Crinoid
UKAFH field trip to Folkestone Sunday 6th October 2019
Another week another hunt! Great stuff! This week we were visiting the late Cretaceous deposits of the Gault Clay and Lower Greensands at Folkestone, Kent. The geology at Folkestone is Albian age, between 90 and 112 million years old. Although there are chalk exposures east of Folkestone, our focus today was west from the beach entrance at the Warren heading towards Copt Point.
We assembled in a quiet residential street (I think the locals have got used to our occasional assemblies of yellow jacketed, hard had wearing groups!) and Sam gave a superb talk with some great show and tell fossils. The rocks at Folkestone we’re formed in a shallow marine environment so the fossils include molluscs such as ammonites, belemnites snd bivalves as well as corals, sharks and other fish, urchins, turtle and occasional marine reptile remains. However the seasonal dryness in the locality is evidenced by scarce dinosaur footprints. Many fossils are exceptionally preserved, retaining original shell preservation, due to the soft and highly anaerobic clay which preserves aragonite and calcite shells in beautiful, iridescent colour. Chris, our leader on the day, briefed the group on the locality and a couple of health and safety messages and we headed down to the beach carefully, then heading West from the chalk to what we hoped would be much exposed clay.
We totally beat the weather forecast, with many of us stripping off the full waterproofs for much of the excursion, and got away with only a couple of showers. Unfortunately we could not contend with the abundance of sand covering a lot of the clay so a chunk of the areas we are used to hunting were covered. This did not mean it was an unproductive hunt though and more than I was expecting was found! Yay!
The first fossils encountered were from the freshly slipped clay. The colourful shells of the bivalves within were evident but were too fragile to collect and we also found an unusual number of equally fragile heart-shaped urchins.
A very large and exceptionally well preserved shark tooth was found by Jo and Isabel and Peter Bines continued his hot streak, finding a little tooth that would have gone unfound without his persistent sieving efforts as well as part of a chimaeroid fish tooth palate which has a distinctive spotted texture and can be found in both the Gault clay and Greensand.
Suzanne, a first time guest was pleased to find some iridescent ammonite sections and see the beautiful but fragile bivalves which look gorgeous on the beach but have a short shelf life once exposed. Meanwhile Louie Fleckley found some beautiful complete ammonites!
Other finds on the day included crinoid stems, a fish vertebra, a solitary coral, many ammonites and ammonite fragments including sections of heteromorph (irregular/uncoiled) ammonites which are unusual but quite common at Folkestone and yet another great find from hawk-eyed Peter who found a beautiful small crab carapace.
Everyone had a fun time and it was absolutely lovely to wander up to Sam and hear that our youngest guest of the day Louie wanted to tell her before he went home that he had a great time and thought we were all lovely! Thanks for the great feedback and that is exactly why we do this. We love to encourage and inspire and share our love for fossils!
Roll on the next hunt!
Chris Tait
Hock Cliff – 30 June 2019
On Sunday the 30th July, UKAFH embarked on a fossiling foray in Gloucestershire, on the River Severn near a small village called Frampton on Severn – a location known as Hock Cliff.
We met at a private car park for which we were very grateful to have received permission to use. (Please note that if visiting Hock Cliff individually parking would need to be sourced elsewhere along the road heading north west from Frampton on Severn). From here, group leader Lizzy Hingley guided us on a short walk through fields before arriving on the riverbank where a cliff, at most 20m tall, is exposed for a stretch of just over 1000m.
