Upper Oxfordian palaeogeography of southern England
Abstract The Upper Oxfordian of southern England consists of a variable series of clays, sands and limestones known as the Corallian Beds. Six sedimentary facies are distinguished: (1) phyllosilicate clay facies (background sedimentation to other facies); (2) quartz sand facies (intertidal sands); (3) coralline facies (coral patch reefs and associated deposits); (4) oosparite-intrasparite facies (high energy carbonates deposited in inter-tidal and supra-tidal environments); (5) micritic facies (low energy environments); (6) iron ore facies (?pro-delta). The palaeogeography of the period was dominated by the Portsdown Swell, which separates two regions of subsidence, the Wessex and Wealden Basins (see Fig.3). Over the swell, quartz sands and high energy carbonates accumulated. During Early Corallian Beds times the eastern part of the swell suffered non-deposition or erosion. Later deposition was resumed in this portion, but ceased to the northwest. The sheltering effect of the swell appears to have caused a northward shift of the facies belts flanking the south side of the London Ridge. Shorelines during the Upper Oxfordian probably trended east-west in the vicinity of London, and paralleled the present-day outcrop a few miles to the north.