PT  - JOURNAL ARTICLE
AU  - Roberts, John C.
TI  - Fracture surface markings in Liassic limestone at Lavernock Point, South Wales
AID  - 10.1144/GSL.SP.1995.092.01.09
DP  - 1995 Jan 01
TA  - Geological Society, London, Special Publications
PG  - 175--186
VI  - 92
IP  - 1
4099  - http://sp.lyellcollection.org/content/92/1/175.short
4100  - http://sp.lyellcollection.org/content/92/1/175.full
SO  - Geological Society, London, Special Publications1995 Jan 01; 92
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.