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The cyclic deposits of the Upper Permian grade upwards into red marls with thin lenses of anhydrite and ultimately thick, dominantly fluvial sandstones of the Triassic Sherwood Sandstone Group in southeast Durham and Tees-side. These deposits are almost completely unfossiliferous and the Permo-Triassic boundary is placed as a matter of convenience at a distinctive level within the marls. The Sherwood Sandstone is succeeded, after a short break, by the Mercia Mudstone Group, a sequence of vari-coloured sandstones and red-brown and green marls, with beds of dolomite, anhydrite and evaporite residues in the lower part. These were the deposits of an extensive coastal plain, intermittently flooded by shallow saline waters from the southeast. Triassic rocks are now known almost exclusively from borehole evidence around Tees-side.
 
The cyclic deposits of the Upper Permian grade upwards into red marls with thin lenses of anhydrite and ultimately thick, dominantly fluvial sandstones of the Triassic Sherwood Sandstone Group in southeast Durham and Tees-side. These deposits are almost completely unfossiliferous and the Permo-Triassic boundary is placed as a matter of convenience at a distinctive level within the marls. The Sherwood Sandstone is succeeded, after a short break, by the Mercia Mudstone Group, a sequence of vari-coloured sandstones and red-brown and green marls, with beds of dolomite, anhydrite and evaporite residues in the lower part. These were the deposits of an extensive coastal plain, intermittently flooded by shallow saline waters from the southeast. Triassic rocks are now known almost exclusively from borehole evidence around Tees-side.
  
Younger deposits, excepting the widespread '''glaciogenic''' sediments of the recent past, are unknown in Northumbria, although evidence from outside the area suggests that the major marine transgressions of the Lower Jurassic and Upper Cretaceous may have covered the area. Any sediments deposited were subsequently removed, particularly during the Tertiary, when the northwestern parts of the British Isles underwent rapid uplift following the northward extension of Atlantic '''seafloor spreading''' between Greenland and Scandinavia. Associated igneous activity in centres in western Scotland extended its influence into Northumbria in the form of tholeiitic dykes, the best known being the Armathwaite-Cleveland Dyke in south Durham ([[Geology and landscape of Upper Teesdale - an excursion|Excursion 16]], [[Carboniferous and Permian rocks in southern County Durham - an excursion|Excursion 17]]), and the Tynemouth and Acklington dykes in Northumberland. All have a similar late Palaeocene age and appear to be far-flung representatives of the Mull dyke swarm.
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Younger deposits, excepting the widespread glaciogenic sediments of the recent past, are unknown in Northumbria, although evidence from outside the area suggests that the major marine transgressions of the Lower Jurassic and Upper Cretaceous may have covered the area. Any sediments deposited were subsequently removed, particularly during the Tertiary, when the northwestern parts of the British Isles underwent rapid uplift following the northward extension of Atlantic seafloor spreading between Greenland and Scandinavia. Associated igneous activity in centres in western Scotland extended its influence into Northumbria in the form of tholeiitic dykes, the best known being the Armathwaite-Cleveland Dyke in south Durham ([[Geology and landscape of Upper Teesdale - an excursion|Excursion 16]], [[Carboniferous and Permian rocks in southern County Durham - an excursion|Excursion 17]]), and the Tynemouth and Acklington dykes in Northumberland. All have a similar late Palaeocene age and appear to be far-flung representatives of the Mull dyke swarm.
  
