Dinton Pastures – Sand and Gravel Lakes
Welcome to Dinton Pastures Country Park. Once farmland, and in the seventeenth century part of the Windsor Forest, it was named Dinton by the farm who bought the land in 1924; he came from the village of Dinton near Aylesbury.
At the published coordinates you will see one of the may lakes at the 180-hectare Dinton Pastures Country Park, none of which are natural but were formed by considerable sand and gravel quarrying between 1969 and 1979. Much of the material was extracted for construction of the M4 motorway. The park opened in 1979 and a nature reserve declared in 1992 on Lavell's Lake.
Today the park has seven lakes, two rivers and surrounding meadows that act as flood plan of the River Loddon.
In July 2024 it hosted a Geocaching Mega event "Piratemania Eight Bells Nigh!" which brought in thousands of visitors from across the world.
Reproduced with the permission of the British Geological Survey ©NERC. All rights Reserved.
Sand and Gravel
Today's geology lesson is about the sand and gravel that have been the reason for former quarries.
Sand and Gravel are naturally occurring unconsolidated rock fragments caused by weathering and the erosion of rocks. The chemical composition of the sand and gravel depends on the original rocks. Most sand and gravel are formed of silica, mainly in the form of quartz. However, other materials can be the base rock, such as Calcium Carbonate and Gypsum (white sands), and Basalts and Magnetite (black sands).
Each individual particle can comprise rough-edged pieces (where erosion has been recent) or smooth-edged pieces (where pieces have been transported over a length of time or distance).
Generally, sand consists of particle sizes of 60nm to 2mm in size; less than 60nm is classed as silt. A cubic metre of dry sand weight about 1600kg.
Gravel consists of particle sizes from 2mm to 64mm; larger than 64mm is classed as cobble. A cubic metre of dry gravel weighs about 1800kg.
Both are important products and much of the world’s extraction of gravel goes to construction of highways.
Erosion and Weathering
Both grains are formed by erosion and weathering. Erosion implies an element of movement or transportation, whereas weathering does not involve movement of the material.
There are many mechanisms for transportation of these grains, including:
Waterways – large amounts of material can be moved by the currents of rivers and by the tides of the sea,
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traction – material is rolled and slides along the bottom of a river
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saltation – material is picked up and dropped by a river
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suspension – material is maintained in the water for some time
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solution – chemically the material dissolves in the water
Glacial – material is held and carried in glaciers for many centuries before dropping as the glacier melts
Wind – in dry desert environments lighter particles can be carried hundreds of kilometres.
Dinton Pasture’s Geology
As you walk around Dinton Pastures it will be evident that there is sand and gravel still remaining.
The bedrock under the sand and gravel is London Clay formed in the Eocene (56-34Ma). This is a mixture of silty brown clay, fine sands and occasional pebble seams.
The sand and gravel at Dinton Pastures are River Terrace Deposits, formed over many millennia, from the end of the last ice age (12ka) to the present.
Logging Requirements
On order to log this EarthCache please first send your answers including your caching name to PirateMania Crew using the Message Centre or by Email.
Do not post your answers in the log. Answers will be checked and those not clearly not meeting the logging requirements will have their log deleted.
1/ Pick up some sand and gravel and let it fall through your fingers - is it made up of fine grained particles of a uniformed colour or is it coarse grained and made up of different colours. Explain what you observed and why do you think it is one or the other.
2/ Sand is predominantly quartz. The lithology of the gravels varies significantly. The gravels consist of chert, limestone, quartzite, granite and mafic rocks around the edge of the lake you will see some gravel. Describe the colour, shape and size range.
3/ Based on your answer to 2, do you think that the gravel was formed locally or travelled some distance? Suggest a possible type of transportation and explain your choice.
4/ Sand deposits found on beaches or in rivers and streams, are mostly quartz (silicon dioxide, SiO2) and are 2mm or smaller where as gravels are chipped or rounded rock fragments that typically range in diameter from about 3 to 75 mm. Which form of erosion do you think travels the shortest and which travel the furthest and why?
5/ (Optional) include in your log a photograph of you or your hand/GPS receiver with the lake in the background.
This cache is placed with the kind permission of Wokingham Countryside Service
References
Wokingham Countryside Services
Wikipedia
The Geological Socierty
British Geological Survey