The cliff and foreshore exposed at Hock Cliff are made up of the lower portions of the Blue Lias formation, an early Jurassic formation about 200 million years old. As well as Gloucestershire, The Blue Lias formation is exposed along the Somerset Coast, in Dorset near Lyme Regis, South Wales and even parts of Yorkshire, so the material here was not unfamiliar to many of the seasoned hunters on this trip. The Blue Lias consist of repeating bands of a blueish limestone and darker shale (The name Blue Lias is derived from the blue colour of the limestone, the colour itself is derived from the high concentration of pyrite in the stone). These sediments were formed in a warm, placid, shallow sea which would have been much closer to the equator than present day. The surprisingly formulaic nature of the repetitive limestone and shale bands can be interpreted as resulting from a Milankovich Cycle. This is a cycle in which the earth wobbles on its longitudinal axis – a result of gravitational influence from other celestial masses – which result in earth’s polar regions becoming closer, then further from the sun and so effecting global climate and sea level; and consequently the sedimentation of this Jurassic sea as finer sediments travel further from their source, effecting the type of sediment produced. Amazingly we can calculate the length of this cycle and so can interpret each section of limestone and shale to represent about 90,000 years of time, which unlike more homogeneous strata allows us to visualise the passage of time throughout the formation.
This location is incredibly fossiliferous with well-preserved examples from much of the familiar early Jurassic marine forna abundant here. Most notably the bivalve Gryphaea (Often called Devil’s Toenails) can be found in quantity but are remarkably well preserved, often with both valves intact and with pronounced growth rings, allowing you to calculate its age when it died. Ammonites are also common, often small and preserved in pyrite, hints of gigantic ammonites can be spotted in the limestone ledges. There is also a crinoidal bed where, if exposed, mudstone packed full of crinoid beautifully preserved in calcite can be found. Hock cliff also has its share of vertebrates including fish, Hybodus sharks and marine reptiles such as ichthyosaurs and plesiosaurs. Further down the River Severn the pterosaur Dimorphodon was found in the Blue Lias above Aust cliff so the chance of terrestrial fauna is not unimaginable.
After a short introduction to the geology and paleaontology of the area, fossils were being found by the group almost immediately. Matilda Brewer was first in with a fantastic Promicroceras ammonite preserved in pyrite and Barry Taylor found an exceptional example of crinoid bed which was not very abundant on this trip. I think everyone found a great example of Gryphaea, some with the tube casts of creatures who made their home on the shell preserved. Rob Howe struck lucky when he found a small, fairly worn but significantly uncommon ichthyosaur vertebra. However, the star of the show was by far the exceptionally rare and beautifully preserved Hybodus shark tooth found by Tegan Watts.
We were not just lucky with our fossil finds but also lucky with the fine weather, which had cooled slightly from the 30C+ the previous day. Importantly the ground was solid – if visiting this site in winter months or after heavy rain it is important to take extra care as the solid ground becomes dangerous mud.
Hock Cliff is a Site of Special Scientific Interest (SSSI) and so the cliffs and foreshore must not be hammered or dug into. However, there are plenty of loose fossils to be collected along the foreshore.
A big thank you to everyone who attended our hunt at Hock Cliff, it was a great day with a great group of fossil hunters! See you all again soon.
Salthill Quarry, Clitheroe, 16th July 2017
Sunday 16th July saw a UKAFH hunt to Salthill Quarry Local Nature Reserve, Clitheroe, Lancashire. Salthill is a former limestone quarry and is known not only for its important geological formations but also the rare wildlife that can be found here. It has been designated a Site of Special Scientific Interest (SSSI) and because of this no hammers were allowed on site, but fossils here could be found loose in the spoil, so all that was needed a was a keen eye!
The rocks at Salthill formed during the Carboniferous period in a shallow, warm tropical sea, like today’s Caribbean, and are packed with crinoid fossils. The site even includes a bench made with panels of carved crinoids.
The day started with a great animated talk from UKAFH leader, Andrew Eaves, on the types of fossils that could be found at the site, before everyone got stuck in and it was all eyes to the ground! It wasn’t difficult – crinoids were abundant and crunched underfoot in places. No members went home empty-handed! Many crinoid columnals were found, along with isolated ossicles and less-commonly, crinoid thecae. Andrew pointed out the rarer blastoids in situ.
Despite mother nature threatening us with a potential downpour, the day turned out sunny and fine. The exposure of interest was contained in a small area on a gentle grassy slope, so there was plenty of opportunity to sit back and enjoy the warm sunshine.
Thanks to everyone who joined us on the day. We hope you enjoyed it!
