Martley Rock

Exposed Units: Malverns Complex, Malvern Quartzite Formation, Raglan Mudstone Formation, Halesowen Formation

Access: The site is located on private land but is open to the public. There is no parking at the site, you will have to park back on the main road close to the village hall.

Martley Pit exposes the most northerly outcrop of the Precambrian Malverns Complex, roughly 15 kilometres north of the main Malverns Complex exposure of the Malvern Hills ridgeline. This inlier of faulted Precambrian Malverns Complex and Cambrian Malvern Quartzite Formation is surrounded by strata of the Halesowen Formation, which unconformably overlies the Silurian Raglan Mudstone Formation.

The site is cut by two trenches. It is within the trenches that the rock units can be observed.

The composition of the Malverns complex rocks vary at the site from acidic to mafic meta-igneous rocks. Most exposures are heavily sheared altered granite/diorites which are also highly weathered.

The Malvern Quartzite is composed of almost wholly rounded grains of the mineral quartz, with some feldspar. The average grain-size is about 0 -5 mm which are bound by quartz cement. The majority of the exposures are stained yellow.

Silurian Raglan Mudstone Formation is seen in the floor of the far western trunk of the trench. It is a dark red-brown mudstone with occasional green spotting.

The Carboniferous Halesowen Formation seen contains a number of layers of wide ranging colours (green-grey, black, dark grey, orange and cream) dipping at a shallow angle to WNW.  The Halesowen Formation lies unconformably on the Raglan Mudstone Formation. Green-grey micacous sandstone has been observed at the site which may Carboniferous in age.

The site is bounded and cross cut by a number of faults. The Cambrian and Precambrian aged rocks have been heavily sheared to varying degrees across the site.

This site is also known locally as White Cottage Coppice, Martley Gravel Pit and Martley Pit.

Terminology

Inlier – An area of older rocks surrounded by younger rocks.

Unconformably –  Where two adjacent rocks units are of markedly different ages, indicating a gap in geological time

Acidic meta-igneous rocks – Rocks comprising more than 10% silica minerals (commonly quartz)

Mafic meta-igneous rocks – Rocks comprising les than 10% silica minerals

Sheared – Where a rock is subject to directional stress (i.e. pressure with a directional element), minerals in the rock to realign according to the direction in which the pressure is directed.

Micaceous – A rock composed of a high percentage of the mineral mica (silicates of aluminium and potassium, and with magnesium and iron in the dark varieties

Fault – A line of weakness within the Earth’s crust along which movement and displacement occurs.

Photos

Martley pit trench showing Malverns Complex and Malvern Quartzite Formation units.

Near western end of the long trench. Raglan Mudstone Formation in the floor of the trench. Halesowen Formation in a variety of colours in the trench walls.

A shear zone in a faulted block of Malvern Quartzite Formation rocks.

Malvern Quartzite Formation.

Malverns Complex; Quartz-plagioclase rock with minor chlorite and white mica minerals.

References

BARCLAY, W.J. and RATHBONE, P.A. 1990, Geology of the Whitbourne district, British Geological Survey Technical Report, WA/90/90.

CALLAWAY, C. 1898, On a quartzite and syenite rock in Worcestershire, Geological Magazine, vol. 4, 5, pp.379.

COLES, C. St. A. 1898, An exposure of Quartzite and Syenite Rock near Martley, Worcestershire, Geological Magazine, vol. 4, 5, pp. 304-5.

EARP, J.R. and HAINS, B.A. 1971, The Welsh Borderland (Third Edition), British Regional Geology. Institute of Geological Sciences.

GROOM, T. 1898, Note on the Martley Quartzite, Geological Magazine, vol. 4, 5, pp. 562-4.

GROOM, T.T. 1900, On the geological structure of portions of the Malvern and Abberley Hills. Quarterly Journal of the Geological Society of London, vol. 56, pp. 138-97.

HOLLINGWORTH, S.E. 1938, In Summary of Progress of the Geological Survey of Great Britain for 1937, Part 1, 34.

MITCHELL, G.H., POCOCK, R.W. and TAYLOR, J.H. 1962, Geology of the country around Droitwich, Abberley and Kidderminster, Memoir of the Geological Survey of Great Britain.

MURCHISON, R.I. 1839, Silurian System. London.

PHILLIPS, J. 1848, The Malvern Hills compared with the Palaeozoic districts of Abberley, Woolhope, May Hill, Tortworth and Usk, Memoir of the Geological Survey of Great Britain, Vol. II, part I.

PHIPPS, C.B. and REEVE, F.A.E. 1969, Structural geology of the Malvern, Abberley and Ledbury hills. Quarterly Journal of the Geological Society, vol. 125, pp. 1-37.

SYMONDS, W.S. 1872, Records of the Rocks. London, John Murray.

March 2011