Editing Geological history of Northumbria

Jump to navigation Jump to search

Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.

The edit can be undone. Please check the comparison below to verify that this is what you want to do, and then save the changes below to finish undoing the edit.

This page supports semantic in-text annotations (e.g. "[[Is specified as::World Heritage Site]]") to build structured and queryable content provided by Semantic MediaWiki. For a comprehensive description on how to use annotations or the #ask parser function, please have a look at the getting started, in-text annotation, or inline queries help pages.

Latest revision Your text
Line 35: Line 35:
 
Only part of the Upper Coal Measures and no Stephanian sediments are preserved in Northumbria. A period of uplift, tilting and foiding, followed by deep weathering and erosion, occurred in late Carboniferous-early Permian times due to the compressional effects of the '''Variscan Orogeny''' to the south, and a major '''eustatic''' sea-level fall as water was locked up in the glaciation of the southern continent of Gondwana. A regional unconformity exists below the earliest Permian deposits, which overstep folded Coal Measures in the south of County Durham to rest on Namurian and locally Dinantian beds. Climatic conditions had changed from the tropical hot, wet regime of the Westphalian to a hot, arid regime in the early Permian as the British Isles drifted northwards from the equator. These conditions led to the formation of a zone of reddening 5–10 m, exceptionally 300 m, thick below the Permian unconformity. On this continental landscape, east of higher ground in the region of the Pennines, the surface had been reduced to a vast, rolling peneplain extending out into the area of the North Sea, on which the earliest sediments preserved are '''lag''' breccias and breccio-conglomerates ([[:File:YGS_NORTROCK_FIG_00_3.jpg|Figure 3]]e). The succeeding Yellow Sands, now preserved as a series of east-northeast–west-southwest ridges up to 60 m thick in County Durham, are dune sands containing large-scale cross-bedded units indicating derivation from the east and northeast ([[Carboniferous and Permian rocks between Tynemouth and Seaton Sluice - an excursion|Excursion 8]], [[Magnesian Limestone between South Shields and Seaham - an excursion|Excursion 13]]).
 
Only part of the Upper Coal Measures and no Stephanian sediments are preserved in Northumbria. A period of uplift, tilting and foiding, followed by deep weathering and erosion, occurred in late Carboniferous-early Permian times due to the compressional effects of the '''Variscan Orogeny''' to the south, and a major '''eustatic''' sea-level fall as water was locked up in the glaciation of the southern continent of Gondwana. A regional unconformity exists below the earliest Permian deposits, which overstep folded Coal Measures in the south of County Durham to rest on Namurian and locally Dinantian beds. Climatic conditions had changed from the tropical hot, wet regime of the Westphalian to a hot, arid regime in the early Permian as the British Isles drifted northwards from the equator. These conditions led to the formation of a zone of reddening 5–10 m, exceptionally 300 m, thick below the Permian unconformity. On this continental landscape, east of higher ground in the region of the Pennines, the surface had been reduced to a vast, rolling peneplain extending out into the area of the North Sea, on which the earliest sediments preserved are '''lag''' breccias and breccio-conglomerates ([[:File:YGS_NORTROCK_FIG_00_3.jpg|Figure 3]]e). The succeeding Yellow Sands, now preserved as a series of east-northeast–west-southwest ridges up to 60 m thick in County Durham, are dune sands containing large-scale cross-bedded units indicating derivation from the east and northeast ([[Carboniferous and Permian rocks between Tynemouth and Seaton Sluice - an excursion|Excursion 8]], [[Magnesian Limestone between South Shields and Seaham - an excursion|Excursion 13]]).
  
