Structure of the western Somali Basin

Bunce, Elizabeth T.; Langseth, Marcus G.; Chase, R. L.; Ewing, William M.

doi:10.1029/jz072i010p02547

Cited by 39 publications

(20 citation statements)

References 7 publications

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“…The break-up of the African plate to form the Red Sea and Gulf of Aden must have occurred during the recent spreading period. The sediment distribution in the Western Somalia basin discussed by Bunce et al (1967) agrees with the history derived from the magnetic lineations. They found that the thick sediments in the Somali Abyssal Plain thinned eastwards where large magnetic anomalies were observed (Bunce et al 1967 , Fig.…”

supporting

confidence: 78%

“…The other major feature of the Arabian Sea-floor is the Owen fracture zone (Matthews 1966), which separates Arabia from the greater part of the Arabian Sea, and is also weakly seismic. Matthews suggested the Chain ridge, which lies to the south of the Carlsberg ridge and is not seismically active, forms the southern extension of Owen fracture zone, though others (Bunce et al 1967) do not agree. The northern boundary of the Arabian Sea is the eastward continuation of the Zagros fold belt, and is the only boundary of the sea which is at present a plate boundary.…”

Section: The Arabian Seamentioning

confidence: 99%

“…The change in sediment thickness is sharp and occurs across a small ridge, which is approximately in line with a southern continuation of Chain Ridge further north. Rocks dredged from the Amirante (Fisher et al 1968) and Chain Ridges (Bunce et al 1967) have been dated by radiometric methods as 82 My and 89.6 My old respectively. Both these dates are compatible with the formation of the Arabian Sea since the Cretaecous, since both show that rocks do exist on the margins of the sea which are older than the oldest lineations recognized.…”

mentioning

confidence: 99%

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The Evolution of the Indian Ocean since the Late Cretaceous

McKenzie

Sclater²

1971

Geophysical Journal International

846

361

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All available ship and aeroplane tracks across the Indian Ocean were searched for identifiable magnetic anomalies and transform faults, and hence the age and direction of motion at the time of formation of about two-thirds of the floor of the ocean established. The magnetic lineations show that India moved away from Antarctica at about 18 cm/y for 20 My in the Early Tertiary. This rapid motion ceased in the Eocene and was followed by a period in which little or no spreading took place west of the Ninety East Ridge. Australia separated from Antarctica during this period. The present spreading episode began about 36 My ago. This detailed study has permitted instantaneous poles of rotation to be obtained, and has established that Africa is now moving northward at 2cm/y relative to Antarctica in the South West Indian Ocean. The evolution of the triple junction between the South East, South West and Central Indian Ridges is clearly reflected in the topography and magnetic lineations. The depth of parts of the ocean formed since the Late Cretaceous increases with age in the manner expected from the temperature structure of a cooling plate, and supports the evolution determined from the magnetic lineations in a most remarkable way. Heat flow observations are more scattered but also consistent with the same thermal model. The proposed evolution agrees with the distribution of known continental fragments and with the Late Cretaceous palaeomagnetic poles from surrounding continents and one obtained from the shape of the magnetic lineations south of India. It is, however, not yet clear how to reconstruct Gondwanaland from the Late Cretaceous reconstructions.

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supporting

confidence: 78%

Section: The Arabian Seamentioning

confidence: 99%

mentioning

confidence: 99%

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The Evolution of the Indian Ocean since the Late Cretaceous

McKenzie

Sclater²

1971

Geophysical Journal International

846

361

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“…Very little can be said about the westernmost Indian Ocean. It is, however, probable that Madagascar and the Seychelles were detached from the African continent in the earliest phase of drift, as suggested by the large sediment accumula,tions [Bunce et al, 1967] and the recovery of various samples of Mesozoic sediments (Figure la).…”

Section: ) the Change Of The Pole Of Rotation To 26øn 21øementioning

confidence: 99%

Magnetic anomalies in the Indian Ocean and sea-floor spreading

Pichon¹,

Heirtzler²

1968

J. Geophys. Res.

295

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A reconnaissance survey of the magnetic anomaly pattern over the Indian Ocean is interpreted in terms of the spreading floor hypothesis. The recent movements of the oceanic crustal blocks and of the adjacent continents are deduced from an examination of the axial magnetic pattern over the mid‐ocean ridge. An active branch of ridge runs SE‐NW from south of Australia to the Gulf of Aden, and the spreading along its axis corresponds to a relative rotation of Africa away from Asia with the pole of rotation centered near 26°N and 21°E. A southwest branch of ridge running from Mauritius to south of Africa has not been the site of measurable spreading since the Mesozoic era. A description of the anomaly pattern over the flanks of the ridge leads to a hypothetical history of the fragmentation of the Gondwana continent.

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“…The Northern Somali Basin has been described by Bunce et al [1966Bunce et al [ , 1967. They found that it is characterized by a flat abyssal plain morphology underlain by about 2 s of flat layered sediments.…”

Section: Introductionmentioning

confidence: 99%

Somali Basin, Chain Ridge, and origin of the Northern Somali Basin gravity and geoid low

Cochran¹

1988

J. Geophys. Res.

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The Northern Somali Basin, located between Chain Ridge and the Horn of Africa north of 4°N, is characterized by a distinct 5‐m geoid low and by large negative gravity anomalies. The boundaries of the basin are marked by steep gradients in both gravity and geoid. Basement in Northern Somali Basin is 1–2 km deeper than on the Carlsberg Ridge flank to the southeast or on the Sheba Ridge flank to the north with a sharp discontinuity across the boundary of the basin. The Western Somali Basin, to the south, was created in the Late Jurassic and Early Cretaceous by the movement of Madagascar away from Africa. Reinterpretation of the magnetic anomalies in the Western Somali Basin shows that they record both limbs of a mid‐ocean ridge that was active by M22 time (Kimmeridgian) and died soon after MO (Aptian). Magnetic and gravity data allow the relict ridge crest to be traced from Davie Ridge near the African coast to the Dhow‐VLCC‐ARS fracture zone complex at 50°E. Davie Ridge is a transform fault connecting the Western Somali Basin spreading center with a similar age spreading center in the Mozambique Basin. The Dhow‐VLCC‐ARS complex can be shown to continue north of the 4°N bathymetric high separating the Northern and Western Somali Basins and to intersect the African margin near 7°N, The Northern Somali Basin thus appears to be the third of a series of oceanic basins separated by long transform faults created during movement between East and West Gondwanaland. The original Northern Somali Basin was split apart by the northward motion of India in the Late Cretaceous and Chain Ridge formed along the new boundary. Thermal and gravity modeling shows that the flexure resulting from differential subsidence across Chain Ridge combined with the difference in lithospheric thermal structure (Late Jurassic vs. Early Tertiary) on either side of it explains well the amplitude and shape of the observed geoid step and gravity anomalies across Chain Ridge. The geoid step up from the basin up to the African coast can be modeled as an edge effect between the juxtaposed Jurassic oceanic and African continental crust. Thus, the geoid and gravity low over the Northern Somali Basin results from the superposition of a continental edge effect anomaly and the fracture zone edge effect anomaly.

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Structure of the western Somali Basin

Cited by 39 publications

References 7 publications

The Evolution of the Indian Ocean since the Late Cretaceous

The Evolution of the Indian Ocean since the Late Cretaceous

Magnetic anomalies in the Indian Ocean and sea-floor spreading

Somali Basin, Chain Ridge, and origin of the Northern Somali Basin gravity and geoid low

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