| Computer Code: |
MHVO |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Tournaisian Age (CT)
— Tournaisian Age (CT) |
| Lithological Description: |
The lower part of the member comprises upward-coarsening multi-coloured mainly red-brown and green tuffs, with bioclastic material. Lapilli-rich beds, 3 to 5 cm thick, within this unit also increase in grain size upwards. Associated with the tuffs are thin-bedded limestones, some planer stratified or showing symmetrical ripples. The multi-coloured tuffs are overlain by green, graded and ungraded lapilli-tuffs, with clasts of devitrified amygdaloidal basalt and bioclastic material. Calcite vein networks are prominent locally. Within the upgraded lapilli-tuffs there are matrix- and clast-supported conglomerates, with clasts of chert nodules and limestones. Also associated with the lapilli-tuffs are beds of bioclastic limestones and both cross-stratified and laminated sandstones. Within the lapilli-tuffs is a prominent, laterally impersistent basaltic pillow lava [3.5 to 4.3 m thick], very weathered with abundant calcite-filled amygdales up to 10 cm across. The upper surface of the basalt is very irregular and highly amygdaloidal. |
| Definition of Lower Boundary: |
The boundary is placed at a sharp conformable boundary where bioturbated wackestones and packstones of the Black Rock Limestone Subgroup, are overlain by multi-coloured tuffs |
| Definition of Upper Boundary: |
The upper boundary is taken at a sharp, erosive boundary where red nodular limestones with green tuff laminae and beds are overlain by cross-bedded, bioclastic grainstones of the Black Rock Limestone Subgroup. |
| Thickness: |
From 37 m thick at Swallow Cliff in the west, to 4 m in the east of the site, at ST 348 669. |
| Geographical Limits: |
Middle Hope at ST 322 659, north Somerset. |
| Parent Unit: |
Black Rock Limestone Subgroup (BRL)
|
| Previous Name(s): |
Woodspring Lava and Tuff [Obsolete Name and Code: Use MHVO]
(-1697)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
Swallow Cliff at Middle Hope, north Somerset. Whittaker and Green, 1983. |
| Reference(s): |
| Whittaker A and Green G W. 1983. Geology of the country around Weston-super-Mare. Memoir of the Geological Survey, England and Wales, Sheet 279 with parts of sheets 263 and 295. |
| Geikie A, and Strahan A. 1899. Summary of progress of the Geological Survey for 1898. Memoir of the Geological Survey of Great Britain, 104-111. |
| Faulkner T J. 1989. The Early Carboniferous (Courceyan) Middle Hope Volcanics, of Weston-Super-Mare: Development and demise of an offshore volcanic high. Proceedings of the Geologists' Association, Vol.100, 93-106. |
| Jeffreys, D H, 1979. Sedimentology of the Dinantian Volcaniclastic carbonate rocks of Middle Hope and Spring Cove, Weston-Super-Mare, University of Reading, Unpublished M.Sc Thesis. |
| Matthews, S, Butler, M and Sadler, P. 1973. Lower Carboniferous successions in North Somerset. Report by Directors of Field Meeting. Proceedings of the Geologists' Association, Vol.84, 175-179. |
| Morgan C, and Reynolds S. 1904. The igneous rocks associated with the Carboniferous Limestone of the Bristol District. Quarterly Journal of the Geological Society of London, 60, 137-157. |
| Reynolds S. 1917. Further work on the igneous rocks associated with the Carboniferous Limestone of the Bristol District. Quarterly Journal of the Geological Society of London, 72, 23-42. |
| Speedyman D L. 1977. Volcanic rocks of the Bristol Region. In: Geological Excursions in the Bristol district (Editor: Savage R J G.), pp. 47-54, University of Bristol. |
| Waters, C N. 2003. Carboniferous and Permian igneous rocks of central England and the Welsh Borderland. In: Carboniferous and Permian Igneous Rocks of Great Britain North of the Variscan Front. (editors Stephenson D, Loughlin S C, Millward D, Waters C N, and Williamson I T.), pp. 279-316, Geological Conservation Review Series, No. 27 (JNCC). |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E279
|
