Four geological periods in forty metres
Four geological periods in forty metres
Access: Private land
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.
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.
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.
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