BGR Bundesanstalt für Geowissenschaften und Rohstoffe

Marine seismic survey area: Off Africa / Pakistan - Reflection seismic data

Refraction seismic data

Working area: Off Africa / Pakistan
(1) Off NW Africa(1)(2) Off Angola / Namibia(3) Off Pakistan / Makran(4) Off Madagascar
ME67 (Meteor) 1984
ME39 (Meteor) 1975SO75 (Sonne) 1991BGR91 (Bin Hai) 1991SO122 (Sonne) 1997BGR07(M.Dufresne) 2007
ME46 (Meteor) 1977ME20 (Meteor) 1992BGR95A (Ak. Nemchinov) 1995SO231 (Sonne) 2014
VA79 (Valdivia) 1979BGR85 (Prospekta) 1985BGR03 (Sea Surveyor) 2003
ME53 (Meteor) 1980BGR88 (Prospekta) 1988


Working Area Off Africa and PakistanWorking Area Off Africa and Pakistan Source: BGR

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Cruise Meteor 39 (ME39) 1975

Vessel Meteor

West Africa

Multichannel seismic data acquisition parameters:
Total length of lines302 km
Sampling rate4 ms
Record length10 000 ms
Streamerdigital - 24 channels

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Cruise Meteor 46 (ME46) 1977

Vessel Meteor

West Africa

Multichannel seismic data acquisition parameters:
Total length of lines1.831 km 
Sampling rate4 ms
Record length10 000 ms
Streamerdigital - 24 channels

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Cruise Valdivia 79 (VA79) 1979

Vessel Valdivia

West Africa

Multichannel seismic data acquisition parameters:
Total length of lines1.831 km 
Sampling rate4 ms
Record length10 000 ms
Streamerdigital - 24 channels

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Cruise Meteor 53 (ME53) 1980

Vessel Meteor

West Africa

Multichannel seismic data acquisition parameters:
Total length of lines1.195 km 
Sampling rate4 ms
Record length10 000 ms
Streamerdigital - 24 channels

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Cruise Meteor 67 (ME67) 1984

Vessel Meteor

West Africa

Multichannel seismic data acquisition parameters:
Total length of lines4.378 km 
Sampling rate4 ms
Record length10 000 ms
Streamerdigital - 24 channels

Summary

The area of the 1st Leg of METEOR cruise no. 67 lies off the Moroccan coast between longitudes 32.5°N und 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 20, 1984 to February 13, 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 Program" 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 flatlying 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, . 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.

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Cruise SONNE 75 (SO75) 1991

Vessel SONNE

Portugal

Multichannel seismic data acquisition parameters:
Total length of lines3600 km
Sampling rate4 ms
Record length12 000 ms
Streamerdigital - 48 channels

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Cruise Meteor 20 (ME20) 1992

Vessel Meteor

West Africa

Multichannel seismic data acquisition parameters:
Total length of lines3700 km
Sampling rate4 ms
Record length12 000 ms -millisecond
Streamerdigital - 48 channels

Summary 

The METEOR cruise M20/3 had two scientific objectives: One research topic was to study the variability of the Mesozoic oceanic crust along two flow-line profiles located north of the Kane and Hayes Fracture Zones. The other research topic was the investigation of the weak magnetic anomalies in the Jurassic magnetic quiet zone north of the Canary Islands. Seismic data with a coverage of 2 400 % were acquired together with magnetic, gravimetric and hydroacoustic data along the two flow-line profiles with a total length of 1 595 km. Magnetic, gravimetric and hydroacoustic measurements were carried out on 31 profiles with a total length of 6 069 km in the Jurassic quiet zone north of the Canary Islands. On 10 of these lines multichannel seismic reflection data (2 138 km) have been acquired.

Although Cenozoic volcanism - equivalents of the Madeira Islands and Cape Verde Islands volcanism - has strongly affected the region of the Mesozoic oceanic crust surveyed by the two flow-line profiles, an at least 74 km wide oceanic crustal structure characterized by a divergent pattern of reflectors having ubiquitous seaward dip was observed. This remarkable structure was found beneath the Madeira-Torre Rise north of the Hayes Fracture Zone in the region of the distinct magnetic anomalies M0 to M4. The structure is interpreted to represent a voluminous buildup of layered extrusive rocks formed during a short and excessive episode of volcanism at the spreading center during Barremian through Early Aptian time. The oceanic crustal structure has magnetization of about 7 A/m. According to our present state of knowledge the sequence of seaward dipping basement reflectors in most cases consists of strongly magnetized rocks with uniform polarity of the magnetization. Strikingly high magnetic anomalies in oceanic crustal areas can be considered as hint on such volcanic features.

