Bedrock Geology UK South: Triassic - Revision history

Dbk: /* 251 to 200 million years ago */

2014-06-19T12:23:44Z

251 to 200 million years ago

← Older revision		Revision as of 13:23, 19 June 2014
Line 16:		Line 16:
	'''The early to mid Triassic was dominated by the deposition of sand and gravel''' ('''Figure P785823''') along the course of the rivers that drained Armorica and the northern part of the Variscan Mountains. The Variscan Mountains lay to the south and their denudation supplied debris to rivers flowing northwards across southern Britain into the East Irish Sea Basin or the Southern North Sea Basin. These deposits now form the Sherwood Sandstone Group (T1), which can be traced from the English Channel through the Worcester, Cheshire and the East Irish Sea basins, the East England Shelf and the North Sea Basin. The sediments are dominated by fluvial channel and sheet sands ('''Plate P535767''') but also show a strong aeolian influence, and are a distinctive red colour. In the Cheshire Basin and in the Midlands, the lowest strata are conglomeratic or pebbly sandstone, which contains characteristic quartzite pebbles that persist in the soil on weathering (Kidderminster, Nottingham Castle Sandstone and Chester Pebble Beds formations). Equivalent strata in the south-west are the Budleigh Salterton Pebble Beds Formation. At Nottingham, the Permian–Triassic boundary is placed within the Lenton Sandstone Formation (P4) a fluvial–aeolian sandstone that underlies the pebbly Nottingham Castle Sandstone Formation. The sandstones are important aquifers onshore, and offshore act as the reservoir for the East Irish Sea gas field.		'''The early to mid Triassic was dominated by the deposition of sand and gravel''' ('''Figure P785823''') along the course of the rivers that drained Armorica and the northern part of the Variscan Mountains. The Variscan Mountains lay to the south and their denudation supplied debris to rivers flowing northwards across southern Britain into the East Irish Sea Basin or the Southern North Sea Basin. These deposits now form the Sherwood Sandstone Group (T1), which can be traced from the English Channel through the Worcester, Cheshire and the East Irish Sea basins, the East England Shelf and the North Sea Basin. The sediments are dominated by fluvial channel and sheet sands ('''Plate P535767''') but also show a strong aeolian influence, and are a distinctive red colour. In the Cheshire Basin and in the Midlands, the lowest strata are conglomeratic or pebbly sandstone, which contains characteristic quartzite pebbles that persist in the soil on weathering (Kidderminster, Nottingham Castle Sandstone and Chester Pebble Beds formations). Equivalent strata in the south-west are the Budleigh Salterton Pebble Beds Formation. At Nottingham, the Permian–Triassic boundary is placed within the Lenton Sandstone Formation (P4) a fluvial–aeolian sandstone that underlies the pebbly Nottingham Castle Sandstone Formation. The sandstones are important aquifers onshore, and offshore act as the reservoir for the East Irish Sea gas field.

	[[Image:P535767.jpg\|thumb\|left\|200px\|Cross-bedded, pale-coloured fluvial sandstone and brighter orange, poorly bedded aeolian sandstone of the Helsby Sandstone Formation (Sherwood Sandstone Group) at Hilbre Island in the Dee estuary, Mersyside P535767.]]'''During the mid Triassic, depositional areas were gradually increased''', establishing continuity with the East England Shelf and the North Sea Basin. The Mercia Mudstone Group (T2) rests conformably on the Sherwood Sandstone but also oversteps it along the basin margins ('''Plate P667862'''). It is predominantly red-brown mudstone, deposited as loess or wind-blown dust derived by lateritic weathering of adjacent terrain. Some interbedded greenish grey mudstone, siltstone and sandstone, for example the Tarporley Siltstone and Sneinton formations, are probably water-laid deposits. The Arden Sandstone Formation ('''Plate P212583''') is a varicoloured (green, brown, purplish) horizon that can be traced from Gloucestershire to Nottinghamshire, and separates the Sidmouth and Branscombe mudstone formations. Halite is widespread in some of the depositional basins, gypsum/anhydrite and dolomite less so. Halite was formed as sea water, which flooded the low-lying coastal areas from time to time, evaporated in coastal marine sabkhas to produce a near-pure salt or in places a chaotic mix of halite and mudstone. The main halites of west Lancashire and the Cheshire Basin are up to 400m thick; they have been mined extensively causing subsidence in places. The maximum thickness of the Mercia Mudstone Group, about 1340m, was proved in a borehole at Prees in the Cheshire Basin.		[[Image:P535767.jpg\|thumb\|left\|200px\|Cross-bedded, pale-coloured fluvial sandstone and brighter orange, poorly bedded aeolian sandstone of the Helsby Sandstone Formation (Sherwood Sandstone Group) at Hilbre Island in the Dee estuary, Mersyside. P535767.]]'''During the mid Triassic, depositional areas were gradually increased''', establishing continuity with the East England Shelf and the North Sea Basin. The Mercia Mudstone Group (T2) rests conformably on the Sherwood Sandstone but also oversteps it along the basin margins ('''Plate P667862'''). It is predominantly red-brown mudstone, deposited as loess or wind-blown dust derived by lateritic weathering of adjacent terrain. Some interbedded greenish grey mudstone, siltstone and sandstone, for example the Tarporley Siltstone and Sneinton formations, are probably water-laid deposits. The Arden Sandstone Formation ('''Plate P212583''') is a varicoloured (green, brown, purplish) horizon that can be traced from Gloucestershire to Nottinghamshire, and separates the Sidmouth and Branscombe mudstone formations. Halite is widespread in some of the depositional basins, gypsum/anhydrite and dolomite less so. Halite was formed as sea water, which flooded the low-lying coastal areas from time to time, evaporated in coastal marine sabkhas to produce a near-pure salt or in places a chaotic mix of halite and mudstone. The main halites of west Lancashire and the Cheshire Basin are up to 400m thick; they have been mined extensively causing subsidence in places. The maximum thickness of the Mercia Mudstone Group, about 1340m, was proved in a borehole at Prees in the Cheshire Basin.

