tvrigs.org.uk » Permian

February 2010 – Evaporites

admin — Mon, 01 Feb 2010 09:12:55 +0000

Evaporites are non-clastic, or chemical sediments, created through the precipitation of dissolved salts from water. They most frequently occur at the site of a former large water body such as a lake or landlocked sea, on coastal plains (sabkha zones), or where rivers feed very arid desert areas. As the water involved slowly evaporates the salts become more concentrated and at well-defined concentrations they begin to recrystallise. They are different to the more conventional clastic sedimentary rocks which include mudstone, siltstone and sandstone in being soluble in water and much more mobile under pressure.

Sylvinite - This specimen from Russia.
Image courtesy of shakko.

These rocks form an economically important group of minerals. Sylvinite (a mixture of potassium chloride, sodium chloride and clay minerals) and halite (rock salt) are extracted by Cleveland Potash Ltd. from their mine at Boulby, near Staithes. The sylvinite lies within Permian strata over a kilometer below the surface. It is a little under 290 million years old and was laid down when a shallow ancient sea, dubbed the Zechstein – and which occupied an area between Northern England, through the North Sea Basin, to Poland – underwent several cycles of evaporation and transgression. Sea water comprises ~3.5% dissolved salts of which the bulk is sodium chloride or common salt. Evaporation yields successively limestone, anhydrite (calcium sulphate), halite and finally potassium and magnesium salts. Anhydrite was formerly mined and processed at Billingham on Teesside.

Cleveland Potash Mine, Boulby, Cleveland. UK

Evaporite deposits can flow under pressure producing salt-domes which disturb the strata through which the pass and internally exhibit complex folding. They also retain heat and may be a target for future geothermal energy projects.

Credit: Commons Wikimedia" title="Anhydrite" width="390" height="253" class="size-full wp-image-559" />

Anhydrite - Once mined at Billingham on Teesside, UK.
Credit: Commons Wikimedia

Crimdon Dene

admin — Tue, 06 May 2003 10:13:00 +0000

Contents

Site Description
Site Map
Site Assessment
Surveyors

Grid Reference NZ 471 371
BGS Sheet 27
OS Sheet 93
Forwarded as RIGS 30/09/2003

Site Description

Site Status SNCI
Description of Geodiversity Deep gorge environment revealing exposures of Magnesian limestone. The gorge forms steep sides consisting of face of Magnesian limestone in a fluvial environment. Glacial erratics can be found in the stream bed.
Literature References The Geology of the Country Between Durham and West Hartlepool – Denis Smith 1967

Site Map

Site Assessment

Access and Safety	Comments	Rating
Safety of access	Along Hart to Haswell walkway
Safety of exposure	View from river channel
Restricting conditions	High flow episodes
Multiple exposure	Gorge length from walkway to viaduct
Note	It is strongly suggested that on-site safety be the responsibility of the party leader(s), as the safety information above is given only as a guide.

Education and Science	Comments	Rating
Surface processes	Fluvial processes and glacial processes	10
Geomorphology	River gorge	10
Sedimentary rock	Magnesian limestone and possible evaporite layer	10
Igneous rock	Erratics in stream bed	2
Metamorphic rock	Erratics in stream bed	2
Fossils	None specific	1
Minerals	None specific	1
Structural features	Dip examples of up to 20°	7
Stratigraphy	Brecciated Magnesian limestone material above evaporite layer	8

Geodiversity Value	Comments	Rating
Education	Due to access education potential questionable	1
Scientific	Study of Earth scientists	10
Historical	Limited historical significance	1
Aesthetic	Excellent examples of geodiversity and biodiversity	10

Surveyors

Andrew Carter, John Waring

Hartlepool Headland

admin — Thu, 03 Apr 2003 10:34:50 +0000

Contents

Site Description
Site Map
Site Assessment
Surveyors

Grid Reference NZ 524 344
BGS Sheet 27
OS Sheet 93
Forwarded as RIGS 30/09/2003

Site Description

Site Status SNCI
Description of Geodiversity Wave washed platform of Magnesian limestone. The exposure reveals examples of stack an pillar coastal features.
Literature References The Geology of the Country Between Durham and West Hartlepool – Denis Smith 1967

Site Map

Site Assessment

Access and Safety	Comments	Rating
Safety of access	Care needed underfoot on access steps	5
Safety of exposure	Tide Table should be consulted	5
Restricting conditions	High tide and adverse weather	5
Multiple exposure	The whole headland exposure	10
Note	It is strongly suggested that on-site safety be the responsibility of the party leader(s), as the safety information above is given only as a guide.

Education and Science	Comments	Rating
Surface processes	Coastal processes	10
Geomorphology	Wave washed platform	10
Sedimentary rock	Magnesian limestone	10
Igneous rock	None
Metamorphic rock	None
Fossils	None specific	2
Minerals	None specific	2
Structural features	Dip angle of up to 2°	5
Stratigraphy	Well exposed Magnesian limestone	5

Geodiversity Value	Comments	Rating
Education	Coastal processes	8
Scientific	Limited scope for study	5
Historical	Limited historical value	5
Aesthetic	Excellent coastal wave washed platform	10

Surveyors

Andrew Carter