Reassessing the Bartonian unit stratotype at Alum Bay (Isle of Wight, UK): an integrated approach

The Global Stratotype Section and Point (GSSP) for the base of the Bartonian, currently remains undefined. The Bartonian unit stratotype is located at the Barton coastal section in the Hampshire Basin, on the South Coast of the UK. The base of the “Barton beds” was originally placed at the lowest occurrence of Nummulites prestwichianus, and this is still the basis of the recognition of the unit Bartonian Stage as a formal chronostratigraphic unit of the Paleogene. However, this biostratigraphic marker is not widely applicable elsewhere. The base of the lithostratigraphic unit, the Barton Clay Formation, also extends below this level creating further complication. The parastratotype section is located at Alum Bay, 7 km away, on the Isle of Wight. Despite a number of studies carried out in 1970s and ‘80s on both sections, global correlation remains problematic. Here we present an integrated (micropalaeontological, stratigraphic, palaeomagnetic) study of the Lutetian-Bartonian transition at Alum Bay, and aim at improving the stratigraphy of this section to better define the base of the Bartonian and contribute towards a decision on the GSSP.