During the cruise with S.V. EXPLORA within the Ross Sea on the second marine-geophysical expedition of the Federal Institute for Geosciences and Natural Resources (BGR) to Antarctica, in total 6,745 km of magnetic, gravity and digital reflection seismic lines and additionally 1,400 km gravity lines were acquired in the period from January 10th to March 2nd 1980. On 43 stations sonobuoy refraction measurements have been carried out. The main results are: (1) In the eastern part of the Ross Sea Shelf two striking discontinuities have been identified in the reflection seismics representing gaps in the sediments at the turn-over of the Upper Miocene to the Pliocene (ca. 7 mio years B.P.) and between the Middle and Upper Miocene (ca. 11.5 mio. years B.P.) according to results of DSDP boreholes. (2) In the southern part of the Ross Sea Shelf the basement is uncovered at depths over 700m due to a thrust of the shelf ice recently. (3) A structural unit extends alongside the meridian of 180° separating the Ross Sea into two different geologic regions. This unit is characterised by two basement highs with seismic velocities exceeding 5 km/sec. (4) In relation with the GANOVEX expedition two profiles have been measured off northern Victoria Land which indicate two large faults with a faulting amount of 2 km. Another area is characterised by intrusive and volcanic bodies.
The POLARSTERN cruise ANTVIII/6 from 14. March to 30. April 1990 incorporated an integrated geophysical reconnaissance survey consisting of multichannel seismic measurements in parallel with gravimetric and magnetic measurements. The survey covered the plateaus Maud Rise, Astrid Ridge and Gunnerus Ridge off Queen Maud Land and the oceanic crust in their vicinity. Severe ice and weather conditions allowed seismic work only on the Gunnerus Ridge and on the oceanic crust. Together with previous BGR lines on the Astrid Ridge and the Maud Rise the new data improve considerably the understanding of the area. The main results are: 1. The oldest identified sea-floor spreading anomaly was M11 before the cruise, now it is M24. Thus spreading has begun not only 135 mill. years B.P., but at least 160 mill. years B.P. 2. The Gunnerus Ridge is strongly asymmetric. The mainly weak magnetic anomalies indicate that in contrast to the Astrid Ridge volcanism was not important during its development. 3. The magnetic anomalies are much stronger on the Astrid Ridge and west of it than east of the Astrid Ridge and on the Gunnerus Ridge. 4. The roughness of the basement surface of the oceanic crust varies in a wide range.
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 Sonne Cruise SO122 was carried out by the Federal Institute for Geosciences and Natural Resources (BGR, Hannover) from 3rd August to 9th September 1997, in cooperation with GEOMAR (Kiel), the National Institute of Oceanography (NIO, Karachi) and the Hydrocarbon Development Institute of Pakistan (HDIP). During the joint project with R/V SONNE the Makran accretionary wedge off Pakistan should have been investigated in detail with multi-channel reflection seismics, magnetics and gravimetry. Intense fishery offshore Pakistan forced a change of the area of investigation to the south with the following objectives: investigation of the crustal structure and occurrence of the bottom simulating reflector (BSR) in the Makran accretionary wedge; investigation of the structure of the Murray Ridge System in order to reconstruct the geodynamic evolution of the eastern Indian Plate margin; determination of the origin of the crust underlying the Indus Fan and reconnaissance of the sedimentary history of the Indus Fan in order to reveal the uplift and erosion history of the Himalayas.
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 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.