The flow line profile north of the Kane Fracture Zone does not show the expected oceanic basement unit of seaward dipping reflectors in the area of anomalies M0 - M4. The amplitudes of the magnetic anomalies are normal. They can be modelled easily with the Mesozoic reversal time scale. The crust of anomaly M0 age is strongly affected by Tertiary volcanism.

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Cruise BGR85 1985

Vessel Prospekta

West Africa

Multichannel seismic data acquisition parameters:
Total length of lines5.362 km
Sampling rate4 ms
Record length10 000 ms
Streamerdigital - 60 channels

Summary

A geophysical reconnaissance survey across oceanic fracture zones has been carried out by the BGR in the eastern North Atlantic using S.V. -search vessel 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 F.Z., the Atlantis F.Z. and the Kane F.Z respectively.

24 geophysical lines with a total length of 5.362 km r have been measured. Besides intracrustal seismic events a deep coherent seismic event is often recognizable in the monitor records between 10 - 12 s d (TWT) along several lines, which probably is a reflection from the crust-mantle boundary.

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Cruise BGR88 1988

Vessel Prospekta

West Africa

Multichannel seismic data acquisition parameters:
Total length of lines1.760 km
Sampling rate4 ms
Record length11 000 ms
Streamerdigital - 62 channels

Summary

In continuation of a fracture zone survey of BGR in 1985, there was a multichannel seismic survey of the Hayes Fracture Zone between 20°W and 27°W in the time from October 26th to November 11th, 1988. In spite of bad weather conditions, it was possible to collect a total of 1.760 km seismic and gravity data on 11lines.

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Cruise BGR91 1991

Vessel Bin Hai

West Africa / Angola / Namibia

Multichannel seismic data acquisition parameters:
Total length of lines4.500 km
Sampling rate4 ms
Record length15 000 ms
Streamerdigital - 120 channels

Summary

The BGR 1991 cruise with ‚M.V. BIN HAI 511‘ was designed to study the variability of the oceanic crustal structure along flow-line profiles perpendicular to the ridge axis over Early Tertiary through Cretaceous old oceanic crust of the eastern Atlantic Ocean.

Seismic data with a coverage of 3,000 % were acquired along four flow-line profiles with a total length of 4,194 km, and in addition 270 km, of MCS data were collected.

The most intriguing new observation from the seismic flow-line profiles is the discovery of two huge oceanic crustal structures characterized by an internally divergent to planar pattern of reflectors having ubiquitous seaward dip. These remarkable structures were found within an about 1,300 km long oceanic crust segment of the eastern South Atlantic located between the Bode Verde Fracture zone in the north and the Rio Grande Fracture Zone in the south. These structures resemble the prominent wedges of seaward dipping reflectors on the widespread volcanic rifted continental margins described in the literature.

They are interpreted to represent voluminous build-ups of layered extrusive rocks formed during three excessive episodes of volcanism that accompanied the Cretaceous opening of the South Atlantic. These episodes of excessive volcanism/magmatism are: An episode immediate prior to, and during the first stage of seafloor spreading in the South Atlantic, i.e. during about Hauterivian through about early Aptian; an episode of inferred subaerial and/or shallow marine volcanism along the central South Atlantic spreading ridge during the Albian; and an episode of inferred subaerial and/or shallow marine volcanism along the South Atlantic spreading ridge during latest Cenomanian/earliest Turonian through early Campanian.

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Cruise BGR95A 1995

Vessel M/V Akademik Nemchinov

Angola / Namibia

Summary

The BGR95 cruise in December 1995 with M.S. AKADEMIK NEMCHINOV was designed to acquire new marine geophysical data for a better understanding of the geological processes and structural variations of the Cretaceous-aged oceanic crust of the Angola Basin in the South Atlantic regarding its reflectivity pattern, its shape of the basement surfaces and its crustal thickness. These evaluations were extended onshore to the ‘Damara Igneous Province’. The aim of this study was the investigation of the rift-related volcanic-magmatic processes accompanying the initial stage of the opening of the South Atlantic Ocean.

The survey was a co-operation of

The M.S. AKADEMIK NEMCHINOV generated the seismic signals by a tuned airgun array of 3260 cu.in. (= 53.4 .) together with two AWI owned large volume guns of 2 x 2000 cu.in. (= 65.6 l), recorded the MCS signals with a 3000 m streamer and controlled the shot releases for the ocean bottom hydrophones (OBH’s) and the onshore seismic stations (PEDAS).

