|
Fault Analysis and Diagenesis |
Petroleum Geology and Basin Analysis Group, British Geological Survey, Keyworth, Nottinghamshire NG12 5GG, UK
The Cheshire Basin forms a segment of the N-S trending English Channel-East Irish Sea rift. The southern part of the basin has classic half-graben geometry, with the Wem-Bridgmere-Red Rock Fault system forming its southeast margin, whereas its northern part is much more symmetrical with much smaller basin margin faults. Fault strikes also show systematic differences between the southern and northern parts of the basin. In the south, dominant NE-SW (Caledonoid) fault-strikes indicate a strong degree of basement control, particularly at the faulted southeast margin. Farther north, numerous faults with N-S strikes constitute the majority of faults within the basin. They are interpreted to have formed perpendicular to the initial basin-forming extension (roughly E-W), and suggest a much weaker basement influence. Fault displacement analysis also reveals a N-S split, with two distinct fault populations showing different fractal (power-law) distributions. In the south, extension was concentrated on the large, dominantly oblique-slip basin margin faults, whereas in the north, extension was distributed on numerous small to medium-sized dip-slip faults. The two fault populations are attributed to a variable degree of basement control. Major reactivated Caledonian basement structures controlled basin faulting in the southern part of the basin, whereas farther north the basin faults developed more-or-less independently of a less faulted, more isotropic basement. Estimates of extension magnitude, incorporating the ‘hidden’ contributions of small faults, indicate local basin extension factors in the range 1.07–1.16 (7–16%). However, because of difficulties in measuring the true heaves of the basin margin faults, these values are likely to be minimum estimates.
This article has been cited by other articles:
 |
|
 |
|
  D. Praeg Diachronous Variscan late-orogenic collapse as a response to multiple detachments: a view from the internides in France to the foreland in the Irish Sea Geological Society, London, Special Publications, 2004; 223: 89 - 138. [Abstract] [PDF]
|
|
