Early Tertiary igneous activity west of the Outer Hebrides, Scotland — Evidence from magnetic anomalies and dredged basaltic rocks

Jones, E. J. W.; Mitchell, J. G.; Perry, R.G

doi:10.1016/0025-3227(86)90110-6

Cited by 7 publications

(13 citation statements)

References 15 publications

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“…In general terms, a phase of Palaeocene basalt extrusion was followed by the deposition of late Palaeocene-early Eocene volcanogenic shallowwater sandstones. The volcanogenic detritus is regarded as epiclastic in origin, in contrast to the pyroclastic tufts recovered by Jones & Ramsay (1982), although these latter sediments were dated exclusively as Eocene (late Ypresian NPll-12) and thus may be slightly younger in age. In this scheme, the basalts of the northern Hebrides Shelf and the Wyville-Thomson Ridge are correlated with the Faeroes Lower Series and the basalts of DSDP Hole 117A.…”

Section: Discussionmentioning

confidence: 94%

“…It has been interpreted from gravity modelling as a thick pile of Palaeocene basaltic lavas extruded along NW-SE trending fissures and contemporaneous with the formation of the Faeroe Shelf and Lousy, Bill Bailey and Faeroe Banks (Roberts et al 1983). On seismic reflection profiles the basalts appear to be overlain by sediments (Himsworth 1973), a view supported by Jones & Ramsay (1982) who dredged early Eocene pyroclastic tufts from the north-western end of the ridge (see Fig. 1).…”

mentioning

confidence: 80%

“…2). The outer shelf in this region consists of a westerlythickening wedge of Tertiary and Quaternary sediments (Jones et al 1986b;Stoker & Hitchen, in press) underlain by an irregular reflector identified on shallow seismic data and coincident with strong magnetic anomalies (Fig. 4).…”

Section: Geological Setting Of the Boreholesmentioning

confidence: 99%

“…Gravity and magnetic studies have suggested the presence of early Tertiary igneous and sedimentary rocks on the Hebrides Shelf (Bullerwell 1972;Jones 1978;Brewer & Smythe 1986). Basaltic rocks, yielding a mean age of 43.4+ 1.0 Ma by K-Ar dating, have been recovered in dredge hauls between the known early Tertiary centre of St. Kilda and the Precambrian Flannan Isles (Jones et al 1986a), while an early Oligocene chalk has been collected from the Geikie escarpment, NW of St. Kilda (Jones et al 1986b).…”

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confidence: 99%

“…Basaltic rocks, yielding a mean age of 43.4+ 1.0 Ma by K-Ar dating, have been recovered in dredge hauls between the known early Tertiary centre of St. Kilda and the Precambrian Flannan Isles (Jones et al 1986a), while an early Oligocene chalk has been collected from the Geikie escarpment, NW of St. Kilda (Jones et al 1986b). The BGS borehole data have been tied to a network of shallow seismic profiles throughout the study area, thus extending these earlier observations and allowing a fuller understanding to be gained of the early Tertiary succession bordering the northern Rockall Trough.…”

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confidence: 99%

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Early Tertiary basalts and tuffaceous sandstones from the Hebrides Shelf and Wyville-Thomson Ridge, NE Atlantic

Stoker¹,

Morton²,

Evans³

et al. 1988

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A sequence of Palaeocene basalts and late Pataeocene-early Eocene tuffaceous sandstones has been recovered from three boreholes on the northern Hebrides Shelf and Wyville-Thomson Ridge. The basalts, cored in boreholes 85/5B and 85/7 on the northern Hebrides Shelf, can be seismically correlated with the extensive N Atlantic lava sequence. The basalt in 85/5B displays major element chemistry typical of alkali-basalts but trace and rare-earth element (REE) patterns are typical of olivine-tholeiites. In contrast, the basalt in 85/7 displays geochemical characteristics typical of a depleted tholeiite. Despite their different compositions, the basalts have similar ratios of the highly incompatible elements La and Ta which may reflect different degrees of partial melting of similar source material. The tuffaceous sandstones, cored in borehole 85/2B on the Wyvitle-Thomson Ridge, were deposited in a warm, shallow marine environment contemporaneous with the reworking of nearby basaltic terrains. Nummulites rockallensis Hinte & Wong occurs abundantly throughout the sandstones; its only previous known occurrence is from latest Palaeocene--earliest Eocene sediments at DSDP Site 117A on Rockall Bank. Regional mapping indicates that the tuffaceous sandstones overlie the basalts, thus the latter can be assigned to the Palaeocene (or oIder). This is consistent with K-Ar dates of 57.3-63.1 Ma obtained from the basalts.

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Section: Discussionmentioning

confidence: 94%

mentioning

confidence: 80%

Section: Geological Setting Of the Boreholesmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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