Lulworth Crumple - Lulworth, Dorset
Posted by: SMacB
N 50° 37.115 W 002° 15.149
30U E 552881 N 5607677
The Lulworth Crumple is a minor fold structure within the major monocline of Alpine (Tertiary) age in the Lulworth Cove area. It is particularly well seen in the east side of Stair Hole.
Waymark Code: WMNPF0
Location: Southern England, United Kingdom
Date Posted: 04/13/2015
Views: 6
Here viewed from the viewpoint on the south west coastpath.
"The Lulworth Crumples are minor folds within the north limb of the major monocline. There are several of these and although they are best seen in the Lulworth area, the place where deformation due to Tertiary tectonics is most severe. Similar small folds, however, occur along the outcrop as far east as Peveril Point, Swanage. Specific examples have been exposed near Blashenwell (in the Purbeck marble), at Herston (west of the school) and are complex at Peveril Point itself (Cosgrove and Hearn, 1966). Undoubtedly there are others. They show both the broad structures and the minor structures within it. Evidence of shortening of the Middle and Upper Purbeck Group is most obvious. Local compression can be seen. Phillips (1964) has shown there are also extensional features, resulting from compression, at the lower levels of the Purbeck Group within the structure (i.e. south).
There are several small faults and shears within the structure. The direction of movement within these is quite variable. Occurring within the eastern cliff face are the Stair Hole "Snakes Heads". These resemble on a small scale the snake's head structures of thrusts (see for example McClay, 1989, fig. 3.13, p. 56), although the strata here are vertical. They are occurring near the top of the Intermarine Member, with the Cinder Bed visible on the right. The strata are younging towards the left.
It is important to note that the complex structures are not entirely confined to the Purbeck Group. The Wealden strata, stratigraphically above the Purbeck, are exposed in an irregular manner in the collapsed slopes of the back (north side) of Stair Hole. These are overturned in much of the exposure, and they also show much faulting. It is not initially obvious because the Wealden does not contain conspicuous thin-bedded limestones. Nevertheless it should be appreciated that the Lulworth Crumples involve Wealden strata to some extent, in addition to the Purbeck limestones and shales."
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