Editing Geological history of Yorkshire

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 50: Line 50:
 
Uplift and gentle folding terminated this marine sequence and the Middle Jurassic consists of about 250 m of fluviatile and deltaic sandstones, siltstones, shales and minor coals with marine intercalations, resting unconformably on various levels of the Lower Jurassic ([[Jurassic, Tertiary and Quaternary around Great Ayton and Roseberry Topping, Cleveland Hills - an excursion|Excursion 11]], [[Lower–Middle Jurassic sequences between Whitby and Saltwick - an excursion|Excursion 17]], [[Lower and Middle Jurassic rocks between Robin Hood's Bay and Hawsker Bottoms - an excursion|Excursion 18]], [[Middle–Upper Jurassic sequence between Layton Bay and Yons Nab - an excursion|Excursion 19]]). These deposits were laid down by south-flowing river systems originating immediately to the north. South of Yorkshire, they pass transitionally into the fully marine sequence of central and southern England ([[:File:YGS_YORKROCK_FIG_03_00.jpg|Figure 3]]d). Fossils are often common in the marine interbeds and the marshy delta-top environment supported a rich flora which is locally well preserved. A transgression returned fully marine conditions to the area late in the Middle Jurassic. The first sediments deposited were a variety of sandstones, shales and limestones up to 50 m thick, many highly fossiliferous, principally with bivalves and ammonites.
 
Uplift and gentle folding terminated this marine sequence and the Middle Jurassic consists of about 250 m of fluviatile and deltaic sandstones, siltstones, shales and minor coals with marine intercalations, resting unconformably on various levels of the Lower Jurassic ([[Jurassic, Tertiary and Quaternary around Great Ayton and Roseberry Topping, Cleveland Hills - an excursion|Excursion 11]], [[Lower–Middle Jurassic sequences between Whitby and Saltwick - an excursion|Excursion 17]], [[Lower and Middle Jurassic rocks between Robin Hood's Bay and Hawsker Bottoms - an excursion|Excursion 18]], [[Middle–Upper Jurassic sequence between Layton Bay and Yons Nab - an excursion|Excursion 19]]). These deposits were laid down by south-flowing river systems originating immediately to the north. South of Yorkshire, they pass transitionally into the fully marine sequence of central and southern England ([[:File:YGS_YORKROCK_FIG_03_00.jpg|Figure 3]]d). Fossils are often common in the marine interbeds and the marshy delta-top environment supported a rich flora which is locally well preserved. A transgression returned fully marine conditions to the area late in the Middle Jurassic. The first sediments deposited were a variety of sandstones, shales and limestones up to 50 m thick, many highly fossiliferous, principally with bivalves and ammonites.
  
Minor episodes of gentle warping and erosion broke up the Upper Jurassic succession on the Yorkshire coast ([[Middle–Upper Jurassic sequence between Layton Bay and Yons Nab - an excursion|Excursion 19]], [[Jurassic, Cretaceous and Quaternary rocks of Filey Bay and Speeton - an excursion|Excursion 20]]), whilst inland and to the south of the county the widely uniform muds of the Oxford Clay became established. This facies only extended to the coast in upper Oxford Clay times where it is 45 m thick. There, it is succeeded by a highly variable 100 m thick complex of limestones, including coral patch-reefs, and fine-grained calcareous sandstones. These too show lateral facies changes north of the Market Weighton area to marine muds typical of much of the eastern Midlands.
+
Minor episodes of gentle warping and erosion broke up the Upper Jurassic succession on the Yorkshire coast ([[Middle–Upper Jurassic sequence between Layton Bay and Yons Nab - an excursion|Excursion 19]], [[Jurassic, Cretaceous and Quaternary rocks of Filey Bay and Speeton - an excursion|Excursion 20]]), whilst inland and to the south of the county the widely uniform muds of the Oxford Clay became established. This facies only extended to the coast in upper Oxford Clay times where it is 45 m thick. There, it is succeeded by a highly variable too m thick complex of limestones, including coral patch-reefs, and fine-grained calcareous sandstones. These too show lateral facies changes north of the Market Weighton area to marine muds typical of much of the eastern Midlands.
  
