Editing Jurassic, Tertiary and Quaternary around Great Ayton and Roseberry Topping, Cleveland Hills - an excursion

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=== Locality 3 [NZ 570 118]–[NZ 576 116] ===
 
=== Locality 3 [NZ 570 118]–[NZ 576 116] ===
  
The deep ravines through this wooded ridge result from extensive extraction of the dyke rock for road metal. Large blocks of the tholeiite, containing large crystals (phenocrysts) of '''feldspar''' set in a fine-grained matrix, can still be seen scattered throughout the workings. In some areas of the south wall minor leaves of the dyke, with associated sediment screens, may still be viewed ''in situ. ''All the wall rocks of the dyke show incipient contact metamorphism and these more indurate sediments form the sheer walls and pinnacles. '''''(This locality can be dangerous, with sheer drops masked by trees and shrubs; there is also the danger of falling blocks from the wall areas.)'''''
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The deep ravines through this wooded ridge result from extensive extraction of the dyke rock for road metal. Large blocks of the tholeiite, containing large crystals (phenocrysts) of feldspar set in a fine-grained matrix, can still be seen scattered throughout the workings. In some areas of the south wall minor leaves of the dyke, with associated sediment screens, may still be viewed ''in situ. ''All the wall rocks of the dyke show incipient contact metamorphism and these more indurate sediments form the sheer walls and pinnacles. '''''(This locality can be dangerous, with sheer drops masked by trees and shrubs; there is also the danger of falling blocks from the wall areas.)'''''
  
The dyke has been intruded into Lower Jurassic sediments. Approaching from the west the first sediments encountered are the silty shales of the Ironstone Shales (Lower Pliensbachian; Upper Redcar Mudstone Formation). These shales with nodule horizons are characteristic of the upper part of the Lower Lias; they tend to be poorly fossiliferous but occasional '''bivalves''' and the characteristic '''ammonite''' ''Androgynoceras (davoei '''''Biozone''') may be found.
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The dyke has been intruded into Lower Jurassic sediments. Approaching from the west the first sediments encountered are the silty shales of the Ironstone Shales (Lower Pliensbachian; Upper Redcar Mudstone Formation). These shales with nodule horizons are characteristic of the upper part of the Lower Lias; they tend to be poorly fossiliferous but occasional bivalves and the characteristic ammonite ''Androgynoceras (davoei ''Biozone) may be found.
  
Eastwards, the sediments become more silty and eventually grade imperceptibly into the silts and sandstones of the shallower-water deposits of the Staithes Formation (Middle Lias; Upper Pliensbachian). It is difficult to view these sediments ''in situ ''as they often form the upper levels of the quarry ravines. However, numerous fallen blocks show these marine impure sandstones to be richly fossiliferous with common Middle Lias bivalves such as ''Pseudopecten, Protocardia, Pseudolima, Liostrea ''and ''Pholadomya ''as well as numerous '''belemnites''' and the '''brachiopod''' ''Tetrarhynchia. ''More rarely, the index ammonite ''Amaltheus ''might be found ''(margaritatus ''Biozone), and brittle stars. The fossils almost always occur as natural moulds as the rock has been decalcified.
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Eastwards, the sediments become more silty and eventually grade imperceptibly into the silts and sandstones of the shallower-water deposits of the Staithes Formation (Middle Lias; Upper Pliensbachian). It is difficult to view these sediments ''in situ ''as they often form the upper levels of the quarry ravines. However, numerous fallen blocks show these marine impure sandstones to be richly fossiliferous with common Middle Lias bivalves such as ''Pseudopecten, Protocardia, Pseudolima, Liostrea ''and ''Pholadomya ''as well as numerous belemnites and the brachiopod ''Tetrarhynchia. ''More rarely, the index ammonite ''Amaltheus ''might be found ''(margaritatus ''Biozone), and brittle stars. The fossils almost always occur as natural moulds as the rock has been decalcified.
  
 
Return westwards to the start of the ravine area and take a path to the right to join the public right of way through the woods to the north of the quarry area.
 
Return westwards to the start of the ravine area and take a path to the right to join the public right of way through the woods to the north of the quarry area.

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