From 1 - 10 / 79
  • 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.

  • 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.

  • During RV SONNE cruise 137 from 21st November to 28th December 1998 Geoscientific Investigations on the active Convergence Zone between the east Eurasian and Indo-Australian Plate (GINCO I) were carried out along the Sunda Arc, off Sumatra, Java and the Sunda Strait. The studies were headed by the BGR in close cooperation with German and Indonesian research institutions. A total amount of 5,500 km of magnetic, gravity and swath bathymetric profiles were recorded of which multi-channel seismic data exceeded 4,100 km. The scientific objectives were: (1) investigation of the structure and age of the accretionary wedges, outer arc highs and fore-arc basins off Sumatra and Java with special emphasis on the evolution of the Sunda Strait and the Krakatau area (2) differences in tectonic deformation between oblique (Sumatra) versus frontal (Java) subduction (3) search for oceanic crustal splinters in the accretionary wedges (4) definition of seismic sequences, thicknesses and ages of the fore-arc basin sediments as a pre-requisite for later on hydrocarbon assessments (5) identification and regional occurrence of bottom simulating reflectors (BSR) indicating gas hydrates. From the GINCO I project there is evidence for the existence of two accretionary wedges along the Sunda Arc: wedge I is of assumed Paleogene age and wedge II of Neogene to Recent age. The first inner wedge I is composed of tectonic flakes which are correlated from SE Sumatra across the southern Sunda Strait to NW Java. This implies a very similar plate tectonic regime at the time of the flake development during the Upper Oligocene to Lower Miocene and without marked differences in plate convergence direction from Java to Sumatra. Wedge I shows backthrusting along the northern transition toward the fore-arc basin. Today, wedge I forms the outer arc high and the backstop for the younger, outer wedge II. Magnetic, gravity and seismic results show, that within both wedges, there are no indications for an oceanic crustal splinter as hitherto postulated. Both wedges are underlain by oceanic crust of the subducting Indo-Australian slab which could be correlated from the trench off Sumatra up to 135 km to the northeast and up to 65 km from the trench off Java. Since the top of the oceanic crust differs considerably in reflectivity and surface relief we distinguished two types in the seismic records. One type is characterized by strong top reflections and a smooth surface and underlies accretionary wedge II and the southwest part of the wedge I (outer arc high) off Sumatra and Java. The second type has a low reflectivity and a rougher relief and underlies the tectonic flakes of accretionary wedge I (outer arc high) between the southwestern tip of Sumatra, the SundaStrait and NW Java. The missing outer arc high off the southern entrance of the Sunda Strait is explained by Neogene transtension in combination with arc-parallel strike-slip movements. The NW-SE running, transpressional Mentawai strike-slip fault zone (MFZ) was correlated from the SE Sumatra fore-arc basin to the NW Java fore-arc basin. Off the Sunda Strait northward bending branches of the MFZ are connected with the Sumatra Fault zone (SFZ). It is speculated that the SFZ originally was attached to the Cimandiri-Pelabuhan-Ratu strike-slip faults and shifted from the volcanic arc position into the fore-arc basin area due to clockwise rotation of Sumatra with respect to Java as well as due to increasingly oblique plate convergence since the late Lower Miocene. We explain the transtension of the western Sunda Strait (Semangka graben) and the transpression with inversion of the eastern Sunda Strait, along the newly detected Krakatau Basin, by this rotation. Seismostratigraphic interpretation revealed 5 main sequences (A - E), tentatively dated as Paleogene to Recent in age. The oldest seismic sequence A of assumed Eocene to Oligocene age is bounded at the top by a major erosional unconformity that was identified on all GINCO seismic profiles. The seaward diverging seismic pattern of sequence A is interpreted as a correlative sequence to the prograding Paleogene deltaic sediments encountered by wells offshore central and northern Sumatra. This is opposed to previous interpretation which assumed seaward dipping reflector sequences of basaltic origin erupted along the former Mesozoic passive margin of Sumatra. According to constructed time structure maps, the main NW-SE running depocentres of the post-Paleogene sediments are arc-parallel off Sumatra and Java with thicknesses of 3 s (TWT) and 5 s (TWT), respectively. The main depocentres of the Semangka graben and of the Krakatau Basin of the Sunda Strait strike north-south and have infills of 2 s - 5 s (TWT). Bottom simulating reflectors (BSR) occur within the upper sequences C - D along the flanks of the fore-arc basins and along doming structures but could not be detected in basin centres. Empiric relations of heat flow values and depths of BSR were determined indicating that with increasing waterdepth and decreasing heat flow the depths of the BSR increase.

  • 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.

