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

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The sediments above the Double Band contain the ammonite ''Echioceras'' indicative of the ''raricostatum'' Biozone. These form the upper parts of the Siliceous Shales.
 
The sediments above the Double Band contain the ammonite ''Echioceras'' indicative of the ''raricostatum'' Biozone. These form the upper parts of the Siliceous Shales.
  
Opposite the slipway at Bay Town, rare ammonites in the shales of Ground Wyke Hole indicate the start of the Ironstone/Pyritous Shales (Lower Pliensbachian). All ten subzones of the Lower Pliensbachian have been determined in the Ironstone/Pyritous Shales on the north side of Robin Hood's Bay between Bay Town and Castle Chamber. Ammonites are sporadic and poorly preserved in these sediments (which are characteristically cyclic shale-silt units with prominent ironstone concretion levels) but the genera ''Acanthopleuroceras'', ''Apoderoceras'', ''Platypleuroceras'', ''Tropidoceras'' and ''Androgynoceras'' are represented. Most of the beds also contain a variety of bivalves, belemnites, '''brachiopods''' and wood debris; they are also very bioturbated, commonly with ''Chondrites'', but also with ''Rhizocorallium'', ''Ophiomorpha'' and ''Teichichnus''.
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Opposite the slipway at Bay Town, rare ammonites in the shales of Ground Wyke Hole indicate the start of the Ironstone/Pyritous Shales (Lower Pliensbachian). All ten subzones of the Lower Pliensbachian have been determined in the Ironstone/Pyritous Shales on the north side of Robin Hood's Bay between Bay Town and Castle Chamber. Ammonites are sporadic and poorly preserved in these sediments (which are characteristically cyclic shale-silt units with prominent ironstone concretion levels) but the genera ''Acanthopleuroceras'', ''Apoderoceras'', ''Platypleuroceras'', ''Tropidoceras'' and ''Androgynoceras'' are represented. Most of the beds also contain a variety of bivalves, belemnites, brachiopods and wood debris; they are also very bioturbated, commonly with ''Chondrites'', but also with ''Rhizocorallium'', ''Ophiomorpha'' and ''Teichichnus''.
  
 
=== Locality 6 [NZ 953 052] ===
 
=== Locality 6 [NZ 953 052] ===
  
From this point (where curious vertical 'starlike' '''pyrite''' bodies may be seen in the shales) onwards, the sediments of the ''ibex ''Biozone are rich in the large bivalve ''Pinna. ''Over beds some 26.5 m thick the communities of ''Pinna ''can be seen either in life position, with the open aperture probably facing the predominant bottom current direction (the planed-off bivalve shells having a distinctive lozenge appearance), or with the large triangular shells current sorted and lying parallel to the bedding planes (storm redistribution?).
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From this point (where curious vertical 'starlike' pyrite bodies may be seen in the shales) onwards, the sediments of the ''ibex ''Biozone are rich in the large bivalve ''Pinna. ''Over beds some 26.5 m thick the communities of ''Pinna ''can be seen either in life position, with the open aperture probably facing the predominant bottom current direction (the planed-off bivalve shells having a distinctive lozenge appearance), or with the large triangular shells current sorted and lying parallel to the bedding planes (storm redistribution?).
  
 
=== Locality 7 [NZ 954 054] ===
 
=== Locality 7 [NZ 954 054] ===
  
Throughout the remaining part of this section almost to Castle Chamber, horizons of red '''sideritic''' nodules are well displayed in cliffs and on the foreshore where they often display a ramifying and connected appearance. These ironstone nodules usually have '''septarian''' centres. A prominent nodule horizon may be seen at the base of the cliff with diffused reddish margins and cream-coloured septarian interiors. This is near a prominent normal fault (you might like to pause and try to work out the throw on this fault).
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Throughout the remaining part of this section almost to Castle Chamber, horizons of red sideritic nodules are well displayed in cliffs and on the foreshore where they often display a ramifying and connected appearance. These ironstone nodules usually have septarian centres. A prominent nodule horizon may be seen at the base of the cliff with diffused reddish margins and cream-coloured septarian interiors. This is near a prominent normal fault (you might like to pause and try to work out the throw on this fault).
  
 
Working northeast towards Ness Point (North Cheek) the slight northern dip on the northern limb of the Robin Hood's Bay dome brings in younger horizons. There are rare ammonites in this part of the section (in nodules and as pyritic nuclei in shales/siltstones), bivalves are common (i.e. ''Pseudopecten'', ''Pleuromya'' and other myids and ''Gyphaea'') and there are at least three thin and impersistent limestone horizons comprised of current sorted ''Gryphaea'' shells (mixed with belemnites and other bivalves). Cliff exposures near Dungeon Hole [NZ 953 054] show these Pliensbachian sediments to have numerous fining upwards cycles often with minor erosion gutters.
 
Working northeast towards Ness Point (North Cheek) the slight northern dip on the northern limb of the Robin Hood's Bay dome brings in younger horizons. There are rare ammonites in this part of the section (in nodules and as pyritic nuclei in shales/siltstones), bivalves are common (i.e. ''Pseudopecten'', ''Pleuromya'' and other myids and ''Gyphaea'') and there are at least three thin and impersistent limestone horizons comprised of current sorted ''Gryphaea'' shells (mixed with belemnites and other bivalves). Cliff exposures near Dungeon Hole [NZ 953 054] show these Pliensbachian sediments to have numerous fining upwards cycles often with minor erosion gutters.

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