Geodiversity

White Limestone Formation

Some Key Words

facies

Sedimentary facies are bodies of sediment that are recognizably distinct from adjacent sediments that resulted from different depositional environments.

packstone

A packstone is a rock with a grain-supported texture with the intergranular voids filled with a finer matrix.

wackestone

A lime wackestone is a matrix supported carbonate rock containing less than 75% mud-grade (<32 μm) calcite.

Backscattered scanning electron microscope image of a typical well-cemented oolitic packstone from the White Limestone Formation.

 

Note: The calcitic grains are tightly cemented by weakly ferroan calcite (light grey). No significant matrix porosity is visible.

 

[Taken from Milodowski and George, 1985, Harwell Borehole No. 3, 362.4 m].

Parent group:

Great Oolite

Age:

Jurassic/Bathonian

(166.1–168.3 Ma)

Description

A pale grey to off-white or yellowish limestone, peloidal wackestone and packstone with subordinate ooidal and shelly grainstones, recrystallised limestone and/or hardgrounds at some levels with rare sandy limestone, clayey limestone, marl and mudstone or clay. 

Environment of Deposition

The depositional environment for the White Limestone Formation is a protected, shallow marine setting with periods of reduced sedimentation resulting in the formation of hardground.  Higher energy phases are recorded in the rock record by cross-bedded ooid limestones.

Upper Boundary

The upper boundary is commonly a sharp, erosive boundary, with the Forest Marble Formation.

Lower Boundary

The White Limestone Formation is found overlying the marls or fine-grained ooidal grainstones of the Hampen Formation.

Lateral boundaries

Laterally, the White Limestone eventually passes into the Athelstan Oolite Formation south westward and the Blisworth Limestone Formation north eastward.

 

Thickness

10-30 m

Contribution to landscape:

The White Limestone caps escarpments and valley slopes, and forms broad plateaux throughout the north Cotswolds.  The calcareous regolith contributes to the formation of the rendzina facet of the Cotswold catena.            

 

See it in Oxfordshire

Kirtlington Quarry (SP 494 199)

Type area:

The BGS determined 'type area' is the Cherwell Valley from Woodstock to Ardley, where it is commonly ca. 20 metres thick (it can be up to 30 m).

Reference Section:

The type section and reference section are not accessible to the public (Shipton-on-Cherwell Quarry and Ardley Railway Cutting respectively).