LECTURE TO THE MEMBERS OF THE UNIVERSITY OF HULL SCIENCE CLUB
[by Felix Whitham]
12th DEC, 1998.
Good morning everyone,
Perhaps I should first introduce myself and say although I am not a professional geologist or palaeontologist I have had a lifelong and serious amateur interest in fossils from an early age. In my talk today I thought I would try to pass onto you my experience in the collecting and recording of fossils which as you all probably know are the remains of very ancient life. In this instance marine life preserved in deposits of sedimentary rocks, usually in the form of infilled shells or tests of the original organism or as casts where the shell has dissolved leaving behind a cavity which has been infilled by surrounding sediments and solidified. Some ammonites particularly from the early Jurassic period are found encased in a nodule of limestone (like a flattened cannonball)— probably formed by chemical precipitation between the decaying soft parts of the ammonite after it died and the shaly mud of the sea bottom into which it would sink.
I first became interested as a schoolboy in the strange looking objects I occasionally found on the Hessle and N. Ferriby foreshores of the River Humber. These areas were easy to reach with the aid of my bicycle (a luxury in those days). The bullet shaped belemnite guards like this (show specimen), in local folklore were stated to be thunderbolts, mainly because of the sudden appearance of these fossil guards of a squid like marine animal after thunderstorms , which can be explained by heavy downpours of rain washing away the surrounding matrix, usually revealing a well preserved specimen displaying aeronautical features suggesting a projectile from the heavens above. Another common fossil found along the foreshore is the Jurassic oyster Gryphaea (show example) also stated in folklore to be Devil's Toenail, supposedly because of the similarity in shape to the imagined talon like toenail of a mythical devil. Less common ammonites (coiled like a Catherine Wheel) are sometimes found on the foreshore and in folklore were referred to as snake stones show specimen mainly because of their resemblance to a coiled snake. Some traders in fossils used to carve snakes heads at the end of the outermost whorl.
In those early days these finds greatly mystified me so I decided to learn more. I soon found out they were in fact fossils of marine life from the Jurassic period and were about 140 million years old. My learning continued until the outbreak of the 1939-1946 war when I was enlisted into the army for 6 years were much digging took place greatly increasing my interest in self preservation to that of fossil preservation.
After the war I again resumed collecting fossils also learning from books and other sources about the various rocks and fossils and their relationship to each other. The main rock formations within our local region are from the older Jurassic rocks which range in age from about 136 to 195 million years and overlying Cretaceous rocks which rest in most instances unconformably on Jurassic stratas. Show thin film & explain succession. I first collected from the Jurassic sandstones exposed in the pits at South Cave and South Newbald and later from the Jurassic shales and rocks of Staithes, Robin Hood's Bay, and Whitby areas of the north east Yorkshire coast. Fossils were common in these highly fossiliferous stratas and in due course I amassed a large collection of ammonites, belemnites, bivalves, brachiopods and numerous other species (some of which are exhibited here for you to view later). The absence of some parts of successive exposures in the various quarries and coastal sections caused difficulties in building up a continuous stratigraphical succession of rocks and fossils although I did manage to construct continuity of the species which are shown on these panels.
Later on my interest became more focussed on the upper cretaceous chalk which overlies much of the Jurassic stratas apart from isolated outcrops and thin layers here and there of early Cretaceous deposits in East Yorkshire; with thicker beds of clays and red chalk at the type section at Speeton on the east coast. In those early days of collecting there were many small and medium sized pits apart from the extremely large commercial quarries exposing very thick sections of chalk -some up to 50 metres in depth. Additionally the magnificent permanent chalk cliffs in the Flambro, Bempton, Bridlington area were all accessible, providing a huge area for collecting and research. I began to realise that beneath my feet lay a vast and ancient chalk seabed ranging in age from about 100 million to 70 million years ago waiting to be explored.
