A sequence stratigraphy of the Kimmeridgian and Bolonian stages (late Jurassic): Wessex-Weald Basin, southern England

A sequence stratigraphic framework for the late Jurassic Kimmeridgian and B olonian stages of the Wessex-Weald Basin, southern England is proposed, bas ed on the integration of sedimentological, geophysical and geochemical data . The NERC-funded Rapid Global Geological Events (RGGE) boreholes of Swanwo rth Quarry 1 and 2, and Metherhills 1, are used as reference sections. Elev en complete depositional sequences and their component systems tracts are r ecognized within the Kimmeridge Clay Formation, bounded by 12 sequence boun daries (Km1-12). Seventy-four boreholes have been used in this study. Durin g the Kimmeridgian, a major transgression, associated with tectonic movemen ts, led to a marked change in basin geometry. Major deepening of the sea du ring the late Kimmeridgian (Eudoxus Zone) led to a change from unconformiti es of basinwide extent to those confined to the basin margins. The progress ive deepening of the basin towards a highstand in the mid-Bolonian (Wheatle yensis to Pectinatus zones) was associated with a broad-scale change ill se dimentary, faunal and geochemical characters. The 'layer-cake' basin archit ecture and thickening of the Kimmeridge Clay Formation towards the basin ce ntre suggests a dominantly aggradational system. The partially enclosed nat ure of the Kimmeridgian and Bolonian seas generated basin dynamics more ana logous to those of modern day meromictic lakes, Consequently, sequence stra tigraphic approaches derived from continental shelf-margins are inappropria te in epicontinental basins of this type.