The geology of the Peak District National Park in England is dominated by a thick succession of faulted and folded sedimentary rocks of Carboniferous age. The Peak District is often divided into a southerly White Peak where Carboniferous Limestone outcrops and a northerly Dark Peak where the overlying succession of sandstones and mudstones dominate the landscape. The scarp and dip slope landscape which characterises the Dark Peak also extends along the eastern and western margins of the park. Although older rocks are present at depth, the oldest rocks which are to be found at the surface in the national park are dolomitic limestones of the Woo Dale Limestone Formation seen where Woo Dale enters Wye Dale east of Buxton.
There has been extensive mineralization of faults associated with volcanism during Visean times; working of the veins concerned has been a significant industry within the White Peak and has left an often prominent legacy in the landscape. Quarrying of limestone for aggregate and for the chemical industry has also caused considerable landscape change, not least around Buxton and resulting in a sizeable area being excluded from the national park on its designation in 1951. There are areas in the west and along the eastern margins of the Park where Coal Measures rocks are found at the surface and some limited mining for coals has taken place historically.
Within the Dark Peak are innumerable landslips. Some remain active such as the famous Mam Tor slip whilst those at Alport Castles have resulted in dramatic landforms. Valleys incised into the Dark Peak succession have proved attractive sites for reservoir construction.
Pre-Carboniferous
Boreholes have revealed the presence of rocks beneath the Peak District which are significantly older than anything seen at the surface. The Woo Dale borehole penetrated volcanic rocks of possible Precambrian age at a depth of 273m whilst boreholes at Eyam and at Caldon Low proved sedimentary rocks of Ordovician and Devonian age respectively.
Carboniferous
A succession of early Carboniferous limestones, grouped together as the Peak Limestone Group, outcrop across the White Peak. These strata are overlain by Craven Group rocks which are in turn overlain by those of the Millstone Grit. Coal Measures rocks of the late Carboniferous are found overlying the Millstone Grit sequence in parts of both the eastern and western margins of the national park.
Carboniferous Limestone
During the early Carboniferous, northern England was characterised by a series of shallow ‘shelf’ seas and intervening deeper water basins owing their existence to movement on deep-seated faults such as, within the area of the modern Peak District, the Mackworth and Bakewell faults. Different suites of limestone accumulated in the basin and shelf areas with a third depositional environment characterised by reefs at the margins of the two. Together all of these formations comprise the Peak Limestone Group.
On the shelf area, the following sequence developed (youngest/uppermost first); Eyam Limestone Formation Monsal Dale Limestone Formation Bee Low Limestone Formation Woo Dale Limestone Formation
The oldest of these, the Woo Dale limestones are seen in a restricted number of small outcrops, notably Wye Dale and adjacent Woo Dale and also in the Peak Forest and Alstonefield areas. At the small outcrop where Woo Dale joins Wye Dale, east of Buxton, the lowermost part of the formation is dolomitised; this was the site of the drilling of a deep borehole which reached the base of the formation which is otherwise unseen and showed them to lie unconformably on earlier Palaeozoic rocks. The overlying succession characterises the larger part of the limestone outcrop which gives rise to the White Peak stretching south from Winnats Pass.
The south-eastern salient of the limestone outcrop represents the basinal (or ‘off-shelf’) sequence (again youngest/uppermost first): Hopedale Limestone Formation Milldale Limestone Formation
Craven Group
The Craven Group strata are a mix of sandstones, mudstones and limestones with lesser amounts of other lithologies. They range from the Chadian to the Yeadonian substage in age. They include: Bowland Shale Formation Hurdlow Sandstones Minn Sandstones Widmerpool Formation (former Mixon Limestone-Shales) Onecote Sandstones Member Ecton Limestone Formation / Hopedale Limestone Formation Milldale Limestone Formation Rue Hill Dolomite Formation (borehole only?)