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| Merseyside (Halton, Sefton, Liverpool, Knowsley, St Helens, Warrington and the Wirral Districts) |
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| Overview |
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The Merseyside area is largely defined by its low-lying relief and its generally urban nature which masks the underlying geology and main landscape features. The solid geology of the area is dominated by sandstones and mudstones of Triassic age, with the sandstones forming the higher ground at the northern end of the Wirral and Liverpool. The south-western edge of the Lancashire Coalfield, comprising Upper Carboniferous rocks, outcrops beneath St. Helens and east Liverpool.
Surface outcrops of the underlying geology are rare and the majority of the area is mantled by thick deposits of till and pockets of sand and gravel deposited by glaciers at the end of the last ice age, some 15,000 years ago. |
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| Carboniferous |
| The oldest rocks occur in the St. Helens-Knowsley area and are of Carboniferous age (354-290 million years old), forming the south-westernmost part of the Lancashire Coalfield. Although not exposed, the rocks belong to the Upper Carboniferous Coal Measures. The sediments now forming these rocks were deposited on an extensive series of low-lying, swampy river deltas built out into shallow marine waters. The periodic flooding and building of the deltas along the coastline resulted in the deposition of a series of coals (representing the compressed remains of the luxuriant swamp vegetation) interspersed with thicker layers of shale, clay, sandstone and mudstone. |
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| Triassic |
The Triassic (248-205 million years old) period is represented by red mudstones and sandstones that underlie virtually the entire area. These rocks were deposited under arid, desert conditions. The Lower Triassic sandstones of the Sherwood Sandstone Group form low, but prominent ridges at Wallasea and Birkenhead on the Wirral Peninsula and Crosby on the north side of the Mersey Estuary. The Sherwood Sandstone Group consists largely of red, yellow, and brown sandstones that often show colour mottling. Pebbles are scattered through much of the sequence and include the well known Chester Pebble Bed. The smoothness and roundness of the pebbles within the Chester Pebble Bed indicates that they were transported by a large and powerful braided-river system, probably on the margin of an arid, desert mountain range. The sandstones, where present close to the surface, give rise to free-draining soils which support heathland vegetation such as at Thurstaston, on the Wirral.
The mudstones of the overlying Triassic Mercia Mudstone Group probably represent wind-blown dust that settled in shallow salt-lakes and sun-baked mudflats on the extensive flood plain. These rocks underlie much of the land to the north of the Mersey Estuary and east to Warrington. The arid conditions under which these rocks were deposited are indicated by the occurrence of numerous layers of salt, which formed through the evaporation of mineral-rich water under the intense desert sun. |
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| Quaternary |
Over the last two million years the climate of Britain has varied tremendously with periods of temperate climate interrupted by repeated advances and retreats of glaciers and ice sheets. Collectively these periods have become known as the Ice Age (we are still in one of the temperate phases) and the actions of the ice sheets have been instrumental in forming the landscape we see today.
The main deposit of Quaternary age is till (or boulder clay), which formed in and beneath glaciers and ice-sheets. During the last glacial advance some 20,000 years ago, ice invaded from the Irish Sea area and deposited till, sands and gravels over much of the Merseyside area. Also associated with the glacial advance are deposits of fine, wind transported silt known as loess. |
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| Geological Highlights: |
- The Sefton coast is of special interest for the diversity
of coastal landforms that occur here, in particular for
the large, mobile dune system. The whole range of dune types
can be seen, from shifting dunes along the shoreline with
marram grass to fixed dunes with vegetation including areas
of creeping willow. Between the dunes, there are lower-lying
areas known as dune slacks which support areas of more wetland
vegetation. The zone of dunes around Formby Point has been
eroding since 1906 while areas north and south of this zone
are accreting (where the nature of the coast allows). The
rapid erosion is therefore reducing the area of shifting
dunes at Formby, and high, steep eroding dunes abut the
beach with extensive areas of blown sand immediately inland.
The dune complex is complemented by features of deposition
and erosion on the foreshore including multiple sand bars,
relatively stable bar features in the intertidal zone and
many different types of sedimentary structures formed by
tidal and current action.
- At Formby Point, coastal erosion of the foreshore has
revealed the footprints of humans (adult and child), animals
(aurochs, cattle, red deer, roe deer, unshod horse, dog
/ wolf, wild boar, sheep / goat) and wading birds (crane,
oystercatcher and rail) preserved in laminated silts. These
have been dated to a period some 7,000-5,000 years ago.
In total, 184 human footprint trails have been recorded
to date. Study of the trails indicate that the women and
children were mainly occupied in gathering food (e.g. shrimps,
razor-shells and other seafood). Male footprints are sometimes
directly associated with red and roe deer tracks, suggesting
that the animals were perhaps being hunted.
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| Local sites |
| The following localities represent, in part, the geology of this county. Each locality has a grid reference, a brief description of how to get there and a short summary of the geology you are likely to find. All the localities listed are openly accessible. |
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| Sefton Coast - Ainsdale Sand Dunes |
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