The beginning of the Upper Permian was marked by the rapid inundation of the low lying areas east and west of the Pennines ([[:File:YGS_NORTROCK_FIG_00_3.jpg|Figure 3]]e). In the North Sea Basin, the Zechstein Sea reworked the upper part of the Yellow Sands. The deposits in the sea are strongly cyclic due to eustatic sea level rise and fall, resulting in the repeated expansion and contraction of the marine area under strongly evaporitic conditions. At the base of the first cycle is a very finely laminated deposit of alternating limestone or dolomite with organic rich layers, formed on the euxinic sea floor. This, the Marl Slate, is famous for the beautiful preservation of palaeoniscid fish, which swam in the oxygenated near surface waters, together with the remains of reptiles that fell or were transported into the sea. '''Euxinic''' conditions persisted throughout the first cycle in deeper parts of the basin but around the shallow oxygenated margins, '''oolitic carbonates''' developed, protected on their seaward side by a massive '''bryozoan-algal''' shelf edge reef, up to 100  m thick and more than 30 km long, that is well exposed in County Durham ([[Magnesian Limestone between South Shields and Seaham - an excursion|Excursion 13]]). The cycle is completed by the basin-ward development of the Hartlepool Anhydrite, probably as a primary precipitate on the basin floor during a fall in sea-level. Four further cycles of carbonate and/or marl deposition, of decreasing thickness, with overlying and basin-ward '''evaporites''' are known. The carbonates are often oolitic and stromatolitic, with restricted faunas. Those of the second cycle pass into deeper water slope carbonates showing signs of slumping, and in which a wide range of '''concretionary''' structures are developed. At the top of the third cycle, the Billingham Anhydrite and overlying Boulby Halite have been extensively mined beneath Tees-side where they formed the basis for the local chemical industry. Further south in east Yorkshire, the halite gives way in its upper part to the Boulby Potash, which is mined at depth northwest of Whitby. Thus the third cycle represents the most complete development of an evaporitic mineral sequence in the region.
+
The beginning of the Upper Permian was marked by the rapid inundation of the low lying areas east and west of the Pennines ([[:File:YGS_NORTROCK_FIG_00_3.jpg|Figure 3]]e). In the North Sea Basin, the Zechstein Sea reworked the upper part of the Yellow Sands. The deposits in the sea are strongly cyclic due to eustatic sea level rise and fall, resulting in the repeated expansion and contraction of the marine area under strongly evaporitic conditions. At the base of the first cycle is a very finely laminated deposit of alternating limestone or dolomite with organic rich layers, formed on the euxinic sea floor. This, the Marl Slate, is famous for the beautiful preservation of palaeoniscid fish, which swam in the oxygenated near surface waters, together with the remains of reptiles that fell or were transported into the sea. Euxinic conditions persisted throughout the first cycle in deeper parts of the basin but around the shallow oxygenated margins, oolitic carbonates developed, protected on their seaward side by a massive bryozoan-algal shelf edge reef, up to 100 m thick and more than 30 km long, that is well exposed in County Durham ([[Magnesian Limestone between South Shields and Seaham - an excursion|Excursion 13]]). The cycle is completed by the basin-ward development of the Hartlepool Anhydrite, probably as a primary precipitate on the basin floor during a fall in sea-level. Four further cycles of carbonate and/or marl deposition, of decreasing thickness, with overlying and basin-ward evaporites are known. The carbonates are often oolitic and stromatolitic, with restricted faunas. Those of the second cycle pass into deeper water slope carbonates showing signs of slumping, and in which a wide range of concretionary structures are developed. At the top of the third cycle, the Billingham Anhydrite and overlying Boulby Halite have been extensively mined beneath Tees-side where they formed the basis for the local chemical industry. Further south in east Yorkshire, the halite gives way in its upper part to the Boulby Potash, which is mined at depth northwest of Whitby. Thus the third cycle represents the most complete development of an evaporitic mineral sequence in the region.
  
 
The cyclic deposits of the Upper Permian grade upwards into red marls with thin lenses of anhydrite and ultimately thick, dominantly fluvial sandstones of the Triassic Sherwood Sandstone Group in southeast Durham and Tees-side. These deposits are almost completely unfossiliferous and the Permo-Triassic boundary is placed as a matter of convenience at a distinctive level within the marls. The Sherwood Sandstone is succeeded, after a short break, by the Mercia Mudstone Group, a sequence of vari-coloured sandstones and red-brown and green marls, with beds of dolomite, anhydrite and evaporite residues in the lower part. These were the deposits of an extensive coastal plain, intermittently flooded by shallow saline waters from the southeast. Triassic rocks are now known almost exclusively from borehole evidence around Tees-side.
 
The cyclic deposits of the Upper Permian grade upwards into red marls with thin lenses of anhydrite and ultimately thick, dominantly fluvial sandstones of the Triassic Sherwood Sandstone Group in southeast Durham and Tees-side. These deposits are almost completely unfossiliferous and the Permo-Triassic boundary is placed as a matter of convenience at a distinctive level within the marls. The Sherwood Sandstone is succeeded, after a short break, by the Mercia Mudstone Group, a sequence of vari-coloured sandstones and red-brown and green marls, with beds of dolomite, anhydrite and evaporite residues in the lower part. These were the deposits of an extensive coastal plain, intermittently flooded by shallow saline waters from the southeast. Triassic rocks are now known almost exclusively from borehole evidence around Tees-side.

Please note that all contributions to Earthwise may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here.
You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see Earthwise:Copyrights for details). Do not submit copyrighted work without permission!

Cancel Editing help (opens in new window)

  [] · [[]] · [[|]] · {{}} · · “” ‘’ «» ‹› „“ ‚‘ · ~ | °   · ± × ÷ ² ³ ½ · §
[[Category:]] · [[:File:]] · <code></code> · <syntaxhighlight></syntaxhighlight> · <includeonly></includeonly> · <noinclude></noinclude> · #REDIRECT[[]] · <translate></translate> · <languages/> · ==References== · {{reflist}} · ==Footnote== · {{reflist|group=note}} · <ref group=note> · __notoc__ · {{DEFAULTSORT:}} <div class="someclass noprint"></div> {{clear}} <br>

Templates used on this page: