An overview of the lithostratigraphical framework for the Quaternary deposits on the United Kingdom continental shelf

This stratigraphical framework report presents a lithostratigraphical scheme for the Quaternary succession on the United Kingdom continental shelf (UKCS). The emphasis has been placed on the delineation and definition of a series of lithostratigraphical groups that provide the basis for first-order correlation between Quaternary deposits, both offshore and onshore. The proposed scheme is based on information derived from the extensive marine dataset acquired by the British Geological Survey (BGS) since the late 1960s, and published as a series of offshore maps and regional reports. The first part of the report (Chapter 1) introduces the project and in particular focuses upon the fundamental differences between onshore and offshore stratigraphical approaches. Resolving this problem is fundamental to creating a unified stratigraphical scheme that is applicable to both domains. The timescale that we use defines the base of the Quaternary System/Period and the Pleistocene Series/ Epoch at 2.58 Ma, as formally ratified by the International Union of Geological Sciences (IUGS) (Gibbard et al., 2010). This is followed in Chapter 2 by a brief description of the methodology that underpins the existing offshore stratigraphy. Although this scheme has been constructed largely on the basis of seismic stratigraphy, information on the nature and age of the stratigraphical units is provided by a wealth of borehole and short core data. Consequently, the offshore scheme is best described as a hybrid of seismic, litho- and biostratigraphy. Chapter 3 outlines the principles behind the new proposed lithostratigraphical scheme. Although the scheme is not wholly lithostratigraphical in nature, the hierarchy of lithostratigraphical nomenclature is adopted as the most practical terminology for describing a succession that is mappable at several levels, is divided by distinctive regional bounding surfaces, and displays significant lithological variation. By adopting a lithostratigraphical nomenclature we retain consistency with a recently published BGS onshore lithostratigraphical framework, thereby promoting an integrated land–sea approach to Quaternary correlation. A brief description of the new lithostratigraphical scheme is presented in Chapter 4, with emphasis at the group level. We define twelve groups from the Atlantic margin, North Sea and Celtic Sea–Irish Sea region that represent regional subdivision into predominantly non-glacial Lower–Middle Pleistocene, and glacially-dominated Middle Pleistocene– Holocene units. The proposed defining formations from each group are presented in a series of accompanying tables. Some of the larger estuaries (e.g. Moray Firth) and the English Channel–South-west Approaches region remain undivided at the present time. A comparison of the UKCS lithostratigraphical scheme with those in adjacent international sectors is presented in Chapter 5, with specific focus on the Dutch and Norwegian sectors. A major concern across the international boundaries is that the lithostratigraphical hierarchy of equivalent units varies between countries. Chapter 6 presents some recommendations for further work in order that the stratigraphical scheme be fully utilised by the scientific community and industry. This includes: 1) complete revision, update and population of the offshore entries in the BGS Stratigraphical Lexicon of Named Rock Units; 2) the production of a full framework report that details all aspects of the offshore Quaternary succession (groups, formations, members, etc); 3) a review of areas where the Quaternary stratigraphy is ambiguous or poorly defined; 4) the development of a single onshore–offshore classification scheme that can be captured seamlessly within the BGS Geological Spatial Database (GSD); and 5) the development of a unified North-west European Quaternary stratigraphical scheme. It is concluded that tasks 1 and 4 are essential corporate issues that underpin the entire BGS superficial deposits framework.