Exploring the Geological Layers of Hunstanton Cliffs
The iconic Hunstanton Cliffs, located in the seaside town of Hunstanton in Norfolk, England, are a frequent source of fossils and geological interest for us at Frugeo. This remarkable natural feature is designated a Site of Special Scientific Interest (SSSI), reflecting its profound biological and geological significance. Uniquely for Britain’s east coast, the cliffs face west, providing a spectacular view across The Wash, the large bay and estuary separating Norfolk from Lincolnshire.
The cliffs are famed globally for their vivid bands of colour, with each hue representing a distinct type of rock. These readily visible layers offer a fascinating insight into the area’s geological history. While the local stratigraphy is significantly complex upon closer examination, focusing on the three primary rock types provides a solid and accurate foundation for understanding this unique coastal feature.
1. The Base Layer: Carrstone Formation
At the very foundation of the cliffs lies the Carrstone Formation, a coarse, reddish-brown sandstone conglomerate often referred to locally as "ginger carrstone" due to its resemblance to gingerbread. This sedimentary rock was formed during the Lower Cretaceous Period (specifically the Albian Stage, approximately 108 million years ago), having originated in shallow marine environments. Carrstone is a notable building material throughout north Norfolk and owes its distinctive red colour to iron oxide cemented within the sediment. The amount of iron oxide determines its variant, such as the less common grey "silver carrstone". This rock is typically pebbly and contains minerals like feldspar and glauconite nodules, as well as small amounts of fossils.
2. The Middle Layer: Hunstanton Formation
Directly above the Carrstone lies a striking red layer that is often mistaken for limestone but is actually composed of chalk. This layer, which forms part of the Hunstanton Formation, was also created during the Lower Cretaceous (Albian Stage, approximately 101 million years ago), but under significantly deeper marine conditions. The rich red hue of this chalk layer results from the presence of limonite, a form of iron ore. The Hunstanton Formation is exceptionally rich in macrofossils, making it an invaluable treasure trove for palaeontologists and fossil enthusiasts. Its excellent exposure at Hunstanton contributes significantly to the site's scientific value.
3. The Top Layer: Ferriby Chalk Formation
Capping the cliff face is the lightest layer, the Ferriby Chalk Formation. This white-grey chalk was deposited during the Cenomanian Stage at the start of the Upper Cretaceous Period (approximately 99 million years ago). Formed under deep marine conditions, this rock often contains fossils and is characterized by a series of distinct beds and structures rather than a single, uniform layer of chalk.
The Hunstanton Cliffs are not simply a visual spectacle but a rich, open geological textbook. Their unique stratigraphy tells a clear story of profound environmental change over millions of years, tracing the transition from shallow marine to deep-sea conditions right here on the Norfolk coast.
