Preliminary Results of a Seismic Refraction Study in the Meriadzek-Trevelyan Area, Bay of Biscay

Avedik, F.; Howard, David

doi:10.2973/dsdp.proc.48.153.1979

Cited by 10 publications

(15 citation statements)

References 9 publications

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“…In contrast, Upper Jurassic and possibly lowermost Cretaceous sedimentary rocks up to 3 km thick cap basement fault-blocks in the northern Bay of Biscay . This is in agreement with the ideas of Avedik and Howard (1979), based on seismic refraction work: they suggested that the north Biscay margin crosscuts the Western Approaches Mesozoic Basin, and that the Goban Spur margin crosscuts the structurally high Cornubian Ridge (see .…”

Section: Pre-rift Geology: the Continental Basementsupporting

confidence: 90%

Regional Geology of the Goban Spur Continental Margin

Masson¹,

Montadert²,

Scrutton³

1985

Initial Reports of the Deep Sea Drilling Project

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All available geophysical data have been integrated with the Leg 80 drilling results to produce a regional geological synthesis of the Goban Spur passive continental margin. The thin sediment sequence overlying basement is divided into three seismostratigraphic sequences. The lowest of these, sequence 3, occurs in fault-bounded basins, often wedgeshaped in cross-section. Intraformational reflector geometry shows that faulting and tilting of the underlying basement occurred simultaneously with the deposition of formation 3. The upper two sequences are draped over the basement topography and postdate any large-scale fault movement. The early history of the margin, the rift phase, was characterized by the formation of an "en-échelon" series of margin-parallel normal faults, most of which downthrow to the west, toward the incipient ocean. No evidence of fractures perpendicular to the margin has been found. 3 Estimates of upper-crustal thinning, derived from the geometry of fault blocks, are in the range 1.03 to 2.20. They show no relationship with whole-crustal extension values derived from gravity modeling, indicating that the uniform extension model of passive-margin formation cannot be applied to Goban Spur. Evidence from one drill site (549) indicates that the rift phase had a duration of about 15 m.y. However, the age of the rifting-to-spreading transition derived from Site 549 is between 2 and 4 m.y. greater than the age derived from Site 550, drilled on the ocean crust. A possible explanation is that extension within the upper continental crust was taken up by dyke injection, particularly within the rift axis, during the later stages of rifting. Syn-rift volcanic activity, identified from seismic profiles and magnetic-anomaly modeling, may be evidence for this phenomenon. At the end of rifting, a wide zone of fault-bounded basement highs and sedimentary basins, with a relief of ± 1 km relative to sea level, existed east of Pendragon Escarpment. West of the escarpment lay a narrow trough, with water depths up to 2 km. Ocean crust began to accrete in this deep-water area in the middle Albian. The post-Albian structural history of the margin has been dominated by thermal subsidence.

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Section: Pre-rift Geology: the Continental Basementsupporting

confidence: 90%

Regional Geology of the Goban Spur Continental Margin

Masson¹,

Montadert²,

Scrutton³

1985

Initial Reports of the Deep Sea Drilling Project

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“…I, continental shelf; II, continental slope; III, 'neck area'; IV, ocean-continent transition zone; V, true oceanic domain; NBR, North Biscay Ridge. Avedik & Howard (1979) and Montadert et al (1979). (b) The Armorican margin from Le Pichon & Sibuet (1981).…”

Section: Introductionmentioning

confidence: 93%

“…Following these observations, most workers (e.g. Avedik & Howard 1979;Montadert et al 1979b) have shown that the Western Approaches margin from the shelf to the true oceanic crust is characterized by a striking succession of tilted fault blocks beneath which occurs the S reflector (Fig. 3a).…”

Section: Introductionmentioning

confidence: 95%

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Deep structure of the Armorican Basin (Bay of Biscay): a review of Norgasis seismic reflection and refraction data

