Hostname: page-component-cd9895bd7-dk4vv Total loading time: 0 Render date: 2024-12-23T16:07:54.477Z Has data issue: false hasContentIssue false
  • English
  • Français

Some constraints on the form of the Welsh Basin from regional gravity and aeromagnetic data, with particular reference to Central Wales

Published online by Cambridge University Press:  01 May 2009

R. M. Carruthers ,
C. J. N. Fletcher ,
A. J. W. McDonald  and
R. B. Evans
R. M. Carruthers
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, U.K.
C. J. N. Fletcher
Affiliation:
British Geological Survey, Bryn Eithyn Hall, Llanfarian, Aberystwyth, Dyfed SY23 4BY, U.K.
A. J. W. McDonald
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, U.K.
R. B. Evans
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, U.K.
Get access Rights & Permissions [Opens in a new window]

Abstract

Gravity and aeromagnetic data sets provide systematic coverage over the whole of the Welsh Basin. Physical property information shows considerable overlap in densities within the Lower Palaeozoic and Precambrian formations, with relatively few units of the exposed succession being strongly magnetic. While the geophysical anomalies cannot be interpreted unambiguously in terms of these sources, the data can still be used to test different geological models and to indicate the range of possible solutions. The major fault zones are seen to influence the anomaly patterns in a variety of ways, reflecting a combination of differing near-surface contrasts and effects within the underlying basement. The general increase in gravity values towards Cardigan Bay may originate from the lower crust, and the large amplitude aeromagnetic low seen over Cardigan Bay indicates that a distinctive change in the character of the crust occurs here. Two-dimensional modelling in central Wales shows that a westward thickening of the Welsh Basin, to a maximum of about 10 km, may also be significant. It is necessary to postulate a separation of the base of denser, Lower Palaeozoic rocks from the underlying, more magnetic basement in order to account for offsets in anomaly source locations. This implies the presence of less dense Cambrian sediments and/or non-magnetic components of the Precambrian basement.

Type
Articles
Information
Geological Magazine , Volume 129 , Issue 5 , September 1992 , pp. 515 - 522
Copyright
Copyright © Cambridge University Press 1992

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Allen, P. M. & Jackson, A. A. 1985. Geology of the country around Harlech. Memoir of the British Geological Survey, Sheet 135 (England and Wales).Google Scholar
Bamford, D., Faber, S., Jacob, B., Kaminski, W., Nunn, K., Prodehl, C., Fuchs, K., King, R. & Willmore, P. 1976. A lithospheric profile in Britain. i. Preliminary results. Geophysical Journal of the Royal Astronomical Society 44, 145–60.CrossRefGoogle Scholar
Blundell, D. J., Davey, F. J. & Graves, L. J. 1971. Geophysical surveys over the South Irish Sea and Nymphe Bank. Journal of the Geological Society 127, 339–75.CrossRefGoogle Scholar
Bott, M. H. P. 1968. The geological structure of the Irish Sea basin. In Geology of shelf seas (ed. Donovan, D. T.) pp. 93–115. Edinburgh: Oliver and Boyd.Google Scholar
Cook, A. H. & Thirlaway, H. I. S. 1956. The geological results of measurements of gravity in the Welsh Borders. Quarterly Journal of the Geological Society of London 111, 47–70.CrossRefGoogle Scholar
Cornwell, J. D. & Cave, R. 1986. An airborne geophysical survey of part of west Dyfed, South Wales, and some related ground surveys. Mineral Reconnaissance Programme Report of the British Geological Survey no. 63.Google Scholar
Evans, R. B. & Greenwood, P. G. 1988. Outcrop magnetic susceptibility measurements as a means of differentiating rock types and their mineralization, with examples from U.K. and overseas, including SE Asia. Institute of Mining and Metallurgy, Asian Mining '88, 45–57.Google Scholar
Lee, M. K. 1988. Density variations within Lake District granites and Lower Palaeozoic rocks. Technical Report of the Regional Geophysics Group of the British Geological Survey no. WK/98/1.Google Scholar
McDonald, A. J. W., Fletcher, C. J. N., Carruthers, R. M., Wilson, D. & Evans, R. B. 1992. Interpretation of the regional gravity and magnetic surveys of Wales, using shaded relief and Euler deconvolution techniques. Geological Magazine 129, 523.CrossRefGoogle Scholar
Meissner, R., Matthews, D. & Wever, TH. 1986. The “Moho” in and around Great Britain. Annales Geophysicae 4 B, 659–64.Google Scholar
Powell, D. W. 1956. Gravity and magnetic anomalies in North Wales. Quarterly Journal of the Geological Society of London 111, 375–97.CrossRefGoogle Scholar
Trench, A. & Torsvik, T. H. 1991. A revised Palaeozoic apparent polar wander path for southern Britain (Eastern Avalonia). Geophysical Journal International 104, 227–33.CrossRefGoogle Scholar
Turnbull, G. 1987. Bouguer densities from mainland Britain determined from linear regression of gravity anomalies with topographic relief. Project Note of the Regional Geophysics Group of the British Geological Survey no. 87/3.Google Scholar