User guide for the BGS Offshore Quaternary 250K dataset

This offshore Quaternary geology dataset shows the distribution of interpreted lithostratigraphical units within the shallow subsurface. The dataset represents the Quaternary geology immediately beneath the active seabed sediment layer. Large areas of the UK offshore are covered at a scale of 1:250 000. The dataset is composed of vector polygons, each representing an area where a particular formation has been mapped. This dataset is a compilation of individual map sheets released between 1984 and 1992 and directly reflects this legacy mapping. There are several known polygon boundary matching and consistency issues present within this digital compilation. The decision to present the legacy mapping 'as it was', boundary matching issues included, is intentional. The map compilation is not informed by new data or analyses, so attempting to smooth or 'correct' these boundary issues would be potentially misleading, offering a false sense of accuracy that is not based on systematic analysis. While work to refine the stratigraphical framework is ongoing, the principal drive behind this release was to make the original 250K map data available in a digital format. Information from the original map sheets has been included in the attribute fields in this dataset, including a lithological description for each formation. Additional data has also been provided where it was deemed to add value. The BGS Lexicon code for each formation has been supplied so users can research any formation of interest. The maximum and minimum age of each formation, in a variety of formats, has also been added. This key lithostratigraphical information was sourced from Stoker et al. (2011). Our understanding of the Quaternary lithostratigraphy is evolving due to the increased data collection associated with renewable energy development. However, no formal update of the regional lithostratigraphical framework has been completed at the time of release. This dataset therefore reflects the understanding at the time of original publication. Inaccuracies in the dataset may have since been resolved and the level of uncertainty regarding the age or character of a formation may have changed. Nonetheless, this dataset contains valuable information and this digital version will help facilitate access to this for users. The information provided in this user guide is intended to provide a quick-start guide to using and understanding this BGS digital product. The map citation, metadata and overview can be found here: British Geological Survey. (2026). Offshore Quaternary 250k UK. British Geological Survey. (Dataset). https://doi.org/10.5285/e1f03873-9619-4c69-8190-371330274108