	'''The youngest Triassic strata represent a transgression''' that re-established marine deposition over much of England and at least part of Wales. The Blue Anchor Formation ('''Plate P579282''') at the top of the Mercia Mudstone Group marks the beginning of this process. It consists of greenish grey dolomitic mudstone with thin limestones, and in south Wales, where it is about 16m thick, it has been interpreted as a lacustrine facies. Around Cardiff, it interfingers with a marginal facies of dolomitised breccia and bedded shore-face conglomerate that rests on the remnants of Triassic wave-cut platforms carved in the underlying Carboniferous limestone. The Penarth Group ('''Plate P007705''') overlies the Blue Anchor Formation and both units are well exposed along the coast of south Wales and north Somerset. The Penarth Group comprises dark grey mudstone with subordinate sandstone (Westbury Formation) overlain by pale greenish grey mudstone with subordinate limestone (Lilstock Formation), and is about 12m thick. These thin units can be traced across the UK and have been identified to the north of the Lake District, near Carlisle.		'''The youngest Triassic strata represent a transgression''' that re-established marine deposition over much of England and at least part of Wales. The Blue Anchor Formation ('''Plate P579282''') at the top of the Mercia Mudstone Group marks the beginning of this process. It consists of greenish grey dolomitic mudstone with thin limestones, and in south Wales, where it is about 16m thick, it has been interpreted as a lacustrine facies. Around Cardiff, it interfingers with a marginal facies of dolomitised breccia and bedded shore-face conglomerate that rests on the remnants of Triassic wave-cut platforms carved in the underlying Carboniferous limestone. The Penarth Group ('''Plate P007705''') overlies the Blue Anchor Formation and both units are well exposed along the coast of south Wales and north Somerset. The Penarth Group comprises dark grey mudstone with subordinate sandstone (Westbury Formation) overlain by pale greenish grey mudstone with subordinate limestone (Lilstock Formation), and is about 12m thick. These thin units can be traced across the UK and have been identified to the north of the Lake District, near Carlisle.

Dbk at 12:23, 19 June 2014

2014-06-19T12:23:24Z

← Older revision		Revision as of 13:23, 19 June 2014
Line 16:		Line 16:
	'''The early to mid Triassic was dominated by the deposition of sand and gravel''' ('''Figure P785823''') along the course of the rivers that drained Armorica and the northern part of the Variscan Mountains. The Variscan Mountains lay to the south and their denudation supplied debris to rivers flowing northwards across southern Britain into the East Irish Sea Basin or the Southern North Sea Basin. These deposits now form the Sherwood Sandstone Group (T1), which can be traced from the English Channel through the Worcester, Cheshire and the East Irish Sea basins, the East England Shelf and the North Sea Basin. The sediments are dominated by fluvial channel and sheet sands ('''Plate P535767''') but also show a strong aeolian influence, and are a distinctive red colour. In the Cheshire Basin and in the Midlands, the lowest strata are conglomeratic or pebbly sandstone, which contains characteristic quartzite pebbles that persist in the soil on weathering (Kidderminster, Nottingham Castle Sandstone and Chester Pebble Beds formations). Equivalent strata in the south-west are the Budleigh Salterton Pebble Beds Formation. At Nottingham, the Permian–Triassic boundary is placed within the Lenton Sandstone Formation (P4) a fluvial–aeolian sandstone that underlies the pebbly Nottingham Castle Sandstone Formation. The sandstones are important aquifers onshore, and offshore act as the reservoir for the East Irish Sea gas field.		'''The early to mid Triassic was dominated by the deposition of sand and gravel''' ('''Figure P785823''') along the course of the rivers that drained Armorica and the northern part of the Variscan Mountains. The Variscan Mountains lay to the south and their denudation supplied debris to rivers flowing northwards across southern Britain into the East Irish Sea Basin or the Southern North Sea Basin. These deposits now form the Sherwood Sandstone Group (T1), which can be traced from the English Channel through the Worcester, Cheshire and the East Irish Sea basins, the East England Shelf and the North Sea Basin. The sediments are dominated by fluvial channel and sheet sands ('''Plate P535767''') but also show a strong aeolian influence, and are a distinctive red colour. In the Cheshire Basin and in the Midlands, the lowest strata are conglomeratic or pebbly sandstone, which contains characteristic quartzite pebbles that persist in the soil on weathering (Kidderminster, Nottingham Castle Sandstone and Chester Pebble Beds formations). Equivalent strata in the south-west are the Budleigh Salterton Pebble Beds Formation. At Nottingham, the Permian–Triassic boundary is placed within the Lenton Sandstone Formation (P4) a fluvial–aeolian sandstone that underlies the pebbly Nottingham Castle Sandstone Formation. The sandstones are important aquifers onshore, and offshore act as the reservoir for the East Irish Sea gas field.