The CINCA marine geoscience investigations on the convergent continental margin of Chile between 19°S and 33°30'S were accomplished during three legs of RV SONNE cruise SO-104, from 22. July to 15. October 1995. The objectives of the first leg are to contribute to an understanding of the geological architecture and of the tectonic mechanism in the area of the Chile convergent zone through a geophysical assessment of the tectonic structures of the Chile continental margin and the adjacent oceanic Nazca plate. During the first leg from 22. July to 24. August 1995 multichannel seismic reflection data with BGR's new digital streamer were collected along a systematic grid with a total traverse length of 4,494 km simultaneously with the acquisition of magnetic, gravimetric, Hydrosweep and Parasound data over a total traverse length of 7,012 km. GFZ's mobile land array of 12 seismic stations recorded the air gun shots fired by RV SONNE within the CINCA area. Three seismic lines were surveyed between 32°30'S and 33°30'S in the area of the CONDOR project. Here, the surface of the downbending oceanic crust is smooth. The 5,000 m to 6,000 m deep trench floor is underlain by sediments, in excess 2,500 m thick. The inner trench slope consists of a landward thickening accretionary wedge which terminates against a body forming the base of a fore arc basin near Valparaiso. The principal area of the CINCA project extends between 19°S and 26°S and comprises the convergent continental margin, the Peru-Chile trench and the seaward adjacent part of the Nazca plate up to approximately 75°W longitude. The tectonic regime of these units of the CINCA area is very different from the tectonic system of the respective units of the CONDOR area. The Eocene-aged and sediment-starved oceanic crust of the Nazca plate becomes blockfaulted when approaching the outer trench slope break. The 50 km to 70 km wide outer trench slope is characterized by a complex system of horst and graben structures in the CINCA area probably resulting from the strong downbending. Steep fault scarps forming the flanks of the horsts reach vertical offsets varying between few hundreds of metres to 1,000 m, and locally even more. The 7,000 m to 8,l00 m deep trench is very narrow and mostly sediment-starved in the CINCA area. Morphology and architecture of the continental margin of the CINCA area are controlled by planar and listric faulting and tilted blocks of inferred continental nature, which apparently slid down into the trench. The inferred continental blocks, overlying a reflective mass, are covered by sediments of presumably turbiditic nature. An accretionary wedge is difficult to define on the seismic single channel records from the CINCA area. However, processed seismic data show a deep reflective mass underlying the downfaulted blocks of inferred continental nature. This deep reflective mass is interpreted to consist of a tectonically eroded and underplated continental crust-basalt melange forming the transition between the downfaulted continental upper plate and the subducting oceanic lower plate. Complex structural highs of still unknown origin and nature have been observed on the upper continental slope at 20°S, 24°S and 25°S. The northernmost structural high represents the seaward termination of the Iquique fore arc basin. The accuracy of the acquired gravity and bathymetric data is very good, i.e. better than 1 mGal and less than 10 m. The Chile trench is associated with strong negative gravity anomalies, and the continental margin is characterized by several positive and negative gravity anomalies of varying size and amount. The first results of magnetic modeling show, that the intensive blockfaulting of the oceanic crust across the outer trench slope causes no loss of the magnetization of the oceanic crust. The air gun shots fired by RV SONNE in 50 m intervals along 17 seismic traverses were recorded by GFZ's mobile land array in the coastal area of Chile. Good quality data were obtained out to about 100 km distance and in some cases even out to about 150 km.
