East Riding of Yorkshire
The geology of the East Riding of Yorkshire represents a continuation of the Jurassic and Cretaceous rocks of southern England and the East Midlands.
Upper cretaceous chalk cliffs overlain by Quaternary sediments at Flamborough
There is a relatively simple arrangement with the older, marine clays, limestones and sandstones of Jurassic age occurring in the west of the County and younger Cretaceous rocks in the east. The topography of the area is dominated by the Chalk Wolds which are a crescent shaped series of hills stretching from the coast north of Bridlington to the Humber Bridge.
Jurassic
The main Jurassic (195-140 million years ago) is to the south of Market Weighton (Market Weighton is thought to have been an area of high ground during the Jurassic). The oldest part of the Jurassic sequence present comprises shallow marine clays and thin limestones known as the Lias. The Lias is overlain by marine limestones belonging to the Inferior Oolite and the Great Oolite and including the Cave Oolite which is exposed in old quarries and cuttings in the South Cave area. These rocks were deposited in shallow seas, tidal mudflats, lagoons and large river deltas and contain many fossil shells such as small oysters and other bivalves.
The continuation of marine conditions led to deposition of the Kellaways Beds, a series of sands and sandstones that yield a rich fossil fauna comprising ammonites, brachiopods, oysters and belemnites. Deeper marine mudstones; the Oxford Clay and the Ampthill Clay complete the remainder of the Jurassic sequence, but are significantly reduced in thickness compared with outcrops to the south.
Cretaceous
The end of the Jurassic Period and the beginning of the Cretaceous (142-65 million years ago) was marked by a global fall in sea-level and the retreat of the sea from the area now occupied by the East Riding of Yorkshire. This led to the formation of land and a period of erosion began. After a considerable interval, the early Cretaceous sea flooded this land area from the east. The first sediments laid down in this sea are represented by the Lower Cretaceous Speeton Clay which occurs along the north-eastern edge of the Wolds, and is exposed on the coast at Speeton. These fossiliferous marine clays yield well preserved ammonites, belemnites and bivalves, which indicate deposition in a tropical, shallow sea.
Over the rest of the area there was no deposition during most of the early Cretaceous, the oldest deposit being a thin layer of Carstone (a marine sand and iron-rich sandstone) along the south-western edge of the Wolds. The Carstone grades upward into the Red Chalk, comprising a pink limestone and brick red marl which are rich in fossil bivalves, ammonites and other marine creatures. A major phase of sea-level rise and deepening of the Cretaceous sea marked the beginning of the Upper Cretaceous. The almost pure limestone of the Chalk, which forms the bulk of the Wolds, was deposited in this warm, sub-tropical sea.
In East Yorkshire, the Chalk forms a crescent, beginning on the River Humber foreshore at Hessle and terminating in the sheer sea-cliffs of Flamborough Head. The highest chalk cliffs in Britain are at Bempton, their height perhaps reflecting the fact that the Chalk in this area is much harder than the Chalk of southern Britain. A common feature of the Chalk sequence is the presence of marl bands (calcareous clays).
The chalk crescent forms a steep west- and north-facing escarpment, which are particularly pronounced at the north-west angle where the chalk meets the limestone of the Howardian Hills. Most of the land on the Wolds is between 50m-200m in elevation, in marked contrast to adjacent areas.
Quaternary
Over the last two million years the climate of Britain has varied tremendously with periods of temperate climate interrupted by repeated advances and retreats of glaciers and ice sheets. Collectively these periods have become known as the Ice Age (we are still in one of the temperate phases) and the actions of the ice sheets have been instrumental in forming the landscape we see today.
Around 450,000 years ago a severe cold phase known as the Anglian glaciation lead to an ice sheet spreading across East Anglia and most of East Yorkshire. All but the highest parts of the Wolds lay beneath a thick sheet of ice grinding slowly south, eroding massive quantities of Chalk and other rocks, and depositing till (or boulder clay). During the following Ipswichian interglacial a rising sea covered the eastern part of the County forming an ancient sea cliff which can be traced from Sewerby, just north of Bridlington, along the eastern edge of the Wolds to Hessle.
It began to get colder again around 115,000 years ago, marking the beginning of the Devensian glaciation. During this time, ice flowed along the Yorkshire coast and left a thick mantle of till which forms much of the low-lying area of Holderness. For 100,000 years the Wolds stood above the ice, experiencing severe tundra conditions, with snow and meltwaters seasonally cutting valleys into rocks that were permanently frozen below the surface.
By 10,000 years ago the ice had melted and the ensuing rise in sea level created the North Sea and the inundation of the Humber Estuary and surrounding coastal plain. Marine-brackish sediments and freshwater peats were deposited on the till surface forming the present-day flat landscape around the Humber Estuary. The present-day coast is dominated by saltmarshes, coastal dunes and wide beaches.
Geological Highlights:
- South of Bridlington the 60Km long sweep of the Holderness coast is a rapidly eroding (average of 2m/yr) section of low glacial till cliffs. Within the till are a wide variety of rocks transported from the north by the ice sheet at the end of the last glaciation some 15,000 years ago. Rock types found along the Holderness beaches include Larvikite and Rhomb Porphyry from Norway, Shap Granite from the Lake District, Carboniferous Limestone from County Durham, granites, schists and gneiss from Scotland and Jurassic fossil ammonites and oysters from the Whitby area.
- Between 116,000 and 128,000 years ago, prior to the deposition of the tills of Holderness, the East Yorkshire coast ran westwards of the current coastline running on a curving line running just to the west of Driffield, Beverley and Cottingham. Traces of the former coastal cliff can be seen, such as a slight break of slope near Harland Way, Cottingham. Although now largely obscured, the cliff line was formerly well exposed at Sewerby, just to the north-east of Bridlington. When exposed (a rare occurrence) an interglacial shingle beach can be seen about 1 m above the modern beach. The raised beach contains vertebrate remains including straight tusked elephants, narrow nosed rhinoceros and hippopotamus dating the beach to the last (Ipswichian) interglacial.
- Spurn Head, at the southern end of the Holderness coast is a 4km long sand-dune capped shingle spit at the entrance to the Humber Estuary. This coastal landform has been studied in detail over several decades and illustrates very clearly the interaction of tidal and other coastal processes in a complex and actively developing environment. A cyclical development pattern of growth, breaching and decay over a period of more than 250 years has been demonstrated for the spit.
Local sites
The following localities represent, in part, the geology of this county. Each locality has a grid reference, a brief description of how to get there and a short summary of the geology you are likely to find. All the localities listed are openly accessible.
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