Renewed transgression extended marine clay facies back across the Yorkshire area with the deposition of the Kimmeridge Clay, the most laterally persistent and uniform of all late Jurassic sediments and the principal source rock for North Sea oil. Unfortunately, the unit is poorly exposed in Yorkshire although in boreholes it may reach about 270 m in thickness. The latest Jurassic and very earliest Cretaceous strata are not represented in Yorkshire because renewed earth movements resulted in the uplift of an extensive landmass extending from central England into western Europe.
+
Renewed transgression extended marine clay facies back across the Yorkshire area with the deposition of the Kimmeridge Clay, the most laterally persistent and uniform of all late Jurassic sediments and the principal source rock for North Sea oil. Unfortunately, the unit is poorly exposed in Yorkshire although in boreholes it may reach about 270 m in thickness. The latest Jurassic and very earliest Cretaceous strata are not represented in Yorkshire because renewed earth movements resulted in the uplift of an extensive landmass extending from central England into western Europe.
  
 
== Cretaceous ==
 
== Cretaceous ==
Transgression early in the Cretaceous returned marine conditions to Yorkshire with the deposition of a richly fossiliferous sequence of soft shales and clay some 100 m thick (Excursion 20). The principal fossils are ammonites and belemnites and almost the whole of the lower Cretaceous is represented by this uniform sequence, making it the best and most complete example of this period in the U.K. Towards the end of early Cretaceous time, the supply of mud ceased and the sea deepened and cleared. This began the period of maximum transgression in the Mesozoic ([[:File:YGS_YORKROCK_FIG_03_00.jpg|Figure 3]]e), with uniform marine conditions across the whole of western Europe ([[Jurassic and Cretaceous rocks of the Market Weighton area - an excursion|Excursion 15]], [[Jurassic, Cretaceous and Quaternary rocks of Filey Bay and Speeton - an excursion|Excursion 20]], [[Chalk of Flamborough Head - an excursion|Excursion 21]]). Calcareous oozes formed, composed almost wholly of the minute platelets of '''coccoliths''' (unicellular algae) which abounded in surface waters. Initially, iron oxides stained the oozes and up to 30 m of red '''chalk''' is recorded in southeast Yorkshire, with varied faunas of '''sponges''', bivalves, brachiopods, echinoids, and crinoids. In the late Cretaceous, the red chalk is succeeded by the familiar white chalk which reaches a maximum thickness locally of 500 m. The rock is more marly and harder, due to calcite cementation, than in southern England and '''flints''' are present between about 40 m and 210 m above the base. The fauna is similar to that of the red chalk, although ammonites are also sporadically found. Distinctive laterally continuous marl and flint layers have proved excellent marker beds for local correlation between sections. The highest parts of the chalk do not crop out in Yorkshire, although they are present in part under the glacial deposits of Holderness.
+
Transgression early in the Cretaceous returned marine conditions to Yorkshire with the deposition of a richly fossiliferous sequence of soft shales and clay some too m thick (Excursion 20). The principal fossils are ammonites and belemnites and almost the whole of the lower Cretaceous is represented by this uniform sequence, making it the best and most complete example of this period in the U.K.
 +
 
 +
Towards the end of early Cretaceous time, the supply of mud ceased and the sea deepened and cleared. This began the period of maximum transgression in the Mesozoic ([[:File:YGS_YORKROCK_FIG_03_00.jpg|Figure 3]]e), with uniform marine conditions across the whole of western Europe ([[Jurassic and Cretaceous rocks of the Market Weighton area - an excursion|Excursion 15]], [[Jurassic, Cretaceous and Quaternary rocks of Filey Bay and Speeton - an excursion|Excursion 20]], [[Chalk of Flamborough Head - an excursion|Excursion 21]]). Calcareous oozes formed, composed almost wholly of the minute platelets of coccoliths (unicellular algae) which abounded in surface waters. Initially, iron oxides stained the oozes and up to 30 m of red chalk is recorded in southeast Yorkshire, with varied faunas of sponges, bivalves, brachiopods, echinoids, and crinoids. In the late Cretaceous, the red chalk is succeeded by the familiar white chalk which reaches a maximum thickness locally of 500 m. The rock is more marly and harder, due to calcite cementation, than in southern England and flints are present between about 4.0 m and 210 m above the base. The fauna is similar to that of the red chalk, although ammonites are also sporadically found. Distinctive laterally continuous marl and flint layers have proved excellent marker beds for local correlation between sections. The highest parts of the chalk do not crop out in Yorkshire, although they are present in part under the glacial deposits of Holderness.
  
 
== Tertiary ==
 
== Tertiary ==

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: