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

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=== Locality 5 [NZ 798 180] ===
 
=== Locality 5 [NZ 798 180] ===
  
Immediately beyond the obstruction, isolated blocks of Saltwick Formation on the foreshore are perched on shale pedestals which the blocks have protected from erosion. These are the Sheep Stones. At the level of the cliff foot, the Grey Shale Member, with common ''Dactylioceras ''spp., passes up transitionally into the Mulgrave Shale Member. This latter is a sequence of dark to black, laminated pyritic shales rich in hydrocarbons. Freshly broken rock smells strongly of oil. Calcareous concretions, some pyrite-skinned, are common and may contain ammonites such as ''Harpoceras falciferum, ''with rare specimens having oil in their chambers. Flattened specimens ''of Harpoceras, ''often pyritized, are abundant in the shales, together with the pelagic bivalves ''Pseudomytiloides dubius ''and ''Bositra radiata. ''Note the lack of any benthonic fauna, indicating reducing conditions at the sea floor. Signs of excavations for jet can be seen. Adits, '''which are extremely dangerous''', were usually roofed by a thin bed of limestone concretions, the 'Top Jet Dogger'. Rare masses of jet occur in the 3 m of beds below this level. Small faults bring the Grey Shale Member up to cliff-foot level again just before Port Mulgrave.
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Immediately beyond the obstruction, isolated blocks of Saltwick Formation on the foreshore are perched on shale pedestals which the blocks have protected from erosion. These are the Sheep Stones. At the level of the cliff foot, the Grey Shale Member, with common ''Dactylioceras ''spp., passes up transitionally into the Mulgrave Shale Member. This latter is a sequence of dark to black, laminated pyritic shales rich in hydrocarbons. Freshly broken rock smells strongly of oil. Calcareous concretions, some pyrite-skinned, are common and may contain ammonites such as ''Harpoceras falciferum, ''with rare specimens having oil in their chambers. Flattened specimens ''of Harpoceras, ''often pyritized, are abundant in the shales, together with the pelagic bivalves ''Pseudomytiloides dubius ''and ''Bositra radiata. ''Note the lack of any benthonic fauna, indicating reducing conditions at the sea floor. Signs of excavations for jet can be seen. Adits, '''which are extremely dangerous''', were usually roofed by a thin bed of limestone concretions, the 'Top Jet Dogger'. Rare masses of jet occur in the 3 m of beds below this level. Small faults bring the Grey Shale Member up to cliff-foot level again just before Port Mulgrave.
  
 
=== Locality 6 [NZ 799 177] ===
 
=== Locality 6 [NZ 799 177] ===
  
The harbour at Port Mulgrave was built for shipping ironstone, principally from mines 3.5 km to the west. For the last 1.5 km, the tramline entered an inclined tunnel to reach the harbour at shore level; the bricked-up exit can be seen in the cliff at the back of the bay. The piers were severely damaged in the storm surge of 1953. The Alum Shale Member is exposed in the cliffs above Rosedale Wyke just beyond Port Mulgrave. A detour may be made to the southeastern part of Rosedale Wyke where the Top Jet Dogger reaches shore level and beyond which, the upper part of the Mulgrave Shale Member may be examined. The cliff-top can be gained at Port Mulgrave by a steep path immediately behind the harbour.
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The harbour at Port Mulgrave was built for shipping ironstone, principally from mines 3.5 km to the west. For the last 1.5 km, the tramline entered an inclined tunnel to reach the harbour at shore level; the bricked-up exit can be seen in the cliff at the back of the bay. The piers were severely damaged in the storm surge of 1953. The Alum Shale Member is exposed in the cliffs above Rosedale Wyke just beyond Port Mulgrave. A detour may be made to the southeastern part of Rosedale Wyke where the Top Jet Dogger reaches shore level and beyond which, the upper part of the Mulgrave Shale Member may be examined. The cliff-top can be gained at Port Mulgrave by a steep path immediately behind the harbour.
  
 
== [[Yorkshire rocks and landscape: a field guide#Glossary|Glossary]] ==
 
== [[Yorkshire rocks and landscape: a field guide#Glossary|Glossary]] ==

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