Rock Edge

Also within

Oxfordshire County

Condition (Natural England)

Geology & landscape

Mining / Industrial: Quarry · Geological Period: Jurassic · Rock Type: Limestone

Description

Area, 1.8 hectares 4.5 ac Description This geologically important site exposes an Upper Jurassic coral rich limestone known as the Coral Rag, believed to be approximately 145 million years old. The study of the rock sequence at Rock Edge or Cross Roads Quarry has provided valuable information which has enabled geologists to partially reconstruct the geography of 145 million years ago, when much of the area that is now Oxfordshire was covered by a warm, shallow sea. Similar conditions to those found in the Bahama Banks today are believed to have existed at the time. At Rock Edge the Coral Rag is rich in fossil remains, derived from corals reefs that formed in the ancient shelf sea. Close examination reveals the presence of two types of limestone, reflecting the close proximity of the reef margin. One variety consists primarily of coarse fragments broken off the reef, whilst the other is finer grained, representing the lime sand accumulating on the sea bed a short distance from the reef. Actual in situ reefs were previously visible in quarries located a few metres to the south. The study of this crucial site has helped to demonstrate the existence of the so called 'Headington reef' in this area during Upper Jurassic times.