Editing Chalk of Flamborough Head - an excursion

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== Geological background ==
 
== Geological background ==
  
The chalk succession exposed between Sewerby and Bempton Cliffs, about 400 m thick, is subdivided on '''biostratigraphical''' and '''lithostratigraphical''' criteria ([[:File:YGS_YORKROCK_FIG_21_02.jpg|Figure 21.2]]). These criteria also distinguish the chalk of Flamborough Head from that of Southern Britain as Northern Province Chalk. The chalk represents slow deposition of carbonate material in a clear tropical ocean. '''Clastic''' material is at a minimum except for '''marl''' bands, which may represent air-borne ash falls associated with volcanic activity as the proto-Atlantic opened to the south. Within the middle chalk, '''flint''' is found as nodules and thicker beds, some of which can be used with the marl bands as marker horizons throughout Flamborough and the Yorkshire Wolds ([[:File:YGS_YORKROCK_FIG_15_01.jpg|Figure 15.1]]). In the upper chalk, large nodules of '''marcasite''' can be found, often converted to rusty masses of iron carbonate.
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The chalk succession exposed between Sewerby and Bempton Cliffs, about 400 m thick, is subdivided on biostratigraphical and lithostratigraphical criteria ([[:File:YGS_YORKROCK_FIG_21_02.jpg|Figure 21.2]]). These criteria also distinguish the chalk of Flamborough Head from that of Southern Britain as Northern Province Chalk. The chalk represents slow deposition of carbonate material in a clear tropical ocean. Clastic material is at a minimum except for marl bands, which may represent air-borne ash falls associated with volcanic activity as the proto-Atlantic opened to the south. Within the middle chalk, flint is found as nodules and thicker beds, some of which can be used with the marl bands as marker horizons throughout Flamborough and the Yorkshire Wolds ([[:File:YGS_YORKROCK_FIG_15_01.jpg|Figure 15.1]]). In the upper chalk, large nodules of marcasite can be found, often converted to rusty masses of iron carbonate.
  
In late Cretaceous times, the chalk sea '''transgressed''' over the '''fault'''-controlled topography of the Market Weighton Block, and represents a contrast in depositional history to that displayed at Speeton. The earliest beds (Hunstanton Formation or Red Chalk) rest with marked '''unconformity''' on early Jurassic rocks in the Market Weighton area, with isolated patches of basal '''conglomerates''' and sands (see Excursion 15). The sea finally covered the block and deepened in the faulted basins to the north and south, with the chalk sections of the Wolds thinner than that on the coast. In the Tertiary, pressure from the east gently '''folded''' the chalk into a saucer-like basin, producing scarps in the west and north Wolds and reactivating the older marginal faults along the Howardian–Flamborough Fault System, resulting in a compressional/extensional fracture zone running east–west across the Wolds and exposed on the coast. The chalk was compressed and recrystallized to form the resistant Flamborough headland. Marine erosion has exploited the many minor faults associated with the crush belt, forming the magnificent coastal scenery of arches, stacks, caves and coves.
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In late Cretaceous times, the chalk sea transgressed over the fault-controlled topography of the Market Weighton Block, and represents a contrast in depositional history to that displayed at Speeton. The earliest beds (Hunstanton Formation or Red Chalk) rest with marked unconformity on early Jurassic rocks in the Market Weighton area, with isolated patches of basal conglomerates and sands (see Excursion 15). The sea finally covered the block and deepened in the faulted basins to the north and south, with the chalk sections of the Wolds thinner than that on the coast. In the Tertiary, pressure from the east gently folded the chalk into a saucer-like basin, producing scarps in the west and north Wolds and reactivating the older marginal faults along the Howardian–Flamborough Fault System, resulting in a compressional/extensional fracture zone running east–west across the Wolds and exposed on the coast. The chalk was compressed and recrystallized to form the resistant Flamborough headland. Marine erosion has exploited the many minor faults associated with the crush belt, forming the magnificent coastal scenery of arches, stacks, caves and coves.
  
The chalk is covered by '''drift''' from the most recent Devensian ice-sheet that banked up against the headland to form the Flamborough '''Moraine''', which contains exotic '''erratics''' from Northern England and Scandinavia.
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The chalk is covered by drift from the most recent Devensian ice-sheet that banked up against the headland to form the Flamborough Moraine, which contains exotic erratics from Northern England and Scandinavia.
  
 
== Excursion details ==
 
== Excursion details ==

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