Nibley Knoll

Also within

Gloucestershire County Cotswolds Scenic Area Cotswold Way National Trail

Condition (Natural England)

Geology & landscape

Geological Period: Jurassic · Rock Type: Limestone

Description

Area, 3.2 ha. 7.9 ac. Description This is an important geological locality showing a thick section of Lower and Middle Jurassic rocks, spanning the junction between the Aalenian and Bajocian Stages. The lowest stratum visible is the Cotswold Sand Formation of the Upper Lias, exposed in the sunken lane cuttings. Above is a thick section of the 'Cephalopod bed', the topmost of the Aalenian Stage, here similar to that at Wotton Hill. The Lower Inferior Oolite Freestones, of early Bajocian age, are capped by an excellent example of a 'hardground', a thin layer of tough limestone encrusted with fossil mollusc shells, formed when environmental changes caused deposition of the limestones to slow down or cease altogether. Above the Freestonelies the Upper 'Trigonia' Grit of the Upper Inferior Oolite of which this is one of the best and most fossiliferous sections. The Middle Inferior Oolite is entirely absent here, clearly demonstrating the effects of an important phase of uplift and warping of the earth’s crust during the Lower Bajocian. In combination with the presence of the hardground at the top of the underlying Freestones this provides one of the best illustrations in the Cotswolds of the effects of this important phase of earth movement.