GeologyRocks

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Jon
Imperial College London

Boggle Hole is halfway between Robin Hood's Bay and can be reached by turning down Bridge Holm Lane from the A171 (Whitby-Scarborough road). There is car park at the end of the road. Start at Boggle Hole car park. Walk down the path to the beach, past the Youth Hostel.

Figure 1: Map of Robin Hood's Bay. Map from Google Maps.

On the beach, make your way right, past the cliff and cave, until you reach the obvious Pleistocene sands in the cliff. This marks the middle of the Robin Hood’s Bay dome.

Figure 2: Pleistocene sands near Boggle Hole.

Turn and walk back towards Boggle Hole. The rock here contains abundant bioturbidation in the form of Rhizocorallium and Diplocraterio. The rocks can be broken down into two main types: an dark shale and a paler siltstone. The dark shale, although appearing anoxic with pyritised ammonites, cannot be as it also contains bioturbation and bivalves in life position. There are also numerous ammonites, belemnites, bivalves and crinoids.

Figure 3: Pyritised ammonite and abundant evidence of bioturbation.

Figure 4: Examples of the fauna at Boggle Hole.

Some of the fossil seems to be concentrated in burrow structures such as this collection.

Figure 5: Abundant fossils collected in a burrow(?)

There are also isolated fragments of wood.

Figure 6: Fossilised wood fragment.

Each cycle of sedimentation appears to be capped with a courser grained siltstone, which is extensively burrowed and resistant to weathering, often has a “knobbly” appearance. This bed is thought to represent a storm deposit. This would put the whole succession being deposited between fair and storm wave base – between 25 and 50m water depth.

Figure 7: Possible storm deposit bed.

As you approach the town of Robin Hood’s Bay (the town), you will notice that the prominent siltstone layers disappear. This marks a move to deeper water. Bioturbation is far less common. Bivalves and ammonites are abundant, although exposure is often limited to where the seaweed has not colonised!

On the walk to Robin Hood’s bay there is ample opportunity to observe modern sedimentary processes. There are often both symmetrical and asymmetrical ripple marks formed by the ebbing tide. Looking into the channels that contain water running off due to the falling tide, one can often see ripples migrating in the flow.

Figure 8: Modern assymetrical ripples

Ascending the slipway to Robin Hood’s Bay, turn left and follow the Cleveland Way (it’s just before the B&B). Climb the step to the top of the cliff. From there you should be able to see the structure of the Robin Hood’s Bay dome.

Figure 9: View of Robin Hood's Bay. Ravenscar is on the headland in the distance. You can see the beds curve around from the left of the picture towards the centre. This shows the dome structure.

As you walk along the path, back to Boggle Hole, keep an eye out for faults in the dome structure. Arrive back at Boggle Hole and ascend back to the car park.

Figure 10: Faulting picked out by "seaweed" horizons. All faults are radial and point towards the centre of the dome.