This huge platform of chalk dipping out under the north sea stretched from the Flambro area with a broad spread through East Yorkshire, Lincolnshire and Norfolk and was laid down in a separate basin to that of southern England. In some respects with very different deposits (which is another story, but not today) this vast seabed accumulated very slowly, probably in warm shallow waters similar to the Bahama banks type deposits which are being laid down off the coast of Florida U.S.A. at the present time. Most of the chalk as we know it today is composed of about 80% tiny calcite crystals derived from the disintegration of complex ring like structures known as coccoliths, secreted by a family of highly specialised unicellular green algae. the remainder is made up of microfossils including foraminiferas, plankton skeletons, ostracods, bryozoa, ground up bivalves, tests and spines of echinoids , starfish ossicles, and crinoids. This whole mixture of calcitic material would be winnowed by currents and turbulence, settling on the seabed in the form of a vast chalky ooze which slowly compacted into a more solid deposit, reaching rock building proportions which we now know as Chalk. Some complete examples of the marine life which existed at that time were preserved intact in the seabed and we are able to find their fossilised remains at various levels in the Chalk today, (some examples are exhibited here) and can be used to identify specific horizons in the Chalk succession.
If you imagine the chalk layers of varying thicknesses interspaced with thin marl bands, bedding planes and in some parts flint bands, it is possible to identify the different beds by the fossils they contain, once you know the biostratigraphy, in other words the fossil succession which I will refer to later.
The chalk sea of the northern province which I have already mentioned, spread out from Eastern England, across the north sea, - into Northern Germany and extended to some parts of Russia, its chalky ooze deposits eventually becoming bedrock. Over a great period of geological time some parts of the sea bed were uplifted and became the land we see at the present time, (the Yorkshire Wolds). Careful collecting of in situ macro & microfossils in succession has shown that it is possible to correlate these fossils very closely with those found in the chalk quarries of the Hanover, Lagardorf and Misburg/Hover districts of Northwest Germany with those of Eastern England similar species also occur on the Russian platform.
The chalk exposures on land in the north of England, north of the Humber, are about 542 metres (1776 ft) thick on the coast confirmed by drilling during the creation of natural gas chambers at Atwick near Hornsea, thickening eastwards into the North Sea gas fields up to 800 metres.
The Yorkshire Wolds form a broad crescent shaped exposure which sweeps inland from Bempton cliffs, Flambro Head and Sewerby buried cliff. The original chalk coast before the ice age, started at Sewerby cliff end, where an abrupt junction of Chalk and boulder clay can be seen, this chalk cliff virtually follows the route of the Bridlington to Driffield road, then down to Beverley, Willerby. Anlaby, and Hessle where near to the railway station, the buried cliff was exposed when the new road to the M 62 was cut.
The whole of the plain of Holderness is made up of boulder clays with numerous deposits of sands and gravels, left behind by successive ice ages, and resting on planed down Chalk. The Chalk of the Yorkshire Wolds is continuous across the Humber and into Lincolnshire. The very basal part of the Chalk is brick red, followed by a grey gritty Chalk without flint, which is succeeded by Chalks which are mostly flinty and interspaced with many different types of flints, including burrow, nodular, lenticular and tabular, the latter forming vast sheets in some areas which can be used to identify different horizons in the succession. Also present are numerous bands of clay rich marls, some containing volcanic ash. Marl bands occur throughout the chalk succession. The higher parts of the chalk are flintless and are mostly present along the coast from High Stacks Flamborough Head to Sewerby Steps (? Show thin film) and in a few inland quarries.
Over the last 45 years or so I have been privileged in being allowed access to measure many chalk quarries in East Yorkshire where I have been able to and log sections (? Show thin film composite) and at the same time collect and locate various fossil groups to specific horizons including the coastal chalk cliffs, it has been possible to link together over 450 metres of chalk stratas in stratigraphic succession with key fossil ranges which can be related to specific marl bands, flint bands and hard beds.
Throughout the upper chalk era numerous extinctions in marine life occurred and many new species appeared. Their fossil remains occur in bands and in some instances in thick beds with occasional isolated individuals between these levels.
In the Jurassic period ammonites were very common and the numerous species could be utilised to zone successive stratas. However in the northern Cretaceous Chalk, ammonites are rare, found mainly in the lower and highest beds and therefore not of much use for stratigraphical purposes.