	'''During the mid Triassic, depositional areas were gradually increased''', establishing continuity with the East England Shelf and the North Sea Basin. The Mercia Mudstone Group (T2) rests conformably on the Sherwood Sandstone but also oversteps it along the basin margins ('''Plate P667862'''). It is predominantly red-brown mudstone, deposited as loess or wind-blown dust derived by lateritic weathering of adjacent terrain. Some interbedded greenish grey mudstone, siltstone and sandstone, for example the Tarporley Siltstone and Sneinton formations, are probably water-laid deposits. The Arden Sandstone Formation ('''Plate P212583''') is a varicoloured (green, brown, purplish) horizon that can be traced from Gloucestershire to Nottinghamshire, and separates the Sidmouth and Branscombe mudstone formations. Halite is widespread in some of the depositional basins, gypsum/anhydrite and dolomite less so. Halite was formed as sea water, which flooded the low-lying coastal areas from time to time, evaporated in coastal marine sabkhas to produce a near-pure salt or in places a chaotic mix of halite and mudstone. The main halites of west Lancashire and the Cheshire Basin are up to 400m thick; they have been mined extensively causing subsidence in places. The maximum thickness of the Mercia Mudstone Group, about 1340m, was proved in a borehole at Prees in the Cheshire Basin.		[[Image:P535767.jpg\|thumb\|left\|200px\|Cross-bedded, pale-coloured fluvial sandstone and brighter orange, poorly bedded aeolian sandstone of the Helsby Sandstone Formation (Sherwood Sandstone Group) at Hilbre Island in the Dee estuary, Mersyside P535767.]]'''During the mid Triassic, depositional areas were gradually increased''', establishing continuity with the East England Shelf and the North Sea Basin. The Mercia Mudstone Group (T2) rests conformably on the Sherwood Sandstone but also oversteps it along the basin margins ('''Plate P667862'''). It is predominantly red-brown mudstone, deposited as loess or wind-blown dust derived by lateritic weathering of adjacent terrain. Some interbedded greenish grey mudstone, siltstone and sandstone, for example the Tarporley Siltstone and Sneinton formations, are probably water-laid deposits. The Arden Sandstone Formation ('''Plate P212583''') is a varicoloured (green, brown, purplish) horizon that can be traced from Gloucestershire to Nottinghamshire, and separates the Sidmouth and Branscombe mudstone formations. Halite is widespread in some of the depositional basins, gypsum/anhydrite and dolomite less so. Halite was formed as sea water, which flooded the low-lying coastal areas from time to time, evaporated in coastal marine sabkhas to produce a near-pure salt or in places a chaotic mix of halite and mudstone. The main halites of west Lancashire and the Cheshire Basin are up to 400m thick; they have been mined extensively causing subsidence in places. The maximum thickness of the Mercia Mudstone Group, about 1340m, was proved in a borehole at Prees in the Cheshire Basin.

	'''The youngest Triassic strata represent a transgression''' that re-established marine deposition over much of England and at least part of Wales. The Blue Anchor Formation ('''Plate P579282''') at the top of the Mercia Mudstone Group marks the beginning of this process. It consists of greenish grey dolomitic mudstone with thin limestones, and in south Wales, where it is about 16m thick, it has been interpreted as a lacustrine facies. Around Cardiff, it interfingers with a marginal facies of dolomitised breccia and bedded shore-face conglomerate that rests on the remnants of Triassic wave-cut platforms carved in the underlying Carboniferous limestone. The Penarth Group ('''Plate P007705''') overlies the Blue Anchor Formation and both units are well exposed along the coast of south Wales and north Somerset. The Penarth Group comprises dark grey mudstone with subordinate sandstone (Westbury Formation) overlain by pale greenish grey mudstone with subordinate limestone (Lilstock Formation), and is about 12m thick. These thin units can be traced across the UK and have been identified to the north of the Lake District, near Carlisle.		'''The youngest Triassic strata represent a transgression''' that re-established marine deposition over much of England and at least part of Wales. The Blue Anchor Formation ('''Plate P579282''') at the top of the Mercia Mudstone Group marks the beginning of this process. It consists of greenish grey dolomitic mudstone with thin limestones, and in south Wales, where it is about 16m thick, it has been interpreted as a lacustrine facies. Around Cardiff, it interfingers with a marginal facies of dolomitised breccia and bedded shore-face conglomerate that rests on the remnants of Triassic wave-cut platforms carved in the underlying Carboniferous limestone. The Penarth Group ('''Plate P007705''') overlies the Blue Anchor Formation and both units are well exposed along the coast of south Wales and north Somerset. The Penarth Group comprises dark grey mudstone with subordinate sandstone (Westbury Formation) overlain by pale greenish grey mudstone with subordinate limestone (Lilstock Formation), and is about 12m thick. These thin units can be traced across the UK and have been identified to the north of the Lake District, near Carlisle.

