Editing Lower and Middle Jurassic rocks between Robin Hood's Bay and Hawsker Bottoms - an excursion

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== Geological background ==
 
== Geological background ==
  
This 11.5 km section is on the northern limb of the Robin Hood's Bay dome structure, one of several inversion structures (intra-Jurassic) found in the Cleveland–Sole Pit Trough Depositional Basin (Kent ''in ''Rayner & Hemingway, 1974). This well-defined and classically exposed equidimensional structure ([[:File:YGS_YORKROCK_FIG_18_01.jpg|Figure 18.1]]) is truncated to the east by the north-south Peak '''Fault''', considered to be both a late Liassic synsedimentary fault and a sinistral transcurrent fault which has displaced the seaward part of the dome possibly some 8 km southwards (Hemingway ''in ''Rayner & Hemingway, 1974). The base of the Lias (Hettangian Stage) is not exposed even at the lowest tides in Robin Hood's Bay and there may be some slight discrepancy in the actual thicknesses of the lower Liassic sequences which are exposed on the extensive wave-cut platform. A summary geological succession is given in [[:File:YGS_YORKROCK_FIG_18_01.jpg|Figure 18.1]].
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This 11.5 km section is on the northern limb of the Robin Hood's Bay dome structure, one ofseveral inversion structures (intra-Jurassic) found in the Cleveland–Sole Pit Trough Depositional Basin (Kent ''in ''Rayner & Hemingway, 1974)
  
There are thick deposits of '''tills''' in the central areas of Robin Hood's Bay and it has been suggested that these Late Quaternary deposits infill valley features at two points: The Sands, just South of Bay Town [NZ 954 045], and at Stoupe Beck [NZ 958 035]. Indeed the base of the pre-glacial valley at Stoupe Beck seems to be below present sea level. These tills contain '''erratics''' from a variety of sources and supply exotic beach pebbles in the central section of the Bay (identifying them provides an interesting pastime when waiting for the tide to go out!). The cliffs predominantly composed of till are unstable and subject to extensive landslips but occasionally the tills can be seen to be divided by a central sandy sequence.
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This well-defined and classically exposed equidimensional structure ([[:File:YGS_YORKROCK_FIG_18_01.jpg|Figure 18.1]]) is truncated to the east by the north-south Peak Fault, considered to be both a late Liassic synsedimentary fault and a sinistral transcurrent fault which has displaced the seaward part of the dome possibly some 8 km southwards (Hemingway ''in ''Rayner & Hemingway, 1974)
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The base of the Lias (Hettangian Stage) is not exposed even at the lowest tides in Robin Hood's Bay and there may be some slight discrepancy in the actual thicknesses of the lower Liassic sequences which are exposed on the extensive wave-cut platform. A summary geological succession is given in [[:File:YGS_YORKROCK_FIG_18_01.jpg|Figure 18.1]].
 +
 
 +
There are thick deposits of tills in the central areas of Robin Hood's Bay and it has been suggested that these Late Quaternary deposits infill valley features at two points: The Sands, just South of Bay Town [NZ 954 045], and at Stoupe Beck [NZ 958 035]
 +
 
 +
Indeed the base of the pre-glacial valley at Stoupe Beck seems to be below present sea level. These tills contain erratics from a variety of sources and supply exotic beach pebbles in the central section of the Bay (identifying them provides an interesting pastime when waiting for the tide to go out!). The cliffs predominantly composed of till are unstable and subject to extensive landslips but occasionally the tills can be seen to be divided by a central sandy sequence.
  
 
== Excursion details ==
 
== Excursion details ==

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