1986, using the PRAKLA-SEISMOS vessel EXPLORA chartered by the BGR. The research cruise is a continuation of BGR’s marine geoscientific studies in the South China Sea and in the Sulu Sea with the German research vessels VALDIVIA (1977), SONNE (1982/83) and EXPLORA (1984). The previous investigations provided new information regarding the geological and tectonic history of the southern part of the South China Sea in the context of plate tectonics. According to the interpretation of the large amount of geophysical, geological and geochemical data collected by BGR on previous cruises the widely accepted hypotheses of the presence of an ancient subduction zone beneath the Sabah-Palawan Trough has to be revised. The main objective of the EXPLORA cruise was to search for an Oligocene-Early Miocene carbonate platform off Sabah and in the western Sulu Sea. On the continental margin off Sabah 27 lines were surveyed with gravity and multichannel reflection seismics and partly with magnetics, with a total length of 3,126 km. A strong reflector interpreted as reflector BLUE of previous BGR cruises off Palawan was recognizable beneath the Sabah Trough in depth between 4 and 7 sec (TWT). The isochrones of the reflector strike approximately 50°N. The surface of the reflector dips with 2 to 3 degree towards southeast. Toward the north-western part of the Sabah Trough the reflector is disrupted by a basement high. According to the preliminary interpretation of the gravity data, the prominent free-air anomaly associated with the Sabah Trough and adjacent areas has the same shape as the anomaly observed across the Palawan Trough. Therefore it is concluded that the Sabah Trough is underlain by a thinned continental crust.
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.
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.
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.
During the second leg of cruise BGR78 from 22th of February to 29th of March 1978 with R/V EXPLORA the following measurements have been carried out as presite- and postsite surveys of DSDP sites: (1) in the region of the eastern Walvis Ridge 4,350 km multichannel seismic reflection profiles, 4,540 km magnetic measurements, 5,000 km gravimetric measurements and sonobuoy refraction measurements on 11 stations (2) on the Guinea Plateau 740 km multichannel seismic reflection profiles in parallel with gravimetric and magnetic measurements (3) between Cape Verde islands and Mauretania 980 km multichannel seismic reflection profiles in parallel with magnetic measurements, 1,480 km gravimetric measurements and sonobuoy refraction measurements on 2 stations. The geophysical measurements show that the structure of the Walvis Ridge is determined by two main tectonic directions (WSW-ENE and SSW-NNE). Presumably the genesis of the fracture zone in the Walvis Ridge area can be traced back to the sea-floor spreading with overprinting effects due to an inhomogeneity in the mantle ("hot spot"). Both DSDP drilling projects in this part of the Walvis Ridge led to a fragmentary knowledge because site 362 got stuck at a depth of 1.100 m in the Oligocene. BGR's measurements indicate a gap of at least 1.000 m of sediments, especially from the cretaceous period, down to the (acoustic) basement. Site 363 at a submarine high has gaps in the depositional sequence and stops at a depth of 700 m shortly above the basement. So for a better understanding of the geologic development of the Walvis Ridge, further DSDP drillings with a recovery of the complete sedimentary sequence and the following basement cores are necessary. Therefore BGR's measurements of this cruise propose new DSDP sites.
The initial study area of the cruise MSM14/2 GeoNORM (Geophysik im noerdlichen Roten Meer) was the northern Red Sea. However, because of not given research permissions from Egypt and Saudi Arabia, the study area had to be changed to the alternative study area Eratosthenes Seamount (ESM), south of Cyprus. The ESM is supposed to represent a continental fragment of the former African-Arabian Plate that is entering the subduction zone south of Cyprus i.e. the subduction turns into collision in the area of the ESM. This changed the entire tectonic setting in the Eastern Mediterranean. Therefore, the tectonic evolution of the area is rather complex with phases of extension, subduction, compression, salt tectonics and gravitational processes and not comprehensively understood. Because of the isolation of the ESM as a continental fragment this region is an ideal spot to investigate the transition from regular subduction to continental collision and its associated tectonic processes i.e. faults were activated or reactivated, transform motion has to be compensated, the overriding plate has been elevated. This impacts the ongoing geological and tectonic processes in this region but also influences the social and economic life in the Eastern Mediterranean as earthquakes and submarine landslides are possible geohazards and the entering of the ESM to the subduction trench alters the thermal history of the adjacent sedimentary basins significantly what should have an influence on the maturity processes within the source rock sediments and new faults open new migration paths for hydrocarbon fluids or gases.
The previous BGR-cruises with RV AURELIA in 2003 and 2004 were designed to collect a grid of seismic MCS-data which should enable us to get a high-resolution overview over the upper 1 s TWT of the sediments of the German North Sea sector. The data format is Society of Exploration Geophysicists SEG Y. Together with the previously acquired data these new data should help to extend our knowledge of the Late Tertiary and Quaternary evolution of the German North Sea Sector. For the current measurements under the scope of the DFG-funded project RE2424/1-1 ‚Nordsee’ the research vessel RV HEINCKE was made available by the ‘Senatskommission für Ozeanographie’ of the DFG. During the cruise a total ca. 1400 km of high quality MCS lines were surveyed and simultaneously measured by a sediment echosounder system that enabled additional profiles during transits with speeds > 5 kn. The BGR high-resolution multichannel seismic reflection system consisting of a GI-Gun (0.8 l) and a 300 m streamer with 24 channels and a sediment echosounder type SES 2000 standard by Innomar, Rostock. While the BGR-seismic system was used to observe the shallow subsurface down to 2 s TWT penetration depth, the sediment echosounder with a penetration depth of several meters was primarily intended to identify sampling positions for the deployment of the BGR vibration corer during the succeeding Leg 2. Additionally, the echosounder system enables the relationship to the highest-resolution multichannel seismic measurements of the group of the University of Bremen on FK SENCKENBERG. All seismic records were processed onboard for the quality control and for a first interpretation.
In the period from February 13th to March 2nd 1980 4,037 km of magnetic, gravity and bathymetric lines and 1,195 km of digital reflection seismic lines were recovered on the 2nd leg of METEOR cruise no. 53. Heat flow measurements have been performed on 13 stations; on two stations sonobuoy refraction measurements and dredging have been carried out. From a preliminary interpretation of the seismic monitor records the Mazagan Plateau is part of the Moroccan Meseta. Seawards of this stable swell lies the 75 km wide, downfaulted rift graben characterized by salt diapirs. A submarine body, 150 square kilometres large, lying at the foot of the Mazagan Escarpment in water depths of 3000 m - 3800 m beneath sea level, from which western flank few granitic fragments were retrieved, is interpreted as a subsided and tilted block of the Mazagan Plateau. The north-trending magnetic anomalies, discovered during METEOR cruise no. 46 within the Essaouira continental margin segment have also been recognized within the Tafelney Plateau segment, situated between latitudes 30°45'N and 31°30'N off Morocco. Two neo-volcanic zones were found west of the Conception Bank and west of the Betancuria Massif/Fuerteventura Is. The Mesozoic and Tertiary depositional sequences are highly deformed by small piercement structures interpreted as dykes within these zones.
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