Dbk: /* 251 to 200 million years ago */

2014-06-19T10:51:51Z

251 to 200 million years ago

← Older revision		Revision as of 11:51, 19 June 2014
Line 4:		Line 4:

	[[Image:P785847.jpg\|thumb\|200px\|P785847.]]		[[Image:P785847.jpg\|thumb\|200px\|P785847.]]
			[[Image:P212668.jpg\|thumb\|200px\|A major fault separates the Malvern Hills (Neoproterozoic and Lower Palaeozoic rock) from the younger and lower lying Triassic of the Worcester Basin seen in the distance. P212668.]]

	'''The outcrop of Triassic strata''' follows approximately that of the Permian in the north of England, but it forms a continuous arc around the southern end of the Pennines and extends southwards through Leicestershire, Staffordshire, Worcestershire, south Wales and into Somerset and Devon. It is particularly well exposed on the north coast of Somerset and on the south coast of Devon. The outcrop is wider, reflecting, in part, the gentler dip and the greater thickness, over 5000m in some places.		'''The outcrop of Triassic strata''' follows approximately that of the Permian in the north of England, but it forms a continuous arc around the southern end of the Pennines and extends southwards through Leicestershire, Staffordshire, Worcestershire, south Wales and into Somerset and Devon. It is particularly well exposed on the north coast of Somerset and on the south coast of Devon. The outcrop is wider, reflecting, in part, the gentler dip and the greater thickness, over 5000m in some places.

Dbk at 10:44, 19 June 2014

2014-06-19T10:44:32Z

← Older revision		Revision as of 11:44, 19 June 2014
Line 1:		Line 1:
			__NOTOC__
	{{BedS}}		{{BedS}}
	==251 to 200 million years ago==		==251 to 200 million years ago==

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

2014-06-11T12:27:08Z

Protected "Bedrock Geology UK South: Triassic" ([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 10:00, 20 May 2014

2014-05-20T10:00:56Z

← Older revision		Revision as of 11:00, 20 May 2014
Line 22:		Line 22:
	Image:P667862.jpg\|Palaeovalley cut in Neoproterozoic rocks and infilled with Mercia Mudstone, New Cliffe Hill Quarry, Leicestershire. P667862.		Image:P667862.jpg\|Palaeovalley cut in Neoproterozoic rocks and infilled with Mercia Mudstone, New Cliffe Hill Quarry, Leicestershire. P667862.
	Image:P579282.jpg\|The gradational boundary of the Blue Anchor Formation with the underlying red mudstone of the Mercia Mudstone Group, St Audrie's Bay, Somerset. P579282.		Image:P579282.jpg\|The gradational boundary of the Blue Anchor Formation with the underlying red mudstone of the Mercia Mudstone Group, St Audrie's Bay, Somerset. P579282.
	Image:P007705.jpg\|Dark mudstone of the Penarth Group in the foreground, dips toward the camera, and rests on the Blue Anchor Formation. http://geoscenic.bgs.ac.uk/asset-bank/action/viewAsset?id=6527&index=0&total=1&view=viewSearchItem P007705.		Image:P007705.jpg\|Dark mudstone of the Penarth Group in the foreground, dips toward the camera, and rests on the Blue Anchor Formation. [http://geoscenic.bgs.ac.uk/asset-bank/action/viewAsset?id=6527&index=0&total=1&view=viewSearchItem P007705.]
	</gallery>		</gallery>

Dbk at 09:59, 20 May 2014

2014-05-20T09:59:32Z

← Older revision		Revision as of 10:59, 20 May 2014
Line 2:		Line 2:
	==251 to 200 million years ago==		==251 to 200 million years ago==

	[[Image:P785847.jpg\|thumb\|200px\|~~[http://bgsintranet/asset-bank/action/viewFullSizedImage?id=379991&size=1000~~ P785847.]]]		[[Image:P785847.jpg\|thumb\|200px\|P785847.]]

	'''The outcrop of Triassic strata''' follows approximately that of the Permian in the north of England, but it forms a continuous arc around the southern end of the Pennines and extends southwards through Leicestershire, Staffordshire, Worcestershire, south Wales and into Somerset and Devon. It is particularly well exposed on the north coast of Somerset and on the south coast of Devon. The outcrop is wider, reflecting, in part, the gentler dip and the greater thickness, over 5000m in some places.		'''The outcrop of Triassic strata''' follows approximately that of the Permian in the north of England, but it forms a continuous arc around the southern end of the Pennines and extends southwards through Leicestershire, Staffordshire, Worcestershire, south Wales and into Somerset and Devon. It is particularly well exposed on the north coast of Somerset and on the south coast of Devon. The outcrop is wider, reflecting, in part, the gentler dip and the greater thickness, over 5000m in some places.
Line 8:		Line 8:
	'''The Triassic Period was the beginning of the Mesozoic or ‘middle age’''' of planet Earth. At that time, southern Britain was located 15º to 20º north of the Equator. The climate was strongly seasonal, perhaps monsoonal, in the early part of the period but later became extremely hot in the interior of the supercontinent of Pangaea.		'''The Triassic Period was the beginning of the Mesozoic or ‘middle age’''' of planet Earth. At that time, southern Britain was located 15º to 20º north of the Equator. The climate was strongly seasonal, perhaps monsoonal, in the early part of the period but later became extremely hot in the interior of the supercontinent of Pangaea.

