Superficial deposits
Encyclopedia
Superficial deposits refer to geological deposits typically of Quaternary
age. These recent unconsolidated sediment
s 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
.
. These were formed in periods of climate change during the ice age
s. 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 flint
s.
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
'.
dust deposited under extremely cold, dry conditions that can be used for making house brick
s. The Brickearth is normally represeneted on 1:50,000 solid and drift edition geological maps. 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".
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'. 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.
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
age. These recent unconsolidated sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s may include stream
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
channel and floodplain
Floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...
deposits, beach sands, talus
Scree
Scree, also called talus, is a term given to an accumulation of broken rock fragments at the base of crags, mountain cliffs, or valley shoulders. Landforms associated with these materials are sometimes called scree slopes or talus piles...
gravels and glacial drift
Drift
- Film and literature :* Drift , a 2002 Doctor Who novel* Drift , a series of Japanese films written and directed by Futoshi Jinno* Drift, 2007 experimental short film by Max Hattler* Drift , a fictional character...
and moraine
Moraine
A moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past glacial maximum. This debris may have been plucked off a valley floor as a glacier advanced or it may have...
. All pre-quaternary deposits are referred to as bedrock
Bedrock
In stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil...
.
Types and history
There are several types of superficial deposit, including raised beaches and brickearthBrickearth
Brickearth is a term used in southeast England for loess, a wind-blown dust deposited under extremely cold, dry, peri- or postglacial conditions. The name arises from its use in making house bricks. The Brickearth is normally represented on 1:50,000 solid and drift edition geological maps...
. These were formed in periods of climate change during the ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
s. The raised beaches were generally formed during periods of higher sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
, 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 flint
Flint
Flint is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of chert. It occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones. Inside the nodule, flint is usually dark grey, black, green, white, or brown in colour, and...
s.
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
Gravel
Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...
, sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
, silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...
and clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
, 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
Peat
Peat is an accumulation of partially decayed vegetation matter or histosol. Peat forms in wetland bogs, moors, muskegs, pocosins, mires, and peat swamp forests. Peat is harvested as an important source of fuel in certain parts of the world...
'.
Brickearth
Brickearth is originally a wind-blown loessLoess
Loess is an aeolian sediment formed by the accumulation of wind-blown silt, typically in the 20–50 micrometre size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate...
dust deposited under extremely cold, dry conditions that can be used for making house brick
Brick
A brick is a block of ceramic material used in masonry construction, usually laid using various kinds of mortar. It has been regarded as one of the longest lasting and strongest building materials used throughout history.-History:...
s. The Brickearth is normally represeneted on 1:50,000 solid and drift edition geological maps. 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".
It is a superficial deposit of homeogenous structureless loam
Loam
Loam is soil composed of sand, silt, and clay in relatively even concentration . Loam soils generally contain more nutrients and humus than sandy soils, have better infiltration and drainage than silty soils, and are easier to till than clay soils...
or silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...
. It requires little or no admixture of other materials to render them suitable for the manufacture of 'stock bricks'. Brickearth typically occurs in discontinuous spreads, about 2m to 4m thick, overlying chalk
Chalk
Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores....
, Thanet Beds or London Clay
London Clay
The London Clay Formation is a marine geological formation of Ypresian age which crops out in the southeast of England. The London Clay is well known for the fossils it contains. The fossils from the Lower Eocene indicate a moderately warm climate, the flora being tropical or subtropical...
. There are extensive brickearth deposits in Kent
Kent
Kent is a county in southeast England, and is one of the home counties. It borders East Sussex, Surrey and Greater London and has a defined boundary with Essex in the middle of the Thames Estuary. The ceremonial county boundaries of Kent include the shire county of Kent and the unitary borough of...
, particularly on the North Downs
North Downs
The North Downs are a ridge of chalk hills in south east England that stretch from Farnham in Surrey to the White Cliffs of Dover in Kent. The North Downs lie within two Areas of Outstanding Natural Beauty , the Surrey Hills and the Kent Downs...
dip slope and on the Hoo peninsula
Hoo Peninsula
The Hoo Peninsula is a peninsula in England separating the estuaries of the rivers Thames and Medway. It is dominated by a line of sand and clay hills, surrounded by an extensive area of marshland composed of alluvial silt. The name Hoo is the Old English word for spur of land.-History:The Romans...
, sections of the Medway
Medway
Medway is a conurbation and unitary authority in South East England. The Unitary Authority was formed in 1998 when the City of Rochester-upon-Medway amalgamated with Gillingham Borough Council and part of Kent County Council to form Medway Council, a unitary authority independent of Kent County...
and Stour
Stour
Stour may refer to:* HMS Stour, a Royal Navy River-class destroyer purchased in 1909.* Stour-class destroyer, the sub-class of Royal Navy destroyers of which HMS Stour was the lead ship.-See also:* East Stour...
valleys. The mineral content of brickearth is critical for brickmaking and precise proportions of chalk, clay, and iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
.
In 1986 there were four active stock brick works in Kent, at Otterham Quay, Funton, Murston
Murston
Murston is a suburb of Sittingbourne in Kent, England....
and Ospringe
Ospringe
Ospringe is a village and civil parish in the English county of Kent. It has a population of 715. Located south of Faversham, Ospringe forms part of the Borough of Swale...
.
In Chichester
Chichester
Chichester is a cathedral city in West Sussex, within the historic County of Sussex, South-East England. It has a long history as a settlement; its Roman past and its subsequent importance in Anglo-Saxon times are only its beginnings...
, 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.