In the period from 22nd December, 1987 to 15th January, 1988 a geophysical reconnaissance survey has been carried out with S.V. EXPLORA on the Argentine Eastern continental margin. A total of 3,675 km of digital seismic reflection profiles in parallel with gravimetric and in part magnetic measurements, and 13 sonobuoy refraction profiles were recorded during this survey. The general aim of the survey was to search the Argentine eastern continental margin between 37°S and 47°S for evidence of continent-ocean boundary structures previously recognized by us off South Africa. The following preliminary results were obtained: (1) Five regional seismic markers/unconformities have been observed, named from bottom to top AR V to AR I. (2) Two units are recognizable on all reflection seismic records: A buried lower unit the top of which is marked by the distinct 'AR IV' unconformity of presumably Beriasian/Valangian age, and a tectonically undisturbed upper sedimentary unit. (3) The dominant feature of the lower unit is a 50 km to 100 km broad wedge-shaped body characterized by an internally divergent pattern of reflection horizons having seaward dip. The seismic characteristics and recent ODP drilling is consistent with the wedge being formed from extrusive basaltic rocks. (4) The more than 5000 m thick wedge is parallel with the shelf edge and can be traced continuously for 1200 km. Its landward pinchout coincides with the magnetic slope anomaly 'G'. (5) A giant contourite mound of Neogene age has been recognized in the southeastern part of the survey area. (6) Bottom simulating reflectors have been recognized. Their occurrence is associated with the contourite mound.
The aims of cruise SO197 RISE (Rift Processes in the South China Sea) with RV SONNE from Manila, 28th March 2008 to Singapore, 2nd May 2008 are (1) To gain a better understanding of the processes leading to continental breakup and subsequently formation of oceanic crust. (2) To study the evolution of the South China Sea oceanic basin. The South China Sea is particularly well suited for studying rift processes at the transition from extension of continental lithosphere to the formation of oceanic crust. This relatively young marginal basin is currently in a stadium which is characterised by still preserved differences in subsidence and thermal history resulting from rifting. The initial, complex and hardly quantifiable rift processes, however are long enough ago. The area under study comprises the eastern subbasin of the South China Sea, the West Luzon Basin and the transition area from oceanic crust to extended continental crust between the continental blocks of Reed Bank and the islands of Palawan/Calamian Group. By including existing data of earlier cruises (SO-23, -27, -49) a comparison of conjugated margin transects is intended later within the project. A major goal of the project is to study structures at the transition from continental rifting to oceanic spreading and processes resulting from extension of continental lithosphere to the formation of oceanic crust in time and space. The sequence stratigraphy of the synrift and drift sediments will give insights into the formation and evolution of the individual rift basins. The distribution and thickness of the postrift sediments on the continental fragment of the NW Palawan area define the subsidence history. The depth and topography of the Moho show the location of the stretched and thinned crust. By a joint interpretation of the structural setting, the position, distribution and architecture of the basin bounding faults a reasonable rift model will be derived. In addition, we will investigate the transition of a passive rifted margin (off Palawan) to a convergent margin (off Luzon). The timing of the evolution of the South China Sea basin will be more exactly determined by comparing the magnetic anomalies from the eastern subbasin of the South China Sea with existing data from the central/western basin. Particularly the question of a symmetric/asymmetric opening of the oceanic basin and the timing and location of the individual rift/drift episodes will be investigated. Therefore, we investigated rift structures at the southeastern margin of the South China Sea by means of reflection seismology, gravity, magnetics, bathymetry and sediment echosounder and we performed magnetic measurements to identify seafloor spreading anomalies in the eastern subbasin of the South China Sea.