	[[Image:P785823.jpg\|thumb\|left\|200px\|Mid Triassic palaeogeographical sketch map. ~~[http://bgsintranet/asset-bank/action/viewFullSizedImage?id=379967&size=1000~~ P785823.]]]		[[Image:P785823.jpg\|thumb\|left\|200px\|Mid Triassic palaeogeographical sketch map. P785823.]]

	'''Regional extension''' that was directed roughly east–west continued as the dominant tectonic process and persisted throughout the Mesozoic. Many faults, both major and minor, cut the Mesozoic strata. Some of these controlled subsidence of the major depocentres such as the Cheshire and Worcester ('''Plate P212668''') basins and the thickness of preserved strata changes dramatically across them: many are reactivated basement structures.		'''Regional extension''' that was directed roughly east–west continued as the dominant tectonic process and persisted throughout the Mesozoic. Many faults, both major and minor, cut the Mesozoic strata. Some of these controlled subsidence of the major depocentres such as the Cheshire and Worcester ('''Plate P212668''') basins and the thickness of preserved strata changes dramatically across them: many are reactivated basement structures.
Line 19:		Line 19:

	<gallery mode="packed">		<gallery mode="packed">
	Image:P212583.jpg\|The Arden Sandstone Formation at the type section at Shrewley Canal cutting, Warwickshire. [http://~~bgsintranet~~/asset-bank/action/~~viewFullSizedImage~~?id=21134&~~size~~=~~1000~~ P212583.]		Image:P212583.jpg\|The Arden Sandstone Formation at the type section at Shrewley Canal cutting, Warwickshire. [http://geoscenic.bgs.ac.uk/asset-bank/action/viewAsset?id=21134&index=0&total=1&view=viewSearchItem P212583.]
	Image:P667862.jpg\|Palaeovalley cut in Neoproterozoic rocks and infilled with Mercia Mudstone, New Cliffe Hill Quarry, Leicestershire. ~~[http://bgsintranet/asset-bank/action/viewFullSizedImage?id=61183&size=1000~~ P667862.]		Image:P667862.jpg\|Palaeovalley cut in Neoproterozoic rocks and infilled with Mercia Mudstone, New Cliffe Hill Quarry, Leicestershire. P667862.
	Image:P579282.jpg\|The gradational boundary of the Blue Anchor Formation with the underlying red mudstone of the Mercia Mudstone Group, St Audrie's Bay, Somerset. ~~[http://bgsintranet/asset-bank/action/viewFullSizedImage?id=135909&size=1000~~ P579282.]		Image:P579282.jpg\|The gradational boundary of the Blue Anchor Formation with the underlying red mudstone of the Mercia Mudstone Group, St Audrie's Bay, Somerset. P579282.
	Image:P007705.jpg\|Dark mudstone of the Penarth Group in the foreground, dips toward the camera, and rests on the Blue Anchor Formation. [http://~~bgsintranet~~/asset-bank/action/~~viewFullSizedImage~~?id=6527&~~size~~=~~1000~~ P007705.]		Image:P007705.jpg\|Dark mudstone of the Penarth Group in the foreground, dips toward the camera, and rests on the Blue Anchor Formation. http://geoscenic.bgs.ac.uk/asset-bank/action/viewAsset?id=6527&index=0&total=1&view=viewSearchItem P007705.
	</gallery>		</gallery>

Dbk: /* 251 to 200 million years ago */

2014-05-15T15:37:17Z

251 to 200 million years ago

← Older revision		Revision as of 16:37, 15 May 2014
Line 2:		Line 2:
	==251 to 200 million years ago==		==251 to 200 million years ago==

	~~{\| class="wikitable" width="100pt" style="margin-left~~:~~40px; margin-right:0px; margin-bottom:10px; float:right; text-align:left;"~~		[[Image:P785847.jpg\|thumb\|200px\|[http://bgsintranet/asset-bank/action/viewFullSizedImage?id=379991&size=1000 P785847.]]]
	\| ~~<img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=379991&width=200&height=200">~~
	\|-
	\| [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=379991&size=1000 P785847.]
	\|}

	'''The outcrop of Triassic strata''' follows approximately that of the Permian in the north of England, but it forms a continuous arc around the southern end of the Pennines and extends southwards through Leicestershire, Staffordshire, Worcestershire, south Wales and into Somerset and Devon. It is particularly well exposed on the north coast of Somerset and on the south coast of Devon. The outcrop is wider, reflecting, in part, the gentler dip and the greater thickness, over 5000m in some places.		'''The outcrop of Triassic strata''' follows approximately that of the Permian in the north of England, but it forms a continuous arc around the southern end of the Pennines and extends southwards through Leicestershire, Staffordshire, Worcestershire, south Wales and into Somerset and Devon. It is particularly well exposed on the north coast of Somerset and on the south coast of Devon. The outcrop is wider, reflecting, in part, the gentler dip and the greater thickness, over 5000m in some places.
Line 12:		Line 8:
	'''The Triassic Period was the beginning of the Mesozoic or ‘middle age’''' of planet Earth. At that time, southern Britain was located 15º to 20º north of the Equator. The climate was strongly seasonal, perhaps monsoonal, in the early part of the period but later became extremely hot in the interior of the supercontinent of Pangaea.		'''The Triassic Period was the beginning of the Mesozoic or ‘middle age’''' of planet Earth. At that time, southern Britain was located 15º to 20º north of the Equator. The climate was strongly seasonal, perhaps monsoonal, in the early part of the period but later became extremely hot in the interior of the supercontinent of Pangaea.

