Oxfordshire Rock Types

The oldest rocks to crop out are in the north, of the county, in the Banbury area, and are of Lower Jurassic age, circa 200 million years old. Younger rocks Mezozoic formations crop out successively towards the south-east.  The harder rock types are relatively more resistant to weathering and erosion and these form hills. These more resistant rocks are known as limestone and chalk.   The intervening vales are bottomed by clays and sands.

A simplified Jurassic stratigraphy of Oxfordshire

161 Million Years Ago

145 Million Years Ago

UPPER/

LATE

JURASSIC

Purbeck

thin limestones and shales

Portland

limestone and sandstone

clay and sandstone

Kimmeridge

coral limestone and sandstone

Corallian

clays and sandstone

Oxford Clay

176 Million Years Ago

161 Million Years Ago

MIDDLE

JURASSIC

Kellaways Beds

sands and clays

Great

Oolite

Group

rubbly, iron-stained 

limestone

Cornbrash

flaggy limestone & clay

Forest Marble

fossilferous limestone

White Limestone

Hampen 

thin limestones interbedded with marls

Taynton

shelly oolitic limestone

thin-bedded clay

Sharp's Hill

Horsehay Sand

oolitic limestone

Clypeus Grit

sandstone, ironstone

Northampton Sands

Ancholme

Group

Inferior

Oolite

Group

Chipping Norton

176 Million Years Ago

LOWER/

EARLY

JURASSIC

161 Million Years Ago

Upper

mainly clay

Middle

silt, sand and muddy marlstone

Lower

clay and muddy limestone