Bedrock Geology UK South: Jurassic - Revision history

Dbk at 12:26, 19 June 2014

2014-06-19T12:26:54Z

← Older revision		Revision as of 13:26, 19 June 2014
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	[[Image:P785824.jpg\|thumb\|left\|200px\|Mid Jurassic palaeogeographical sketch map. P785824.]]		[[Image:P785824.jpg\|thumb\|left\|200px\|Mid Jurassic palaeogeographical sketch map. P785824.]]

	'''The palaeogeographical landscape''' was inherited from the late Triassic so that the Worcester, Wessex and Cleveland basins continued as the main depositional areas with the East England Shelf as a long-lived stable area stretching east towards the deep North Sea graben ('''Figure P785824'''). The palaeolatitude is calculated at 30º to 40º north (:File:P785800.jpg\|'''Figure P785800f''']]). There was a subtropical climate with a strong seasonal influence on rainfall and temperature, but some thin gypsum and red beds are recorded offshore in the Middle and Upper Jurassic of the Bristol Channel and indicate periods of severe aridity.		'''The palaeogeographical landscape''' was inherited from the late Triassic so that the Worcester, Wessex and Cleveland basins continued as the main depositional areas with the East England Shelf as a long-lived stable area stretching east towards the deep North Sea graben ('''Figure P785824'''). The palaeolatitude is calculated at 30º to 40º north ([[:File:P785800.jpg\|'''Figure P785800f''']]). There was a subtropical climate with a strong seasonal influence on rainfall and temperature, but some thin gypsum and red beds are recorded offshore in the Middle and Upper Jurassic of the Bristol Channel and indicate periods of severe aridity.

	'''Besides the famous dinosaur bones''', these rocks are richly fossiliferous with the remains of a variety of marine creatures that include reptiles, fish and some mammals, but it is perhaps the ammonites that are most characteristic of the Jurassic strata.		'''Besides the famous dinosaur bones''', these rocks are richly fossiliferous with the remains of a variety of marine creatures that include reptiles, fish and some mammals, but it is perhaps the ammonites that are most characteristic of the Jurassic strata.

Dbk at 12:26, 19 June 2014

2014-06-19T12:26:33Z

← Older revision		Revision as of 13:26, 19 June 2014
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			__NOTOC__
	{{BedS}}		{{BedS}}
	==200 to 145 million years ago==		==200 to 145 million years ago==
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	[[Image:P785824.jpg\|thumb\|left\|200px\|Mid Jurassic palaeogeographical sketch map. P785824.]]		[[Image:P785824.jpg\|thumb\|left\|200px\|Mid Jurassic palaeogeographical sketch map. P785824.]]

	'''The palaeogeographical landscape''' was inherited from the late Triassic so that the Worcester, Wessex and Cleveland basins continued as the main depositional areas with the East England Shelf as a long-lived stable area stretching east towards the deep North Sea graben ('''Figure P785824'''). The palaeolatitude is calculated at 30º to 40º north ('''Figure ~~785800f~~'''). There was a subtropical climate with a strong seasonal influence on rainfall and temperature, but some thin gypsum and red beds are recorded offshore in the Middle and Upper Jurassic of the Bristol Channel and indicate periods of severe aridity.		'''The palaeogeographical landscape''' was inherited from the late Triassic so that the Worcester, Wessex and Cleveland basins continued as the main depositional areas with the East England Shelf as a long-lived stable area stretching east towards the deep North Sea graben ('''Figure P785824'''). The palaeolatitude is calculated at 30º to 40º north (:File:P785800.jpg\|'''Figure P785800f''']]). There was a subtropical climate with a strong seasonal influence on rainfall and temperature, but some thin gypsum and red beds are recorded offshore in the Middle and Upper Jurassic of the Bristol Channel and indicate periods of severe aridity.

	'''Besides the famous dinosaur bones''', these rocks are richly fossiliferous with the remains of a variety of marine creatures that include reptiles, fish and some mammals, but it is perhaps the ammonites that are most characteristic of the Jurassic strata.		'''Besides the famous dinosaur bones''', these rocks are richly fossiliferous with the remains of a variety of marine creatures that include reptiles, fish and some mammals, but it is perhaps the ammonites that are most characteristic of the Jurassic strata.

Jeth1 at 09:19, 17 June 2014

2014-06-17T09:19:31Z

← Older revision		Revision as of 10:19, 17 June 2014
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	[[Image:P785824.jpg\|thumb\|left\|200px\|Mid Jurassic palaeogeographical sketch map. P785824.]]		[[Image:P785824.jpg\|thumb\|left\|200px\|Mid Jurassic palaeogeographical sketch map. P785824.]]

	'''The palaeogeographical landscape''' was inherited from the late Triassic so that the Worcester, Wessex and Cleveland basins continued as the main depositional areas with the East England Shelf as a long-lived stable area stretching east towards the deep North Sea graben ('''Figure P785824'''). The palaeolatitude is calculated at 30º to 40º north ('''Figure 4f'''). There was a subtropical climate with a strong seasonal influence on rainfall and temperature, but some thin gypsum and red beds are recorded offshore in the Middle and Upper Jurassic of the Bristol Channel and indicate periods of severe aridity.		'''The palaeogeographical landscape''' was inherited from the late Triassic so that the Worcester, Wessex and Cleveland basins continued as the main depositional areas with the East England Shelf as a long-lived stable area stretching east towards the deep North Sea graben ('''Figure P785824'''). The palaeolatitude is calculated at 30º to 40º north ('''Figure 785800f'''). There was a subtropical climate with a strong seasonal influence on rainfall and temperature, but some thin gypsum and red beds are recorded offshore in the Middle and Upper Jurassic of the Bristol Channel and indicate periods of severe aridity.

	'''Besides the famous dinosaur bones''', these rocks are richly fossiliferous with the remains of a variety of marine creatures that include reptiles, fish and some mammals, but it is perhaps the ammonites that are most characteristic of the Jurassic strata ~~('''Plate 53''')~~.		'''Besides the famous dinosaur bones''', these rocks are richly fossiliferous with the remains of a variety of marine creatures that include reptiles, fish and some mammals, but it is perhaps the ammonites that are most characteristic of the Jurassic strata.

