Geodiversity

Taynton Formation

Some Key Words

facies

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

grainstone

Grain-supported sedimentary rock (>15wt% iron) with grains >50% iron-bearing minerals (>15wt% iron). <15% matrix, (particles <0.032mm), Grain size not defined.

ooidal

A limestone that is formed of abundant ooids (sometimes called ooliths), small spheres of calcium carbonate that look like fish eggs. This is sometimes called 'oolitic limestone'

Backscattered scanning electron microscope image of a rock sample from the Forest Marble Formation.

 

It comprises sub-rounded worn shell fragments composed of calcite (grey) with a matrix of fine microporous micritic calcite. Fine grained authigenic pyrite (white) is disseminated within the microporous matric.

 

[Taken from Milodowski and George, 1985, Harwell Borehole No. 3, 342.7 m].

Parent group:

Great Oolite

Age:

Jurassic/Bathonian

(166.1–168.3 Ma)

Description

The Taynton Limestone is a buff/brown to pale brown, rock. It is typically well-sorted, often medium  to coarse-grained and commonly it is described as a moderate to high  bioclastic, ooidal grainstone.  Typically it is cross-bedded. In some localities it can be fine to very coarse-grained or medium to thickly well-bedded. Thin shell-detrital marl seams and discrete calcareous sandstone beds are not uncommon.

 

Environment of Deposition

A high-energy, shallow marine, transient ooid bank or bar.  In addition there is evidence of lower-energy environments with carbonate and terrigenous sedimentation.

Boundaries

Vertically, the conformable, lower boundary is with the Sharp's Hill Formation. The upper boundary is marked by the upward passage into the finer Hampen Formation.

 

Spatial distribution

Burford and area, Oxfordshire.

Type section

Lee's Quarry, Taynton Down, Oxfordshire (SP 236 152).  7 m of the formation is exposed here, the chracteristic cross-bedded bioclastic/ooid grainstone facies. The thick beds are separated by thin. calcareous mudstones. The base of the formation is not exposed at this site. The upper boundary with the Hampen Formation is present.

Landform contribution

The Taynton Limestone Formation frequently forms ledges on valley sides and minor plateaux.