A total of 5,114 km of multichannel seismic reflection data in parallel with magnetic and gravity measurements have been collected onboard the M.S. AKADEMIK NEMCHINOV. 1069.4 km of the seismic work was done on 3 combined refraction/wide angle offshore and onshore traverses. The offshore part was recorded by 7 ocean bottom hydrophones (OBH) operated by the M.V. POLAR QUEEN (Reichert et al., 1996). The registration onshore Namibia was performed by 25 mobile seismic landstations (PEDAS) on each profile (Schulze et al., 1996).

First results are described in the offshore and onshore reports of these investigations (Reichert et al., 1996, and Schulze et al., 1996). The data clearly show distinct series of the seaward dipping reflector sequences (SRDS) and isochronous variations in the accretion of the oceanic crust. The onshore and offshore registrations show deep arrivals from diving and refracted waves in a range up to 200 to 400 km,

Aside of the geoscientific aims technical studies about the random shot releases, the shot distance distributions and the signal strength and signal spectres of the different seismic source configurations were made aboard the M.S. AKADEMIK NEMCHINOV. 

Multichannel seismic data acquisition parameters:
Total length of lines5.114 km
Sampling rate4 ms
Record length14 000 ms
Streamerdigital - 120 channels


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Cruise BGR03 2003

Vessel Sea Surveyor

Breakup of the South Atlantic (BOSA) / Cape Town

Multichannel seismic data acquisition parameters:
Total length of lines3.260 km,
Sampling rate4 ms
Record length14 336 ms
Streamerdigital - 132 channels

Summary

From april 17th to june 06th 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.

There's a very complex distribution of offshore volcanic rocks (Seaward Dipping Reflector Sequences, SDRS) along the South African Atlantic margin. On the one hand widespread well developed wedges of SDRS are present in the North. One the other hand multiple wedges of SDRS subdivided by strong single reflection bands indicate an episodicity during the emplacement of the volcanics in the South. A first interpretation of the very uneven distribution of offshore volcanics north and south of the area of the Cape Peninsula could be due to the presence of a fracture zone. A similar fracture zone was postulated on the conjugated Argentine margin ('Colorado Offset') where an old suture originates on the continent and continues offshore into a typical oceanic fracture zone.

Also the sediment distribution varies strongly along the South African margin. In one case the maximum sediment accumulation is found at the upper and middle continental slope and in the other case the maximum could be found on the shelf.

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Cruise SO122 (SO122) 1997

Vessel SONNE

East Arabian Sea off Pakistan

Multichannel seismic data acquisition parameters:
Total length of lines3.600 km
Sampling rate4 ms
Record length12 000 ms
Streamerdigital - 48 channels

Summary

The Sonne Cruise SO 122 was carried out by the Federal Institute for Geosciences and Natural Resources (BGR, Hannover) from 3 August - 9 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;
  • reconnaissance of the sedimentary history of the Indus Fan in order to reveal the uplift and erosion history of the Himalayas.

Major results of the expedition are:

  • The Little Murray Ridge is a Cretaceous(?), magmatic ridge. Its eastern parts become subducted in the vicinity of the Eurasian, Indian, Arabian Plates triple junction.
  • Sequences of dipping basement reflectors along the northern Murray Ridge and around 20°30'N / 64°30'E (Indus Fan) are interpreted as basalts extruded during the initial continental break up and marking the ocean-continent transition.
  • The Murray Ridge System is of continental origin and experienced a multi-phase volcanism lasting until Upper Miocene/Pliocene. The Murray Ridge System borders the Indian and Arabian Plates and is active since the Paleogene. Recently the Murray Ridge System is in a trantensional, dextral strike-slip setting.
  • The Indus Fan is underlain by thinned continental crust in the area of investigation. Relict sedimentary ridges of the Mesozoic(?) age are onlapped by hemipelagic drift sediments and deposits of the Indus Fan.

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Cruise BGR07 MOBAMASIS 2007

Vessel Marion Dufresne

Madagascar

Multichannel seismic data acquisition parameters:
Total length of lines3800 km
Sampling rate2 ms
Record length14 000 ms
Streamerdigital - 240 channels



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Cruise SO231 PAGE4 2014

Vessel SONNE

Mosambik

Multichannel seismic data acquisition parameters:
Total length of lines4300 km
Sampling rate2 ms
Record length14 000 ms
Streamerdigital - 324 channels



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Contact

    
Dr. Volkmar Damm
Phone: +49-(0)511-643-3226
Fax: +49-(0)511-643-3661

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