SeaCause cruise SO186-2, aboard the RV Sonne, was carried out off northern Sumatra between 21st January and 24th February 2006, with mobilisation and demobilisation in Singapore and Penang, Malaysia, respectively. The geophysical survey acquired multichannel seismic data (MCS) using a 240 channel, 3 km Sercel 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, subseabed data using the hull mounted high resolution Parasound profiler together with gravity and magnetic data were also acquired. The main scientific objective of the survey was to investigate the southern part of the rupture zone of the 26th December 2004 9.3 magnitude earthquake, that caused the catastrophic tsunami of that date, and the rupture zone of the 8.7 magnitude earthquake of March 28th 2005. Specifically, to identify the segment boundary between the two earthquakes, as recognised by the distribution of their aftershocks. This was to be achieved by mapping the structure of the subduction zone including the dip angle of the subducted plate, the architecture of the accretionary prism and the structure of the forearc basins, particularly their strike-slip fault systems. Also to be investigated was whether there was a contribution to the 2004 tsunami from major submarine failures. During the survey a total of 5358 line kilometres of MCS data were acquired, mainly on lines oriented orthogonal to the subduction zone and extending from the ocean basin across the trench and accretionary prism to the forearc basins offshore Sumatra. The orthogonal survey lines were located on average approximately 40 km apart. The survey was planned using the bathymetry from the HMS Scott, RV Natsushima and RV Sonne cruises carried out in 2004. The morphology of the trench and sediment thickness varies from north to south. In the north the trench is poorly defined with shallow seabed dip but with sediment thickness of ~3.5 secs (TWT). The seafloor dips increase southwards, but sediment thickness decreases to ~2.5 secs (TWT) off Nias. Both the ocean basin and trench sediments are dissected by numerous normal faults, oriented subparallel to the plate boundary, with many that penetrate the oceanic crust. In the south Fracture Zones were identified. The structure of the deformation front on the seaward margin of the accretionary prism is highly variable. While the younges main thrust are predominantly landward vergent there are examples for seaward verging thrusts. The frontal fold develops in some cases already in the french while in most cases the frontal fold is at the beginning of the accretionary wedge. At some locations there are large sediment slumps on the frontal thrusts, the slope angle of the prism varies between 6 to 15 degrees, an angle that explains the large scale slumping. The width of the accretionary prism is widest in the north of the area at 140 km and narrows southwards until in the vicinity of the islands it is 40 km. In the north and central parts of the survey area the passage from the deformation front landwards into the older prism is rapid and the seabed gradients steep. The dip of the oceanic crust remains low and there is an obvious twofold increase (6-7 seconds TWT) in the sediment thickness. The basal decollement of the thrusts at the deformation front is in the lower sediment layer overlying oceanic basement. This is traced northeastward. A possible explanation for the increase in thickness of the prism is therefore considered to be the formation of a thrust duplex. Perhaps this is due to the subducted sediment thickness. In this region the prism forms a plateau and the internal pattern of the uppermost sediments shows striking similarities to the trench fill. Offshore of Simeulue Island the prism structure changes and it forms the more usually seen taper. The offscraped sediment forms a thinner section, the thrusts are more steeply dipping. The dip of the subducted plate here is greater than in the north. Three forearc basins were surveyed. In the north the western margin of the Aceh Basin lies along the West Andaman Fault. Within the main basin the sediments are internally undeformed. Farther south in the Simeulue Basin the northern and central parts there are numerous, active steeply dipping faults. In southern part of the basin there is a transpressional fault similarly to the Mentawi Fault off southern Sumatra. There are notable ‘bright spots’ in the upper section that may indicate the presence of hydrocarbon gas. There are also widespread Bottom Simulating Reflectors indication the presence of gashydrates and there may be also one double BSR. At the southern end of the surveyed area the Nias Basin may be subdivided along its length into two parts by a northnorthwest to southsoutheast trending carbonate platform development. The basin has had a varying subsidence history, in the south the subsidence was completed before the northern part started.