A general trend in global cooling begun in the early Tertiary culminated in the sequence of cold and temperate climates which have affected the British Isles over the last 2.6 '''Ma'''. Several advances of ice probably covered Northumbria but almost all the deposits now preserved relate to the last extensive ice sheet glaciation in the late Devensian, around 17 000 yr '''B.P.''' ([[:File:YGS_NORTROCK_FIG_00_3.jpg|Figure 3]]f; [[The Quaternary of South Tynedale - an excursion|Excursion 12]]). In upland regions, most of the soils and unconsolidated deposits were stripped off and the hills and ridges moulded and streamlined. Ice, moving southwards from Scotland and the Cheviot, and extending into the westernmost part of the North Sea Basin, deflected to the southeast ice moving into the region from the Lake District and Galloway. Vast quantities of debris were deposited in the lowlands, as tills and water-laid deposits, smoothing out the pre-Quaternary relief of southeast Northumberland and eastern Durham. River valleys, some graded to cold stage sea levels down to −50 m O.D., were plugged by clays, sands and gravels. As the ice withdrew, most rivers re-established themselves close to their original courses. Ice melt resulted in the formation of widespread sheets of '''glaciofluvial''' sand and gravel, some now standing as terraces above the main rivers, and also areas of hummocky ice-contact deposits including '''kames, kame terraces''' and '''eskers''', with many '''kettle holes''' and dead-ice hollows. The persistence of coastal and sea ice dammed the eastward drainage of meltwaters leading to the formation of lakes in low-lying areas. In these, laminated clays and silts were deposited with sand and gravel deltas and fans at the margins. In upland areas, fine series of '''meltwater channels''', such as those around the Cheviots, were eroded mainly by water flowing beneath the ice during melting.
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A general trend in global cooling begun in the early Tertiary culminated in the sequence of cold and temperate climates which have affected the British Isles over the last 2.6 Ma. Several advances of ice probably covered Northumbria but almost all the deposits now preserved relate to the last extensive ice sheet glaciation in the late Devensian, around 17 000 yr B.P. ([[:File:YGS_NORTROCK_FIG_00_3.jpg|Figure 3]]f; [[The Quaternary of South Tynedale - an excursion|Excursion 12]]). In upland regions, most of the soils and unconsolidated deposits were stripped off and the hills and ridges moulded and streamlined. Ice, moving southwards from Scotland and the Cheviot, and extending into the westernmost part of the North Sea Basin, deflected to the southeast ice moving into the region from the Lake District and Galloway. Vast quantities of debris were deposited in the lowlands, as tills and water-laid deposits, smoothing out the pre-Quaternary relief of southeast Northumberland and eastern Durham. River valleys, some graded to cold stage sea levels down to −50 m O.D., were plugged by clays, sands and gravels. As the ice withdrew, most rivers re-established themselves close to their original courses. Ice melt resulted in the formation of widespread sheets of glaciofluvial sand and gravel, some now standing as terraces above the main rivers, and also areas of hummocky ice-contact deposits including kames, kame terraces and eskers, with many kettle holes and dead-ice hollows. The persistence of coastal and sea ice dammed the eastward drainage of meltwaters leading to the formation of lakes in low-lying areas. In these, laminated clays and silts were deposited with sand and gravel deltas and fans at the margins. In upland areas, fine series of meltwater channels, such as those around the Cheviots, were eroded mainly by water flowing beneath the ice during melting.
  
The main event of the present interglacial has been the rise in sea level to give the coastal morphology we see today. Evidence of the rise is found in submerged forests and peats, extending to at least −5 m O.D., present on the coasts of Northumberland and Durham. With a low tide, and not too much beach sand, these features can be readily seen in several places, such as Hartlepool, Seaburn, Blyth Beach, Cresswell, and Hauxley south of Amble. In the uplands, extensive peat deposits have formed in the higher, wetter areas.
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The main event of the present interglacial has been the rise in sea level to give the coastal morphology we see today. Evidence of the rise is found in submerged forests and peats, extending to at least −5 m O.D., present on the coasts of Northumberland and Durham. With a low tide, and not too much beach sand, these features can be readily seen in several places, such as Hartlepool, Seaburn, Blyth Beach, Cresswell, and Hauxley south of Amble. In the uplands, extensive peat deposits have formed in the higher, wetter areas.
  
 
== [[Northumbrian rocks and landscape: a field guide#Glossary|Glossary]] ==
 
== [[Northumbrian rocks and landscape: a field guide#Glossary|Glossary]] ==

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