	'''The transgression that had started during the late Triassic''' continued throughout the early Jurassic. The peneplained landscape was flooded as a result of a rise in sea level (these changes are well documented in the North Sea) combined with a steady regional subsidence that affected both basins and highs. A warm shallow sea covered most of southern Britain, lapping against the landmasses, with lagoonal and brackish water sediments marking the imprecise boundary between land and sea.		'''The transgression that had started during the late Triassic''' continued throughout the early Jurassic. The peneplained landscape was flooded as a result of a rise in sea level (these changes are well documented in the North Sea) combined with a steady regional subsidence that affected both basins and highs. A warm shallow sea covered most of southern Britain, lapping against the landmasses, with lagoonal and brackish water sediments marking the imprecise boundary between land and sea.
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	'''To the south, more open marine but generally shallow-water conditions prevailed''', and ooidal and bioclastic limestones accumulated; these form the numerous named limestones of the Cotswolds, the Inferior Oolite Group (J2) and Great Oolite Group (J3). Mud deposition (Fuller’s Earth and Forest Marble formations) dominated to the south of the Mendip Hills, where the Frome Clay Formation replaces many of the Great Oolite limestones. At the top of the Great Oolite Group, the Cornbrash Formation is thin, but this fossiliferous limestone can be traced from Yorkshire through the Midlands to the south coast, which suggests that a marine transgression swept across a uniform landscape.		'''To the south, more open marine but generally shallow-water conditions prevailed''', and ooidal and bioclastic limestones accumulated; these form the numerous named limestones of the Cotswolds, the Inferior Oolite Group (J2) and Great Oolite Group (J3). Mud deposition (Fuller’s Earth and Forest Marble formations) dominated to the south of the Mendip Hills, where the Frome Clay Formation replaces many of the Great Oolite limestones. At the top of the Great Oolite Group, the Cornbrash Formation is thin, but this fossiliferous limestone can be traced from Yorkshire through the Midlands to the south coast, which suggests that a marine transgression swept across a uniform landscape.

	[[Image:P006771.jpg\|thumb\|left\|200px\|Cornbrash and Osgodby formations (lower cliff) and Oxford Clay (middle cliff; J4) capped by Lower Calcareous Grit of the ~~Coralian~~ Group (J5), Cayton Bay, near Scarborough. [http://geoscenic.bgs.ac.uk/asset-bank/action/viewAsset?id=5795&index=0&total=1&view=viewSearchItem P006771.]]]		[[Image:P006771.jpg\|thumb\|left\|200px\|Cornbrash and Osgodby formations (lower cliff) and Oxford Clay (middle cliff; J4) capped by Lower Calcareous Grit of the Corallian Group (J5), Cayton Bay, near Scarborough. [http://geoscenic.bgs.ac.uk/asset-bank/action/viewAsset?id=5795&index=0&total=1&view=viewSearchItem P006771.]]]

	'''More uniform conditions existed after the Cornbrash transgression''' of the mid Jurassic. Sand was deposited (Kellaways Formation, Osgodby Formation J4; ('''Plate P006771''') before mud spread over all but the most northerly parts. The Oxford Clay Formation (J4) was deposited in quiet marine conditions, but rhythmic changes are evident within it. The mudstones have been worked extensively in the past for the manufacture of bricks, and is partially self-firing owing to the relatively high carbon content. The mudstone is richly fossiliferous; the tougher fossils, belemnites and oysters such as Gryphaea, survive weathering and can often be seen on newly ploughed land ~~('''Plate 53''')~~.		'''More uniform conditions existed after the Cornbrash transgression''' of the mid Jurassic. Sand was deposited (Kellaways Formation, Osgodby Formation J4; ('''Plate P006771''') before mud spread over all but the most northerly parts. The Oxford Clay Formation (J4) was deposited in quiet marine conditions, but rhythmic changes are evident within it. The mudstones have been worked extensively in the past for the manufacture of bricks, and is partially self-firing owing to the relatively high carbon content. The mudstone is richly fossiliferous; the tougher fossils, belemnites and oysters such as Gryphaea, survive weathering and can often be seen on newly ploughed land.

	'''The Corallian Group (J5) crops out in Yorkshire''' and can be traced from the south Midlands to Dorset. It is arenaceous in the lower part and calcareous above, and was deposited in shallow-marine conditions. Small coral reefs developed and patchworks of broken coral colonies are preserved locally as ‘rag’ rock. The reef environment sustained a rich variety of organisms whose remains were commonly reworked into bioclastic limestone. In the north and east Midlands, mudstone deposition dominated throughout this time (West Walton Formation).		'''The Corallian Group (J5) crops out in Yorkshire''' and can be traced from the south Midlands to Dorset. It is arenaceous in the lower part and calcareous above, and was deposited in shallow-marine conditions. Small coral reefs developed and patchworks of broken coral colonies are preserved locally as ‘rag’ rock. The reef environment sustained a rich variety of organisms whose remains were commonly reworked into bioclastic limestone. In the north and east Midlands, mudstone deposition dominated throughout this time (West Walton Formation).

