RT Journal Article
SR Electronic
T1 Fracture surface markings in Liassic limestone at Lavernock Point, South Wales
JF Geological Society, London, Special Publications
JO Geological Society, London, Special Publications
FD Geological Society of London
SP 175
OP 186
DO 10.1144/GSL.SP.1995.092.01.09
VO 92
IS 1
A1 Roberts, John C.
YR 1995
UL http://sp.lyellcollection.org/content/92/1/175.abstract
AB A study of fracture surface markings (FSM) on three joint sets, striking at 190, 335 and 280°, cutting a 2.5 m thick slice of interbedded limestones and mudstones of lower Liassic age, yields evidence which enables determination of the orientation of the palaeostress field at the time of joint formation. A specific element of the FSM, namely the border planes, or the twist hackle, has been used to determine the orientation of σ1, in that these twist-hackle structures are considered to be developed normal to the remote tensile stress σ3. In the case of the joint sets striking at 335 and 190°, the sense of rotation of the twist plane would suggest that for both sets σ1 was aligned N-S and almost parallel to bedding. Other FSM features suggest that the 190° set propagated rapidly with S-type plumose markings being the most common. The small angle of border plane rotation (10–15°) suggests that all of the joint sets propagated under relatively low confining pressures. The sense of border plane rotation on the 335 and 190° sets suggests that there is a possible conjugate relationship between them. However, the other main joint set which strikes at 280° cannot be accounted for by simultaneous development in a N-S aligned σ1 which might have caused the development of the 335–190° joint sets.