Humberside Geologist no 8

published 1991

Report of the field meeting held on 14th July 1990

F Whitham & T Rockett

This was a joint field meeting of the Hull Geological Society and the North Eastern Geological Society, with 6 members of the Hull G.S. and 7 of the N.E.G.S. attending. Unfortunately due to a confusion over the date of the meeting the leader [Richard Myerscough]  failed to arrive; so the members attending had to improvise, with the help of the Geologists' Association guide to the Yorkshire Coast and Felix Whitham's experience.

The main exposure at Betton Farm Quarry is part of a coral reef occurring in the lower part of the Coralline Oolite Formation. Several solitary corals were seen, together with some stromatolite type patterns in the rock. A number of fossil bivalves were observed in situ, including Astarte, Modiola and Ostrea. Fossil gastropods were represented by Bourgetia saemanni and Pseudomalenia heddingtonensis.

After some members had visited the Betton Farm shop the party rendezvoused for lunch at the cliff top car park at Cayton Bay. Felix Whitham took on the role of leader and the party spent four hours on the beach at the base of High Red Cliff moving into Gristhorpe Bay. The following succession of rocks were examined :

Lower Calcareous Grit

Hackness Rock

Kellaways Beds Shales of the Cornbrash

Upper Cornbrash Limestone reef (at beach level).

It was pointed out that some of the hard ferruginous nodules scattered at the base of the cliffs contained examples of the ammonite Kepplerites and other larger fallen blocks of Kellaways Rock had in the past yielded species of Proplanulites in addition to numerous brachiopods including Ornithella and Thurmanella. Numerous examples of Thalassinoides burrows were observed on the surface of large fallen blocks of Lower Calcareous Grit.

Further along the beach members paused to examine the exposed part of the Upper Cornbrash Limestone underlain by soft dark grey shales. Several bivalves were recovered from this limestone including Lopha marshii, Trigonia scarburgensis, Goniomya literata and Pleuromya uniformis. A large flattened example of the zonal ammonite Macrocephalites macrocephalus was discovered by Terry Rockett in a block of shale, but unfortunately the specimen proved to be too fragile to remove from its matrix.

Beyond this point towards Yons Nab in a south-easterly direction, the beach is strewn with large blocks of Lower Grit, making for strenuous going for several hundred metres before reaching the Red Cliff Fault and beds of the Middle Deltaics. One of the fallen blocks of grit was observed to contain a large calcareous nodule packed with many beautifully preserved specimens of the rhynchonellid Thurmannella thurmanni. This nodule proved to be quite friable and most members were able to collect numerous specimens.

The plant beds exposed on the shore near low tide level below the Red Cliff fault area, have in the past been heavily exploited, and most of the material containing the plants has been dug out, although member of the party were able to observe some plant remains in the thin shaly bands still exposed. The Deltaic beds in the cliffs were examined and some interesting structures observed, including thin bands of coal and occasional fragments of fossil wood.