Vertical Surface Motions Of The Southern U.K. During The Cenozoic

The Cenozoic long wavelength uplift and subsidence patterns in the UK have been assumed to reflect the North Atlantic opening and Alpine |Orogenic sequences. Shorter wavelength variations are generally neglected and may give important clues to the processes driving vertical motions.

To understand the vertical surface motions of the south east UK a stratigraphic backstripping technique was applied which provides a record of long-term changes and can give indications of short term drivers or short wavelength variations. Traditionally backstripping has been applied to deep marine sequences but the Cenozoic onshore stratigraphic record consists of shallow marine and near shore deposits. This study shows that the use of shallow marine deposits provide effective constraints on interpreting palaeo-water depths.

Subsidence analysis of the Cenozoic succession indicates temporary uplift in the Paleogene, recorded between 56 and 55.8 Ma. This uplift may correlate with the 1 Myr duration uplift recorded in the Faroe-Shetland trough during North Atlantic opening, suggesting a long wavelength influence on the southern UK during the early Paleogene. The London Basin subsidence models suggested deposition most likely occurred above present day sea-level until sea-level began to fall around 54.7 Ma. Tectonic surfaces suggested south-eastern basement tilts were prevalent during the Paleogene and may be a result of magmatic underplating. Subsidence analysis also revealed larger subsidence rates and sediment accumulation in the Hampshire Basin than in the rest of southeast England. Reactivation of Variscan faults during the deposition of Cenozoic sediments appears to have taken place concomitantly with tectonic shortening and suggests phases of compression affected the UK from the mid-Paleogene and through the Neogene. Fault reactivation records a north-west strain during the Eocene as a result of Alpine orogenic phases that may have developed a WNW trajectory by the Oligocene.

From our data it seems likely the present-day topography of the Cretaceous Chalk in southern England began to develop during the Paleogene, while the short wavelength variations are a result of the older North Atlantic opening from the north-west and Alpine orogenic compression from the south-east.