Report: Ken Brooks “Local Geology and Fossils”

Ken introduced himself as an adult education tutor in Geology of the Hastings area, and in advance of the talk thanked Diana, his wife, who was handling the computer with his illustrations.

The talk began with a description of the world 140 million years ago, when the super-continent Pangaea started to break up into separate tectonic plates, forming new continents, among them Laurasia and the wonderfully named Gondwanaland. Looking at the cliffs near Hastings from Ore to Pett which show layers of a lower Ashdown foundation sandstone, Wadhurst formations of clay and bedded sandstone and Wadhurst shales and clays, it is possible to construct a paleo-environment, a slide showed this with the modern coastline superimposed. With the London area uplands to the north, rivers drained south and broke up into many tributaries over a vast floodplain towards a shallow lake. An aerial view of the Nazca plains showed very similar topographical features. Evidence for a river channel at Pett can be seen as a curving structure cut through a horizontal bed as a wedge shaped strata, this can be interpreted as a point-bar deposit at a curve in a river where the fast moving stream at the outer edge of a curve cuts away silts, whilst the slow-moving inner edge of the curve deposits silts. One has to look for the minutest of clues. Colours vary as iron in solution precipitates out in different forms, Haematite giving reds, Siridite oranges, and Liminite yellows.

Using the scale of a £1.00 coin Ken illustrated the emergence of life as bioturbation, which is sediments disturbed by activity, ie 20mm tubes formed by crustacean, probably early forms of shrimps or crayfish. Interpretations can change, but the marks are not bivalves or nemotodes/worms. Bivalves do appear as catastrophic burial deposits, which can be interpreted as volumes of bivalves displaced by storm activity and buried with sediments swept down a river. All gastropod evidence points to fresh water, there is no evidence for a salty sea.

At Cliff End in what is known as the bone beds, there are many shark’s teeth, and occasional shark’s fin spines, fish scales, crocodile teeth and dinosaur bones. A rare find is a Scheenstea fish head, with many scales and sometimes complete parts of a body. The scales show dark and light colours and survive well because they evolved to be thick as a type of armour and therefore good fossil material. Scheenstea looks much like a modern fish, but is 65 million years extinct, the living sturgeon and bowfin being near relatives. Sharks on the other hand survive virtually unchanged, but are mainly cartilage, and apart from their teeth and fin spines, are seldom found as bodies in the fossil record. A skeleton of a modern shark jaw illustrated why so many shark teeth survive, each tooth has multiple teeth waiting behind it to grow forward if any are damaged or lost. Each shark could produce and lose many hundreds in a lifetime.

On land, plant fossils survive in sedimentary silt-stone, which can be split to reveal fronds. If black it will have been carbonised by fire damage. During the Cretaceous the UK was at the equator, and we can get a good idea of plant life 140 million years ago, with horsetails, ferns and cycads. A fern, Pterophyllum, is found mainly as fragments, probably broken up in streams, with only Chiopsis found as a complete frond. Buried rhizomes are found, and at Pett level, Quillwort. Though this is difficult to identify in the field, many are now found. Tenskia is the most common tree fern. From evidence there is an abundance of vegetation, ferns, quillworts, cycads, horsetails, with flowers just beginning to appear, so that it is possible to form a good reconstruction of how the landscape would look.

Also on land, insects were beginning to appear, illustrated by the larva case of a caddis fly, and a spectacular dragon fly which must have fallen in the mud. There is evidence of two types of crocodile, one 15 or 20 ft long, the other much smaller, with grooves in the teeth to hold on to slippery fish. The crocodile’s armoured horny layer survives well in the fossil record, with part of a snout with tooth sockets found at Pett, and another skull 600 mm long found which is almost identical to modern descendants, proving that these at least survived past mass extinctions.

In the 19th Century nothing was known of the distant past, but Dr Gideon Martel of Brighton was interested in natural philosophy as it was called, and travelled all over the country seeking out curiosities from quarries, he found a black shiny rock in the form if a tooth, which he identified as similar to a modern iguana, and coined the name Iguanodon. Further pieces were found, a vertebra from Bexhill, and eventually jumbled pieces for a complete skeleton. The first sketches and reconstructions were of a vertical stance a bit like a kangaroo, but modern interpretations show a classic horizontal stance. Dinosaur footprints are be found around Hastings, with the best so far discovered at Fairlight.  Multiple overlapping prints of different sizes suggest herds or family groups.  Recently discovered is part of a Polacanthus, an armoured herbivore, and a tooth identified to be from a Baryonicx, which had a jaw something like a crocodile, with claws to hook fish, and which was probably a scavenger.

At the end of the Lower Cretaceous, 90 – 100 million years ago, much of the UK was under water, and over the next 20 or 30 million years chalks formed from phaetoplankton and zoo planktons. These animals are so small one needs an electron microscope to view them, with several thousand covering a pin-head, but together they made our enormous chalk cliffs.  The most common fossil found within the chalks are Amonites, in fact the south coast is the best area to find them.

65 million years ago the dinosaurs disappeared in a mass extinction, which most believe was caused by an asteroid impact on the Yucatan peninsula. But did they truly disappear, as many now believe that birds are their direct ancestors, sharing the same skeletal structure, three toes, breastbone, and reproduction by eggs.

What of more recent developments? The North American plate is still moving west at 2 cm a year, but 30-40 million years ago the North African plate collided with Europe and caused extensive and dramatic buckling of the crust, forming mountains in North Africa and Europe, with a ripple effect reaching the UK shown by the folds at Lulworth Cove, and fractures and faults in sandstones. 30 thousand years ago ice sheets and glaciers covered the north of the UK forming valleys and escarpments. The ice did not come south of the Thames, but ice melt from the ice ages did form the hills and valleys that we see today. The London basin still has a layer of chalk beneath it, but all the chalk over the Weald, including Hastings, has all eroded away. The Pevensey levels were formed only 20,000 years ago, which is geologically only yesterday, with Fairlight at the eastern edge formed by a hard outcrop of sandstone.

In answering the many questions Ken told us of the Melancovich chemical cycle which effects marine life density and saturation in water, and which made the conditions right for forming flint. Different densities of chalk are also formed, with Melbourne rock being a very hard form containing a higher density of calcite, which can be used as a building stone. The Purbeck beds are also near the surface, and can be used for building. There are supposed to be oil and gas near Fairlight, but even though natural gas lit the station at Netherfield at one time, it has not yet been found in commercially viable amounts.

The vote of thanks for this detailed and fascinating talk was given by Robin Reffell, and the meeting was most appreciative in its applause.

Report by John Warren

Details of Ken Brooks latest book: Geology and Fossils of the Hastings Area Published by Ken and Diana Brooks ISBN: 0-9540513-3-5  Price: £8