Dbk: Protected "Bedrock Geology UK South: Jurassic" ([Edit=Allow only administrators] (indefinite) [Move=Allow only administrators] (indefinite)) [cascading]

2014-06-11T12:27:21Z

Protected "Bedrock Geology UK South: Jurassic" ([Edit=Allow only administrators] (indefinite) [Move=Allow only administrators] (indefinite)) [cascading]

← Older revision	Revision as of 13:27, 11 June 2014
(No difference)

Dbk at 10:07, 20 May 2014

2014-05-20T10:07:44Z

← Older revision		Revision as of 11:07, 20 May 2014
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	'''To the south, more open marine but generally shallow-water conditions prevailed''', and ooidal and bioclastic limestones accumulated; these form the numerous named limestones of the Cotswolds, the Inferior Oolite Group (J2) and Great Oolite Group (J3). Mud deposition (Fuller’s Earth and Forest Marble formations) dominated to the south of the Mendip Hills, where the Frome Clay Formation replaces many of the Great Oolite limestones. At the top of the Great Oolite Group, the Cornbrash Formation is thin, but this fossiliferous limestone can be traced from Yorkshire through the Midlands to the south coast, which suggests that a marine transgression swept across a uniform landscape.		'''To the south, more open marine but generally shallow-water conditions prevailed''', and ooidal and bioclastic limestones accumulated; these form the numerous named limestones of the Cotswolds, the Inferior Oolite Group (J2) and Great Oolite Group (J3). Mud deposition (Fuller’s Earth and Forest Marble formations) dominated to the south of the Mendip Hills, where the Frome Clay Formation replaces many of the Great Oolite limestones. At the top of the Great Oolite Group, the Cornbrash Formation is thin, but this fossiliferous limestone can be traced from Yorkshire through the Midlands to the south coast, which suggests that a marine transgression swept across a uniform landscape.

	[[Image:P006771.jpg\|thumb\|left\|200px\|Cornbrash and Osgodby formations (lower cliff) and Oxford Clay (middle cliff; J4) capped by Lower Calcareous Grit of the Coralian Group (J5), Cayton Bay, near Scarborough. [http://geoscenic.bgs.ac.uk/asset-bank/action/viewAsset?id=5795&index=0&total=1&view=viewSearchItem P006771.]]		[[Image:P006771.jpg\|thumb\|left\|200px\|Cornbrash and Osgodby formations (lower cliff) and Oxford Clay (middle cliff; J4) capped by Lower Calcareous Grit of the Coralian Group (J5), Cayton Bay, near Scarborough. [http://geoscenic.bgs.ac.uk/asset-bank/action/viewAsset?id=5795&index=0&total=1&view=viewSearchItem P006771.]]]

	'''More uniform conditions existed after the Cornbrash transgression''' of the mid Jurassic. Sand was deposited (Kellaways Formation, Osgodby Formation J4; ('''Plate P006771''') before mud spread over all but the most northerly parts. The Oxford Clay Formation (J4) was deposited in quiet marine conditions, but rhythmic changes are evident within it. The mudstones have been worked extensively in the past for the manufacture of bricks, and is partially self-firing owing to the relatively high carbon content. The mudstone is richly fossiliferous; the tougher fossils, belemnites and oysters such as Gryphaea, survive weathering and can often be seen on newly ploughed land ('''Plate 53''').		'''More uniform conditions existed after the Cornbrash transgression''' of the mid Jurassic. Sand was deposited (Kellaways Formation, Osgodby Formation J4; ('''Plate P006771''') before mud spread over all but the most northerly parts. The Oxford Clay Formation (J4) was deposited in quiet marine conditions, but rhythmic changes are evident within it. The mudstones have been worked extensively in the past for the manufacture of bricks, and is partially self-firing owing to the relatively high carbon content. The mudstone is richly fossiliferous; the tougher fossils, belemnites and oysters such as Gryphaea, survive weathering and can often be seen on newly ploughed land ('''Plate 53''').

Dbk at 10:03, 20 May 2014

2014-05-20T10:03:27Z

Dbk: /* 200 to 145 million years ago */

2014-05-16T07:32:43Z

200 to 145 million years ago

← Older revision		Revision as of 08:32, 16 May 2014
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	==200 to 145 million years ago==		==200 to 145 million years ago==

	~~{\| class="wikitable" width="100pt" style="margin-left~~:~~40px; margin-right:0px; margin-bottom:10px; float:right; text-align:left;"~~		[[Image:P785848.jpg\|thumb\|200px\|[http://bgsintranet/asset-bank/action/viewFullSizedImage?id=379992&size=1000 P785848.]]]
	\| ~~<img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=379992&width=200&height=200">~~
	\|-
	\| [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=379992&size=1000 P785848.]
	\|}

	'''The Jurassic outcrop curves southwards''' from the coast of Yorkshire to Dorset with an extension running westward through the Bristol Channel into south Wales. An outlier occurs near Prees in the Cheshire Basin, with a significant occurrence at Mochras, concealed beneath younger sediments, on the west coast of Wales. The landscape is one of vales and escarpments. Many of the steeper slopes are wooded ('''Plate P667863'''), and villages with cottages of local stone in a variety of muted colours create the classic English landscape. Along the coast there are spectacular sea cliffs in Yorkshire, south Wales and Dorset.		'''The Jurassic outcrop curves southwards''' from the coast of Yorkshire to Dorset with an extension running westward through the Bristol Channel into south Wales. An outlier occurs near Prees in the Cheshire Basin, with a significant occurrence at Mochras, concealed beneath younger sediments, on the west coast of Wales. The landscape is one of vales and escarpments. Many of the steeper slopes are wooded ('''Plate P667863'''), and villages with cottages of local stone in a variety of muted colours create the classic English landscape. Along the coast there are spectacular sea cliffs in Yorkshire, south Wales and Dorset.