Im Rahmen des weit gespannten SPOC-Projektes (Subduction Processes off Chile) wurden zwischen dem 16.10. und 29.11.2001 vor Zentralchile zwischen 28° und 44°S die SONNE-Fahrten SO161 Leg 2 und 3 durchgeführt. In diesem Zeitraum wurden etwa 5.300 km mit vielkanal-/reflexionsseismischen (MCS), magnetischen, gravimetrischen, hochauflösenden bathymetrischen und echographischen Methoden vermessen. Hinzu kamen etwa 3.900 km mit denselben Verfahren, jedoch ohne MCS. Die Gesamtzahl der 2D-Profile betrug 48. Auf vier Ost-West-Traversen wurden amphibische (d. h. in Land-/See-Kombination) weitwinkel-/refraktionsseismische Beobachtungen durchgeführt. Darüber hinaus wurden die ausgesandten marin-seismischen Signale an Land von einem zweidimensionalen seismischen Mobilstationsnetz, das zwischen 37° und 39°S aufgestellt war, aufgezeichnet. Ziel der Untersuchungen war die Veränderlichkeit der Subduktionseigenschaften zwischen den konvergenten Nazca (ozeanisch) und Südamerika (kontinental) Platten sowie die verschiedenen Begleiterscheinungen, die den Subduktionsprozess beeinflussen können wie: (1) Alter der ozeanischen Kruste, (2) ihre Struktur und ihr Aufbau, (3) ihre sedimentäre Bedeckung, (4) ihr thermischer Zustand, (5) Subduktionswinkel und -schiefe sowie (6) der terrigene Sedimentzufluss von der Kontinentseite. Weiterhin waren die Subduktionsfront, die Subduktionsflächen, die Struktur des Kontinenthanges ebenso wie Struktur und Entwicklungsgeschichte der Forearcbecken und die Verteilung von Gashydrat anzeigenden "Meeresboden simulierenden Reflektoren" (BSRs) Gegenstand der Untersuchungen. Die Ergebnisse sollen mit früheren Studien am aktiven chilenischen Kontinentalrand in Vergleich gesetzt werden, z. B. mit CONDOR (SO101 und 103) und CINCA (SO104). Das SPOC-Zielgebiet war in zwei Untergebiete A und B unterteilt. A erstreckt sich von 36°S bis 40°S und war ausersehen für eine detaillierte Untersuchung mit Hilfe eines engabständigen Profilnetzes sowie für eine enge Verbindung mit den landseitigen Aktivitäten des Sonderforschungsbereichs SFB 267 ("Deformationsprozesse in den Anden") der Deutschen Forschungsgemeinschaft (DFG), des GeoForschungsZentrums Potsdam, der FU Berlin und anderer Partner. Dieses Gebiet ist charakterisiert durch einen deutlich anderen Kontinentrandtyp und andere Eigenschaften des Tiefseegrabens als die Gebiete nördlich davon. Gebiet B wurde ausgewählt, weil in diesem Bereich eine Übergangszone oder eine Grenze zwischen dem subduktionserosiven Kontinentrandtyp vor Nordchile und dem Typ, der im Süden vorherrscht, vermutet wird. Darüber hinaus tritt in dieser Region der Juan Fernandez Rücken in die Subduktionszone ein, der ebenfalls ein wichtiges Erkundungsziel des Projektes ist. Günstige Umstände erlaubten die Vermessung eines Ost-West-Profils südlich von Chiloé zwischen 43°S und 44°S, das über die abgesunkene Küstenkordillere bis in das geflutete Valle Longitudinal verläuft. Dieses Gebiet wird als "C" bezeichnet. Anhand einer ersten an Bord durchgeführten Interpretationen ergeben sich für Fahrtabschnitt 2 und 3 folgende Resultate: In beiden Gebieten A und B konnte kein "Subduction Bulge" (Outer High) festgestellt werden. Möglicherweise reichen die Profile hierfür nicht weit genug. Die sedimentäre Bedeckung der ozeanischen Kruste ist sehr dünn und die ozeanische Krustendicke im allgemeinen sehr "normal" mit ungefähr 7 km, abgeleitet aus relativ schwachen Moho-Reflexionen. In Gebiet B konnte eine bis jetzt magnetisch unkartierte Region vermessen werden, woraus sich recht sichere Alter für die ozeanische Kruste ergeben sowie starke Anhaltspunkte dafür, dass die Challenger Fracture Zone westlich des Untersuchungsgebietes aufhört. Die Arbeiten im Gebiet "C" erbrachten wertvolle Information über die Trench-Morphologie und das bis jetzt einzige MCS-Profil südlich von Chiloé, welches einen sehr breiten Trench anzeigt und weitgehend die Extrapolation der Eigenschaften, die im Gebiet A angetroffen wurden, nach Süden bis etwa 44°S erlaubt.