	~~{\| class="wikitable" width="100pt" style="margin-left:0px; margin-right:40px; margin-bottom:10px; float:left; text-align:left;"~~		[[Image:P785823.jpg\|thumb\|left\|200px\|Mid Triassic palaeogeographical sketch map. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=379967&size=1000 P785823.]]]
	~~\| <font color="red">IMAGE NOT SHOWING? ERROR IN ASSETBANK</font><img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=287841&width=220&height=150">~~
	\|-
	~~\| A major fault separates the Malvern Hills (Neoproterozoic and Lower Palaeozoic rock) from the younger and lower lying Triassic of the Worcester Basin seen in the distance.~~ [~~http~~:~~//bgsintranet/asset-bank/action/viewFullSizedImage?id=287841&size=1000 P212668~~.]
	\|-
	\| ~~<img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=379967&width=250&height=175">~~
	\|-
	\| Mid Triassic palaeogeographical sketch map. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=379967&size=1000 P785823.]
	\|}

	'''Regional extension''' that was directed roughly east–west continued as the dominant tectonic process and persisted throughout the Mesozoic. Many faults, both major and minor, cut the Mesozoic strata. Some of these controlled subsidence of the major depocentres such as the Cheshire and Worcester ('''Plate P212668''') basins and the thickness of preserved strata changes dramatically across them: many are reactivated basement structures.		'''Regional extension''' that was directed roughly east–west continued as the dominant tectonic process and persisted throughout the Mesozoic. Many faults, both major and minor, cut the Mesozoic strata. Some of these controlled subsidence of the major depocentres such as the Cheshire and Worcester ('''Plate P212668''') basins and the thickness of preserved strata changes dramatically across them: many are reactivated basement structures.

	'''The early to mid Triassic was dominated by the deposition of sand and gravel''' ('''Figure P785823''') along the course of the rivers that drained Armorica and the northern part of the Variscan Mountains. The Variscan Mountains lay to the south and their denudation supplied debris to rivers flowing northwards across southern Britain into the East Irish Sea Basin or the Southern North Sea Basin. These deposits now form the Sherwood Sandstone Group (T1), which can be traced from the English Channel through the Worcester, Cheshire and the East Irish Sea basins, the East England Shelf and the North Sea Basin. The sediments are dominated by fluvial channel and sheet sands ('''Plate P535767''') but also show a strong aeolian influence, and are a distinctive red colour. In the Cheshire Basin and in the Midlands, the lowest strata are conglomeratic or pebbly sandstone, which contains characteristic quartzite pebbles that persist in the soil on weathering (Kidderminster, Nottingham Castle Sandstone and Chester Pebble Beds formations). Equivalent strata in the south-west are the Budleigh Salterton Pebble Beds Formation. At Nottingham, the Permian–Triassic boundary is placed within the Lenton Sandstone Formation (P4) a fluvial–aeolian sandstone that underlies the pebbly Nottingham Castle Sandstone Formation. The sandstones are important aquifers onshore, and offshore act as the reservoir for the East Irish Sea gas field.		'''The early to mid Triassic was dominated by the deposition of sand and gravel''' ('''Figure P785823''') along the course of the rivers that drained Armorica and the northern part of the Variscan Mountains. The Variscan Mountains lay to the south and their denudation supplied debris to rivers flowing northwards across southern Britain into the East Irish Sea Basin or the Southern North Sea Basin. These deposits now form the Sherwood Sandstone Group (T1), which can be traced from the English Channel through the Worcester, Cheshire and the East Irish Sea basins, the East England Shelf and the North Sea Basin. The sediments are dominated by fluvial channel and sheet sands ('''Plate P535767''') but also show a strong aeolian influence, and are a distinctive red colour. In the Cheshire Basin and in the Midlands, the lowest strata are conglomeratic or pebbly sandstone, which contains characteristic quartzite pebbles that persist in the soil on weathering (Kidderminster, Nottingham Castle Sandstone and Chester Pebble Beds formations). Equivalent strata in the south-west are the Budleigh Salterton Pebble Beds Formation. At Nottingham, the Permian–Triassic boundary is placed within the Lenton Sandstone Formation (P4) a fluvial–aeolian sandstone that underlies the pebbly Nottingham Castle Sandstone Formation. The sandstones are important aquifers onshore, and offshore act as the reservoir for the East Irish Sea gas field.