	{\| ~~class="wikitable" width="100pt" style="margin-~~left~~:0px; margin-right:40px; margin-bottom:10px; float:left; text-align:left;"~~		[[Image:P667863.jpg\|thumb\|left\|200px\|The floor of this Jurassic vale is mudstone of the Lias Group, with the Dyrhum and Marlstone Rock formations forming the higher wooded slopes, Vale of Belvoir, Leicestershire. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=61186&size=1000 P667863.]]]
	~~\| <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=61186&width=200&height=150">~~		[[Image:P785824.jpg\|thumb\|left\|200px\|Mid Jurassic palaeogeographical sketch map. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=379968&size=1000 P785824.]]]
	\|-
	\| The floor of this Jurassic vale is mudstone of the Lias Group, with the Dyrhum and Marlstone Rock formations forming the higher wooded slopes, Vale of Belvoir, Leicestershire. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=61186&size=1000 P667863.]
	\|-
	\| ~~<img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=379968&width=200&height=135">~~
	\|-
	\| Mid Jurassic palaeogeographical sketch map. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=379968&size=1000 P785824.]
	\|}

	'''The palaeogeographical landscape''' was inherited from the late Triassic so that the Worcester, Wessex and Cleveland basins continued as the main depositional areas with the East England Shelf as a long-lived stable area stretching east towards the deep North Sea graben ('''Figure P785824'''). The palaeolatitude is calculated at 30º to 40º north ('''Figure 4f'''). There was a subtropical climate with a strong seasonal influence on rainfall and temperature, but some thin gypsum and red beds are recorded offshore in the Middle and Upper Jurassic of the Bristol Channel and indicate periods of severe aridity.		'''The palaeogeographical landscape''' was inherited from the late Triassic so that the Worcester, Wessex and Cleveland basins continued as the main depositional areas with the East England Shelf as a long-lived stable area stretching east towards the deep North Sea graben ('''Figure P785824'''). The palaeolatitude is calculated at 30º to 40º north ('''Figure 4f'''). There was a subtropical climate with a strong seasonal influence on rainfall and temperature, but some thin gypsum and red beds are recorded offshore in the Middle and Upper Jurassic of the Bristol Channel and indicate periods of severe aridity.
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	'''Jurassic strata generally rest conformably on the topmost Triassic (Rhaetian)''' in the basinal areas, but towards the London Platform, which probably serves as a model for the other landmasses, the Lower Jurassic Lias Group becomes progressively thinner; the lower beds are overlapped by younger ones and eventually the group dies out across the ancient landmass.		'''Jurassic strata generally rest conformably on the topmost Triassic (Rhaetian)''' in the basinal areas, but towards the London Platform, which probably serves as a model for the other landmasses, the Lower Jurassic Lias Group becomes progressively thinner; the lower beds are overlapped by younger ones and eventually the group dies out across the ancient landmass.

	~~{\| class="wikitable" width="100pt" style="margin-left~~:~~40px; margin-right:0px; margin-bottom:10px; float:right; text-align:left;"~~		[[Image:P006953.jpg\|thumb\|200px\|Alternating shale and limestone of the Blue Lias Formation, Kilve, Somerset. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=5928&size=1000 P006953.]]]
	\| ~~<img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=5928&width=200&height=150">~~
	\|-
	\| Alternating shale and limestone of the Blue Lias Formation, Kilve, Somerset. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=5928&size=1000 P006953.]
	\|}

	'''The Lias Group (J1) consists mainly of grey mudstone''' (Charmouth Mudstone and Whitby Mudstone formations) but thin alternations of limestone are common especially in the basal part (Blue Lias Formation; '''Plate P006953'''), and sandstone and siltstone occur higher in the group (Dyrham, Bridport Sand and Staithes Sandstone formations). Ferruginous limestone (Marlstone Rock and Cleveland Ironstone) was formerly an important source of iron for the blast furnaces of the Midlands and Yorkshire. The Lias Group is well exposed along the Dorset coast particularly at Lyme Regis, a focus for fossil hunters over the centuries including Mary Anning who collected the first Ichthyosaurus, Plesiosaurus and Pterodactylus in the early 1800s.		'''The Lias Group (J1) consists mainly of grey mudstone''' (Charmouth Mudstone and Whitby Mudstone formations) but thin alternations of limestone are common especially in the basal part (Blue Lias Formation; '''Plate P006953'''), and sandstone and siltstone occur higher in the group (Dyrham, Bridport Sand and Staithes Sandstone formations). Ferruginous limestone (Marlstone Rock and Cleveland Ironstone) was formerly an important source of iron for the blast furnaces of the Midlands and Yorkshire. The Lias Group is well exposed along the Dorset coast particularly at Lyme Regis, a focus for fossil hunters over the centuries including Mary Anning who collected the first Ichthyosaurus, Plesiosaurus and Pterodactylus in the early 1800s.
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	'''To the south, more open marine but generally shallow-water conditions prevailed''', and ooidal and bioclastic limestones accumulated; these form the numerous named limestones of the Cotswolds, the Inferior Oolite Group (J2) and Great Oolite Group (J3). Mud deposition (Fuller’s Earth and Forest Marble formations) dominated to the south of the Mendip Hills, where the Frome Clay Formation replaces many of the Great Oolite limestones. At the top of the Great Oolite Group, the Cornbrash Formation is thin, but this fossiliferous limestone can be traced from Yorkshire through the Midlands to the south coast, which suggests that a marine transgression swept across a uniform landscape.		'''To the south, more open marine but generally shallow-water conditions prevailed''', and ooidal and bioclastic limestones accumulated; these form the numerous named limestones of the Cotswolds, the Inferior Oolite Group (J2) and Great Oolite Group (J3). Mud deposition (Fuller’s Earth and Forest Marble formations) dominated to the south of the Mendip Hills, where the Frome Clay Formation replaces many of the Great Oolite limestones. At the top of the Great Oolite Group, the Cornbrash Formation is thin, but this fossiliferous limestone can be traced from Yorkshire through the Midlands to the south coast, which suggests that a marine transgression swept across a uniform landscape.

