Hostname: page-component-5c6d5d7d68-ckgrl Total loading time: 0 Render date: 2024-08-22T02:52:18.632Z Has data issue: false hasContentIssue false
  • English
  • Français

A Gravity Investigation of the Pickwell Down Sandstone, North Devon

Published online by Cambridge University Press:  01 May 2009

Hamid Nassar Al-Sadi
Hamid Nassar Al-Sadi
Affiliation:
Ministry of Oil, Baghdad, Iraq.
Get access Rights & Permissions [Opens in a new window]

Abstract

The area to the north of Barnstaple (North Devon) was covered by a detailed gravity survey. The main gravity gradient of the Bouguer anomaly map (estimated to be 1·2 mgals per mile) confirmed the conclusions drawn by Bott et al. (1958), who attributed it to a basin of possibly Carboniferous sediments and/or Old Red Sandstone, about 4 miles thick, separated from the outcropping Devonian rocks by an assumed thrust plane.

A negative residual gravity anomaly is located over the outcrop of the Pickwell Down Sandstone. Analyses of the anomaly show that it is caused by the southwards dipping belt of sandstone and that the angle of dip of the formation decreases with depth. At a depth of about 2 miles the formation becomes nearly horizontal. Alternatively, it may terminate against an assumed thrust plane underlying the whole outcropping Devonian.

The aeromagnetic map of the area shows an elongated magnetic “high” following the outcrop of the Morte Slates. The anomaly is probably caused by near surface, highly magnetized rocks in association with the Morte Slates.

Type
Articles
Information
Geological Magazine , Volume 104 , Issue 1 , February 1967 , pp. 63 - 72
Copyright
Copyright © Cambridge University Press 1967

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

REFERENCES

Bott, M. H. P., Day, A. A., and Masson-Smith, D., 1958. The geological interpretation of gravity and magnetic surveys in Devon and Cornwall. Phil. Trans. R. Soc., 251 A, 161–191.Google Scholar
Bott, M. H. P., and Masson-Smith, D., 1957. The geological interpretation of a gravity survey of the Alston Block and the Durham Coalfield. Q. Jl geol. Soc. Lond., 113, 93–117.CrossRefGoogle Scholar
Bott, M. H. P., 1959. The use of electronic digital computers for the evaluation of gravimetric terrain corrections. Geophys. Prospect., 7, 45–54.CrossRefGoogle Scholar
Bott, M. H. P., and Scott, P., 1964. Recent geophysical studies in southwest England. In: “Present Views on some aspects of the geology of Cornwall and Devon,” published for the 150th Anniversary of the Royal Geological Society of Cornwall, by Oscar Blackford, Ltd., pp. 25–44.Google Scholar
Bott, M. H. P., and Smith, R. A., 1958. The estimation of the limiting depth of gravitating bodies. Geophys. Prospect., 6, 1–10.CrossRefGoogle Scholar
Bullard, E. C, and Jolly, H. L. P., 1936. Gravity measurements in Great Britain. Mon. Not. R. astr. Soc. geophys. Suppl., 3, (9), 443–477.CrossRefGoogle Scholar
Dewey, H., 1935. British Regional Geology. South-west England. London: H.M. Stationery Office.Google Scholar
Evans, J. W., 1922. The geological structure of the country round Combe Martin, North Devon. Proc. Geol. Ass., 33, 201–234.CrossRefGoogle Scholar
Talwani, M., Worzel, J. L., and Landisman, M., 1959. Rapid gravity computation for two-dimensional bodies with application to the Mendocine submarine fracture zone. J. geophys. Res., 64, 49–59.CrossRefGoogle Scholar