Thinon

Matias²,

Réhault

et al. 2003

JGS

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137

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International audienceThe Bay of Biscay is bounded to the North by the North Biscay margin, which comprises the Western Approaches and Armorican segments. In the 1970s and 1980s, most researchers considered this margin typical of a non-volcanic passive margin: It is characterized by a striking succession of tilted blocks beneath which occurs the S reflector and the continent/ocean boundary is abrupt. This paper examines the Armorican segment and is based on a study of all early seismic profiles together with new multichannel reflection and refraction seismic data (NORGASIS cruise). An important result is the discovery of a 80-km wide Ocean-Continent Transition zone that coincides with the Armorican Basin (a deep sedimentary basin). It is characterized by a High-Velocity Layer-Crust (7.4-7.5 km/s) overlain by sediments. The other results are: i) the main crustal thinning occurs exclusively under the narrow continental slope. ii) The tilted blocks and the S-reflector are observed only at the base of the continental slope in the narrow domain called "neck area". iii) the North Biscay Ridge is a large oceanic plateau present only off the NW Armorican margin rather than a long ridge elongated off the whole North Biscay Margin

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“…2b). Comparison with early refraction data suggested that this reflector corresponded to the boundary between a 4.9 and 6.3 km.sec ^ layer (Avedik & Howard, 1979). De Charpal et al (1979 and Montadert et al (1979) interpreted the 6.3 km.…”

mentioning

confidence: 99%

A seismic refraction and reflection study of the continent-ocean transition beneath the north Biscay margin

1982

Deep Sea Research Part B. Oceanographic Literature Review

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(Ziegler, 1978 and this volume) and the adjacent margins of the North Atlantic Ocean.It has become clear that extension may also occur in strike slip and convergent settings (Bally & Snelson, 1979), and examples include the Western Mediterranean (Biju-Duval et al., 1977) , the Pannonian Basin (Royden & Sclater, 1981) and the Great Basin (Profett, 1977).The occurrence of crustal extension, expressed by rifting, in these different geological settings emphasises that very little is known of the mechanisms producing the rifting process, including its initiation, which cause the profound changes in crustal structure revealed by attenuation and ultimately by the formation of a spreading ocean basin. . "Several innovative theoretical models (McKenzie, 1978;Royden et al., 1980;Royden and Keen, 1980; Sclater & Christie, 1981;Turcotte, 1981) have proposed mechanisms for lithospheric extension and have attempted to evaluate quantitatively the mechanical and thermal consequences of each model in terms of histories of margin and basin subsidence. These models may have a potential practical value in predicting the thermal history and thus the degree of.hydrocarbon maturity in sedimentary basins formed in response to a lithospheric extension (Royden & Keen, 1980;Royden et al., 1980;Sclater & Christie, 1980). However, a rigorous description of the deep crustal structure beneath a cratonic sedimentary basin or a passive continental margin that would provide sufficient data to quantify the extension in order to constrain these models has been lacking as has a comprehensive study of the geological and thermal history of basins that have evolved in response to lithospheric extension.In this paper, we present some of the results of a detail seismic refraction and reflection study of the northern or Armorican margin of the Bay of Biscay. The study examined the deep crustal structure (Montadert, Roberts et al., 1977;Montadert et al. , 1979). -The overall tectonic style consists of tilted and rotated fault blocks whose downthrow is consistently down toward the ocean. The pattern of faults is probably en-echelon or anastomosing. Many of the fault blocks are bounded by listric normal faults ( Fig. 2a) with throws of up to 3000 m. The listric faults flatten out with depth close to the top of a sub-horizontal group of reflectors called 'S' (Fig. 2b). Comparison with early refraction data suggested that this reflector corresponded to the boundary between a 4.9 and 6.3 km.sec ^ layer (Avedik & Howard, 1979). De Charpal et al. (1979 and Montadert et al. (1979) interpreted the 6.3 km. sec ^ refractor as the boundary between the upper brittle and the lower ductile continental crust. Refraction data on the shelf (Holder & Bott, 1971) suggested that the Moho shoaled from 25 km beneath the shelf break to 12 km near the continent-ocean transition where, from the available refraction data, the observed ductile crust was estimated to be only 3 km -2-in thickness. These early results showed that the observed thinning of the crust could not be ful...

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Preliminary Results of a Seismic Refraction Study in the Meriadzek-Trevelyan Area, Bay of Biscay

Cited by 10 publications

References 9 publications

Regional Geology of the Goban Spur Continental Margin

Regional Geology of the Goban Spur Continental Margin

Deep structure of the Armorican Basin (Bay of Biscay): a review of Norgasis seismic reflection and refraction data

A seismic refraction and reflection study of the continent-ocean transition beneath the north Biscay margin

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