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A brief introduction to the geology of East Yorkshire

A long abstract for a lecture to the Yorkshire Society meeting in Hull Minster on 11th May 2024

By Mike Horne FGS – Honorary General Secretary of the Hull Geological Society and Honorary Research Fellow at the University of Hull.

The Hull Geological Society was founded in 1888 and it is now a Registered Educational Charity with the following aims – “… extend knowledge of and to promote research in Geology … especially in East Yorkshire and North Lincolnshire…”. In 2017 it merged with the East Yorkshire RIGS Group which was founded in 1992. We have designated Local Geological Sites in the geographical area of East Yorkshire and they have a non-statutory conservation status under various categories – one for its Historical interest, two for their educational use, 3 for the landscape features (geomorphology), nine in Hull for the educational use and 55 purely for scientific and research value. There are also 9 geological SSSIs in the county of East Yorkshire and 3 more that have features of geological interest.

The rocks that occur in the East Riding shape its landscape and determine the habitats and agricultural use – be that chalk grassland for grazing animals or wetland areas. If you look at a topographic map of the area you will notice the crescent of the Wolds formed by the Chalk separating the Vale of York and Vale of Pickering from low lands of Holderness. If you look closely you will see how much of the area is less than 5 metres above sea level – which will make it prone to flooding due to sea level rise by the end of this century. The coast of Holderness is rapidly eroding: more than a mile has been lost since Roman times and the rate of erosion could be increasing due to climate change (increased rainfall and sea level rise).

The rocks provide us with building materials such as building stone in the Newbald area and toughened Chalk in the Flamborough area, gravels from the Vale of York and Holderness and clay and silt for brick and tile making. The Chalk of the Wolds is a major aquifer that has provided fresh drinking water, just look at a map and see the spring-line settlements both sides of the Wolds, such as North Cave, Newbald, Market Weighton, Driffield, Cottingham … But this aquifer is prone to pollution from nitrates from farming and salt water incursion through over extraction. We build our houses and roads on top of these rocks in Hull and Holderness vale of York – hence the subsidence and putholes! The geology has been in the news recently due to concerns over proposals to frack for oil deep beneath the Wolds and to bury nuclear waste below South Holderness.

For this short talk given in Hull Minster I will present a simple story about the geology we would encounter if we put a borehole down below the Minster. We will encounter in our imaginary borehole rocks that can be seen in an east to west cross section of the geology, because the beds of rock dip gently to the east. However, this means I am ignoring the interesting structural history we would encounter if we looked at a north-south cross section, which would include the unique Speeton Clay and the effects of the mid-Cretaceous unconformity that can be seen at Rifle Butts SSSI near Market Weighton. It also means that I am examining the rocks from the top down, unlike the stratigraphical convention of starting with the oldest rocks.

The first thin layer we encounter in our borehole is archaeological which might include soil and building rubble. Then there will be the Recent unconsolidated deposits – perhaps river alluvium, clays and silts, perhaps beds of sand or even peat. This is above the Boulder Clay that was deposited during recent Ice Ages and as the name implies it is a mixture of clay, silt, pebbles and some large boulders. Generally in Hull this averages 15m in depth, but here near the River Hull it might be much thicker because it might be filling a deep valley of a Proto-River Hull that formed when sea levels were much lower. The Boulder Clays can be seen in the cliffs of the Holderness coast and the pebbles that have been brought to this area by glaciers from Scotland, the Lake District, Scandinavia as well as northern England and the bed of the North Sea (which was dry land during the Ice Ages).

The first consolidated rock we encounter is the Chalk and here under Hull it is the flinty Chalk (the younger flint-less Flamborough Formation has been eroded away). Yorkshire flints are grey and some of the tabular flint layers are up to 25 cm thick; they will be tough to drill through! Here the flinty chalk will be less than 160m thick and it sits upon the flint-less Ferriby Chalk Formation with the thin Black Band Member in between, which represents a major worldwide extinction event.

Below the Chalk will be some dark grey Upper Jurassic clays. These could be seen until recently in quarries at Melton and South Ferriby. These clays were mixed with Chalk and used for making Portland cement. Beneath these there will be some middle Jurassic sandstones, sands and limestones. The sands were good quality and were used in foundries and the Cave Oolite limestone was used in villages as a quality building stone in the Newbald and South Cave area. Deeper in our imaginary borehole we would find some more grey clays and perhaps even some ironstones. These Lower Jurassic clays were exposed in the gravel pits at the North Cave wetlands when the chalk gravels of the Vale of York are removed. The ironstone bands have been exploited for steelmaking in the Scunthorpe area. Further west at the Wetlands and stratigraphically lower than the clays are red mudrocks of Triassic age that formed in desert like conditions when the UK was warmer and nearer the equator.

If we were to drill down deeper we would encounter the Magnesian Limestone which crops out in the Doncaster area. This limestone was used to build the Houses of Parliament and, along with locally made bricks, Hull Minister. Deeper still we would encounter the Upper Carboniferous, the coal from which fuelled the Industrial Revolution and now of interest as a source of oil. 

(copyright M Horne 2024)


Copyright - Hull Geological Society 2024

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