  • The cruise SO267 ARCHIMEDES I started on December 11th, 2018 in Suva (Fidji) and ended in Suva on January 26th, 2019. Over half of the world´s presently exploited metal deposits were formed during major episodes of crustal growth related to subduction and microplate tectonics. These processes are observed today along the entire margin of the Western Pacific, where complex microplate mosaics offer unique opportunities to study accretion and the emergence of new continental crust. The focus of SO267 was a series of crustal cross-sections at the outer edge of the Indo- Australian Plate, in the largely uncharted waters of the Kingdom of Tonga. The project, entitled “Arc Rifting, Metallogeny and Microplate Evolution – An Integrated Geodynamic, Magmatic and Hydrothermal Study of the Fonualei Rift System”, was designed to document the geological evolution of an emerging microplate mosaic in the NE Lau Basin, a region with some of the fastest growing crust on Earth, and to better understand the sequence of events that cause arc rifting and related magmatic-hydrothermal activity. Using a coordinated approach of high-resolution 2D seismics, electromagnetics and sampling, ARCHIMEDES I imaged the deep structure of the Fonualei Rift system and adjoining back-arc crust of the Niuafo’ou microplate. The goal was to address a major unsolved question concerning crustal growth in complex arc-backarc systems: at what stage in the structural and thermal evolution of the crust does arc rifting occur and seafloor spreading initiate? Planned operations included large-scale reflection and refraction seismic surveys, and a dense program of gravity, magnetics, heat flow, bathymetric mapping and sidescan imaging using the AUV ABYSS and ship-based multibeam systems. This ambitious program was made possible by a close collaboration between GEOMAR and BGR scientists, bringing together diverse expertise and state-of-the-art technologies. To understand the large-scale tectonic processes, we studied 6 different locations within an area of 300 km x 300 km: i) the southern Fonualei Rift Spreading Center (S-FRSC), ii) the region between the S-FRSC and the Eastern Lau Spreading Center (FRSC-ELSC Transfer Zone), iii) the northern tip of the Eastern Lau Spreading Center (ELSC), iv) the northern tip of the Fonualei Rift system (N-FRSC), v) the Mangatolu Triple Junction (MTJ), and vi) the southward propagating Northeast Lau Spreading centre (NELSC). The combined data represent one of the most comprehensive records of microplate formation from the modern oceans.

  • 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.

  • 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.

  • Continuing the systematic work which was started during a previous BGR expedition with RV AURELIA in Sept./Oct. 2003 the late Tertiary and Quaternary development of the German EEZ was further investigated by seismic profiling. The data format is Society of Exploration Geophysicists SEG Y. Again the research vessel AURELIA was chartered for a period of 21 days from 31st of May to 19th of June 2004. During the cruise the grid of seismic profiles which was aquired in 2003 was completed and data gaps were closed. A total of 2618km of high quality MCS lines were surveyed.

  • 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 area of the 1st leg of METEOR cruise no. 67 lies off the Moroccan coast between longitudes 32.5°N and 35°N and latitude 12°W. Within this continental margin segment multichannel reflection seismic measurements were carried out in parallel with magnetic and gravimetric measurements on 22 lines with a total length of 4,378 km during the period from January 20th to February 13th 1984, with the research objectives: i) to collect new geophysical data for a better understanding of magmatic-volcanic and tectonic processes during the initial drifting phase, and ii) to search for suitable positions for deep drilling sites of the "Ocean Drilling Programme" in the transition zone between continental and oceanic crust. A distinct and sharp reflection seismic boundary running from about 31°30'N/11°W in the south to 34°30'N/10°25'W in the north separates flat-lying Mesozoic sediments overlying slightly structured basement of the Jurassic "Magnetic Quiet Zone" from the complex Moroccan piercement zone in the east. A prominent magnetic anomaly, called S1, is nearly coincident with the sharp reflection seismic boundary, and is thought to represent most probably the initial drifting zone. The Moroccan piercement zone is interpreted to represent the eastern part of a pre-Jurassic rift-basin which conjugated western part lies off Nova Scotia/Canada. Subsidence associated with small-scale rotational block-faulting was time-transgressive in the Moroccan piercement zone, e.g. it started in Triassic time in the central part of the rift-basin and affected successively its landward parts apparently due to successively cooling of the stretched and thinned crust. Weak magnetic anomalies trending approximately NE-SW were recorded within the Jurassic "Magnetic Quiet Zone" lying west of magnetic anomaly S1. These anomalies can be correlated over distances of up to 300 km. They are interpreted to represent either variations of the geomagnetic field intensity or field reversals during a time of weak geomagnetic field.

Barrierefreiheit | Datenschutz | Impressum