Cornbrash

Middle Jurassic (Bathonian-Callovian)

Lithology
Limestone, medium- to fine-grained, predominantly bioclastic wackestone and packstone with sporadic peloids; generally and characteristically intensely bioturbated and consequently poorly bedded, although better bedded, commonly somewhat arenaceous units occur in places, particularly in the upper part. Generally bluish grey when fresh, but weathers to olive or yellowish brown. Thin argillaceous partings or interbeds of calcareous mudstone may occur.

Upper Boundary
Base of succeeding Kellaways Formation; comprising mudstone, commonly shelly at base, resting generally sharply and conformably or non-sequentially on bioclastic limestone of the Cornbrash.

Lower Boundary
Generally sharp, disconformable non-sequence: bioclastic limestone resting upon mudstone (and bioclastic ooidal limestones, locally) of the Forest Marble Formation.

Representative Sites
South Cerney Railway Cutting
Avon Ford Cutting

Information on lithology and boundaries taken from the British Geological Survey Lexicon of Named Rock Units