Superficial deposits
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Superficial deposits refer to geological deposits typically of Quaternary age. These recent unconsolidated sediments may include stream channel and floodplain deposits, beach sands, talus gravels and glacial drift and moraine. All pre-quaternary deposits are referred to as bedrock.
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[edit] Types and history
There are several types of superficial deposit, including raised beaches and brickearth. These were formed in periods of climate change during the ice ages. The raised beaches were generally formed during periods of higher sea level, when ice sheets were at a minimum, and the sand and shingle deposits can be seen in many low cliffs. The brickearth is originally a wind-blown dust deposited under extremely cold, dry conditions but much has been re-deposited by flood water and mixed with flints.
Superficial deposits were originally recorded only onshore and around the coast where they were laid down by various natural processes such as action by ice, water and wind. More recently offshore deposits have been mapped and may be separate sea-bed sediments.
Most of these superficial deposits are unconsolidated sediments such as gravel, sand, silt and clay, and onshore they form relatively thin, often discontinuous patches. Almost all of these deposits were formerly classified on the basis of mode of origin with names such as, 'glacial deposits', 'river terrace deposits' or 'blown sand'; or on their composition such as 'peat'.
[edit] Brickearth
Brickearth is originally a wind-blown loess dust deposited under extremely cold, dry conditions that can be used for making house bricks. The Brickearth is normally represeneted on 1:50,000 solid and drift edition geological maps.[1] In the Thames Valley area, where the brickearth overlies certain river terrace Gravels, this has been reclassified on more recent maps as the "Langley Silt Complex".[2]
It is a superficial deposit of homeogenous structureless loam or silt. It requires little or no admixture of other materials to render them suitable for the manufacture of 'stock bricks'.[3] Brickearth typically occurs in discontinuous spreads, about 2m to 4m thick, overlying chalk, Thanet Beds or London Clay. There are extensive brickearth deposits in Kent, particularly on the North Downs dip slope and on the Hoo peninsula, sections of the Medway and Stour valleys. The mineral content of brickearth is critical for brickmaking and precise proportions of chalk, clay, and iron.
In 1986 there were four active stock brick works in Kent, at Otterham Quay, Funton, Murston and Ospringe.
In Chichester, the brickearth is flinty brown silty clay up to five metres thick, which occurs on the coastal plain. The brickearth is unfossiliferous but occasionally yields man-made flint implements.
[edit] Additional information
Sweden's quaternary geology databases contain information on the properties of superficial deposits. This information, particularly at a scale of 1:50 000, can be used for a number of different purposes in farming and forestry, including avoiding erosion, assessing growing conditions, gauging risks in terms of nutrient leaching and release of toxic substances, planning site preparation, road construction, felling and extraction operations, judging accessibility etc.[4]
[edit] References
- ^ BGS solid and drift edition 1:50,000 Maps
- ^ Gibbard, P. L., 1985 Pleistocene History of the Middle Thames Valley
- ^ http://www.kent.gov.uk/NR/rdonlyres/CB0996E8-AFC3-4CA0-B8FB-4E3FE3D88568/962/May86Brickearth.pdf
- ^ SGU's website
