Bathonian (Middle Jurassic) carbonate sediments deposited on the northern margins of the Wessex Basin and over the Central Midlands Platform were pervasively cemented by a single generation of sparry calcite cement. The nature and evolution of the hydrologic system responsible for the cementation has been investigated through integrating petrographic and isotopic data with regional tectonic, stratigraphic, and sedimentological information.

The spar cements precipitated in a confined paleoaquifer, sourced by Early Cretaceous meteoric recharge, when tectonic uplift of the basin margins and concomitant fall in relative sea level generated the late Cimmerian unconformity. Isotopic data show that variable degrees of mixing of recharging groundwaters and marine-like pore fluids expelled updip from thick dewatering shales in the Wessex Basin took place during cementation. Consideration of the tectono-stratigraphic history of the basin and surrounding regions, together with diagenetic information from other carbonate formations, indicates that the overall hydrologic system lasted for a maximum of 20 m.y. and extended through much of the Middle and Late Jurassic over a large geographical area. In contrast, earlier, syndeposition l emergence did not provide the necessary conditions for development of extensive paleoaquifers, and did not generate pore filling cements.

This study emphasizes links between basin evolution, basin geometry, subsurface hydrology, and cementation characteristics. Comparisons are drawn with published examples to highlight the importance of an integrated approach to regional diagenesis.