Martley Rock

LOCATION INFORMATION Parish Martley Grid Reference SO 7450 5956 Locality Type Disused Quarry/Pit BGS 1:50 000 Sheet No. 182 OS 1:25 000 Sheet No. Explorer 204

KEY SITE FEATURES CARBONIFEROUS / Halesowen Formation and Etruria Formation. SILURIAN / Raglan Mudstone Formation. Stratigraphy CAMBRIAN ?or ORDOVICIAN / Martley Quartzite. PRECAMBRIAN / Malverns Complex. Halesowen Fmn = grey-green, black-grey, orange clay/mudstone. Etruria Formation = red clay. Raglan Mudstone Fmn = Red clay/mudstone. Lithology Martley Quartzite = Pale grey, quartz-cemented sandstones and interbedded conglomerates. Conglomerates contain mainly quartz pebbles, but also Malverns Complex and volcanic lithologies. Malverns Complex = The composition of the Malverns Complex rocks vary at the site from acidic to mafic meta-igneous rocks. Fossils None seen Mineralisation Structure Fault zone

SITE DETAILS From Martley village head south on the B4197 past the village hall on the left. Take the first right turn on a sharp left hand bend and when the lane turns sharply to the right, continue straight on a track for 100m.

The old Victorian pit at Martley Rock exposes the most northerly outcrop of the Precambrian Malverns Complex, roughly 15 km north of the main Malvernian exposure of the Malvern Hills ridgeline. Cambrian / Ordovician Martley Quartzite, Carboniferous strata of the Halesowen (formerly Highley) Formation and the Etruria Formation, and Silurian Raglan Mudstone Formation are also exposed in a trench, dug in 2010. Observation platforms and information boards have been installed along the trench, so that a visit is probably the simplest way of appreciating the range and relationships of rock types present. The site is on private land, so please stay within the boundaries shown at the entrance. Groups and school parties may book a visit by calling Cob House Fisheries on 01886 888517, [email protected].

The most significant feature of the site is its location on a major fault zone. Martley Rock straddles the junction between the Palaeozoic and Mesozoic rocks of Britain. To the east of Martley Rock lie Triassic sediments, initially Bromsgrove Sandstone Formation, and then further to the east, Mercia Mudstone Group units. To the west of the trench lies the Silurian Raglan Mudstone Formation which then gives way to Devonian aged rocks. The pit itself lies close to the roughly north south line of the East Malvern Fault. Locally this has given rise to the Abberley Hills ridge (Silurian Wenlock and Ludlow aged rocks) to the north; Berrow Hill (capped with Permian aged rocks) and Ankerdine Hill (Silurian May Hill Sandstone Group aged rocks and Much Wenlock Limestone) to the south. The presence of Cambrian and Precambrian strata at Martley Rock is attributed to the fault zone, these ancient rocks having been lifted from depth by major earth movements hundreds of millions of years ago.

Martley Rock has been the subject of scientific interest since it was recorded by the noted geologist Roderick Murchison in 1839, who recognized the Malvernian rocks and the presence of the Old Red Sandstone (Raglan Mudstone Formation), but acknowledged that the field relations were “ill-exhibited” and complex. At least nine other geologists visited and wrote about the site during the 19th and 20th centuries, adding to the observations and interpretation of the rocks present. Yet it is only recently that real progress has been made in understanding the structural relationships, since the Teme Valley Geological Society (TVGS) obtained funding from the European LEADER programme managed by Worcestershire County Council. In 2010, this allowed TVGS to dig the main and side trenches that can be seen now. In 2011, additional temporary trenches dug to the north and east, helped and confirmed some the interpretation, but have since been filled in. The Teme Valley Geological Society collaborated with the Woolhope Naturalists’ Field Club, Herefordshire & Worcestershire Earth Heritage Trust and British Geological Survey on this work, and together have written a scientific paper to be published in the Transactions of the Woolhope Naturalists’ Field Club in 2013. Research at the site is ongoing. See the plan of the site at the end of this information sheet for the location of the trenches.