	~~{\| class="wikitable" width="100pt" style="margin-left:40px; margin-right:0px; margin-bottom:10px; float:right; text-align:left;"~~
	~~\| <font color="red">IMAGE NOT SHOWING? ERROR IN ASSETBANK</font><img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=100443&width=200&height=150">~~
	\|-
	\| Cross-bedded, pale-coloured fluvial sandstone and brighter orange, poorly bedded aeolian sandstone of the Helsby Sandstone Formation. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=100443&size=1000 P535767.]
	\|}

	'''During the mid Triassic, depositional areas were gradually increased''', establishing continuity with the East England Shelf and the North Sea Basin. The Mercia Mudstone Group (T2) rests conformably on the Sherwood Sandstone but also oversteps it along the basin margins ('''Plate P667862'''). It is predominantly red-brown mudstone, deposited as loess or wind-blown dust derived by lateritic weathering of adjacent terrain. Some interbedded greenish grey mudstone, siltstone and sandstone, for example the Tarporley Siltstone and Sneinton formations, are probably water-laid deposits. The Arden Sandstone Formation ('''Plate P212583''') is a varicoloured (green, brown, purplish) horizon that can be traced from Gloucestershire to Nottinghamshire, and separates the Sidmouth and Branscombe mudstone formations. Halite is widespread in some of the depositional basins, gypsum/anhydrite and dolomite less so. Halite was formed as sea water, which flooded the low-lying coastal areas from time to time, evaporated in coastal marine sabkhas to produce a near-pure salt or in places a chaotic mix of halite and mudstone. The main halites of west Lancashire and the Cheshire Basin are up to 400m thick; they have been mined extensively causing subsidence in places. The maximum thickness of the Mercia Mudstone Group, about 1340m, was proved in a borehole at Prees in the Cheshire Basin.		'''During the mid Triassic, depositional areas were gradually increased''', establishing continuity with the East England Shelf and the North Sea Basin. The Mercia Mudstone Group (T2) rests conformably on the Sherwood Sandstone but also oversteps it along the basin margins ('''Plate P667862'''). It is predominantly red-brown mudstone, deposited as loess or wind-blown dust derived by lateritic weathering of adjacent terrain. Some interbedded greenish grey mudstone, siltstone and sandstone, for example the Tarporley Siltstone and Sneinton formations, are probably water-laid deposits. The Arden Sandstone Formation ('''Plate P212583''') is a varicoloured (green, brown, purplish) horizon that can be traced from Gloucestershire to Nottinghamshire, and separates the Sidmouth and Branscombe mudstone formations. Halite is widespread in some of the depositional basins, gypsum/anhydrite and dolomite less so. Halite was formed as sea water, which flooded the low-lying coastal areas from time to time, evaporated in coastal marine sabkhas to produce a near-pure salt or in places a chaotic mix of halite and mudstone. The main halites of west Lancashire and the Cheshire Basin are up to 400m thick; they have been mined extensively causing subsidence in places. The maximum thickness of the Mercia Mudstone Group, about 1340m, was proved in a borehole at Prees in the Cheshire Basin.
Line 36:		Line 18:
	'''The youngest Triassic strata represent a transgression''' that re-established marine deposition over much of England and at least part of Wales. The Blue Anchor Formation ('''Plate P579282''') at the top of the Mercia Mudstone Group marks the beginning of this process. It consists of greenish grey dolomitic mudstone with thin limestones, and in south Wales, where it is about 16m thick, it has been interpreted as a lacustrine facies. Around Cardiff, it interfingers with a marginal facies of dolomitised breccia and bedded shore-face conglomerate that rests on the remnants of Triassic wave-cut platforms carved in the underlying Carboniferous limestone. The Penarth Group ('''Plate P007705''') overlies the Blue Anchor Formation and both units are well exposed along the coast of south Wales and north Somerset. The Penarth Group comprises dark grey mudstone with subordinate sandstone (Westbury Formation) overlain by pale greenish grey mudstone with subordinate limestone (Lilstock Formation), and is about 12m thick. These thin units can be traced across the UK and have been identified to the north of the Lake District, near Carlisle.		'''The youngest Triassic strata represent a transgression''' that re-established marine deposition over much of England and at least part of Wales. The Blue Anchor Formation ('''Plate P579282''') at the top of the Mercia Mudstone Group marks the beginning of this process. It consists of greenish grey dolomitic mudstone with thin limestones, and in south Wales, where it is about 16m thick, it has been interpreted as a lacustrine facies. Around Cardiff, it interfingers with a marginal facies of dolomitised breccia and bedded shore-face conglomerate that rests on the remnants of Triassic wave-cut platforms carved in the underlying Carboniferous limestone. The Penarth Group ('''Plate P007705''') overlies the Blue Anchor Formation and both units are well exposed along the coast of south Wales and north Somerset. The Penarth Group comprises dark grey mudstone with subordinate sandstone (Westbury Formation) overlain by pale greenish grey mudstone with subordinate limestone (Lilstock Formation), and is about 12m thick. These thin units can be traced across the UK and have been identified to the north of the Lake District, near Carlisle.

