- November 11, 2019
- Posted by: GRM Development Solutions
- Category: Service, Team
Deborah Ashton, Principal Geologist at our Welwyn Garden City office, recently attended a guided tour of the Emmer Green Chalk Mine in Reading. The visit was organised by John Wong, from the Home Counties North regional group of the Geological Society. He also led some of the discussions.
Deb’s write-up of the visit is below:
“Emmer chalk mine is thought to date back to the early construction of the town circa 1600 and was rediscovered in 1977 during building works, and subsequently adopted by the 89th Reading Scout Group.
Objects and graffiti within the mine reflect its long history, including candles in chalk holders and smoke stained walls as well as various items relating to the use of the mine for storing archives and treasure during the second world war.
Access is via a 80ft fixed vertical steel ladder through a probable air shaft. The stratum is the Seaford and Newhaven Chalk Formations, undifferentiated, of the White Chalk Group.
BGS describes these as:
Seaford Chalk – firm white chalk with conspicuous semi-continuous nodular and tabular flint seams. Hardgrounds and thin marls are known from the lowest beds. Some flint nodules are large to very large.
Newhaven Chalk – composed of soft to medium hard, smooth white chalks with numerous marl seams and flint bands, including abundant Zoophycos flints (notably at levels near the base). The formation is known to contain distinct phosphatic chalks of limited lateral extent. Equivalent beds, the Margate Chalk of north Kent, are marl-free and contain little flint.
Pictured, you can see the flint beds which are incredibly uniform in their spacing, about a metre apart. There was some discussion on why the flint beds are so uniformly space, one theory being that it is associated with the Milankovitch cycle with another being that flint can only form when the silica is at the optimum concentration. Also attached are photos of a fault line which could be traced through the quarry system.
The chalk was mined up to the next flint bed which then forms the quarry ceiling, the pictures essentially showing you the underside of the flint beds.
What is most interesting is that with conventional boreholes we would not see the blocky structure, realise the uniformity of the flint beds or identify fractures and faults. So more thought is required, on GI techniques, if such information is required.”