In the period from October 16, 1978 to December 9, 1978 geophysical investigations have been carried out on SONNE cruises SO-7A and SO-7B on the Lord Howe Rise off eastern Australia and in the northern Coral Sea by the Federal Institute for Geosciences and Natural Resources (Hannover) in co-operation with the Bureau of Mineral Resources, Geology & Geophysics (Canberra), Department of Scientific and Industrial Research (Wellington), Geological Survey of Papua New Guinea (Port Moresby). A total of 10,500 km of bathymetric, magnetic and gravity profiles, 7,000 km of digital seismic reflection profiles and 50 sonobuoy refraction profiles were recorded during this survey. Objective of cruise SO-7A was to determine the depth and nature of the basement of the Lord Howe Rise, the configuration of the early rift basin, and the thickness and internal structure of the enclosed sediments. A new sea-mount in the southern Norfolk Basin rising some 2200 m above sea floor characterized by a free air anomaly of about 80 mgal and by a magnetic anomaly of some 500 nT was found. A complex horst and graben zone often associated with volcanic intrusions underlies the western flank of the Lord Howe Rise. Within some grabens the "breakup"-unconformity seems to exist, supporting the model that the Lord Howe Rise and the Dampier Ridge were once part of the Australian continent. The thickness of pre-breakup sediments is normally small on the Lord Howe Rise. Only in some grabens the thickness of these sediments exceeds 1 second reflection time. The Oligocene/Eocene unconformity and a Miocene unconformity are clearly recognizable in all our seismic records. Best explanation of these unconformities seems to be relative falls in sea level due to swelling and subsidences of oceanic crust. Strong variations in the character of the acoustic basement have been observed. Besides blocks with flat-lying acoustic basement zones with hummocky and irregular basement surface exist which may relate to areas of stretched continental basement contaminated by basaltic intrusions. The eastern edge of the Lord Howe Rise is characterized by an edge anomaly rising to +1000 nT. The general magnetic and gravity features of the western flank of Lord Howe Rise and the Dampier Ridge are: A generally quiet magnetic field with isolated large anomalies, consistent with the faulted acoustic basement of low or moderate susceptibility, with low susceptibility, dense intrusives in places, and also high susceptibility intrusions or flows. Gravimetric/magnetic "edge anomalies" between the outer and western edge of the Lord Howe/Dampier Ridge and the Tasman Sea are apparently absent. The objective of cruise SO-7B was to search for marginal graben zones off the Queensland and Papuan Plateaus associated with the initial rifting of the Coral Sea Basin. In the seismic records at least two regional unconformities are recognizable which represent periods of erosion or non-deposition during Oligocene/Eocene respectively in Miocene time. Further an older unconformity exists in block-faulted regions of the Queensland and Papuan Plateaus. Beneath the present continental slopes the Miocene and Oligocene/Eocene unconformities lie close together and are sometimes coincident. The transition from oceanic crust of the Coral Sea Basin to continental crust of the Queensland and Papuan Plateaus occurs in the surveyed area over a narrow (< 50 km) zone and is associated with a sediment filled graben. The graben-zone observed beneath the present slope of the Queensland and Papuan Plateaus contains more than 2 sec (reflection time) thick sediments of pre-Oligocene/Eocene age. The oceanic crust, as it approaches the plateaus, either rapidly deepens or abruptly stops and/or changes its seismic character so as not to be recognizable. In the seismic records from the outer part and slope of the Queensland and Papuan Plateaus, 5 to 10 km wide, convex, reflectionless zones exist. These features are interpreted as drowned fossil reefs. All observed reefs lie beneath the Oligocene/Eocene unconformity indicating these present deep-water areas were at shallow depths in pre-Eocene time. In the surveyed area post-Oligocene fossil reefs do not exist suggesting these areas were already at upper bathyal depths in the Oligocene. Assuming a seismic velocity for reefal material of 4000 m/s, the reefs on the outer Papuan Plateau have an approximate thickness of 3000 meters. Assuming a reef-growth rate of 25 m/m.y. the growth of the reefs started in upper Jurassic time (120 m.y. + 29 m.y. (assumed age of the Oligocene/Eocene unconformity) yields to 149 m.y.). The basement of the Papuan and Queensland Plateaus is probably crystalline Paleozoic rocks. This is suggested for the Queensland Plateau in particular by their relatively shallow depth, refraction velocities of 6.0 - 6.3 km/s (Ewing et al.) and > 5.0 (this survey) and high intensity magnetics. A complex system of horst and graben structures exist on the Queensland and Papuan Plateaus. A larger graben appears to trend in an East-West direction on the southern Papuan Plateau. This graben is about 1 second (reflection time) deep and varies in width from 5 to 20 km.
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