Bivalves—play an important role in zoning the Chalk succession and the evolutionary development, the number of species and the limited range of some of the larger inoceramid bivalves provide important stratigraphic markers. They occur commonly at most horizons in the Chalk.
Echinoids (sea urchins) are also of limited use as some species are confined to specific horizons. The ambulacra grooves in the test of Micraster show evolutionary changes which provide recognition of some levels and zones in the Chalk. (see panel)
Brachiopods (lamp shells) show cast of large specimen. This species is very common in most stages of the succession and again show evolutionary changes but at the present time only one two species are named in zonal identification. (see panel)
Belemnites:-show large specimen & see panel. Probably related to the present day Cuttlefish. Squid like creatures which lived in the hollow end of the guard (alveolus) with small octopus like tentacles. They were common in the Jurassic period but less common in the white chalk. Several species occur in the Lower Cenomanian Chalk, re-appearing towards the top of the flinty chalk, and continuing to occur up to the highest beds in Yorkshire. Very common in the basal red chalk and clays below the base of the white chalk, also in the higher beds of chalk of Norfolk. Gonioteuthis belemnites collected on a bed by bed basis from the top of the flinty chalk at high stacks Flambro through to Danes Dyke near Sewerby (a thickness of 105 metres) show a progressive increase in the depth of the alveolus from 4 mm to 17.5 mm (plus 13.5mm). By utilising an approximate radiometric dating of about 47 million years for these beds-statistical work on about 100 belemnites indicates that the depth of the alveolus increases by 1mm per 348,000 years. Based on the estimated depositional time span for this sequence of coastal chalk beds, the rate of deposition is approximately 1 metre of compacted chalk per 44,750 years.
Crinoids, Marsupites and Uintacrinus form important marker zones and the influx of these species which are confined to specific succeeding horizons are used as zonal markers both in England and Germany. Many other macrofossils occur but are not normally used to name fossil zones.
Microfossils nannofloras, are found. In great abundance throughout the chalk succession and are of great value to prospecting companies,-particularly in the oil industry with drilling rigs based in the north sea. Foraminiferas, ostracods and coccoliths show evolutionary tendencies and have frequent extinction rates which can be used with much advantage, proving to be a useful tool as a means of identifying specific horizons. Drill cores can be brought to the surface from great depths from below the sea and on land for microfossil analysis by rig based geologists. Much research is being undertaken at the present time in this field as it is not always possible to pick up macrofossils in drilling rig cores. Once the identification and succession of both macro and microfossils and their evolutionary trends are known and recorded, it is possible to identify and assemble the rocks in stratigraphic order. This means of identification only applies to sedimentary rock.
The lowest exposures of Upper Chalk start at Melton Bottoms, rising through Welton Wood, Enthorpe Railway Cutting, Willerby, Little Weighton and Middleton-on-the Wolds, with higher inland sections seen at Langtoft, Bainton, Beverley, Ruston Parva and Nafferton Grange, also including the magnificent coastal sequences in the Bridlington area and the Flambro Head exposures.
Apart from the vast fossil record contained within these huge thicknesses of chalk sea bed, which rests upon an even older marine formation of Jurassic age, perhaps we should also remember the commercial and human advantages of these valuable minerals particularly from the chalk, such as cement making, plasters, fillers, paint, paper, toothpaste, and many other uses including lime for agricultural purposes. The chalk of the Yorkshire Wolds acts as a huge aquifer storing water which we use in the Hull area every day.
In the short time available to me 20/25 minutes I have only been able to give you
The briefest glimpse of the fossil record and the geological events which commenced nearly 200 million years with the laying down of Jurassic clays, limestones, and sandstones, followed by the clays and chalk of the Cretaceous period. These ancient seabeds which lie beneath our feet are here for you to research and discover new findings in the future.
As you probably know, the dinosaurs became extinct at the end of the Cretaceous period, and it has been suggested they were killed off due to the impact of a giant meteorite or comet striking the earth and blotting out the sunlight for many months. A friend of mine had a different theory, suggesting they died of boredom looking at the chalk. I do hope that none of you have suffered a similar fate listening to me today.
Thank you very much.
[scanned and edited 26/8/2010. MH]
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