	<~~center>~~		<gallery mode="packed">
	~~{\| class="wikitable" width="100pt" style~~="~~margin-left:0px; margin-right:0px; margin-bottom:10px; float:center; text-align:left;"~~		Image:P212583.jpg\|The Arden Sandstone Formation at the type section at Shrewley Canal cutting, Warwickshire. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=21134&size=1000 P212583.]
	~~\| <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=21134&width=200&height=150~~">		Image:P667862.jpg\|Palaeovalley cut in Neoproterozoic rocks and infilled with Mercia Mudstone, New Cliffe Hill Quarry, Leicestershire. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=61183&size=1000 P667862.]
	~~\| <img src="http~~:~~//bgsintranet/asset-bank/action/directLinkImage?assetId=61183&width=200&height=150">~~		Image:P579282.jpg\|The gradational boundary of the Blue Anchor Formation with the underlying red mudstone of the Mercia Mudstone Group, St Audrie's Bay, Somerset. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=135909&size=1000 P579282.]
	~~\| <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=135909&width=200&height=150">~~		Image:P007705.jpg\|Dark mudstone of the Penarth Group in the foreground, dips toward the camera, and rests on the Blue Anchor Formation. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=6527&size=1000 P007705.]
	~~\| <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=6527&width=200&height=150">~~		</gallery>
	~~\|-valign="top"~~
	\| The Arden Sandstone Formation at the type section at Shrewley Canal cutting, Warwickshire. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=21134&size=1000 P212583.]
	\| Palaeovalley cut in Neoproterozoic rocks and infilled with Mercia Mudstone, New Cliffe Hill Quarry, Leicestershire. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=61183&size=1000 P667862.]
	\| The gradational boundary of the Blue Anchor Formation with the underlying red mudstone of the Mercia Mudstone Group, St Audrie's Bay, Somerset. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=135909&size=1000 P579282.]
	\| Dark mudstone of the Penarth Group in the foreground, dips toward the camera, and rests on the Blue Anchor Formation. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=6527&size=1000 P007705.]
	\|}
	</~~center~~>

	'''By the end of the Triassic Period''', the landmasses that were to influence the sedimentation patterns of the Jurassic and Cretaceous periods had emerged—the Lake District, Wales, Cornubia and the Anglo-Brabant massif or London Platform. Another mass extinction appears to have affected life on Earth, this time wiping out perhaps 50 per cent of the species.		'''By the end of the Triassic Period''', the landmasses that were to influence the sedimentation patterns of the Jurassic and Cretaceous periods had emerged—the Lake District, Wales, Cornubia and the Anglo-Brabant massif or London Platform. Another mass extinction appears to have affected life on Earth, this time wiping out perhaps 50 per cent of the species.

	[[Category:Bedrock Geology UK South\| 08]]		[[Category:Bedrock Geology UK South\| 08]]

Dbk: /* 251 to 200 million years ago */

2014-01-23T14:56:38Z

251 to 200 million years ago

← Older revision		Revision as of 15:56, 23 January 2014
Line 13:		Line 13:

	{\| 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:0px; margin-right:40px; margin-bottom:10px; float:left; text-align:left;"
	\| <font color="red">IMAGE NOT SHOWING?</font><img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=287841&width=220&height=150">		\| <font color="red">IMAGE NOT SHOWING? ERROR IN ASSETBANK</font><img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=287841&width=220&height=150">
	\|-		\|-
	\| A major fault separates the Malvern Hills (Neoproterozoic and Lower Palaeozoic rock) from the younger and lower lying Triassic of the Worcester Basin seen in the distance. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=287841&size=1000 P212668.]		\| A major fault separates the Malvern Hills (Neoproterozoic and Lower Palaeozoic rock) from the younger and lower lying Triassic of the Worcester Basin seen in the distance. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=287841&size=1000 P212668.]
Line 27:		Line 27:

	{\| 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;"
	\| <font color="red">IMAGE NOT SHOWING?</font><img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=100443&width=200&height=150">		\| <font color="red">IMAGE NOT SHOWING? ERROR IN ASSETBANK</font><img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=100443&width=200&height=150">
	\|-		\|-
	\| Cross-bedded, pale-coloured fluvial sandstone and brighter orange, poorly bedded aeolian sandstone of the Helsby Sandstone Formation. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=100443&size=1000 P535767.]		\| Cross-bedded, pale-coloured fluvial sandstone and brighter orange, poorly bedded aeolian sandstone of the Helsby Sandstone Formation. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=100443&size=1000 P535767.]

Dbk: /* 251 to 200 million years ago */

2014-01-23T14:56:03Z

251 to 200 million years ago

← Older revision		Revision as of 15:56, 23 January 2014
Line 13:		Line 13:

	{\| 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:0px; margin-right:40px; margin-bottom:10px; float:left; text-align:left;"
	\| IMAGE NOT ~~IN IMAGEBASE~~ <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=287841&width=220&height=150">		\| <font color="red">IMAGE NOT SHOWING?</font><img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=287841&width=220&height=150">
	\|-		\|-
	\| A major fault separates the Malvern Hills (Neoproterozoic and Lower Palaeozoic rock) from the younger and lower lying Triassic of the Worcester Basin seen in the distance. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=287841&size=1000 P212668.]		\| A major fault separates the Malvern Hills (Neoproterozoic and Lower Palaeozoic rock) from the younger and lower lying Triassic of the Worcester Basin seen in the distance. [http://bgsintranet/asset-bank/action/viewFullSizedImage?id=287841&size=1000 P212668.]