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.
The SUMATRA cruise SO189 Leg 1, aboard the RV SONNE, was carried out off Sumatra between 3rd August and 3rd September 2006, with mobilisation in Penang, Malaysia and demobilisation in Jakarta, Indonesia, respectively. The survey was dedicated to marine geophysical measurements and acquired multichannel seismic data (MCS) using a 240 channel streamer, and a tuned airgun array comprising 16 airguns with a total capacity of 50.8 litres. Bathymetry data, using the 12 kHz Simrad swath system, sub-seabed data using the hull mounted high resolution PARASOUND profiler together with gravity (G) and magnetic (M) data were also acquired. Along two lines with a total length of ~ 390 km refraction/wide-angle seismic experiments were carried out. During the survey a total of 4,375 line kilometres of MCS, M and G data were acquired and an additional 990 km with M and G alone. The 41 MCS lines cover as close grid three fore-arc basins. Five lines extend nearly orthogonal to the subduction front and, thus, cover the whole subduction system from the adjacent oceanic plate, the trench and accretionary prism over the Outer Arc High to the forearm basins offshore Sumatra. The survey was planned using the bathymetry from the HMS SCOTT, RV NATSUSHIMA, RV MARION DUFRESNE and RV SONNE cruises carried out in 2004, 2005 and 2006. The main scientific objective of the project SUMATRA is to determine or estimate the hydrocarbon (HC) system (source rocks, HC generation, HC migration and reservoir rocks) of the Sumatra fore-arc region (mainly the fore-arc basins). Cruise SO189 Leg 1 was designed to investigate the architecture, sedimentary thickness, sedimentary evolution and subsidence history of the fore-arc basins Siberut, Nias and Simeulue off Sumatra. In the Simeulue Basin it was possible to connect the seismic lines to three industry wells and to correlate the seismic horizons to the results from the wells. The Simeulue Basin is divided into a northern and southern sub-basin. Carbonate build-ups were found in the northern sub-basin only on the very shallow shelf in the north-east. The maximum thickness was determined to be ~ 3 s TWT. In the southern sub-basin carbonate build-ups (which were already identified on some lines of the SEACAUSE project), bright spots and Bottom Simulating Reflectors (BSRs) are wide spread. The narrowest basin surveyed was the Nias Basin. As the Simeulue Basin the Nias Basin is divided into two sub-basins which are separated by a structural high. Although the basin has a maximum width of only 55 km the maximum sediment thickness exceeds 5 s TWT. The largest fore-arc basin is the Siberut Basin. It extends from the equator to ~ 5°S over 550 km and has a maximum width of 140 km between the island of Siberut and Sumatra. The maximum sediment thickness in this basin is 4.8 s TWT. The basin geometry is uniform along its axis. At the basins termination on the western side to the Outer Arc High the Mentawai Fault Zone could be traced. The geometry of this major fault changes significantly along strike. In some areas it is traceable as one single fold whereas in other areas it spreads in up to three different branches indicating splay faults originating from a main fault. In the Siberut Basin BSRs are very wide spread and very good recognizable over the Mentawai Fault Zone. Along the Mentawai Fault and along the eastern rim of the basin the seismic data show strong indications for active venting. The morphology of the Sunda Trench and its sedimentary cover varies from north to south. In the north the trench is poorly defined with shallow seabed dip but with sediment thickness of ~ 3.5 s TWT. The seafloor dips increase southwards, but sediment thickness decreases to ~ 2.5 s TWT off Nias. Both the ocean basin and trench sediments are dissected by numerous normal faults with a maximum displacement of 0.6 s TWT. Along strike the deformation front between Nias and Siberut displays several incipient folds. As offshore northern Sumatra, both landward (BGR06-228) and seaward verging folds (BGR06-227) are developed at the deformation front. For the first time landward verging folds have now been imaged in this domain of the Sunda subduction zone. In contrary to first thoughts during the expedition SO186-2 SEACAUSE, landward verging folds are not limited to the area off Aceh. Two refraction lines were acquired parallel to the subduction front at 2°30'N and 1°30'S approximately 40 - 50 km seaward of Simeulue and Siberut Island, respectively. The lines were designed to identify the segment boundaries in the subduction system as well as to detect and decipher the subducted aseismic Investigator Ridge. The gravity data set consists now of over 38,000 line km (combining the GINCO, SEACAUSE I and II and the SUMATRA data). With this it was possible to compile a map of the free-air gravity from the northern tip of Sumatra (~ 6°30'N/95°E) to Mid Java( ~8°30'S/110°E). Gravity modelling in parallel with refraction seismic data interpretation was carried along two lines during the cruise. The preliminary results show that the incoming oceanic plate is unusual thin both in the north off Simeulue (6 km) and in the south off Nias (5 km).
