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| The Tideswell dolerite quarry |
The planned June 2024 field trip for the Sheffield U3A Geology Group was mainly based on a circular walk that started at Litton and would take us down Tansley Dale and along Cressbrook Dale, before returning along a path that provided excellent high level views of the latter.
Although this provides a good range of geology, geomorphology and industrial archaeology and a reasonable walk of 4.5 km, this wasn’t enough to fill a day, which typically starts at 10:30 and finishes at 15:30. To fill in the time, we therefore included a visit to the old Tideswell dolerite quarry, a denotified SSSI that is a short drive from Litton.
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| Exposures of dolerite in the hillside above the car park |
From the Tideswell Dale car park, Stuart and I could see an exposure of dolerite in the hillside, together with a section of dark brown soil resulting from its weathering and then had a very quick look at a small quarry near to its entrance that I had briefly seen during the partial recce that I had undertaken in February.
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| Weathered dolerite with spheroidal weathering |
The base of the exposure was heavily overgrown and I just collected a piece of dolerite that was lying on the ground, but it was in such a weathered state that the specimen had disintegrated by the time I got home. The original mineralogy has been described as olivine that has been altered to pseudomorphs, andesine feldspar and the clinopyroxene augite.
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| A specimen of weathered dolerite |
Making our way back to the toilet block to check the car parking prices, we stopped at the information board, which we both grumbled about when seeing that it describes the rock obtained from the qurries here as basalt and not dolerite, which the Geological Conservation Review (GCR) Volume 27 and Geological Excursions in the Sheffield Region (GESR) and other publications have described in some detail.
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| The information board at the Tideswell Dale car park |
The Peak District National Park is a great attraction for geologists at all levels and, although we thought that the graphic designer of an otherwise excellent display panel could be forgiven for a basic error like this if not properly informed, it doesn’t help that the British Geological Survey GeoIndex Viewer lists it as an unnamed igneous intrusion described as microgabbro and then, very confusingly, as a basalt in the BGS Lexicon of Named Rock Units.
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| The Tideswell dolerite quarry |
Continuing south along the path for a few hundred metres, passing outcrops of the Bee Low Limestone Formation, we branched off the main path and came to the entrance to the main quarry, which was the picnic area when I first visited it back in 1995, while assessing the RIGS (Regionally Important Geological Sites) in the Peak District National Park for their geotourism value.
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| A large dolerite boulder with spheroidal weathering |
The GESR (1967) also mentions large blocks of marmorised limestone on the quarry floor, which has also been described as occurring beneath the sill on both sides of the dale, but all we found was a large rounded boulder of dolerite, which shows the spheroidal weathering that is very well developed in this quarry.
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| A section through the quarry face |
The dolerite sill has been intruded discordantly into the Lower Miller’s Dale Lava Member, which the GESR describes as occurring in the upper part of the face and above the quarry, but goes on to state that hydrothermal alteration makes it very difficult to discern the junction between the dolerite and the overlying basalt.
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| A view of the upper section of the quarry face |
From behind the fence that now prevents access to the quarry face, there is a very noticeable difference between the deep surface weathering of the upper section section and the lower section of the quarry face, which clearly shows the spheroidal weathering; however, although horizontal structures that may indicate the boundary between dolerite and basalt are present, neither of us were very certain about these.
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| A close up view of the spheroidal weathering |
The GCR states that Arnold Bemrose identified five zones in the sill, with a coarse ophitic olivine dolerite with dominant augite in the centre, sandwiched between a coarse grained variety with dominant feldspar and outer chilled margins consisting of very fine grained olivine dolerite.
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| A section at the southern end of the quarry face |
To the west and south-west of the main quarry face, there are exposures in a small outcrop and a cutting respectively, from which I obtained small samples with my Estwing hammer. Examining these with a hand lens, no crystals of any of the principal minerals are visible and we concluded that these are indicative of the chilled margin.
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| Specimens of very fine grained dolerite |
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