Halesowen Formation Carboniferous Halesowen Formation is seen at the western and south easterly ends of the main trench. At the westerly end, Halesowen Formation beds are exposed in the trench walls for around 7m. This section contains a number of layers of wide ranging colours dipping at 3 – 5⁰ to WNW. The Halesowen Formation lies unconformably on the Raglan Mudstone Formation. After 7m the Halesowen Formation units lie both in the walls and the floor of the trench for around another 3m until the contact with the Martley Quartzite along a thrust plane. The Halesowen Formation is seen both in the floor and sides of the trench at the east end. Here the clays/mudstones are grey–dark grey.

Etruria Formation This is a dark red clay, associated with the Carboniferous Coal Measures, only exposed at the most eastern end of the main trench.

Raglan Mudstone Formation Silurian Raglan Mudstone Formation is seen at the western edge of the trench. It is exposed on the floor of the trench for around 7m and is unconformably overlain by the Halesowen Formation.

Martley Quartzite Martley Quartzite is exposed in the main trench and the side trench to the south-west (within a complex N-S band termed the Martley Rock Fault in the 2013 paper). The quartzite is assumed to correspond with the Cambrian Malvern Quartzite Formation, but this has yet to be confirmed (2012); it may be of early Ordovician age. In the western limb of the main trench it overlies the Carboniferous strata along a low angled thrust plane. The pale grey quartzite is shattered and altered within a fault zone that extends for several metres to a faulted contact with Malverns Complex rocks. The fault zone is also seen in the side trench to the south-west. The quartzite is composed of almost wholly rounded grains of quartz, with some feldspar; a quartzitic sandstone with average grain-size about 0.5 mm and a siliceous cement. The majority of the exposures are stained yellow.

Malverns Complex Precambrian Malverns Complex is exposed in both the main and side trenches. In the western limb of the main trench it is fault bounded against Martley Quartzite within the Martley Rock Fault zone. In the easterly limb of the main trench it is faulted against Martley Quartzite, on its westerly limit, and faulted against the Halesowen Formation on its easterly limit. The composition of the Malverns Complex rocks vary at the site from acidic to mafic metamorphosed igneous rocks. Most exposures are heavily sheared, altered granite/diorites which are also highly weathered. A fresher exposure of pink and green-mottled rock is exposed in a scalloped section of the easterly limb of the main trench.

Martley Quartzite. Distant fence line marks the south-west trench, B-D.

Dark grey and orange clay of the gently dipping beds of the This photograph taken in late 2011, shows the same A–B section of Halesowen Formation in the west end of the main trench the main trench, looking east towards the contact of the Halesowen (section A–B). Red-brown clays of the Raglan Mudstone are Formation with the Martley Quartzite. The Carboniferous beds in the distance and the floor of the trench. The photograph was have weathered in just over a year, but the distinctive colours are taken in the freshly-dug trench in February 2010, looking west. still conspicuous.

The south-west trench B-D, when it was freshly-dug in February The north-western wall of trench B-D showing the tectonised 2010, showing the shear zone and Martley Quartzite in the Martley Quartzite within the shear zone of the Martley Rock foreground. View looking south-west. Fault.

The shear zone in the north-west wall of trench B-D, photograph In Victorian times, this was known as a gravel pit, because of the taken in late 2011. friable nature of the intensely sheared and shattered Martley Quartzite and Malverns Complex rocks at this site.

Close up view of a sample of Martley Quartzite. Close up view of a sample of Malverns Complex rock.

The Martley Quartzite is thrust over green-grey clays of the Malverns Complex rocks are most freshly exposed in a scalloped Halesowen Formation in the west limb (A-B) of the main trench. area on the north-east side of the main trench, where the former This view is looking WSW towards the south side of the trench. pit wall was located. At the west end of the embayment, the rock is dark and mafic in nature; at the east end it is a pink diorite.

A view of the south wall of the A-B section of the main trench The December 2011 extension (C-F) at the east end of the main where the Martley Quartzite is thrust over the Halesowen trench exposed the Triassic Bromsgrove Sandstone – Mesozoic Formation, taken in late 2011, looking south-east. rocks brought into juxtaposition with Palaeozoic rocks by the East Malvern Fault. This is the view west from location F.

The following plan of the site (Barclay et al, in press) shows a simplified representation of the geology and the location of the trenches dug in 2010 and 2011.