During leg 3 of cruise SO81, starting in Caldera/Costa Rica at September 15th and ending in Balboa/Panama at September 28th, 1992, the first 48-channel seismic survey was carried out in the Hess Deep area as a German contribution of pre-site investigations for Leg 147 of the Ocean Drilling Programme. ODP Leg 147 is designed to drill the crust-mantle transition. During leg SO81/3 the BGR collected 662 km of seismic data and in addition gravity and hydroacoustic measurements were carried out. Profile SO81-HD001 runs W-E from and to 1 Ma old oceanic crust across the East Pacific Rise. The profiles SO81-HD002 to SO81-HD007 are located in the proper Hess Deep area passing onto the proposed drill sites. Preliminary on-board evaluation of the seismic monitor records gives a lot of interesting intracrustal reflection events which deserve more elaborate examination after proper processing of the seismic data.
On the first leg of SONNE cruise SO-36 in the period from 11th February to 12th March 1985, geophysical investigations have been carried out on the Lord Howe Rise off eastern Australia by the Federal Institute for Geosciences and Natural Resources (BGR) in co-operation with the Bureau of Mineral Resources, Geology and Geophysics, Canberra. A total of 3,660 km of digital seismic reflection profiles, 6,740 km of gravity, magnetics, multibeam echosounder and sub-bottom profiler profiles, as well as 8 sonobuoy refraction profiles were recorded during this survey. A geomagnetic monitoring station of the BGR was operated during a part of the cruise on Lord Howe Island under the supervision of the BMR. These measurements provided a detailed picture of the structures of the survey area of the Lord Howe Rise. The samples proved that the Lord Howe Rise and the Dampier Ridge west of it consist of continental crust. Indications for structures rich in hydrocarbons were not observed. The 2nd and 3rd leg of SONNE cruise SO-36 were designed to investigate the structure, geological development and hydrocarbon potential of two frontier areas, the western and southwestern continental margin of Tasmania and the South Tasman Rise. On the 2nd leg (12.03.-12.04.1985) multichannel seismic reflection measurements were carried out in parallel with magnetic, gravimetric, sea-beam and 3.5 kHz subbottom profiler measurements on 19 lines with a total length of 3,820 km. In addition, 2,140 km were surveyed with magnetics, gravity meter, sea-beam and 3.5 kHz subbottom profiler in transit from and to Sydney, respectively. On the 3rd leg, which started in Sydney on 12th April 1985 and ended in Suva/Fiji one month later, 63 stations were sampled by dredging and coring with the aim (a) to provide lithology and biostratigraphic information about the seismic sequences mapped during leg 2, and (b) to obtain geochemical evidence of hydrocarbon generation from the character of gases absorbed onto the surficial sediment. Samples came from 33 stations off Western Tasmania, from 23 stations on the South Tasman Rise, and from 7 stations in the region of the Lord Howe Rise and the Dampier Ridge. In transit to the sampling sites, 11 single channel seismic lines with a total length of 470 km were surveyed, and in addition, 4,230 km were surveyed with magnetics, gravity meter, sea-beam, and subbottom profiler. Seven regional seismic unconformities were recognized and sampled, and the structural style of both areas was established. Thermogenic hydrocarbons in substantial concentration were found in the surface sediments at the western Tasmanian slope.
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.
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.
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.
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