Editing Geological history of Yorkshire
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== Ordovician to Silurian == | == Ordovician to Silurian == | ||
− | The Ordovician to Silurian sedimentary sequence, now exposed in the | + | The Ordovician to Silurian sedimentary sequence, now exposed in the inliers along the Craven Fault Belt near Settle ([[Lower Palaeozoic rocks of the Craven Inliers - an excursion|Excursion 1]]), has similarities with that of the Lake District. Turbiditic sandstones, with interbedded siltstone, conglomerate and mudstone (see clastic rocks) of probable Early Ordovician age are possibly several kilometres in total thickness. They were tightly folded, uplifted and eroded in the Middle Ordovician interval when a subaerial volcanic island arc was active on the northern margin of Eastern Avalonia, parts of which are preserved in the Lake District. Subsequent crustal extension produced a foreland basin, resulting in the return of marine conditions with a transgression in the Late Ordovician, when shallow water, mixed clastic–carbonate rocks 450 m thick, which are locally richly fossiliferous, were deposited. In the Silurian, 35 m of graptolitic mudstones and siltstones were laid down in the Llandovery as the seas deepened. The infilling of the foreland basin, the remnant seaway between Laurentia and Avalonia, occurred in the Wenlock and Ludlow, with a 1600 m thick succession of mainly turbiditic sandstones and siltstones. |
− | The collision between Eastern Avalonia, Laurentia and Baltica culminated in the compression and deformation of the Lower Palaeozoic rocks of Northern England in early Devonian times. The Acadian Orogeny, the terminal phase of the | + | The collision between Eastern Avalonia, Laurentia and Baltica culminated in the compression and deformation of the Lower Palaeozoic rocks of Northern England in early Devonian times. The Acadian Orogeny, the terminal phase of the Caledonian Orogenic cycle, formed a continental area of fold mountains and rugged uplands striking northeast-southwest across most of the area that is now the British Isles. Granite magmas were generated at depth during the orogeny and injected as plutons into the deformed sedimentary pile. No granites crop out at the surface in Yorkshire, but the Wensleydale Granite and a probable granite under Market Weighton have been detected at depth by geophysical survey. The Wensleydale Granite has been proved by a borehole and dated at 400 ± 10 Ma. |
== Devonian == | == Devonian == |