	{\| ~~class="wikitable" width="100pt" style="margin-~~left~~:0px; margin-right:40px; margin-bottom:10px; float:left; text-align:left;"~~		[[Image:P006771.jpg\|thumb\|left\|200px\|Cornbrash and Osgodby formations (lower cliff) and Oxford Clay (middle cliff; J4) capped by Lower Calcareous Grit of the Coralian Group (J5), Cayton Bay, near Scarborough. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=5795&size=1000 P006771.]]]
	\| ~~<img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=5795&width=200&height=150">~~
	\|-
	\| Cornbrash and Osgodby formations (lower cliff) and Oxford Clay (middle cliff; J4) capped by Lower Calcareous Grit of the Coralian Group (J5), Cayton Bay, near Scarborough. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=5795&size=1000 P006771.]
	\|}

	'''More uniform conditions existed after the Cornbrash transgression''' of the mid Jurassic. Sand was deposited (Kellaways Formation, Osgodby Formation J4; ('''Plate P006771''') before mud spread over all but the most northerly parts. The Oxford Clay Formation (J4) was deposited in quiet marine conditions, but rhythmic changes are evident within it. The mudstones have been worked extensively in the past for the manufacture of bricks, and is partially self-firing owing to the relatively high carbon content. The mudstone is richly fossiliferous; the tougher fossils, belemnites and oysters such as Gryphaea, survive weathering and can often be seen on newly ploughed land ('''Plate 53''').		'''More uniform conditions existed after the Cornbrash transgression''' of the mid Jurassic. Sand was deposited (Kellaways Formation, Osgodby Formation J4; ('''Plate P006771''') before mud spread over all but the most northerly parts. The Oxford Clay Formation (J4) was deposited in quiet marine conditions, but rhythmic changes are evident within it. The mudstones have been worked extensively in the past for the manufacture of bricks, and is partially self-firing owing to the relatively high carbon content. The mudstone is richly fossiliferous; the tougher fossils, belemnites and oysters such as Gryphaea, survive weathering and can often be seen on newly ploughed land ('''Plate 53''').
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	'''The Corallian Group (J5) crops out in Yorkshire''' and can be traced from the south Midlands to Dorset. It is arenaceous in the lower part and calcareous above, and was deposited in shallow-marine conditions. Small coral reefs developed and patchworks of broken coral colonies are preserved locally as ‘rag’ rock. The reef environment sustained a rich variety of organisms whose remains were commonly reworked into bioclastic limestone. In the north and east Midlands, mudstone deposition dominated throughout this time (West Walton Formation).		'''The Corallian Group (J5) crops out in Yorkshire''' and can be traced from the south Midlands to Dorset. It is arenaceous in the lower part and calcareous above, and was deposited in shallow-marine conditions. Small coral reefs developed and patchworks of broken coral colonies are preserved locally as ‘rag’ rock. The reef environment sustained a rich variety of organisms whose remains were commonly reworked into bioclastic limestone. In the north and east Midlands, mudstone deposition dominated throughout this time (West Walton Formation).

	~~{\| class="wikitable" width="100pt" style="margin-left~~:~~40px; margin-right:0px; margin-bottom:10px; float:right; text-align:left;"~~		[[Image:P005775.jpg\|thumb\|200px\|Portland Group (J7) and Purbeck Group (K1), Stair Hole Cove, Lulworth. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=5032&size=1000 P005775.]]]
	\| ~~<img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=5032&width=200&height=150">~~
	\|-
	\| Portland Group (J7) and Purbeck Group (K1), Stair Hole Cove, Lulworth. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=5032&size=1000 P005775.]
	\|}

	'''The youngest Jurassic beds are the Portland and Purbeck groups''' ('''Plate P005775''') that are well exposed in the cliffs of the Isle of Portland and eastwards at Swanage (Durlston Head). The Portland Group (J7) represents a return to warm shallow-water deposition; glauconitic sandstone and mudstone is overlain by chert and then by ooidal limestone that is famous for its gigantic ammonite fossils, and has been worked extensively to provide the distinctive pale-coloured dimension stone that has been used in many civic buildings around London. The Jurassic–Cretaceous boundary is placed near the base of the overlying Purbeck Group.		'''The youngest Jurassic beds are the Portland and Purbeck groups''' ('''Plate P005775''') that are well exposed in the cliffs of the Isle of Portland and eastwards at Swanage (Durlston Head). The Portland Group (J7) represents a return to warm shallow-water deposition; glauconitic sandstone and mudstone is overlain by chert and then by ooidal limestone that is famous for its gigantic ammonite fossils, and has been worked extensively to provide the distinctive pale-coloured dimension stone that has been used in many civic buildings around London. The Jurassic–Cretaceous boundary is placed near the base of the overlying Purbeck Group.

	'''The Ampthill Clay and Kimmeridge Clay formations''' (Ancholme Group; J6) were deposited over a wide area of southern England and in the North Sea basins. Subsiding basins resulted in deeper water conditions and stratification of the water column, which provided ideal conditions for the preservation of organic matter. These organic-rich strata are the principal source-rock for hydrocarbons, both onshore and in the North Sea.		'''The Ampthill Clay and Kimmeridge Clay formations''' (Ancholme Group; J6) were deposited over a wide area of southern England and in the North Sea basins. Subsiding basins resulted in deeper water conditions and stratification of the water column, which provided ideal conditions for the preservation of organic matter. These organic-rich strata are the principal source-rock for hydrocarbons, both onshore and in the North Sea.


	[[Category:Bedrock Geology UK South\| 09]]		[[Category:Bedrock Geology UK South\| 09]]

Dbk: /* 200 to 145 million years ago */

2013-09-19T10:23:20Z

200 to 145 million years ago

← Older revision		Revision as of 11:23, 19 September 2013
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	'''To the south, more open marine but generally shallow-water conditions prevailed''', and ooidal and bioclastic limestones accumulated; these form the numerous named limestones of the Cotswolds, the Inferior Oolite Group (J2) and Great Oolite Group (J3). Mud deposition (Fuller’s Earth and Forest Marble formations) dominated to the south of the Mendip Hills, where the Frome Clay Formation replaces many of the Great Oolite limestones. At the top of the Great Oolite Group, the Cornbrash Formation is thin, but this fossiliferous limestone can be traced from Yorkshire through the Midlands to the south coast, which suggests that a marine transgression swept across a uniform landscape.		'''To the south, more open marine but generally shallow-water conditions prevailed''', and ooidal and bioclastic limestones accumulated; these form the numerous named limestones of the Cotswolds, the Inferior Oolite Group (J2) and Great Oolite Group (J3). Mud deposition (Fuller’s Earth and Forest Marble formations) dominated to the south of the Mendip Hills, where the Frome Clay Formation replaces many of the Great Oolite limestones. At the top of the Great Oolite Group, the Cornbrash Formation is thin, but this fossiliferous limestone can be traced from Yorkshire through the Midlands to the south coast, which suggests that a marine transgression swept across a uniform landscape.

	{\| class="wikitable" width="100pt" style="margin-left:~~40px~~; margin-right:~~0px~~; margin-bottom:10px; float:~~right~~; text-align:left;"		{\| class="wikitable" width="100pt" style="margin-left:0px; margin-right:40px; margin-bottom:10px; float:left; text-align:left;"
	\| <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=5795&width=200&height=150">		\| <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=5795&width=200&height=150">
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	'''The Corallian Group (J5) crops out in Yorkshire''' and can be traced from the south Midlands to Dorset. It is arenaceous in the lower part and calcareous above, and was deposited in shallow-marine conditions. Small coral reefs developed and patchworks of broken coral colonies are preserved locally as ‘rag’ rock. The reef environment sustained a rich variety of organisms whose remains were commonly reworked into bioclastic limestone. In the north and east Midlands, mudstone deposition dominated throughout this time (West Walton Formation).		'''The Corallian Group (J5) crops out in Yorkshire''' and can be traced from the south Midlands to Dorset. It is arenaceous in the lower part and calcareous above, and was deposited in shallow-marine conditions. Small coral reefs developed and patchworks of broken coral colonies are preserved locally as ‘rag’ rock. The reef environment sustained a rich variety of organisms whose remains were commonly reworked into bioclastic limestone. In the north and east Midlands, mudstone deposition dominated throughout this time (West Walton Formation).

	{\| class="wikitable" width="100pt" style="margin-left:~~0px~~; margin-right:~~40px~~; margin-bottom:10px; float:~~left~~; text-align:left;"		{\| class="wikitable" width="100pt" style="margin-left:40px; margin-right:0px; margin-bottom:10px; float:right; text-align:left;"
	\| <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=5032&width=200&height=150">		\| <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=5032&width=200&height=150">
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Dbk: /* 200 to 145 million years ago */

2013-09-19T10:22:33Z

200 to 145 million years ago

← Older revision		Revision as of 11:22, 19 September 2013
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	{\| class="wikitable" width="100pt" style="margin-left:40px; margin-right:0px; margin-bottom:10px; float:right; text-align:left;"		{\| class="wikitable" width="100pt" style="margin-left:40px; margin-right:0px; margin-bottom:10px; float:right; text-align:left;"
	\| <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=5795&width=200&height=~~200~~">		\| <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=5795&width=200&height=150">
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	\| Cornbrash and Osgodby formations (lower cliff) and Oxford Clay (middle cliff; J4) capped by Lower Calcareous Grit of the Coralian Group (J5), Cayton Bay, near Scarborough. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=5795&size=1000 P006771.]		\| Cornbrash and Osgodby formations (lower cliff) and Oxford Clay (middle cliff; J4) capped by Lower Calcareous Grit of the Coralian Group (J5), Cayton Bay, near Scarborough. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=5795&size=1000 P006771.]
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	'''The Corallian Group (J5) crops out in Yorkshire''' and can be traced from the south Midlands to Dorset. It is arenaceous in the lower part and calcareous above, and was deposited in shallow-marine conditions. Small coral reefs developed and patchworks of broken coral colonies are preserved locally as ‘rag’ rock. The reef environment sustained a rich variety of organisms whose remains were commonly reworked into bioclastic limestone. In the north and east Midlands, mudstone deposition dominated throughout this time (West Walton Formation).		'''The Corallian Group (J5) crops out in Yorkshire''' and can be traced from the south Midlands to Dorset. It is arenaceous in the lower part and calcareous above, and was deposited in shallow-marine conditions. Small coral reefs developed and patchworks of broken coral colonies are preserved locally as ‘rag’ rock. The reef environment sustained a rich variety of organisms whose remains were commonly reworked into bioclastic limestone. In the north and east Midlands, mudstone deposition dominated throughout this time (West Walton Formation).

	{\| class="wikitable" width="100pt" style="margin-left:~~40px~~; margin-right:~~0px~~; margin-bottom:10px; float:~~right~~; text-align:left;"		{\| class="wikitable" width="100pt" style="margin-left:0px; margin-right:40px; margin-bottom:10px; float:left; text-align:left;"
	\| <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=5032&width=200&height=~~200~~">		\| <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=5032&width=200&height=150">
	\|-		\|-
	\| Portland Group (J7) and Purbeck Group (K1), Stair Hole Cove, Lulworth. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=5032&size=1000 P005775.]		\| Portland Group (J7) and Purbeck Group (K1), Stair Hole Cove, Lulworth. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=5032&size=1000 P005775.]

Dbk: /* 200 to 145 million years ago */

2013-09-19T10:21:25Z

200 to 145 million years ago

← Older revision		Revision as of 11:21, 19 September 2013
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	\| The floor of this Jurassic vale is mudstone of the Lias Group, with the Dyrhum and Marlstone Rock formations forming the higher wooded slopes, Vale of Belvoir, Leicestershire. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=61186&size=1000 P667863.]		\| The floor of this Jurassic vale is mudstone of the Lias Group, with the Dyrhum and Marlstone Rock formations forming the higher wooded slopes, Vale of Belvoir, Leicestershire. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=61186&size=1000 P667863.]
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	\| <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=379968&width=200&height=~~100~~">		\| <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=379968&width=200&height=135">
	\|-		\|-
	\| Mid Jurassic palaeogeographical sketch map. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=379968&size=1000 P785824.]		\| Mid Jurassic palaeogeographical sketch map. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=379968&size=1000 P785824.]

← Older revision		Revision as of 11:03, 20 May 2014
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	==200 to 145 million years ago==		==200 to 145 million years ago==

	[[Image:P785848.jpg\|thumb\|200px\|~~[http://bgsintranet/asset-bank/action/viewFullSizedImage?id=379992&size=1000~~ P785848.]]]		[[Image:P785848.jpg\|thumb\|200px\|P785848.]]

	'''The Jurassic outcrop curves southwards''' from the coast of Yorkshire to Dorset with an extension running westward through the Bristol Channel into south Wales. An outlier occurs near Prees in the Cheshire Basin, with a significant occurrence at Mochras, concealed beneath younger sediments, on the west coast of Wales. The landscape is one of vales and escarpments. Many of the steeper slopes are wooded ('''Plate P667863'''), and villages with cottages of local stone in a variety of muted colours create the classic English landscape. Along the coast there are spectacular sea cliffs in Yorkshire, south Wales and Dorset.		'''The Jurassic outcrop curves southwards''' from the coast of Yorkshire to Dorset with an extension running westward through the Bristol Channel into south Wales. An outlier occurs near Prees in the Cheshire Basin, with a significant occurrence at Mochras, concealed beneath younger sediments, on the west coast of Wales. The landscape is one of vales and escarpments. Many of the steeper slopes are wooded ('''Plate P667863'''), and villages with cottages of local stone in a variety of muted colours create the classic English landscape. Along the coast there are spectacular sea cliffs in Yorkshire, south Wales and Dorset.

	[[Image:P667863.jpg\|thumb\|left\|200px\|The floor of this Jurassic vale is mudstone of the Lias Group, with the Dyrhum and Marlstone Rock formations forming the higher wooded slopes, Vale of Belvoir, Leicestershire. ~~[http://bgsintranet/asset-bank/action/viewFullSizedImage?id=61186&size=1000~~ P667863.]]]		[[Image:P667863.jpg\|thumb\|left\|200px\|The floor of this Jurassic vale is mudstone of the Lias Group, with the Dyrhum and Marlstone Rock formations forming the higher wooded slopes, Vale of Belvoir, Leicestershire. P667863.]]
	[[Image:P785824.jpg\|thumb\|left\|200px\|Mid Jurassic palaeogeographical sketch map. ~~[http://bgsintranet/asset-bank/action/viewFullSizedImage?id=379968&size=1000~~ P785824.]]]		[[Image:P785824.jpg\|thumb\|left\|200px\|Mid Jurassic palaeogeographical sketch map. P785824.]]

	'''The palaeogeographical landscape''' was inherited from the late Triassic so that the Worcester, Wessex and Cleveland basins continued as the main depositional areas with the East England Shelf as a long-lived stable area stretching east towards the deep North Sea graben ('''Figure P785824'''). The palaeolatitude is calculated at 30º to 40º north ('''Figure 4f'''). There was a subtropical climate with a strong seasonal influence on rainfall and temperature, but some thin gypsum and red beds are recorded offshore in the Middle and Upper Jurassic of the Bristol Channel and indicate periods of severe aridity.		'''The palaeogeographical landscape''' was inherited from the late Triassic so that the Worcester, Wessex and Cleveland basins continued as the main depositional areas with the East England Shelf as a long-lived stable area stretching east towards the deep North Sea graben ('''Figure P785824'''). The palaeolatitude is calculated at 30º to 40º north ('''Figure 4f'''). There was a subtropical climate with a strong seasonal influence on rainfall and temperature, but some thin gypsum and red beds are recorded offshore in the Middle and Upper Jurassic of the Bristol Channel and indicate periods of severe aridity.
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	'''Jurassic strata generally rest conformably on the topmost Triassic (Rhaetian)''' in the basinal areas, but towards the London Platform, which probably serves as a model for the other landmasses, the Lower Jurassic Lias Group becomes progressively thinner; the lower beds are overlapped by younger ones and eventually the group dies out across the ancient landmass.		'''Jurassic strata generally rest conformably on the topmost Triassic (Rhaetian)''' in the basinal areas, but towards the London Platform, which probably serves as a model for the other landmasses, the Lower Jurassic Lias Group becomes progressively thinner; the lower beds are overlapped by younger ones and eventually the group dies out across the ancient landmass.

	[[Image:P006953.jpg\|thumb\|200px\|Alternating shale and limestone of the Blue Lias Formation, Kilve, Somerset. [http://~~bgsintranet~~/asset-bank/action/~~viewFullSizedImage~~?id=5928&~~size~~=~~1000~~ P006953.]]]		[[Image:P006953.jpg\|thumb\|200px\|Alternating shale and limestone of the Blue Lias Formation, Kilve, Somerset. [http://geoscenic.bgs.ac.uk/asset-bank/action/viewAsset?id=5928&index=0&total=1&view=viewSearchItem P006953.]]]

	'''The Lias Group (J1) consists mainly of grey mudstone''' (Charmouth Mudstone and Whitby Mudstone formations) but thin alternations of limestone are common especially in the basal part (Blue Lias Formation; '''Plate P006953'''), and sandstone and siltstone occur higher in the group (Dyrham, Bridport Sand and Staithes Sandstone formations). Ferruginous limestone (Marlstone Rock and Cleveland Ironstone) was formerly an important source of iron for the blast furnaces of the Midlands and Yorkshire. The Lias Group is well exposed along the Dorset coast particularly at Lyme Regis, a focus for fossil hunters over the centuries including Mary Anning who collected the first Ichthyosaurus, Plesiosaurus and Pterodactylus in the early 1800s.		'''The Lias Group (J1) consists mainly of grey mudstone''' (Charmouth Mudstone and Whitby Mudstone formations) but thin alternations of limestone are common especially in the basal part (Blue Lias Formation; '''Plate P006953'''), and sandstone and siltstone occur higher in the group (Dyrham, Bridport Sand and Staithes Sandstone formations). Ferruginous limestone (Marlstone Rock and Cleveland Ironstone) was formerly an important source of iron for the blast furnaces of the Midlands and Yorkshire. The Lias Group is well exposed along the Dorset coast particularly at Lyme Regis, a focus for fossil hunters over the centuries including Mary Anning who collected the first Ichthyosaurus, Plesiosaurus and Pterodactylus in the early 1800s.
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	'''To the south, more open marine but generally shallow-water conditions prevailed''', and ooidal and bioclastic limestones accumulated; these form the numerous named limestones of the Cotswolds, the Inferior Oolite Group (J2) and Great Oolite Group (J3). Mud deposition (Fuller’s Earth and Forest Marble formations) dominated to the south of the Mendip Hills, where the Frome Clay Formation replaces many of the Great Oolite limestones. At the top of the Great Oolite Group, the Cornbrash Formation is thin, but this fossiliferous limestone can be traced from Yorkshire through the Midlands to the south coast, which suggests that a marine transgression swept across a uniform landscape.		'''To the south, more open marine but generally shallow-water conditions prevailed''', and ooidal and bioclastic limestones accumulated; these form the numerous named limestones of the Cotswolds, the Inferior Oolite Group (J2) and Great Oolite Group (J3). Mud deposition (Fuller’s Earth and Forest Marble formations) dominated to the south of the Mendip Hills, where the Frome Clay Formation replaces many of the Great Oolite limestones. At the top of the Great Oolite Group, the Cornbrash Formation is thin, but this fossiliferous limestone can be traced from Yorkshire through the Midlands to the south coast, which suggests that a marine transgression swept across a uniform landscape.

	[[Image:P006771.jpg\|thumb\|left\|200px\|Cornbrash and Osgodby formations (lower cliff) and Oxford Clay (middle cliff; J4) capped by Lower Calcareous Grit of the Coralian Group (J5), Cayton Bay, near Scarborough. [http://~~bgsintranet~~/asset-bank/action/~~viewFullSizedImage~~?id=5795&~~size~~=~~1000~~ P006771.]]]		[[Image:P006771.jpg\|thumb\|left\|200px\|Cornbrash and Osgodby formations (lower cliff) and Oxford Clay (middle cliff; J4) capped by Lower Calcareous Grit of the Coralian Group (J5), Cayton Bay, near Scarborough. [http://geoscenic.bgs.ac.uk/asset-bank/action/viewAsset?id=5795&index=0&total=1&view=viewSearchItem P006771.]]

	'''More uniform conditions existed after the Cornbrash transgression''' of the mid Jurassic. Sand was deposited (Kellaways Formation, Osgodby Formation J4; ('''Plate P006771''') before mud spread over all but the most northerly parts. The Oxford Clay Formation (J4) was deposited in quiet marine conditions, but rhythmic changes are evident within it. The mudstones have been worked extensively in the past for the manufacture of bricks, and is partially self-firing owing to the relatively high carbon content. The mudstone is richly fossiliferous; the tougher fossils, belemnites and oysters such as Gryphaea, survive weathering and can often be seen on newly ploughed land ('''Plate 53''').		'''More uniform conditions existed after the Cornbrash transgression''' of the mid Jurassic. Sand was deposited (Kellaways Formation, Osgodby Formation J4; ('''Plate P006771''') before mud spread over all but the most northerly parts. The Oxford Clay Formation (J4) was deposited in quiet marine conditions, but rhythmic changes are evident within it. The mudstones have been worked extensively in the past for the manufacture of bricks, and is partially self-firing owing to the relatively high carbon content. The mudstone is richly fossiliferous; the tougher fossils, belemnites and oysters such as Gryphaea, survive weathering and can often be seen on newly ploughed land ('''Plate 53''').
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	'''The Corallian Group (J5) crops out in Yorkshire''' and can be traced from the south Midlands to Dorset. It is arenaceous in the lower part and calcareous above, and was deposited in shallow-marine conditions. Small coral reefs developed and patchworks of broken coral colonies are preserved locally as ‘rag’ rock. The reef environment sustained a rich variety of organisms whose remains were commonly reworked into bioclastic limestone. In the north and east Midlands, mudstone deposition dominated throughout this time (West Walton Formation).		'''The Corallian Group (J5) crops out in Yorkshire''' and can be traced from the south Midlands to Dorset. It is arenaceous in the lower part and calcareous above, and was deposited in shallow-marine conditions. Small coral reefs developed and patchworks of broken coral colonies are preserved locally as ‘rag’ rock. The reef environment sustained a rich variety of organisms whose remains were commonly reworked into bioclastic limestone. In the north and east Midlands, mudstone deposition dominated throughout this time (West Walton Formation).

	[[Image:P005775.jpg\|thumb\|200px\|Portland Group (J7) and Purbeck Group (K1), Stair Hole Cove, Lulworth. [http://~~bgsintranet~~/asset-bank/action/~~viewFullSizedImage~~?id=5032&~~size~~=~~1000~~ P005775.]]]		[[Image:P005775.jpg\|thumb\|200px\|Portland Group (J7) and Purbeck Group (K1), Stair Hole Cove, Lulworth. [http://geoscenic.bgs.ac.uk/asset-bank/action/viewAsset?id=5032&index=0&total=1&view=viewSearchItem P005775.]]]

	'''The youngest Jurassic beds are the Portland and Purbeck groups''' ('''Plate P005775''') that are well exposed in the cliffs of the Isle of Portland and eastwards at Swanage (Durlston Head). The Portland Group (J7) represents a return to warm shallow-water deposition; glauconitic sandstone and mudstone is overlain by chert and then by ooidal limestone that is famous for its gigantic ammonite fossils, and has been worked extensively to provide the distinctive pale-coloured dimension stone that has been used in many civic buildings around London. The Jurassic–Cretaceous boundary is placed near the base of the overlying Purbeck Group.		'''The youngest Jurassic beds are the Portland and Purbeck groups''' ('''Plate P005775''') that are well exposed in the cliffs of the Isle of Portland and eastwards at Swanage (Durlston Head). The Portland Group (J7) represents a return to warm shallow-water deposition; glauconitic sandstone and mudstone is overlain by chert and then by ooidal limestone that is famous for its gigantic ammonite fossils, and has been worked extensively to provide the distinctive pale-coloured dimension stone that has been used in many civic buildings around London. The Jurassic–Cretaceous boundary is placed near the base of the overlying Purbeck Group.