Oxfordshire Rock Types

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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 STRATIGRAPHIC COLUMN of OXFORDSHIRE ROCK FORMATIONS

A stratigraphic column works by listing the youngest rock formations at the top, down to the oldest rock formations at the bottom. This list is partially interactive - we're working to make it totally interactive by Winter 2022, click on the formation for more information - if a link isn't active yet, it will be very soon.

2.6 Million Years Ago

TERTIARY

66 Million Years Ago

Thames
Group

Lambeth
Group

bioturbated dark clay

London Clay

plastic, mottled clays

Reading 

66 Million Years Ago

UPPER/LATE CRETACEOUS

100.5 Million years ago

White
Chalk

Grey
Chalk

firm, white chalk with tabular flint seams

Seaford Chalk

moderately hard chalk

Lewes Nodular Chalk

moderately hard chalk

New Pit Chalk

nodular chalks with thin flaser marls

Holywell Nodular Chalk

firm, blocky chalk

Zig Zag Chalk

marly, hard chalk

West Melbry Marly Chalk

100.5 Million Years Ago

LOWER/EARLYCRETACEOUS

145 Million Years Ago

Upper Greensand

clay and sandstone

Gault 

blue-grey clay or mudstone

Lower Greensand

sands & sandstone with some clay and silts.

Whitchurch Sands

fine-medium sands

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

Inferior

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

Chipping Norton

oolitic limestone

Clypeus Grit

sandstone, ironstone

Ancholme

Group

176 Million Years Ago

LOWER/

EARLY

JURASSIC

201 Million Years Ago

Lias
Group

Whitby Mudstone

fossiliferous mudstone and siltstone

Marlstone Rock

iron-rich , sandy limestones

Dyrham 

silty and sandy mudstone

Charmouth Mudstone

shales & mudstones

Blue Lias

calcareous mudstone or siltstone