Editing Lower Jurassic rocks between Staithes and Port Mulgrave - an excursion

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=== Locality 3 [NZ 794 188] ===
 
=== Locality 3 [NZ 794 188] ===
  
The ironstones are best seen at Old Nab, where richly fossiliferous surfaces can be examined on the cliff-foot ledges which extend round into Brackenberry Wyke. Among the bivalves ''Pseudopecten equivalvis ''reaches large size, occurring together with ''Oxytoma cygnipes, Pleuromya costata, Pholadomya ''and ''Protocardia, ''the brachiopod ''Tetrarhynchia tetrahedra, ''and rare pleuroceratid and amaltheid ammonites. Fossil wood can be found and more rarely vertebrate remains. On Old Nab itself, where the Main Seam has been mined by pillar and stall workings, the trace fossil ''Rhizocorallium, ''excavated by crustaceans, is widespread on the stall floors, exposed by marine erosion. It consists of horizontal parallel tubes with striated walls, occasionally with the terminal U-bend visible. On the intervening pillars, thin branching tubes of the trace fossil ''Chondrites ''are common. The shale backfill of an old '''adit''' can be seen at one point. In Brackenberry Wyke beyond Old Nab, the Main Seam has been extensively quarried and mined, the material having been carried to Port Mulgrave for shipping by a cliff-foot tramway. '''''The old adits are extremely dangerous.'''''
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The ironstones are best seen at Old Nab, where richly fossiliferous surfaces can be examined on the cliff-foot ledges which extend round into Brackenberry Wyke. Among the bivalves ''Pseudopecten equivalvis ''reaches large size, occurring together with ''Oxytoma cygnipes, Pleuromya costata, Pholadomya ''and ''Protocardia, ''the brachiopod ''Tetrarhynchia tetrahedra, ''and rare pleuroceratid and amaltheid ammonites. Fossil wood can be found and more rarely vertebrate remains. On Old Nab itself, where the Main Seam has been mined by pillar and stall workings, the trace fossil ''Rhizocorallium, ''excavated by crustaceans, is widespread on the stall floors, exposed by marine erosion. It consists of horizontal parallel tubes with striated walls, occasionally with the terminal U-bend visible. On the intervening pillars, thin branching tubes of the trace fossil ''Chondrites ''are common. The shale backfill of an old adit can be seen at one point. In Brackenberry Wyke beyond Old Nab, the Main Seam has been extensively quarried and mined, the material having been carried to Port Mulgrave for shipping by a cliff-foot tramway. '''''The old adits are extremely dangerous.'''''
  
 
=== Locality 4 [NZ 795 182] ===
 
=== Locality 4 [NZ 795 182] ===
  
The base of the Grey Shale Member crosses onto the foreshore about two-thirds of the distance across Brackenberry Wyke to the next headland. In the lower part, the pale grey-weathering shales contain six rows of reddish-brown-weathering sideritic concretions. Higher calcareous nodules, often found loose on the foreshore here, yield ''Dactylioceras tenuicostatum, ''belemnite guards and contain crystals of '''sphalerite'''. Pyrite is common in the shales.
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The base of the Grey Shale Member crosses onto the foreshore about two-thirds of the distance across Bracken-berry Wyke to the next headland. In the lower part, the pale grey-weathering shales contain six rows of reddish-brown-weathering sideritic concretions. Higher calcareous nodules, often found loose on the foreshore here, yield ''Dactylioceras tenuicostatum, ''belemnite guards and contain crystals of sphalerite. Pyrite is common in the shales.
  
 
At the southeastern end of Brackenberry Wyke, fallen blocks of medium to coarse-grained deltaic sandstones of the Middle Jurassic Saltwick Formation, which form the top of the cliffs, obscure the cliff face and block the foreshore. Scramble over the blocks with care.
 
At the southeastern end of Brackenberry Wyke, fallen blocks of medium to coarse-grained deltaic sandstones of the Middle Jurassic Saltwick Formation, which form the top of the cliffs, obscure the cliff face and block the foreshore. Scramble over the blocks with care.

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