The renewed Stratigraphic Nomenclature is largely based on the information that could be found via the online predecessors 'Shallow Nomenclature' and 'Deep Nomenclature'. Broadly speaking, it is a renewed design and representation of existing information. For example, for each unit the order of subjects in relation to the previous version has been changed, new distribution maps have been made and, where possible, key photos have been added. Texts have become shorter and more concise. For the Upper North Sea Group, all texts have been completely revised and members and layers have been added.
Current revisions
The new layout and design are only the beginning of a series of revisions of the Stratigraphic Nomenclature. Now that the technical part has been completed, the definitions of several stratigraphic units are being revised. The following units are currently being worked on:
- Silurian - Devonian: the stratigraphic classification of Silurian and Devonian deposits in the Netherlands is based on Van Adrichem Boogaert & Kouwe (1994). Deposits from the Silurian have not been formally demonstrated. There only is an informal unit called Silurian (OS). For deposits from the Devonian in the south of the Netherlands, the informal Banjaard group (OB) exists. Since the publication of Van Adrichem Boogaert & Kouwe (1994), new borehole and seismic data have become available in both the Netherlands and neighbouring countries, allowing for a revision of the Silurian and Devonian stratigraphy. In addition, the Devonian is of interest for geothermal energy;
- Upper Jurassic - Lower Cretaceous deposits in the Broad Fourteens Basin and the West Netherlands Basin: the stratigraphic classification of Upper Jurassic - Lower Cretaceous deposits in the Broad Fourteens Basin and the West Netherlands Basin is based on Van Adrichem Boogaert & Kouwe (1993). Since that publication many new data have become available, especially in recent years, thanks to geothermal energy exploration. Several studies and publications point out that the existing lithostratigraphic classification is no longer adequate. This is why work is now underway on revising this lithostratigraphy;
- Paleogene - Neogene: definitions of the Dongen Formation are being rewritten due to duplications and inaccuracies. The Tongeren Formation and the Rupel Formation also require adjustments of the definitions, now that changes have been made in the hierarchy to better reflect the Belgian stratigraphic classification. Following the recent publication of proposals to revise the Breda Formation and the Oosterhout Formation, adjustments to the definitions are also to be expected here;
- Holocene: several bottlenecks in the lithostratigraphy of the Holocene have been identified. In some GeoTOP models other definitions are used than those in the Stratigraphic Nomenclature. In order to remedy these bottlenecks, adjustments to the definitions will be made in the short term;
- North Sea: stratigraphic units in the subsurface of the Netherlands Continental Shelf (NCP) have been added to the renewed Stratigraphic Nomenclature in the Upper North Sea Group. The definitions are rather concise and distribution maps are missing. Work is currently underway to expand the information on these units.
Future revisions and extensions
Ongoing geological studies lead to new stratigraphic insights. As a result, adjustments to the definitions of the Stratigraphic Nomenclature will eventually be necessary for the units listed below:
- Dinantian (lower Carboniferous/Mississippian): the SCAN study by TNO and EBN may have gained new insights into the limestone layers from Dinantian;
- Permian: new basal Rotliegend sandstone tapped by borehole N05-01 in 2017 (Ruby discovery);
- Pleistocene: similar to the Holocene, bottlenecks in the lithostratigraphy of the Pleistocene will have to be resolved.
In addition to the above revisions of definitions, efforts are being made to expand the number of units with core photographs, also for units of the North Sea Supergroup. Also, the figures of the type sections will be given a uniform design and new tectono-stratigraphic tables will be created.