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.
During METEOR-Westafrica cruise 46, leg 1, geophysical measurements were carried out off Morocco between 31°30'N and 32°30'N in the time period from the 8th October to the 5th November 1977. Altogether 1,855 km of 24-fold reflection seismic data were collected on lines ME46-02 to ME46-11 and on lines ME46-14 to ME46-19. For the purpose of planning the programme, the reflection seismic data were processed (12-fold stack) aboard. 3,465 km of magnetic, gravimetric and bathymetric data were collected on lines ME46-01 to ME46-26 using the new BGR digital recording system. Along lines ME46-101 and ME46-102 with a total length of 209 km refraction seismic measurements were carried out with 6 moored telemetric buoys. A total of 164 shots with charges of 5 kg up to 200 kg were fired along the two lines in distances of about 1.5 km. A distinct fault zone was discovered in the area of investigation which is associated with a positive magnetic anomaly. The fault zone strikes NNE-SSW and probably marks the ocean-continent boundary. Beside diapiric structures (salt) allochthonous structures - thrust structures - are widespread features east of the discovered fault zone and below the lower continental slope. The seismic data indicate that the evolution of the old continental margin of the East Atlantic was also controlled by large scale gravity tectonics.
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 late Tertiary and Quaternary development of the German EEZ was systematically inverstigated by seismic profiling. The data format is Society of Exploration Geophysicists SEG Y. For that survey the privately owned motor vessel AURELIA was chartered for a period of 24 days from the 16th of September to 10th of October 2003. A more or less equidistant E-W and N-S grid of profiles with a length of 2500 km was surveyed by high-resolution multichannel seismic system. A 0.82 litre GI-Gun was employed every 12.5 m and the reflected signals were recorded by a 300 m long streamer. Simultaneously a deep-towed HUNTEC-Boomer or a GEO-Sparker was run (150km/620km). All seismic records were processed onboard for the quality control and for a first interpretation.
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.
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 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.
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.
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.
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.
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