Near the Yorkshire-Lancashire border, a domineering peak rises from the valley floor and looms over the skyline for miles around. The year is 1612, the reign of the paranoid King James I of England. Ten women and two men stand accused of using witchcraft in order to commit murder. These people were not your broomstick-riding, pointed-hat wearing, green-skinned witches of popular media, they were most likely village healers, skilled in the use of herbs and traditional remedies. These skills however left them open to accusation of witchcraft, which is rather a problem when there are deep running family feuds in the area. All but one of these supposed witches were hanged for their “crimes” but their legend lives on. The area where we lay our scene is, of course, Pendle Hill. Pendle Hill itself rises rather dramatically out of the Ribble Valley and is an area of great geological interest – it even gives its name to a specific time interval in the Carboniferous (the Pendleian, approximately 329 to 328 million years ago). The valley floor is dominated by limestone rocks with patches of reefs from which some rather lovely fossils have been found, such as these goniatites. These rocks would have been formed in a shallow and warm sea with very little sediments being washed in from the land. The rocks overlaying the limestone which make up the hill show a marked change in environment – the dark mudstone suggests a sudden influx of increased mud and sediment from land. These rocks are known as the Bowland Shale. Mudstones don’t usually make big hills though and Pendle Hill is no exception; the upper flanks of the hillside show another change in environment and are dominated by hard-weathering sandstone beds. These can be seen nicely in the Nick of Pendle Quarries along the roadside towards the northeast of the hill, where conveniently there happens to be a carpark! These sandstones are similar to the iconic Millstone Grit rocks of the nearby Pennines although their origin is quite different. Whereas the Millstone Grit was formed by the delta of a large river, the Pendle Grit is the product of those rivers dumping this sand out to open sea. Every now and again those sands would collapse and cascade into the deep mudstone oceans. These colossal cascades of sediment are known as turbidity currents – imagine a huge underwater avalanche made of sand, silt and mud and you’re thinking along the right lines. These currents flow down underwater canyons or channels and spill out to make big sand lobes across the seafloor. The catastrophic origin of these sandstones is suggested by several lines of evidence. The underside of the beds show scour marks made by the erosion of the sediments that were already there. Sometimes these erosive features are quite big and whole beds of sediment can be removed in areas – it depended on how much energy the flow had! These hollows were quickly filled in by sand from the flow, making a natural cast of the scour. On the southwest side of Pendle Hill there are some good internally scoured surfaces, these formed within a single flow when the current cannibalised the sandstones during their deposition, ripping them back up just as they were laid down! Eventually these catastrophic sand avalanches begin to lose their momentum and finer sands can be deposited. These tend to show ripples, and by taking a compass bearing of these you can get an idea of which way turbidity current was flowing. Once the current had passed through there would still be some of the finest particles of sediment left floating around in the water, this silt and mud slowly settled out and draping the ripples and burying them. Between the northeast edge or the Hill at Nick of Pendle and the southwest at Wiswell Quarry there is a change in the amount of sand versus silt and mud. This is because turbidity currents tend to dump their heavy sands pretty quickly. At the Nick of Pendle there are lots of thick sandstone beds which suggests you were closer to the mouth of the river, whereas if you go over to the Wiswell quarries you are further out to sea and so will see thinner sandstones, more ripples and a lot more silt which can be carried further. Pendle Hill preserves only a small section of these vast seafloor sand lobes, with much of them having been removed by uplift and erosion and then carved into the hill we see today by the advance of glaciers during the ice age. Pendle Hill is a great example of how landscapes hold such a wealth of history, both human and deep time. This great Lancashire landform has seen many dramatic events – from the grisly tale of the persecution of the Pendle witches to huge underwater landslides cascading down into the deep dark ocean floor. Author: Jed Atkinson
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The same was true of prehistoric sharks, although some took this curved conveyer belt tooth row to an extreme! The ‘whorl toothed sharks’ were an extremely unusual group that swam in the oceans from 323 to 247 million years ago (the earliest dinosaurs appear on land at around 250 million years ago).
Helicoprion is well-known from fossils from North America and Russia, but few people are aware of its Yorkshire ancestor! One of the earliest whorl toothed sharks is from Carboniferous aged rocks (around 320 million years old) near Brockholes just south of Huddersfield. This beautiful specimen was described as a new species, Edestus newtoni, in 1916. Edestus is unique in having a curved tooth row on both the upper and lower jaw – as our Huddersfield specimen has only one jaw it has been suggested that it might belong to a different genus, Lestrodus, instead (Tapanila et al 2019).
The function of the tooth whorl of Helicoprion, Edestus, and their relatives has been the subject of many different artistic reconstructions throughout the decades – was it the upper jaw? Lower jaw? Both jaws? Spiky fin spine? Could the tooth row unroll like a whip? These different interpretations were famously summarised by the artist Ray Troll: It is now fairly accepted that the tooth whorl formed part of the lower jaw in these sharks, however variation in tooth whorl shape between different species means there is still much debate about how these animals fed. Research published in 2015 by Ramsay et al. analysed the forces on the tooth whorl of Helicoprion and found that it was well adapted to eating animals like ammonites with a soft body in a hard shell. The circular nature of the tooth row creates forces on the prey in different directions simultaneously – the front teeth would push the shell away whilst the back teeth pull and cut the soft body into the mouth. Other interpretations include the outer teeth slashing prey, the upper and lower jaw cutting prey like scissors, or the bottom jaw moving backwards and forwards like a saw (Itano 2019). The tooth whorl of Edestus highlights the ever-changing nature of palaeontological science, constantly refining and adapting ideas based on new techniques and new discoveries. How do you interpret these fossils? What was the function of these teeth? Come by the Fossils in t’Hills stall at one of our upcoming events and have a go at your own reconstruction! Author: Rebecca Bennion References
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