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Geology
Underlying the upper reaches of the Trent, are formations of Millstone Grit and Carboniferous Coal Measures which include layers of sandstones, marls and coal seams. The river crosses a band of Triassic Sherwood sandstone at Sandon, and it meets the same sandstone again as it flows beside Cannock Chase, between Great Haywood and Armitage, there is also another outcrop between Weston-on-Trent and King's Mill.

Downstream of Armitage the solid geology is primarily Mercia Mudstones, the course of the river following the arc of these mudstones as they pass through the Midlands all the way to the Humber. The mudstones are not exposed by the bed of the river, as there is a layer of gravels and then alluvium above the bedrock. In places, however the mudstones do form river cliffs, most notably at Gunthorpe and Stoke Lock near Radcliffe on Trent, the village being named after the distinctive red coloured strata.

The low range of hills, which have been formed into a steep set of cliffs overlooking the Trent between Scunthorpe and Alkborough are also made up of mudstones, but are of the younger Rhaetic Penarth Group.

In the wider catchment the geology is more varied, ranging from the Precambrian rocks of the Charnwood Forest, through to the Jurassic limestone that forms the Lincolnshire Edge and the eastern watershed of the Trent. The most important in terms of the river are the extensive sandstone and limestone aquifers that underlie many of the tributary catchments. These include the Sherwood sandstones that occur beneath much of eastern Nottinghamshire, the Permian Lower Magnesian limestone and the carboniferous limestone in Derbyshire. Not only do these provide baseflows to the major tributaries, the groundwater is an important source for public water supply.

Sand, gravels and alluvium deposits that overlie the mudstone bedrock occur almost along the entire length of the river, and are an important feature of the middle and lower reaches, with the alluvial river silt producing fertile soils that are used for intensive agriculture in the Trent valley. Beneath the alluvium are widespread deposits of sand and gravel, which also occur as gravel terraces considerably above the height of the current river level. There is thought to be a complex succession of at least six separate gravel terrace systems along the river, deposited when a much larger Trent flowed through the existing valley, and along its ancestral routes through the water gaps at Lincoln and Ancaster.

This ‘staircase’ of flat topped terraces was created as a result of successive periods of deposition and subsequent down cutting by the river, a product of the meltwater and glacially eroded material produced from ice sheets at the end of glacial periods through the Pleistocene epoch between 450,000 and 12,000 years BP. Contained within these terraces is evidence of the mega fauna that once lived along the river, the bones and teeth of animals such as the woolly mammoth, bison and wolves that existed during colder periods have all been identified. Another notable find in a related terrace system near Derby from a warmer interglacial period, was the Allenton hippopotamus.



The lower sequences of these terraces have been widely quarried for sand and gravel, and the extraction of these minerals continues to be an important industry in the Trent Valley, with some three million tonnes of aggregates being produced each year. Once worked out, the remaining gravel pits which are usually flooded by the relatively high water table have been reused for a wide variety of purposes. These include recreational water activities, and once rehabilitated, as nature reserves and wetlands.

During the end of the last Devensian glacial period the formation of Lake Humber in the lowest reaches of the river, meant that substantial lake bed clays and silts were laid down to create the flat landscape of the Humberhead Levels. These levels extend across the Trent valley, and include the lower reaches of the Eau, Torne and Idle. In some areas, successive layers of peat were built up above the lacustrine deposits during the Holocene period, which created lowland mires such as the Thorne and Hatfield Moors.

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