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

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=== Locality 3 [NZ 959 038] ===
 
=== Locality 3 [NZ 959 038] ===
  
Walk out into the centre of the bay to the limit of the tide and then work back up-sequence over the harder continuous scars (beach features of calcareous siltstones, fine sandstones and nodule horizons) with intervening softer siltstones and shales (also with nodules) which constitute the Calcareous Shales (lower Redcar Mudstone Formation) at this locality. At the furthest extremity you will be within the ''obtusum ''Biozone (although the reefs furthest out to sea to the southeast contain the '''ammonite''' ''Arnioceras'' indicating the ''semicostatum ''Biozone). About halfway between High Scar and the Double Band at the base of the cliff the ammonite faunas change to ''Gagaticeras'', ''Oxynoticeras'' and ''Epararietites'' indicative of the ''oxynotum'' Biozone. All the sediments exposed as scar features or interleaving shales/siltstones are fossiliferous, with body fossils such as '''bivalves''' (''Gryphaea'', ''Pleuromya''), '''crinoids''' (''Pentacrinites'') and numerous belemnites. These sediments are also extremely '''bioturbated''' with widespread ''Chondrites ''together with more substantial '''trace fossils''' such as ''Teichichnus, Rhizocorallium, Ophiomorpha ''and ''Diplocraterion'' usually associated with the more indurate levels.
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Walk out into the centre of the bay to the limit of the tide and then work back up-sequence over the harder continuous scars (beach features of calcareous siltstones, fine sandstones and nodule horizons) with intervening softer siltstones and shales (also with nodules) which constitute the Calcareous Shales (lower Redcar Mudstone Formation) at this locality. At the furthest extremity you will be within the ''obtusum ''Biozone (although the reefs furthest out to sea to the southeast contain the ammonite ''Arnioceras'' indicating the ''semicostatum ''Biozone). About halfway between High Scar and the Double Band at the base of the cliff the ammonite faunas change to ''Gagaticeras'', ''Oxynoticeras'' and ''Epararietites'' indicative of the ''oxynotum'' Biozone. All the sediments exposed as scar features or interleaving shales/siltstones are fossiliferous, with body fossils such as bivalves (''Gryphaea'', ''Pleuromya''), crinoids (''Pentacrinites'') and numerous belemnites. These sediments are also extremely bioturbated with widespread ''Chondrites ''together with more substantial trace fossils such as ''Teichichnus, Rhizocorallium, Ophiomorpha ''and ''Diplocraterion'' usually associated with the more indurate levels.
  
At some levels within the softer shales and siltstones large, isolated, flat, subcircular, iron-rich, '''concretions''' can be seen. These are usually highly bioturbated and sometimes contain ''Pentacrinites, ''belemnites and ammonites. These have been interpreted as 'scours', where bottom currents winnowed out the finer material leaving marginally coarser-grained sediments and shell debris behind, which then attracted iron '''diagenesis'''. These 'scours' form a sporadic but integral part of the entire section to be viewed for the rest of the day up to the top of the Cleveland Ironstone Formation.
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At some levels within the softer shales and siltstones large, isolated, flat, subcircular, iron-rich, concretions can be seen. These are usually highly bioturbated and sometimes contain ''Pentacrinites, ''belemnites and ammonites. These have been interpreted as 'scours', where bottom currents winnowed out the finer material leaving marginally coarser-grained sediments and shell debris behind, which then attracted iron diagenesis. These 'scours' form a sporadic but integral part of the entire section to be viewed for the rest of the day up to the top of the Cleveland Ironstone Formation.
  
 
Return to the Double Band at the base of the cliff at Boggle Hole and follow this prominent beach feature across Mill Beck (where it is displaced slightly at a small northeast–southwest fault).
 
Return to the Double Band at the base of the cliff at Boggle Hole and follow this prominent beach feature across Mill Beck (where it is displaced slightly at a small northeast–southwest fault).

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