Magdalen Quarry

Also within

Oxfordshire County

Condition (Natural England)

Geology & landscape

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

Description

Area, 0.4 hectares 1.0 ac Description The classic geological site exposes three important rock units Beckley Sand, Shell Pebble Bed and the Wheatley Limestone approximately 145 million years old Upper Jurassic age. The study of the rock sequence at Magdalen Quarry has provided valuable information which has enabled geologists to partially reconstruct the geography of Upper Jurassic times, 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. Most importantly, the rock units at this site indicate the presence of a reef structure in this area, formed by growth on the sea bed of an upstanding mound of lime secreting, marine organisms, such as corals. The proximity of the reef is indicated by the rapid changes in thickness and composition of some of the rock layers, reflecting the importance of the reef as an active source of sedimentary debris. The uppermost unit, the Wheatley limestone, represents a deposit accumulating along the northern flank of the reef. The site is therefore of major importance in the geographical reconstruction of this ancient sea. Furthermore, the presence of fossil ammonites and more specifically Cardioceras densiplicatum, is important in enabling the deposits to be accurately placed within the Upper Jurassic rock succession.